220-301StudyGuide

220-301StudyGuide - Exam : 220-301 (STUDYGUIDE) Title : A+...

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Unformatted text preview: Exam : 220-301 (STUDYGUIDE) Title : A+ Hardware Technologies Ver : 01.19.06 220-301 TABLE OF CONTENTS List of Tables Introduction 1. Computer Components 1.1 The Computer Case 1.2 Power Supplies 1.2.1 Power Supply Connectors 1.2.1.1 AT Motherboard Connectors 1.2.1.2 ATX and ATX12V Motherboard Connectors 1.2.1.3 Peripheral Hardware Connectors 1.2.1.4 Splitters and Extenders 1.2.1.5 Power Supply Problems 1.3 Motherboards 1.3.1 Motherboard Form Factors 1.3.1.1 The AT Form Factor 1.3.1.2 The ATX Form Factor 1.3.1.3 The LPX Form Factor 1.3.1.4 The NLX Form Factor 1.3.2 Chip Sets 1.3.3 The Front System Bus 1.3.4 ROM BIOS 1.3.5 The CMOS Battery 1.3.6 BIOS Support for Hardware Devices 1.3.7 Power-On Self Test 1.3.7.1 Error Messages Before the Video Test Completes 1.3.7.2 Error Messages After the Video Test 1.3.7.3 POST Cards 1.4 The Central Processing Unit 1.4.1 Transistors 1.4.2 Integrated Circuits 1.4.3 Microprocessors 1.4.4 Registers 1.4.5 Codes 1.4.6 The System Clock 1.4.7 Cache Memory 1.4.8 The Intel CPU 1.5 Memory 1.5.1 Memory Controllers 1.5.2 Access Speed 1.5.3 Types of RAM 1.5.3.1 Single Inline Pinned Packages 1.5.3.2 30-Pin Single Inline Memory Modules 1.5.3.3 72-Pin Single Inline Memory Modules 1.5.3.4 168-Pin Dual Inline Memory Modules 1.5.3.5 Double Data Rate SDRAM 1.5.3.6 Rambus Inline Memory Modules CertGuaranteed. Study Hard and Pass Your Exam 220-301 1.5.4 Memory Mapping 1.5.5 Determining Usable Memory 1.6 Expansion Buses 1.6.1 Internal Expansion Buses 1.6.1.1 Industry Standard Architecture 1.6.1.2 Micro Channel Architecture 1.6.1.3 Extended ISA 1.6.1.4 VESA Local Bus 1.6.1.5 Peripheral Component Interconnect 1.6.1.6 Accelerated Graphics Port 1.6.1.7 The ACR, AMR and CNR Expansion Bus 1.6.2 Configuring Expansion Cards 1.6.2.1 I/O Port Addresses 1.6.2.2 Interrupt Request 1.6.2.3 Direct Memory Access 1.6.3 External Expansion Busses 1.6.3.1 Serial Ports 1.6.3.2 Parallel Ports 1.6.3.3 IEEE 1394 FireWire Serial Interface 1.6.3.4 Universal Serial Bus 1.6.4 Cables and Connectors 1.6.4.1 Parallel Printer Cables 1.6.4.2 Serial Port Cables 1.6.4.3 Keyboard Cables 1.7 Input Devices 1.7.1 The Keyboard 1.7.2 Pointing Devices 2. Storage Devices 2.1 Floppy Disk Drives 2.2 Hard Disk Drives 2.2.1 Geometry 2.2.2 Hard Disk Drive Types 22.2.1 ST-506/412 Drives 2.2.2.2 Enhanced Small Device Interface Drives 2.2.2.3 Integrated Device Electronics Drives 2.2.2.4 Enhanced IDE Drives 2.2.2.5 Small Computer System Interface Drives 2.2.3 Installing and Setting Up IDE and EIDE Drives 2.2.4 Maintaining a Hard Disk Drive 2.2.5 Setting Up a SCSI Subsystem 2.3 RAID Arrays 2.4 CD-ROM and DVD Drives 2.4.1 Recordable CD Drives 2.4.2 Recordable DVD Drives 2.4.3 Connecting CD and DVD Drives 2.4.4 Installing CD-ROM and DVD Drives CertGuaranteed. Study Hard and Pass Your Exam 220-301 3. Output Devices 3.1 CRT Monitors 3.2 Flat-Panel Displays 3.3 Display Adapters 3.3.1 Hardware Acceleration 3.3.2 Video Memory 3.3.3 Display Drivers 3.3.4 Troubleshooting Display Systems 3.4 Printers 3.4.1 Impact Printers 3.4.2 Sprayed-Ink Printers 3.4.3 Electrophotographic (EP) Printers 3.4.3.1 Laser Printer Resolution 3.4.3.2 Troubleshooting Laser Printer Problems 3.4.3.3 Printing on Transparencies 3.4.4 Printer Cables 4. Upgrading and Repairing Computers 4.1 Documentation 4.2 Preparing the Work Area 4.3 Disassembling a Computer 4.3.1 Removing the Expansion Cards 4.3.2 Removing the Power Supply 4.3.3 Removing the Disk Drives 4.3.4 Removing the Motherboard 4.4 Upgrading a Computer 4.4.1 Upgrading the Memory 4.4.2 Upgrading the CPU 4.4.3 Upgrading the Motherboard 4.5. Troubleshooting Computer Problems 5. Portable Computers 5.1 Portable Computer Components 5.1.1 The PCMCIA Bus 5.1.2 Portable Computer Display Systems 5.1.3 Portable Computer Processors 5.1.4 Memory 5.1.4.1 The Small Outline Dual Inline Memory Module 5.1.4.2 The 144-Pin Micro Dual Inline Memory Module 5.1.5 Hard Disk Drives 5.1.6 Removable Media 5.1.7 Keyboards 5.1.8 Pointing Devices 5.1.9 USB Ports 5.1.10 Wireless Adapters 5.1.11 Batteries and AC Adapters 5.2 Power Management 6. Network Systems CertGuaranteed. Study Hard and Pass Your Exam 220-301 6.1 Basic Networking 6.1.1 Network Definitions 6.1.2 Benefits of Networks 6.1.3 Types of Networks 6.1.4 Network Topologies 6.1.5 Network Operating System 6.2 The Network Interface Card (NIC) 6.3 Network Cabling 6.3.1 Twisted-Pair Cable 6.3.2 Coaxial Cable 6.3.3 Fiberoptic Cable 6.3.4 Cable Specifications 6.5 LAN Communication 6.5.1 Network Protocols 6.6 Troubleshooting Basic Network Problems 6.7. Advanced Networks 6.7.1 Modems 6.7.1.1 Modem Speeds 6.7.1.2 Modem Communication 6.7.1.2.1 Modem Protocols 6.7.1.2.2 Handshaking 6.7.1.2.3 Modem Standards 6.7.1.3 Modem Commands 6.7.1.4 Troubleshooting Modem Problems 6.7.2 The Internet 6.7.2.1 The World Wide Web 6.7.2.2 Internet Browsers 6.7.2.3 Electronic Mail 6.7.2.4 FTP 6.7.3 TCP/IP 6.7.3.1 Testing IP Configurations 6.7.3.1.1 The IPConfig Utility 6.7.3.1.2 The Ping Utility 6.7.4 Connecting to the Internet 6.8 Wireless Networks 6.8.1 Wireless Network Standards 6.8.1.1 The IEEE 802.11 Standard 6.8.1.2 The IEEE 802.11b Standard 6.8.1.3 The IEEE 802.11a Standard 6.8.1.4 The IEEE802.11g Standard 6.8.2 Wireless Network Modes 6.8.3 Security Features 6.8.4 Bluetooth Appendix A: The Intel Range of CPUs CertGuaranteed. Study Hard and Pass Your Exam 220-301 LIST OF TABLES TABLE 1.1 TABLE 1.2 TABLE 1.3 TABLE 1.4 TABLE 1.5 TABLE 1.6 TABLE 1.7 TABLE 1.8 TABLE 1.9 TABLE 1.10 TABLE 2.1 TABLE 3.1 TABLE 3.2 TABLE 3.3 TABLE 3.4 TABLE 4.1 TABLE 4.2 TABLE 5.1 TABLE 6.1 TABLE 6.2 TABLE 6.3 TABLE 6.4 TABLE 6.5 TABLE 6.6 TABLE 6.7 TABLE 6.8 TABLE 6.9 TABLE 6.10 TABLE 6.11 TABLE 6.12 P8 and P9 Voltage Common Power Delivery Problems AMI and Phoenix BIOS Beep Codes Possible Solutions to POST errors Some Common POST Numeric Error Codes Standard I/O Port Address Assignments Typical IRQ Assignments The Typical DMA Channel Assignments The Standard Computer Ports WIN Key Combinations The Transfer Rate of the CD-ROM The Typical Monitor Adjustments Possible Causes of Common Dot-Matrix Problems Possible Causes of Common Sprayed-Ink Printer Problems Possible Causes of Some Laser Printer Problems Hand Tools Isolating the Problem PCMCIA Standards Network Definitions Benefits of Shared Network Resources Network Cable Specifications Network Devices Some Cause and Solutions to Generic Network Problems CCITT Defined Modem Speeds Some AT Commands Troubleshooting Modem Problems Some Common Internet Domains IPConfig Switches Ping Error Messages Ping Switches CompTIA A+ Core Hardware Service Technician Exam Code: 220-301 Certifications: CompTIA A+ Hardware Technician Core Prerequisites: None About This Study Guide This Study Guide is based on the current pool of exam questions for the CompTIA 220-301 - A+ Core Hardware Service Technician exam. As such it provides all the information required to pass the CompTIA 220-301 exam and is organized around the specific skills that are tested in that exam. This StudyGuide also includes the information required to answer questions related to the CompTIA 220-302 - A+ Operating CertGuaranteed. Study Hard and Pass Your Exam 220-301 System Technologies exam that may be asked during the CompTIA 220-301 exam. Topics covered in this Study Guide includes Computer Components; Installing, Configuring, and Upgrading Computers; Identifying basic System Modules and their Function; Working with Motherboards, Understanding Motherboard Form Factors; Power Supplies; Identifying Processors; Identifying Memory Modules; Storage Devices; Monitors; Modems; BIOS and CMOS; Ports; and Portable Computers; Installing and Configuring Devices; Identifying IRQ, DMA, and I/O Address settings; Identifying common Peripheral Ports, Cabling, and Connectors; Working with Peripheral Devices; Identifying Printers and Printer Connections; Working with IDE/EIDE Devices; Setting IDE/EIDE Devices to Master and Slave; Primary and Secondary IDE/EIDE Channels; Installing and Configuring SCSI Devices; Configuring RAID; Basic Networking; Identifying Network Topographies; Network Protocols; Installing Network Interface Cards; Identifying Network Cabling; Troubleshooting the Basic Network; Diagnosing and Troubleshooting Computer Systems; Basic Troubleshooting Procedures and Techniques; and Understanding Wireless Networks, including Wi-Fi and Bluetooth. Intended Audience This Study Guide is targeted specifically at people who wish to take the CompTIA 220-301 - A+ Core Hardware Service Technician exam. This information in this Study Guide is specific to the exam. It is not a complete reference work. How To Use This Study Guide To benefit from this Study Guide we recommend that you: • Although there is a fair amount of overlap between this StudyGuide, the 220-302 StudyGuide and the N10-002 StudyGuide, the relevant information from the 220-301 StudyGuide and N10-002 StudyGuide are included in this StudyGuide. This is thus the only StudyGuide you will require to pass the 220-301 exam. • Study each chapter carefully until you fully understand the information. This will require regular and disciplined work. Where possible, attempt to implement the information in a lab setup. • Pay attention to the diagrams and illustrations included in this StudyGuide and the differences between the illustrations as the exam includes questions that will ask you to identify illustrations and diagrams. • Perform all labs that are included in this Study Guide to gain practical experience, referring back to the text so that you understand the information better. Remember, it is easier to understand how tasks are performed by practicing those tasks rather than trying to memorize each step. • Be sure that you have studied and understand the entire Study Guide before you take the exam. Note: Remember to pay special attention to these note boxes as they contain important additional information that is specific to the exam. Of course, if you use this StudyGuide in conjunction with our 220-301 - A+ Core Hardware Service Technician Q&A with Explanations product, you will achieve the best results. Good luck! 1. Computer Components 1.1 The Computer Case The computer case, or chassis, is usually constructed of metal, holds all the primary electronic components of the computer and most of the drives. The case provides access to other devices via ports and connectors, and protects the computer's delicate circuitry from possible damage and electromagnetic interference (EMI). It also protects surrounding devices, such as TVs, from the computer's EMI. When recommending a computer for purchase, the size and configuration of the case should be considered. • The bigger the case, the more components it can hold. This provides greater expansion potential. Bigger CertGuaranteed. Study Hard and Pass Your Exam 220-301 cases also provide better air flow which is essential for cooling. And large cases are easier to work with. • The more compact the case, the less expansion potential it has; working on it is often much more difficult, and usually air flow is more restricted. • Smaller cases that come with a power supply usually have lower wattage, reducing the number of internal devices that can be installed. • The more features in a case design, like the power wattage or the number of bays, the higher the cost. In any repair job that involves inspecting or replacing internal components, the technician has to open the case. This usually involves removing four screws at the back of the computer with a Phillips screwdriver and then removing the case's cover. Note: The size of the heatsink and fan required to cool the Pentium 4 CPU can damage a CPU or destroy a motherboard when subjected to vibration or shock. To prevent this, the Pentium 4 chassis has four standoffs to support the heatsink retention brackets. These standoffs allow the chassis to support the weight of the heatsink instead of depending upon the motherboard as with older designs. 1.2 Power Supplies A power supply provides electrical power to the computer components. It draws power from a local, alternating current (AC) source such as a wall outlet and converts it to either 3.3 or 5 volts direct current (DC) for on-board electronic components, and 12 volts DC for motors and hard disk drives. In addition, most Pentium 4 motherboards include voltage regulator modules to power the CPU, which runs on 12V power. The power supply delivers both positive and negative direct current to the computer. Power supplies must also "condition" the power input, i.e., it must smooth out any radical changes in the quality of the electrical supply as many homes and offices have power that fluctuates far more than the delicate computer components can tolerate. Most power supplies have a universal input that will accept either 110 volts alternating current (VAC), 60 hertz (Hz) (U.S. standard power), or 220 VAC, 50 Hz (European, Asian, Southern African standard). If the power supply or its fan should fail or cause the computer to behave erratically, the power supply must be replaced. When replacing a power supply, there are three things to consider: physical size, wattage, and connectors. Power supplies are generally available in two varieties: AT power supplies and ATX power supplies, although the ATX has an ATX24 derivative with a 24 pin connector, used by many server Motherboards before release of the Pentium 4 processor; and an ATX12V derivative with an additional 4-pin 12 volt connector. The two varieties of power supplies are based on the types of motherboard connections they support but do have a few other differences. • The ATX design is preferable as the on-off power control circuit on ATX boards is built into the motherboard and not in the power supply as in AT power supplies. • AT power supplies connect to the motherboard through a pair of six-wire connectors while ATX-style power supplies connect through either a single 20-pin connector or a 20-pin connector and a 4-pin ATX12V connector for Pentium 4 Motherboards. The exception is the ATX24 which has a single 24-pin connector rather than a 20-pin connector. • Generally all older Pentium-based computers and 486-based and earlier computers use AT supplies while almost all Pentium II and Pentium III-based computers use ATX power supplies. All Pentium 4based computers require an ATX12V power supply with a 4-pin ATX12V connector in addition to the normal 20-pin connector. A few motherboards and power supplies provide both AT and ATX fittings and switch support. These are rare, but provide more options should you have to repair such a system. Generally, you should use ATX CertGuaranteed. Study Hard and Pass Your Exam 220-301 power supplies if possible. When replacing a power supply, the main issues to be aware of are how much wattage the computer needs to power its components and how many peripheral connectors are required. The power supply must produce at least enough energy to operate all the computer's components at the same time. You can determine a computer's power consumption by adding the power requirements, measured in watts, for all the devices in the unit. This will provide you with the power supply the computer will consume to operate; however, a computer's operating consumption is always lower than the power required at startup when hard disk drives and other heavy feeders simultaneously compete for the available startup power. Most general-use computers require 130 watts while running and about 200-205 watts when at startup. Servers and highperformance workstations often have an abundance of random access memory (RAM), multiple drives, SCSI (Small Computer System Interface) adapters, and power-hungry video cards, along with one or more network cards. These systems often demand power supplies of 350-500 watts. 1.2.1 Power Supply Connectors FIG 1.1: The P8 and P9 AT Power Connectors Power supplies employ several types of connectors. On the outside of the computer enclosure, a standard male AC plug and three-conductor wire draws current from a wall outlet, with a female connection entering the socket at the back of the power supply. There are three types of connectors on the inside: the power main to the motherboard, which differs in AT and ATX models, and two types of four-pin fittings to supply 5 volts and 3.3 volts of power to peripherals such as the floppy disk and hard disk drives. 1.2.1.1 AT Motherboard Connectors A pair of almost identical connectors, designated P8 and TABLE 1.1: P8 and P9 Voltage P9 (see Figure 1.1), links the power supply to the Cable Color Supply In Tolerance motherboard. These connectors are seated into a row of Yellow +12 V ±10% six pins and matching plastic guides on the motherboard. Blue -12 V ±10% The P8 and P9 connectors must be placed in the proper Red +5 V ±5% orientation with the black wires on each plug side by side White -5 V ±5% and the orange wire on P8 the connectors to the Black Ground N/A motherboard. Table 1.1 shows voltage values for each of the color-coded wires on P8 and P9 connectors. The ground wires are considered 0 volts; all voltage measurements are taken between the black wires and one of the colored wires and the two red wires on P9 on the outside as you attach. CertGuaranteed. Study Hard and Pass Your Exam 220-301 1.2.1.2 ATX and ATX12V Motherboard Connectors The newer ATX power supply has a single 20-pin plug that links the power supply to the motherboard. This plug will only insert in one orientation because it has different hole sizes (see Figure 1.2). In addition, the Pentium 4based computers require a 4-pin ATX12V connector (see Figure 1.3) to provide power to voltage regulator modules used to power the CPU, which runs on 12V power. FIG 1.2: The ATX Power Connector 1.2.1.3 Peripheral Hardware Connectors Two standard types of connectors; the Molex connector and the mini connector, are used to connect the power supply to peripheral hardware: • The Molex connector is the most commonly used power connector. It provides both 12-volt and 5-volt power. Hard disk drives, internal tape drives, CDROM drives, DVD drives, and older 5.25-inch floppy disk drives all use this fitting. The Molex connector has two angled corners and two square corners to ensure that their correct orientation when installed. • Most power supplies provide one or more mini connectors. The mini connector is used primarily for 3.5-inch floppy disk drives. It has four pin-outs and, usually, four wires. Most are fitted with keys that make it difficult, but not impossible, to install upside down. Be sure to orient the connector correctly; applying power with the connector reversed can damage or destroy the drive. FIG 1.3: The ATX Power Connector Figure 1.4 shows the larger Molex connector and the CertGuaranteed. Study Hard and Pass Your Exam 220-301 smaller mini connector. 1.2.1.4 Splitters and Extenders Computers can require more connectors than supplied by the power supply, while computers with large cases can have drives beyond the reach of any connector on the power supply. Extenders and splitters can be used to overcome these problems. • Extenders are wire sets that have a Molex connector on each end; they are used to extend a power connection to a device beyond the reach of the power supply's own wiring. FIG 1.4: Molex and Mini Connector • Splitters are similar to extenders, with the exception that they provide two power connections from a single power supply connector. 1.2.1.5 Power Supply Problems Power supply problems can arise from internal and external sources - a computer component failure can cause a power supply to fail; but the most common failures come from the power source itself. Power supplies are affected by the quality of the local power source. Common power delivery problems such as spikes, surges, sags, brownouts, and blackouts affect the stability and operation of the main power supply and are passed on to the computer. These power delivery problems are discussed in Table 1.2. TABLE 1.2: Common Power Delivery Problems Problem Description Surges These are brief massive increases in the voltage source that often originates due to lightning strikes but can originate from the power source. Spikes These are similar to surges but are of a very short duration being measured in nanoseconds, whereas a surge is measured in milliseconds. Sags These are brief decreases of voltage at the power source. Brownouts If a sag lasts longer than 1 second, it is called a brownout. The overloading of a primary power source can cause brownouts. Some brownouts are "scheduled" by power companies to prevent overloading of circuits. Blackouts A blackout is a complete power failure. When the power returns after a blackout, there is a power spike and the danger of a power surge. There are devices that can be used to protect the computer from power supply problems. These include surge suppressors and uninterruptible power supplies (UPS) • A Surge Suppressor can be used to filter out the effects of voltage spikes and surges that are present in CertGuaranteed. Study Hard and Pass Your Exam 220-301 commercial power sources and smooth out power variations. However, almost nothing will shield a computer from a very close lightning strike. Surge suppressors are available from local computer dealers and superstores. Most power strips within surge protection have a red indicator light. If the light goes out, it means that the unit is no longer providing protection and needs to be replaced. If the indicator light starts flashing, it means the power strip is failing and should be replaced immediately. Surge suppressors smooth out power variations and protect the computer from power fluctuations up to a point; however, for complete protection from power fluctuations and outages, an uninterruptible power supply (UPS) is recommended. • An Uninterruptible Power Supply (UPS) is an inline battery backup that is installed between a computer and the wall outlet. A UPS protects the computer from surges and acts as a battery when the power dips or fails. It also provides a warning when the power source is above or below acceptable levels. Many UPS models can interact with the computer and initiate a safe shutdown in the event of a complete power failure using software that runs in the background and sends a signal through one of the computer's COM ports when the power goes down. The amount of time that a UPS device can keep a system running is determined by battery capacity and the power demands of the equipment connected to it. A more powerful UPS device will need its own line and circuit breaker. One of the principal power drains is the monitor. To keep a system online as long as possible during a power failure, turn off the monitor immediately after the failure commences. When considering a UPS, you must take into account the amount of protection that is needed. The watt rating of the UPS must be sufficient to supply the computer and all its peripherals with power for enough time to safely shut down the system. This can be calculated by adding the power rating of all pieces of equipment that are to be connected to the UPS. You should however beware of plugging a laser printer into a UPS unless the UPS is specifically rated to support that type of device. Laser printers often require more power than a UPS is able to provide. 1.3 Motherboards The motherboard serves as the computer's backbone. All devices in a computer are connected to it in some way; it hosts the largest single collection of chips of any computer component and links all the components, making it possible for them to communicate. The motherboard also defines the computer's limits of speed, memory, and expandability. The motherboard is usually the largest circuit board found inside the computer case. Motherboards come in a number of sizes or form factors of which the AT and ATX form factors are the two main varieties. 1.3.1 Motherboard Form Factors Motherboards come in a number of sizes or form factors but needs to fit into the space in the computer case allocated for it. A motherboard must also be secure in its mounts, must be properly grounded, must receive sufficient ventilation for cooling of the CPU and other heat-sensitive components, and must not conflict with other hardware. There are four basic form factors: ATX, which is the most common; AT, which used to be the standard but has been superseded by ATX; NLX and LPX. These forms describe the shape and size of the motherboards, as well as the layout of the components on the board. The form factor will also determine the type of case you must buy, as the case is laid out differently and uses a different type of power supply. 1.3.1.1 The AT Form Factor The AT form consists of the regular or Full AT and the Baby AT which, were the most common form factor through 1997. These two variants differ primarily in width with the older full AT motherboard being 12" wide and the Baby AT being about 8.5" wide and 13" long, although the Baby AT size may vary a little from board to board. Full AT motherboards were generally employed in 386-based and earlier computers while Baby AT is the form used by many 486 and Pentium motherboards. Many Socket 7 motherboards and a few Pentium II motherboards also used this form factor. CertGuaranteed. Study Hard and Pass Your Exam 220-301 A major problem with the Full AT motherboard was its width which meant that part of the motherboard overlapped the drive bays. This made installation, troubleshooting and upgrading more difficult. With the narrower Baby AT motherboard there is much less overlap with the drive bays. One problem with baby AT boards is that many manufacturers reduce cost by reducing the length of the Baby AT motherboard. This can lead to mounting problems. A problem with both the AT and Baby AT form factors results from its layout. As can be seen in Figure 1.5, the processor socket and memory sockets in the AT motherboards are located at the front with long expansion cards designed to extend over them. When this form factor was designed, processors and memory chips were small and were inserted directly onto the motherboard, hence clearance was not a problem. However, today's memory modules are not inserted directly onto the motherboard, and today's processors require large heat sinks and fans that are mounted on them for cooling. Hence most later Baby AT motherboards have moved the memory sockets to the top of the motherboard, but the processor is still located at the front of the motherboard and can sometimes get in the way of expansion cards. The ATX form factor was designed in part to solve this issue. The other characteristics of the AT form factor are: • They have serial and parallel ports attached to a bracket with cables that attached the ports to I/O Port Connector headers on the motherboard; • Newer models have a PS/2 mouse ports attached to a bracket with cables that attach the port to an I/O Port Connector headers on the motherboard; • They also have a single 5-pin DIN keyboard connector soldered at the back end of the motherboard. FIG 1.5: An AT Motherboard 1.3.1.2 The ATX Form Factor In 1995, Intel released the ATX form factor. Almost all Pentium Pro, Pentium II and later motherboards use the ATX form factor, although there were some AT Pentium II motherboards. Also, most Pentium motherboards were still AT, although many manufacturers released ATX versions. The ATX form factor is generally 12" wide and long and 9.6" long. There are also a 11.2" wide and 8.2" long ATX form factor called the Mini ATX. The only difference between the ATX and Mini ATX is the size difference. The layout of the ATX motherboard, as shown in Figure 1.6, differs from the layout of the AT motherboard. The ATX motherboard has the CPU socket located to the upper rear section of the motherboard, near the power supply connector and the memory slots are located at the top of the motherboard. On some ATX motherboards the memory slots are located at right angles to the expansion slots. The ATX design has several significant advantages over the AT motherboard: • It has integrated I/O Port Connectors for the serial and parallel ports that are soldered directly onto the motherboard. • It has an integrated PS/2 Mouse Connector built into the motherboard. CertGuaranteed. Study Hard and Pass Your Exam 220-301 FIG 1.6: An ATX Motherboard • It has much less overlap between with the drives bays. This means easier access to the board, and fewer cooling problems. • The processor socket and the memory slots are located at the back right hand side of the motherboard, near the power supply. This eliminates the expansion cards clearance problem common to the Baby AT motherboard. • It uses a 20-pin power connector to attach the power supply cable to the motherboard; • It has "Soft Power" Support, i.e., the ATX power supply is switched on and off using signaling from the motherboard rather than a toggle switch. This allows the PC to be turned on and off under software control, allowing much improved power management. • It has 3.3V Power Support to support newer processors almost all of which require 3.3V or lower. 1.3.1.3 The LPX Form Factor The LPX motherboard form factor is similar to the AT form factor in terms of size and were used, up until the advent of the Pentium II, in mass-produced brand name computer systems and fits into the small Slimline or low profile cases. The primary design goal behind the LPX form factor is reducing space usage and cost. This can be seen in its most distinguishing feature: the riser card that is used to hold expansion slots. Instead of having the expansion cards inserted into expansion bus slots on the motherboard, as on AT or ATX motherboards, the LPX form factor motherboards has the expansion bus slots on a riser card that is inserted into the motherboard; the expansion cards are then inserted into the riser card. A riser card usually supports a maximum of only three expansion cards. This means that the expansion cards are parallel to the plane of the motherboard. LPX form factor uses the P8 and P9 AT power connectors and has integrated video display adapter cards built into the motherboard, as well as integrated serial, parallel and PS/2 mouse ports. The LPX form factor however suffered from non-standardization and poor expandability which led to difficulty in upgrading. They also suffered from poor cooling. CertGuaranteed. Study Hard and Pass Your Exam 220-301 FIG 1.7: A NLX Motherboard with Riser Card 1.3.1.4 The NLX Form Factor The NLX form factor is similar to the and was developed by Intel. It uses the same general design as the LPX, but with a smaller motherboard footprint and a riser card for expansion cards. Basically, the NLX adds: • Support for larger memory modules and modern DIMM memory packaging; • Support for the newer processor technologies, including the Pentium II that uses SEC packaging; • Support for AGP video cards; • Better cooling for modern CPUs that run hotter than the older CPUs; • More flexibility in motherboard set up and configuration; • Cables, such as the floppy drive and had drive interface cable, that are attached to the riser card instead of the motherboard; • Support for desktop and tower cases. In addition, the NLX uses a 20-pin power connector similar to that of the ATX power supply. CertGuaranteed. Study Hard and Pass Your Exam 220-301 FIG 1.8: An AT Motherboard showing the Motherboard Components 1.3.2 Chip Sets As illustrated in Figure 1.8, a motherboard comes with a variety of support chips soldered in place. The primary elements constitute the chip set and are designed to work with the central processing unit (CPU). These chips are highly complex and coordinated integrated circuits that help the CPU manage and control the computer system. When replacing a CPU, you must make sure that it is compatible with the chip set and supported by the motherboard. If not, the computer will not work. A basic chip set consists of a Bus Controller; a Memory Controller; a Data and Address Buffer; and a Peripheral Controller. Most modern motherboards also have specialized chips that controls things such as cache memory and highspeed buses. Be careful in choosing motherboards with components like display adapters and sound cards on board. These are components that may not have all the features of their expansion card versions, and customers may decide to upgrade, leaving them with motherboard-based elements that could cause conflicts. 1.3.3 The Front System Bus A microprocessor, which is an integrated circuit that contains a complete CPU on a single chip, uses the external data bus on the motherboard to accesses system resources. On a personal computer, information in binary code is transmitted from one component to another through a bus. The Front System Bus (FSB), also known as the external data bus, the external bus or the data bus, is the primary bus through which data is routed in a computer. All data-handling components or optional data devices are connected to it; therefore, any information placed on that bus is available to all devices connected to the computer. Early computers used eight conductors (an 8-bit data bus), which allowed for the transfer of 1 byte of information at a time. As computers evolved, the width of the external data bus increased to 16, 32, and the current width of 64 conductors. The wider bus lets more data flow at the same time. 1.3.4 ROM BIOS In addition to the chip set, the motherboard also comes with another chip called the ROM BIOS. A ROM BIOS chip contains data that specifies the characteristics of hardware devices, such as memory and hard disk and floppy disk drives, so the system can properly access them. ROM (read-only memory) is a type of memory that stores data even when the main computer power is off. This is necessary so that the system can access the data it needs to start up. When stored in ROM, information that is required to start and run the computer cannot be lost or changed. The BIOS (Basic Input/ Output System) is a software program stored on the ROM chip and is used by the computer during the startup routine to check the computer system and prepare it to run the hardware. The ROM chip on older computers need to be replaced with ROM chips that contained updated BIOS information but newer computer systems use a technology called flash ROM or flash BIOS that allows code in the core chips to be updated by software available through the BIOS or motherboard supplier. The BIOS should only be upgraded if necessary as improper upgrading can render the motherboard useless. BIOS can be divided into three classes, depending on the type of hardware it controls: the first class, called core chips, includes support for the necessary hardware that is common to all computers and never changes; the second class, called updateable chips, encompasses hardware that is also common and necessary, but that might change from time to time; and the third class of chips includes anything that is not included in one of the first two classes. ROM chips for the core chips are often distinctive because they are in dual in-line package (DIP) form. Figure 1.9 shows a chip in dual in-line package as seen from below. These chips are commonly used for the keyboard, parallel ports, serial ports, speakers, and other support devices. Each ROM chip contains between 16 and 64 KB of programming. Some devices on a computer, such as SCSI controllers and video cards, can contain their own flash BIOS or updateable ROMs. Because this information is subject to change, it is often stored on a special chip called the complementary metal-oxide semiconductor (CMOS). Unlike other ROM CertGuaranteed. Study Hard and Pass Your Exam 220-301 chips, CMOS chips do not store programs, but instead store data that actually configures the features of the motherboard. The CMOS chip also maintains date and time information when power to the computer is off and can store 64 KB of data. Typically, the CMOS contains information for the floppy disk and hard disk drive types; the CPU; the RAM size; the date and time; serial and parallel port information; Plug and Play information; and power-saving settings. FIG 1.9: A Chip in DIP Form. To make changes to a CMOS chip, you need to run a CMOS setup program. This program is independent of the operating system in is started by various means depending on the manufacturer of the CMOS chip. There are three companies-American Megatrends (AMI), Phoenix, and Award-that dominate the CMOS market. • The AMI CMOS setup program can be accessed by pressing DELETE when the computer begins to boot. • The Phoenix CMOS setup program can be accessed by pressing CTRL+ALT+ESC, DELETE, or F2 when requested. • The Award CMOS setup program access procedure follows either of the other two procedures. 1.3.5 The CMOS Battery The CMOS chip requires a small amount of voltage from a battery to retain its memory. When the battery gets low or dies, the computer will experience a sudden memory loss and thus lose settings. The voltage of CMOS batteries ranges from 3 to 6 volts. The CMOS chip contains a capacitor that allows you to replace the battery without losing data. For motherboards with soldered on-board batteries, there is usually a connection that allows you to add an external battery to replace a worn-out internal one. Be sure that the external battery has the same voltage as the on-board battery you are replacing. Some older computers use a battery pack with four AA cells or a single 9-volt battery. These should be replaced with a special computer battery pack to provide longer life. 1.3.6 BIOS Support for Hardware Devices BIOS support can be provided for hardware devices, such as display adapters, network interface cards, and sound cards, by means of on-board ROM chip on the hardware device itself, or through the use of device drivers. The latter is a program that acts as an interface between the operating system and the control circuits that operate the device and is the most popular means of providing BIOS support for hardware. How a device driver is invoked is dependant on the operating system, the hardware, and the software design. Some operating systems such as MS-DOS use the config.sys file to load drivers. Every time an MS-DOS based computer is booted up, the config.sys file is read and the device drivers are loaded from the hard disk drive into RAM. The Windows 95, Windows 98, Windows ME, Windows 2000, and Windows XP operating systems have their own drivers that are loaded as part of startup. 1.3.7 Power-On Self Test Every time a computer is booted up or reset using the Reset button or the Windows Restart command, the computer is rebooted and reset to its basic operating condition. The system BIOS program starts by invoking a special program stored on a ROM chip called the power-on self test (POST). The POST sends out standardized commands that check every primary device, in other words, it runs an internal self-diagnostic routine. The POST has two stages: one that occurs before and during the test of the video, and the other that occurs after the video has been tested. This division determines whether the computer will alert you to errors by beeping or showing them on the screen. 1.3.7.1 Error Messages Before the Video Test Completes CertGuaranteed. Study Hard and Pass Your Exam 220-301 The purpose of the first POST test is to check the most basic components. If a problem is encountered during this stage of the POST, i.e., before the video test is completed successfully, the POST sends a series of beep codes that reports the nature of the problem. Table 1.3 lists the basic beep codes for the AMI and Phoenix BIOS. TABLE 1.3: AMI and Phoenix BIOS Beep Codes Number of Beeps Problem 1 DRAM refresh failure 2 Parity circuit failure 3 Base 64 KB or CMOS RAM failure 4 System timer 5 Processor failure 6 Keyboard controller or Gate A20 error 7 Virtual mode exception error 8 Display monitor write/read test failure 9 ROM BIOS checksum error 10 CMOS RAM shutdown register failure 1 long, 3 short Conventional/extended memory test failure 1 long, 8 short Display test and display vertical and horizontal retrace test failure After a beep code has been recognized, there are a few things you can do to troubleshoot the error. Table 1.4 suggests some possible solutions. TABLE 1.4: Possible Solutions to POST Errors Problem Solution DRAM refresh failure Reseat and clean the RAM chips. Parity circuit failure Replace individual memory chips until the problem is resolved. Base 64 KB failure Replace individual memory chips until the problem is resolved. CertGuaranteed. Study Hard and Pass Your Exam 220-301 Keyboard controller Reseat and clean keyboard chip. failure Gate A20 error Check operating system. Replace keyboard. Replace motherboard. BIOS checksum error Reseat ROM chip. Replace BIOS chip. Video errors Reseat video card. Replace video card. Cache memory error Reseat and clean cache chips. Verify cache jumper settings are correct. Replace cache chips. Any other problems Reseat expansion cards. Clean motherboard. Replace motherboard. 1.3.7.2 Error Messages After the Video Test After successfully testing the video, the POST will display any error messages on the screen. These errors are displayed either as numeric error codes or as text error messages. • When a computer generates a numeric error code, the machine locks up and the error code appears in the upper-left corner of the screen. Table 1.5 lists some common numeric error codes. • BIOS manufacturers have stopped using numeric error codes and have replaced them with about 30 text messages that are usually, but not always, self-explanatory. TABLE 1.5: Some Common POST Numeric Error Codes Error Code Problem 161 A battery error. 301 A keyboard error. 1101 A serial card error. 1701 Hard disk drive controller error. 7301 Floppy disk drive controller error. 1.3.7.3 POST Cards Some hardware problem can prevent the POST from issuing any error report. To identify the source of the problem in such an event, you can use a POST card. A POST card is a special diagnostic expansion card that monitors the POST process and displays all codes as the system runs during the POST. These codes are usually in two-digit hexadecimal format and can be decoded using the POST card manufacturer's manual. More advanced POST cards can be used to check direct memory access (DMA), interrupt request (IRQ) and port functions, and can also run advanced series of tests to isolate erratic problems. However, most POST cards are based on the Industry Standard Architecture (ISA) slot that has been phased out by some motherboard manufacturers. 1.4 The Central Processing Unit CertGuaranteed. Study Hard and Pass Your Exam 220-301 The CPU is the part of a computer that controls the operation of the computer. All arithmetic and logical operations, decoding of instructions and the execution of instructions are performed by the CPU. Early computers used several chips to handle the task. Some functions are still handled by support chips, which are often referred to collectively as a chip set. 1.4.1 Transistors Transistors are the main components of microprocessors. They are small, electronic switches and are made from silicon. Transistor switches have three terminals: the source, the gate, and the drain. When positive voltage is applied to the gate, electrons are attracted, forming an electron channel between the source and the drain. Positive voltage applied to the drain pulls electrons from the source to the drain, turning the transistor on. Removing the voltage turns it off by breaking the pathway. 1.4.2 Integrated Circuits An IC is an electronic device consisting of a number of miniature transistors and other circuit elements (resistors and capacitors, for instance). An IC functions just as a large collection of these parts would, but it is a fraction of the size and uses a fraction of the power. ICs make today's microelectronics possible. The original transistors were small plastic boxes about the size of a peanut that could handle only one function. The word integrated denotes that IC devices combine many circuits-and some of their functions-into one package. The microprocessor is an example of this. 1.4.3 Microprocessors Microprocessors are divided into three subsystems: the control unit (CU), the arithmetic logic unit (ALU), and the input/output (I/O) unit. The CU allows CPU operations to be based in part on code provided by an external program. The ALU handles the basic math functions of computation. The I/O unit fetches data from the outside and passes data back to the Front System Bus. 1.4.4 Registers Registers are temporary memory storage areas used during data manipulation. Physically, registers are rows of microscopic switches that are set on or off. Each row forms a binary number: off = 0 and on = 1. The CPU uses these registers to hold data while it works on a task. Changes in data during an operation are also stored in a register, then sent out to other components as the task is completed. The wider the register, the more bits the machine can handle at one time. The CPU can only hold a limited amount of information in its registers. To supplement this, additional chips that temporarily store information that the CPU requires are installed in the motherboard. These chips are called RAM (random access memory). 1.4.5 Codes Computers use various binary-based codes to represent information. These codes are sent on the external data bus by a computer component to be read by other devices. When you press a key on the keyboard, an ASCII code is generated and sent over the data bus. Transferring information to and from the CPU and other hardware is the first step in manipulating data. Other codes are used to display data on the monitor, to communicate with devices such as printers, and to take in data streams from scanners. Each of those operations requires system resources and the manipulation of binary numbers. In addition to the code that requires data, special machine code is required for the CPU to turn the string of numbers into something useful to an application. As with the data code, this machine code is sent in the form of binary numbers on the data bus. 1.4.6 The System Clock A computer has two clocks: one to keep time for date and time calculations and the other clock to set timing and syncronization for the CPU. Synchronization is essential in computer operations. Timing allows the electronic devices in the computer to coordinate and execute all internal commands in the proper synchronized order. Placing a special conductor in the CPU and pulsing it with voltage creates timing. Each CertGuaranteed. Study Hard and Pass Your Exam 220-301 pulse of voltage received by this conductor is called a clock cycle. All the switching activity in the computer occurs while the clock is sending a pulse. Virtually every computer command requires at least two clock cycles to process. The computer's clock speed is measured in megahertz (MHz), or millions of cycles per second and indicates the number of commands that can be completed in two clock cycles. The clock speed is determined by the CPU manufacturer and represents the fastest speed at which the CPU can be reliably operated. The Intel 8088 processor f 1972 had a clock speed of 4.77 MHz by the end of 2002 the Intel Pentium 4 processors had reached a clock speed of 3 Gigahertz (GHz). 1.4.7 Cache Memory Caching, in computer terms, is the holding of a recently or frequently used code or data in a special memory location for rapid retrieval. A high-speed memory chip located on or close to the CPU or other peripheral devices, such as graphics card, is used for this purpose and is called static random access memory (SRAM). Cache memory is much faster than memory nodules or RAM, but is also much more expensive. Unlike memory modules, SRAM does not use capacitors to store 1s and 0s but uses a special circuit called a flipflop. SRAM also does not have to be refreshed because it uses the flip-flop circuit to store each bit. A flipflop circuit will toggle on or off and retain its position, whereas a standard memory circuit that uses capacitors to store 1s and 0s requires constant refreshing. Because the CPU is constantly requesting and using information and executing code it requires quick access to data. The closer the necessary data is to the CPU, the faster the system can locate it and execute the operation. Caches are organized into layers. The highest layer is closest to the CPU. On early computers, caches were usually separate chips. Today, it is not uncommon to have two levels of cache built into the CPU. Since the 486 CPUs, a cache has been included on every CPU. This original on-board cache is known as the level 1 (L1) or internal cache. All commands for the processor go through the cache. An additional cache can be added close to the CPU. This cache is called the level 2 (L2) or external cache. On some motherboards the L2 can be added or expanded. The CPUs on entry-level computers, such as the Celeron based computers, often use a small L1 cache and no L2 cache to reduce costs. These computers are usually much slower than computers that have a CPU of equivalent speed but a larger L1 cache and a L2 cache. Some high level computer systems on the other hand use a level 3 (L3) cache. The primary use of a cache is to increase the speed of data transfers from the memory modules or RAM to the CPU. Some caches immediately send all data directly to RAM, even if it means hitting a wait state. This is called write-through cache. Some caches store the data for a time and then send it to RAM later. This is called write-back cache. Write-back caches are harder to implement but are much more powerful than writethrough caches, because the CPU does not have to stop for the wait state of the RAM. However, write-back caches are more expensive that write-through caches. 1.4.8 The Intel CPU When IBM released the first PC it included an Intel manufactured CPU. Since then, Intel has been the CPU producing CPUs since the early 1970s. It began with the commercial microprocessor Model 4004 which was released on November 15, 1971. The 4004 operated at a clock speed of 108-KHz, had 2300 transistors, 4-bit data bus and could address 640 bytes of RAM. The following year supplier for most IBM compatible computers. However, Intel had been Intel introduced the 8008. The Intel 8080 was introduced in 1974 and formed the core of the Altair computer CertGuaranteed. Study Hard and Pass Your Exam 220-301 FIG 1.10: The Intel 8088 CPU of 1975. It had 6000 transistors, an 8-bit bus, a 2-MHz clock speed and could address 64 KB of RAM. The Intel family of processors for the personal computer, the 808x family beginning with the 8-bit 8088, was a development of the 8080. The 8088 was rectangular chip in a Dual Inline Package, had 40 pins and 29,000 transistors. It operated at a clock speed of 4.77MHz with. The next Intel CPU was the 8086 with a 16-bit external data bus but was compatible with 8-bit expansion cards. The 80x86 series followed with the arrival of the 16-bit 80286 in February 1982. This was the first CPU to implement the Pin Grid Array package (PGA). It operated at clock speeds from 6MHz to 20MHz, could address up to 16MB of RAM, and generated more heat than 808x. The first 32-bit CPU from Intel was the 80386, which had 275,000 transistors and was introduced in June 1985. Up until the release of the 80386, Intel had licensed its technology to other manufacturers. With the 386 Intel decided to stop licensing. This led to other CPU manufacturers, such as AMD and Cyrix, developing their own CPU chips, called the 386SX which was slower and cheaper than the Intel 80386 as it used a 16-bit Front System Bus (FSB). In response Intel renamed its 80386 to the 386DX and developed a 386SX with a 16-bit FSB. The various 386 CPUs ranged in speed from 16MHz to 33MHz and supported multitasking. The 386SX could support 16MB of memory while the 386DX. supported up to 4GB. The Intel 486DX was introduced in April 1989. It had 1.25 million transistors, 32-bit internal and external data bus, 32-bit address bus, an integrated math coprocessor and was the first to have a on-chip cache of 8KB. In 1991 Intel introduced the 486SX, as a cheaper version of the 486 processor without an internal math coprocessor. The 486SX could be upgraded by installing the math coprocessor which was called the 487SX chip. The 486 operated at a maximum FSB speed of 33MHz but supported clock doubling. This allowed the CPU to operate externally at the FSB speed and internally at twice the speed of the FSB. Thus the 33MHz 486DX could operate internally at. CPUs that supported this technology were known as the 486DX2. Not long after the 486DX2 came into production, clock doubling was developed. CPUs that supported clock tripling operated externally at the speed of the FSB, i.e., 33MHz, and internally at 100MHz and were called the 486DX4. The 486 generated excessive heat that could damage the CPU and the motherboard. FIG 1.11: A 486 CPU with Heat Sink and CertGuaranteed. Study Hard and Pass Your Exam 220-301 Fan To ensure stable operating temperatures, a heat sink and a fan powered by the computer was mounted on top of the 486. In the early 1990s Intel sought a way to trademark the names of their CPUs, however, numbers cannot be trademarked. To overcome this problem, Intel gave their next CPU, which was introduced in 1993, the name Pentium processor in 1993. This CPU has 3.1 million transistors, used a 64-bit data path, 32-bit address bus, had 16K on-chip cache, and came in speeds ranging from 60MHz to 200MHz. The Pentium CPU was basically a combination of two 486DX chips in one larger chip. This two-chips-in-one architecture had the advantage of allowing each chip can execute instructions independently of the other. This is a form of parallel processing that Intel calls superscalar. Pentiums required special motherboards as they run significantly hotter than the 486 processors. After the introduction of the Pentium came the Pentium Pro in 1995, designed for high performance business orientated applications. It operated at speeds of 200MHz, in a 32-bit operating system environment. The Pentium CPU made use of what is called MMX technology. This version of the Pentium CPU included 57 new instructions for better video, audio, and graphic capabilities; featured Single Instruction Multiple Data (SIMD) technology, which enables one instruction to give instructions to several pieces of data rather than a single instruction per piece of data; and had a cache of 32KB. For 486 users who wanted to give their computers Pentium performance without the expense having to upgrade the motherboard as well, Intel developed the 486 Overdrive CPU. This CPU operated at approximately two and a half times the motherboard's bus speed which meant that on a motherboard with a bus speed of 33MHz, the Overdrive CPU would operate at approximately 83MHz. These CPUs, however, did not have MMX capabilities. In 1997 Intel introduced the Pentium II, which was code-named Klamath during its development. These CPUs operated at speeds ranging from 233MHz to 450MHz and had 7.5-million-transistor, and used a 66MHz or 100MHz FSB It was designed to be a multimedia chip with special on-chip multimedia instructions and high-speed cache memory. The most unique aspect of the Pentium II was that, instead of the standard PGA package, its use a Single Edge Connector (SEC) to attach the CPU to the motherboard, necessitating a new motherboard. This CPU was initially designed to be used in single CPU computers. For multiprocessor servers and workstations, Intel developed the Pentium II Xeon, based on the circuitry of the Pentium II CPU. For lower-end and entry level computers, Intel released the Celeron CPU that lacked the Pentium II's cache. The Intel Pentium III CPU was released in 1999. It included 70 new instructions and was optimized for voice recognition and multimedia. It operated at speeds ranging from 450 MHz to 1.33 GHz, had 28 million transistors and FSB speeds of 100 to 133 MHz. It can address up to 64GB of RAM. Some Pentium III CPUs use the same SEC connector as the Pentium II but others use the PG A. The Pentium III CPU also incorporated MMX technology, plus streaming SIMD extensions for enhanced floating-point and 3-D application performance. Intel also offered a Xeon version of the Pentium III CPU aimed at highperformance workstations and servers. The Intel Pentium 4 CPU, which was code-named Williamette, was released the following year. It made use of the quad pumped bus technology introduced with the last Pentium III CPUs, using a quad pumped FSB of 400MHz and 533MHz. A second Pentium 4, code-named Northwood, was released in 2001 it was manufactured using the .13 micron, and uses a quad pumped FSB of 533MHz and 800MHz. In 2003, 'Hyper-Threading' was added to the Pentium 4. hyper-Threading enables the CPU to execute two threads in parallel. 1.5 Memory There are various types of computer memory all of which is used to hold binary strings of data to be CertGuaranteed. Study Hard and Pass Your Exam 220-301 manipulated by the CPU. These types of memory can be divided into two major classes of computer memory: nonvolatile memory and volatile memory. • Nonvolatile Memory is retained even if the power to the computer is shut off. Read Only Memory (ROM), generally installed by the vendor of the computer during the process of manufacturing the motherboard or secondary components that need to retain code when the machine is turned off is nonvolatile memory. With the use of ROM, information that is required to start and run the computer cannot be lost or changed. In the modern computer ROM is used to hold the instructions for performing the POST routine and the BIOS information used to describe the system configuration. • Volatile Memory is lost when the computer loses power. Random Access Memory (RAM) is the form of volatile memory used to hold temporary instructions and data for manipulation while the system is running. The term random is applied because the CPU can access or place data to and from any addressable RAM on the system. If power to the system is lost, all data held in RAM is lost. The most common forms of RAM used in the modern computer are dynamic RAM (DRAM) and the newer synchronous DRAM (SDRAM). DRAM works by using a microscopic capacitor and a microscopic transistor to store each data bit. A charged capacitor represents a value of 1, and a discharged capacitor represents a value of 0. A capacitor works like a battery in that it holds a charge and then releases it; but unlike a battery, the capacitors in DRAM hold their charges for only fractions of a second. Therefore, DRAM needs an entire set of circuitry to keep the capacitors charged. The process of recharging these capacitors is called refreshing. Without refreshing, the data would be lost. When a block of code or data that is held in memory is directly accessible to the CPU for reference or manipulation, it is called active memory. When data is located outside the computer system's active memory, it is said to be in storage. Storage devices include floppy disk and hard disk drives, optical media, and tape units. Active memory is faster than storage because the information is already on the system, there are fewer physical and no mechanical operations involved in obtaining the data, and the CPU has direct control over the memory. All computer CPUs handle data in 8-bit blocks. Each block, known as a byte, denotes how many bits the CPU can move in and out of memory at one time. The number is an indication of how rapidly data can be manipulated and arranged in system memory. Each transaction between the CPU and memory is called a bus cycle. The amount of memory that a CPU can address in a single bus cycle has a major effect on overall system performance and determines the design of memory that the system can use. The width of the system's memory bus must match the number of data bits per cycle of the CPU. 1.5.1 Memory Controllers All computers have some form of memory controller, which handles the movement of data to and from the CPU and the system memory banks. The memory controller is also responsible for the integrity of the data as it is swapped in and out. There are two primary methods of ensuring that the data received is the same as the data sent: parity and error-correction coding (ECC). • Parity is a method of ensuring data integrity by adding an extra bit, the parity bit along with each 8-bit bus cycle. There are two kinds of parity: even and odd. Both use a three-step process to validate a bus transaction; however, they do it in opposite ways. In Step 1, both methods set the value of the parity bit based on the even or odd number that represents the sum of the data bits as the first step. In Step 2, the string goes into DRAM. In Step 3, the parity circuit checks the math. If the parity bit matches the parity bit of the number that represents the sum of the binary string sent, the data is passed on. If it fails the test, an error is CertGuaranteed. Study Hard and Pass Your Exam 220-301 reported. Just how that error is handled and reported to the user varies with each operating system. • ECC is a more robust technology that can detect errors beyond the limits of the simpler parity method. It adds extra information about the bits, which is then evaluated to determine if there are problems with individual bits in the data string. 1.5.2 Access Speed Access speed, denoted in nanoseconds (ns), is the amount of time it takes for the RAM to provide requested data to the memory controller. A typical total response time for a 70-ns DRAM chip is between 90 and 120 ns. This includes the time required to access the address bus and data bus. Most 486- and Pentium-based computers use either 70-ns or 60-ns DRAM chips, although 50-ns chips are also available. The access speed of a chip is usually printed on the chip, often as part of the identification number. When adding memory to a computer, the add-on memory should generally be the same speed or faster than any existing memory tough you should check the motherboard specifications for the recommended memory chip speed. 1.5.3 Types of RAM The power of a CPU is expressed in the amount of data it can handle at a time. For example, the original Intel Pentium is a 64-bit CPU, meaning that it can handle a bus cycle of 64 bits, or 8 bytes. The number of bits a memory module provides must meet the demand of the bus cycle. Thus an 8-bit data bus requires 8bit-wide memory to fill one bank, a 16-bit data bus requires 16-bit-wide memory to fill one bank, etc. When the bus cycle demand is greater than the number of bits a memory module provides, more modules must be added to be able to meet the demand. FIG 1.12: A Chip in DIP Form. Early versions of RAM were installed as single chips, usually 1-bit-wide DIP (dual inline package), as shown in Figure 1.12. In some cases, this was soldered onto the motherboard, but most often it was seated in a socket, offering a simpler method of removal and replacement. Some older machines have special memory expansion cards that contain several rows of sockets. These cards are placed in a slot on the motherboard. To upgrade or add memory, new chips had to be individually installed on the motherboard. The notch in one end denoted the side that had pin 1. FIG 1.13: A DIP Socket. As the amount of memory and the need for speed increased, manufacturers started to market modules containing several chips that allowed for easier installation and larger capacity. These modules come in a variety of physical configurations. 1.5.3.1 Single Inline Pinned Packages (SIPPs) The single inline pinned package (SIPP) is one of the first module forms of DRAM. It is a printed circuit board with individual DRAM chips mounted on it, as shown in Figure 1.14. A SIPP module is a rectangular card with a single row of CertGuaranteed. Study Hard and Pass Your Exam 220-301 fragile pins along the bottom edge. The SIPP was short lived because of the fragile nature of these pins. FIG 1.14: A 30-pin SIPP Module 1.5.3.2 30-Pin Single Inline Memory Modules (30-Pin SIMMs) Single inline memory modules (SIMMs) replaced SIPPs because they were easier to install. They can have as few as two or as many as nine individual DRAM chips that are attached to a printed circuit board. 30 gold or tin pins on the bottom of the SIMM provide a connection between the module and a memory slot on the motherboard. The pins on the front and back of a SIMM are connected, providing a single line of communication paths between the module and the motherboard. Each 30-pin SIMM provides an 8-bit data path, FIG 1.15: The 30-pin SIMM i.e., they are 8-bit-wide, and are found in 386 and 486 computers. 30-pin SIMMs are only available with FPM DRAM chips and are approximately 3.5" long and 0.75" high, though its height may vary. They have a single notch on the left end of the pins to ensure their correct orientation when installed. Note: 30-pin SIMMs are 8-bit-wide. Thus, on a 16-bit computer, you will need two rows of 30-pin SIMMs to communicate with the data bus and on a 32bit computer you will need four rows of 30-pin SIMMs. 1.5.3.3 72-Pin Single Inline Memory Modules (72-Pin SIMMs) With the advent of 32- and 64-bit CPUs, the bank began to take up too much space on the motherboard. To overcome this problem, 72-pin SIMMs were introduced. One 72-pin SIMM is 32-bit-wide. They are four times wider than an 8 bit-wide 30-pin SIMM. Some late model 486 computers and almost all Athlon, Pentium and Pentium Pro computers use 72-pin SIMMs. 72-pin SIMMs use either FPM DRAM chips or EDO DRAM chips and are approximately 4.25" long and 1" high, though the heights may vary. They have a notch on the left end of the pins and a notch in the center of the module to ensure their correct orientation when installed. CertGuaranteed. Study Hard and Pass Your Exam 220-301 FIG 1.16: The 72-pin SIMM 1.5.3.4 168-Pin Dual Inline Memory Modules (168-Pin DIMMs) The 168-pin dual inline memory module (168-Pin DIMM) has superseded the 72-pin SIMMs. It is similar to 72-pin SIMMs in appearance, but comes in a package with two rows of 84 pins making a total of 168 pins. The 84 pins on the front and the 84 pins on the back of a 168-Pin DIMM are not connected, providing two communication paths between the module and the motherboard. These are the memory packages used on virtually all Pentium II and Pentium III class motherboards, and FIG 1.17: The 168-pin DIMM on some earlier model and entry level Pentium 4 class motherboards. 168-Pin DIMMs provide larger amounts of RAM on a single module, are 64-bit-wide and are easy to install. SIMMs usually require matched pairs to form a bank of memory, whereas 168-Pin DIMMs require only one card. 168-pin DIMMs with FPM DRAM chips, EDO DRAM chips, PC66 SDRAM chips, PC100 SDRAM chips, and PC133 SDRAM chips are available. The PC66 168-pin DIMM, the PC100 168-pin DIMM and the PC133 168-pin DIMM indicates the system bus speed supported by the various DIMM modules; PC66 supports 66MHz Front System Bus (FSB), PC100 supports up to 100MHz FSB and PC133 supports up to 133MHz. 168-pin DIMMs are approximately 5.375" long and 1.375" high, though the heights may vary. They have two small off-center notches within the row of pins along the bottom of the module to ensure correct orientation on installation. 1.5.3.5 Double Data Rate SDRAM (DDR SDRAM) Double data rate SDRAM (DDR SDRAM) is a newer dual inline memory module. It is essentially the same as DIMMs but has 184-pins and can output data on both the rising and falling edges of the clock cycle. It is sometimes referred to as 184-pin DIMMs because it is similar in appearance to the 168-pin DIMM but has two rows of 92 pins making a total of 184 pins. As is the case with the 168-pin DIMM, the 92 pins on the front and the 92 pins on the back of a DDR SDRAM are not connected, thus providing two communication paths between the module and the motherboard. The DDR SDRAM is also 64-bit-wide. These are the memory packages used on most Pentium 4 class motherboards. DDR200 or PC1600, DDR266 or PC2100, DDR333 or PC2700, DDR400 or PC3200, DDR433 or PC3500, CertGuaranteed. Study Hard and Pass Your Exam 220-301 DDR466 or PC3700, and DDR533 or PC5200 are available. Unlike the 168-pin DIMM whose numbering indicated the FSB supported by the DIMM; DDR SDRAM numbering indicates the effective clock speed in MHz, or the theoretical maximum bandwidth output in MB per second that the DDR SDRAM can achieve. FIG 1.18: The 184-pin DIMM Thus DDR400 or PC3200 has an effective clock speed of 400MHz and a theoretical maximum bandwidth output of 3200 MB/s. In addition, DDR SDRAM is also available in dual channel modules, which allows the memory controller to split the data and simultaneously write to one physical module on the right and one on the left. Dual channel DDR SDRAM requires two DIMM slots and matched pairs to form a bank of memory. DDR SDRAM is approximately 5.375" DRAM chip Technologies The memory module form factor long and 1.25" high, supports various memory though the heights may vary. While DDR technologies, including Fast Page SDRAM and 168-pin DIMMs are Mode (FPM) DRAM; Extended approximately the same size, DDR Data Out (EDO) DRAM; SDRAM has only one off-center notch Synchronous DRAM (SDRAM); within the row of pins to ensure correct orientation upon installation. To use DDR Double Data Rate Synchronous SDRAM modules, your motherboard must DRAM (DDR SDRAM); and have 184-pin DIMM slots and a DDRDirect Rambus. enabled chipset. FPM DRAM offered an advantage over earlier memory technologies 1.5.3.6 Rambus Inline Memory Modules because it enabled faster access to data (RIMMs) located within the same row. Direct Rambus inline memory modules EDO DRAM, released in 1995, was (RIMMs), also known as Direct Rambus similar to FPM, but allowed DRAM (RDRAM) has a runs at data rates consecutive memory accesses to occur of 800MHz (PC800), 1066MHz (PC1066), much faster, enabling the CPU to and 1200MHz (PC1200) with a memory access memory 10 to clock speed of 400MHz, 533MHz and 15% faster than with FPM. 600MHz respectively. It transfers data on SDRAM, released in late 1996, is both clock edges similar to DDR SDRAM, designed to synchronize itself with the but unlike DDR SDRAM, which are 64-bittiming of the CPU, enabling the wide, RIMMs are only 16-bit-wide memory controller to know the exact necessitating the use of RIMMs in pairs; so clock cycle when the requested data its theoretical maximum bandwidth of will be ready, so the CPU no longer 1.6GB/sec is the same as the theoretical has to wait between memory accesses. maximum bandwidth of PC1600 DDR CertGuaranteed. Study Hard and Pass Your Exam 220-301 SDRAM chips also take advantage of SDRAM. These are the memory packages interleaving and burst mode functions, used on early, high end which make memory retrieval even Pentium 4 motherboards. faster. SDRAM modules come in RIMMs use a protocol-based approach to several different speeds so as to transfer data. This synchronize to the clock speeds of the requires a certain amount of overhead that systems they'll be used in. actually increases the amount of time for DDR SDRAM, released in late 2000, the first memory access. Despite its higher allows the memory chip to perform initial access latency, The RIMMs transactions on both the rising and bandwidth utilization is more efficient than falling edges of the clock cycle, DDR SDRAM because it can keep many effectively doubling the memory bus more pages charged at one time than DDR clock rate. SDRAM. The Intel i840 RDRAM DIRECT RAMBUS is a new DRAM controller enables RIMMs to keep up to 32 architecture. Direct Rambus pages open simultaneously. Thus RIMMs technology is extraordinarily fast and can transfer more data in a sustained can transfers data at speeds up to manner than DDR SDRAM, even 1066MHz over a narrow 16-bit bus accounting for latency. called a Direct Rambus Channel. This RIMMs are approximately 5.375" long and high-speed clock rate is possible due 1.375" high, though its height may vary. A to a feature called "double clocked," distinguishing feature of RIMMs is the heat which allows operations to occur on shield that covers the RDRAM chips, although some high speed DDR SDRAM both the rising and falling edges of the modules also incorporate a similar heat clock cycle. shield. RIMMs have two small offcenter notches within the row of pins along the bottom of the module to ensure correct orientation on installation and are installed in pairs. A continuity RIMM (C-RIMM) card must be inserted into all memory slots in the FIG 1.19: The 184-pin RIMM motherboard that are not populated by a RIMM to complete the signal lines which are a serial connection to the Rambus interface. This ensures the electrical integrity of the Rambus interface. 1.5.4 Memory Mapping Memory must be allocated for use by the CPU. This is called memory mapping and it uses hexadecimal addresses to define ranges of memory. The original processors developed by Intel were unable to use more than 1 MB of RAM, and the original IBM computer allowed only the first 640 KB of memory for direct use CertGuaranteed. Study Hard and Pass Your Exam 220-301 by the CPU. All MS-DOS applications were written to conform to this limitation. As application requirements grew, programmers needed to optimize the use of memory to make the most of the available space. This 1 MB of memory was divided into two sections. The first 640 KB was reserved for the operating system and applications and was referred to as conventional memory. The remaining 384 KB of RAM was referred to as upper memory and was used to running the computer's BIOS, video RAM, ROM routines. Although some early computer clones had firmware that could make direct use of the upper memory block Under MS-DOS and Microsoft Windows 3.x operating systems, conventional memory needed to be kept as free as possible for use by applications. MS-DOS memory optimization ensures that MS-DOS applications have as much of this memory as possible. This MS-DOS limitations does not apply to Windows 95 and later operating systems which operates in 32-bit mode or higher. However, the old memory problems still are a factor when running MS-DOS, Windows 3.x-based programs on older machines, or MS-DOS compatibility mode with the more advanced operating systems. Under MS-DOS-based operating systems and in MS-DOS compatibility mode, the memory modules or RAM is usually segmented into smaller blocks for actual use. These are: extended memory, conventional memory, expanded memory and upper memory. • RAM above the 1-MB address is called extended memory. With the introduction of the 80286 processor, memory was addressable up to 16 MB. This was increased to 4 GB with the 80386DX processor. Extended memory is accessed through himem.sys, which is an extended memory manager. The MS-DOS Protected Mode Interface (DPMI) allows multiple applications to access extended memory at the same time. Most memory-managers and applications, including the Microsoft operating systems that run in 32- bit mode, such as Windows 98, Windows ME and Windows 2000, uses DPMI. Some computers use shadow RAM to improve the performance of a computer. Shadow RAM rewrites, or shadows, the contents of the ROM BIOS and/or video BIOS into extended memory. This allows systems to operate faster when application software calls any BIOS routines. • Conventional memory is the first 640 KB of RAM, addressable by a computer operating in real mode, which is the only operating mode supported by MS-DOS. Without the use of special techniques, conventional memory is the only kind of RAM accessible in DOS mode and DOS mode programs. • Expanded memory is a 64-KB Real Mode and Protected section of memory, usually in upper Mode memory, that is used to provide a A computer operating in Real "window" in which data can be Mode can only run one written. Once in this area, the data can application at a time, with this be transferred to the expanded application having full control of memory. The data is paged or swapped the system resources. Real Mode to and from the CPU through this operates within the MS-DOS 1 window Expanded memory can MB RAM limitation. Real Mode provide up to 32 MB of additional is the only mode that is memory, and supported by MSDOS. because it is loaded from a 64-KB Beginning with 80286 section, it is below the 1- MB limit and processors therefore recognizable by MS-DOS. using an operating system such However, MS-DOS applications must as OS/2 or Windows, a computer be specifically written to take can create "virtual machines," advantage of expanded memory. providing all the functionality of Windows applications do not use a computer in Real Mode but expanded memory; 80386 and newer allowing multi-tasking, i.e., the CertGuaranteed. Study Hard and Pass Your Exam 220-301 running of a number of processors can emulate expanded applications at the same time. memory by using memory managers This is called Protected Mode such because the operating system as emm386.exe and himem.sys. An irregularity was found in the Intel protects the system resources from the direct control of chip architecture that allowed MSapplications. Instead the DOS to address the first 64 KB of operating system allocates extended memory on machines with system resources to the 80286 or faster processors. This special area is called the high memory applications. area (HMA). A software driver called an A20 handler must be run to allow the processor to access the HM A. Some versions of Windows use himem.sys for this purpose. However, himem.sys can load only a single program into this area. • Upper memory is the block of memory from 640 KB to 1024 KB, that is designated for hardware use, such as video RAM, BIOS, and memory-mapped hardware drivers that are loaded into high memory. 1.5.5 Determining Usable Memory The MS-DOS command mem, which can be run from a command prompt window in newer versions of Windows, provides a quick way to determine how the different areas in physical memory are being used and the total amount of RAM actually active on the system. Most MS-DOS and many early Windows systems load numerous device drivers and terminate-and-stay-resident (TSR) programs using the config.sys and autoexec.bat routines during the boot cycle. FIG 1.20: The MEM Command Switches TSRs are usually loaded into conventional memory by the operating system, taking up valuable space. Memory-management techniques are used to load these device drivers and TSRs into the upper memory, allowing more lower memory to be made available to applications. The use of 16-bit TSRs in Windows 95, Windows 98, Windows NT, Windows 2000, or Windows degrades system performance and can disable some of the more advanced memory-handling features of Windows. To determine which device drivers and TSRs are loaded, use the mem command with the /c switch. The /c switch is a classify switch. This determines how much conventional memory a certain real-mode program is using. CertGuaranteed. Study Hard and Pass Your Exam 220-301 FIG 1.21: Running MEM /c 1.6 Expansion Buses Expansion buses or slots are standardized connections that allow the installation of devices not soldered to the motherboard, in other words, they are used to connect devices to the computer via the motherboard. They allow the flow of data between internal and external devices via the motherboard's data bus. Early computers moved data between devices and the processor at about the same speed as the processor but as processor speeds increased, the movement of data through the bus became a bottleneck. Therefore, new expansion buses needed to be developed. 1.6.1 Internal Expansion Buses The devices connected to the motherboard through an expansion bus is regulated by the quartz crystal that sets the timing for the computer and provides a common reference point for performing actions. Most central processing units divide the crystal speed by two and every device soldered to the motherboard, including the keyboard chip and the memory controller chip, is designed to run at that speed. Although CPU speeds have continually increased as technology has improved, the speeds of expansion cards or daughterboards that are inserted in expansion buses has remained relatively constant as it was not practical to redesign and replace every expansion card each time a new processor was released. The expansion cards thus lagged behind the CPU in terms of speed. To overcome this dilemma, designers divided the external data bus into two parts: the Front System Bus and the Expansion Bus. • The System Bus or Front System Bus (FSB) supports the CPU, RAM, the keyboard chip, the memory controller chip, and other motherboard components that must run at the same speed as the CPU. • The Expansion Bus supports any add-on devices by means of the expansion slots and runs at a steady rate, based on the specific bus design. Because the CPU runs off the system clock, upgrading a CPU requires changing only the timing of the FSB, and the existing expansion cards continue to run as before. Most motherboards have jumper settings that changes the FSB to match the CPU, though some newer motherboards have their FSB settings controlled in BIOS. CertGuaranteed. Study Hard and Pass Your Exam 220-301 1.6.1.1 Industry Standard Architecture (ISA) The IBM engineers that designed the first personal computer or PC in 1981 designed the computer as an open system, capable of using standard, off-the-shelf add-on components. This allowed third-party developers to manufacture expansion cards that could be inserted into the computer's expansion bus. IBM also allowed competitors to copy and reproduce the expansion bus by establishing an industry standard called the Industry Standard Architecture (ISA) interface. However, the expansion bus was called the PC bus. A host of third-party companies developed products that enhanced the basic computer design and kept prices much lower for add-on components than those for competing proprietary systems such as the Apple II. ISA Cards The first-generation IBM XT with the Although the first computer expansion Intel 8088 processor had an 8-bit bus external data bus and ran at a speed of was based on the Industry Standard 4.77 MHz. These machines were sold Architecture (ISA) interface, it was not with an 8-bit expansion bus that ran at referred to as the ISA bus. The term 8.33 MHz. In 1984, IBM released the ISA AT with the Intel 80286 16-bit only became official in 1990 when the processor. IBM included a new PCI expansion bus that was compatible bus was developed. Therefore, the 8-bit with previously released devices by slot adding an extension bus that allowed was called the XT interface, and the 16the insertion of either an 8- it bit slot expansion card or a 16-bit expansion was called the AT interface. When we card. This change resulted in the refer to standard 16-bit ISA slot. The new 16an ISA slot or an ISA card, we bit expansion bus ran at a top speed of generally refer 8.33 MHz. to the 16-bit AT interface. The ISA expansion bus is usually black and can be found on mostcomputer systems, from the second-generation IBM computer to most of the recent computers. The newest motherboards, especially ones with integrated sound, video and LAN, have tended not to use the ISA design. A reason for this is the ISA interface's lack FIG 1.22: An 8-bit ISA Expansion of speed and compatibility problems Bus stemming from card design. As CPU performance increased and applications became more powerful, expansion cards needed to keep up with improved hard disk drives, display adapters, and similar products. Expansion cards must also use system resources in a way that does not FIG 1.23: A 16-bit ISA Expansion create conflict with other devices. ISA Bus cards often used an array of jumpers and switches to set addresses for memory or interrupt request (IRQ) locations usage. CertGuaranteed. Study Hard and Pass Your Exam 220-301 The need to overcome the expansion card's lack of speed and compatibility problems led to a search for a new, standard expansion card interface. 1.6.1.2 Micro Channel Architecture (MCA) In 1986 the market was by the new 386 computers with 32-bit architecture. Most computer manufacturers continued to use the basic ISA design and MS-DOS. Thus, expansion cards based on ISA technology for the 286 AT class computers could be placed in a new 386 computer without problems. IBM, however, developed the PS/2 (Personal System/2) computer, that included a proprietary expansion bus called the Micro Channel Architecture (MCA) as part of the design. This expansion bus ran at 10 MHz, and offered more performance and provided a 32-bit data path, but was not compatible with older ISA cards. The MCA was able to "self-configure" devices as MCA devices were shipped with a configuration disk that was used to automatically configure the device's usage of system resources. However, the PS/2 and its proprietary MCA expansion bus was not able to compete with the 386. hence, MCA FIG 1.24: The MCA Expansion Bus expansion cards were few and far between, and more expensive than competing interface designs. 1.6.1.3 Extended ISA In 1988 an improved a new 32-bit, 8-MHz version of the ISA called Extended ISA was developed. The EISA slot, like the ISA slot, is usually black and is compatible with the older ISA cards, with a two-step design that uses a shallow set of pins to attach to ISA cards and a deeper connection for attaching to EISA cards. Although EISA is faster and cheaper than MCA, it never gained much more acceptance than MC A. Confusion between MCA and EISA technology-along with a limited need for cards that ran at the faster rate and the fact that only a few display, drive controller, and FIG 1.25 The EISA Expansion Bus network cards were made available-led to the early demise of both bus technologies. 1.6.1.4 VESA Local Bus Expansion card manufacturers had to speed up graphics adapter performance to keep up with the evolving operating system technologies, such as Microsoft Windows. Unlike MS-DOS, the Windows graphical user interface required a much faster display adapter, because every pixel had to be represented and refreshed; not just lines of character data as was the case with MS-DOS. About the same time, laser printers and graphics programs like PageMaker and CorelDRAW entered the mainstream market, extending the desktop publishing revolution. The hardware industry developed the VESA local bus to meet the need for a faster CertGuaranteed. Study Hard and Pass Your Exam 220-301 expansion interface. As shown in Figure 1.26, the VESA local bus slot is usually brown and is located at the end of a 16-bit ISA expansion slot. The VESA local bus had a short life span and was used only in 386 and 486 computers. The expansion FIG 1.26: The VESA Expansion Bus cards based on this design are connected directly to the system-bus side of the computer's external data bus. The speed of the system data bus is based on the clock rate of the motherboard's crystal. This was usually 33 MHz, and VESA local bus cards usually ran at half that rate, far outpacing the ISA bus. The chip design for the VESA local bus controller was relatively simple because most of the core instructions were hosted by the ISA circuits already on the motherboard, but the actual data passes were on the same local bus as the one used by the CPU. The design specification provides two additional performance-boosting features: burst mode and bus mastering. In burst mode, VESA local bus devices gain complete control of the external data bus for up to four bus cycles, passing up to 16 bytes of data in a single burst. Bus mastering allows the VESA local bus controller to arbitrate data transfers between the external data bus and up to three VESA local bus devices without assistance from the CPU. This limit of three devices also limited the maximum number of VESA local bus slots to three and called for the use of a coprocessor. The actual connectors on the motherboard resemble an ISA slot with an additional short slot aligned with it. On systems that support this interface, one to three slots are located on the side of the motherboard closest to the keyboard connection. 1.6.1.5 Peripheral Component Interconnect (PCI) The Peripheral Component Interface (PCI) expansion bus, also known as computerI, was developed in 1990 and is usually a white slot. It overcomes the limitations of ISA, EISA, MCA, and VESA local bus, and it offers the performance needed for today's fast computer systems. There are many similarities between PCI and the older VESA local bus specifications. Both are local bus systems with 32-bit data paths and burst modes. The original PCI design operates at roughly the same speed as the VESA local bus. However, the important differences between them allowed PCI to dominate in expansion bus technology. These differences stem from the following features: • The PCI's special bus and chip set are designed for advanced bus-mastering techniques and full arbitration of the PCI local bus. This allows support of more than three PCI slots. • The PCI bus has its own set of four interrupts, which are mapped to regular IRQs on the computer system. If a computer has more than four PCI slots, some will share interrupts and IRQs. • The PCI bus allows multiple bus-mastering devices. Advanced FIG 1.27: Three PCI Expansion Buses controllers such as SCSI (Small Computer System Interface) cards can incorporate their own internal bus mastering and CertGuaranteed. Study Hard and Pass Your Exam 220-301 directly control attached devices, then arbitrate with the PCI bus for data transfers across the system bus. • The PCI's autoconfiguration allows the computer's BIOS to assign the IRQs and most PCI cards have no switches or jumpers. Most new computers on the market have one or more ISA slots for backward compatibility; however, most expansion cards are now built using the PCI interface. 1.6.1.6 Accelerated Graphics Port (AGP) In the early days of PCI, the major market for that technology was the high-performance display adapter. The popularity of PCI led to its dominance of the expansion bus market. Today, the PCI market includes NICs, sound cards, SCSI adapters, Ultra Direct Memory Access (UDMA) controllers, and DVD (digital video disc) interfaces. However, the variety of devices posed a problem for display-card designers: Having more cards on a single bus FIG 1.28: The AGP Expansion Bus slowed down the performance, just when the increasing popularity of 24-bit graphics and 3D rendering called for greater demands on the display system. This led Intel to developed the Accelerated Graphics Port (AGP), a single slot tuned for the display adapter. The AGP removes all the display data traffic from the PCI bus and gives that traffic its own 525-MB-per-second pipe into the system's chip set and, from there, straight to the CPU. It also provides a direct path to the system memory for handling graphics. The AGP slot is the only one of its kind on the motherboard and is usually the brown slot closest to the keyboard connector. It is also set farther from the back of the computer's case than the PCI slots. AGP connectors are found only on Pentium II-based and later computers or on similar CPUs from non-Intel vendors. As shown in Figure 1.28, the AGP expansion bus is usually brown, is usually the uppermost expansion bus on the motherboard and is set further from the back of the motherboard that the PCI and ISA FIG 1.30: An ACR Sound Card expansion busses. CertGuaranteed. Study Hard and Pass Your Exam 220-301 1.6.1.7 The ACR, AMR and CNR Expansion Bus Almost every PC requires some form of connectivity and sound. Network connectivity devices, such as network cards and modems, as well as sound cards tend to suffer from electronic FIG 1.29: An ACR Expansion Slot (bottom) noise to some degree. To help manufacturers develop a standard connection free of electronic noise for these devices, Intel forwarded the AMR (Audio/Modem Rise) expansion bus that was soon superseded by the CNR (Communication and Networking Riser) and the ACR (Advanced Communications Riser) expansion busses in early 2000, while motherboards with started appearing in 2002. The ACR, AMR and CNR expansion busses is a dedicated expansion bus to support network, modem or sound devices. However, ACR AMR and CNR expansion busses are not defined as an aftermarket expansion bus but is meant to be support devices designed for the specific motherboard by the motherboard manufacturer. The has a standard connection but the pin outs vary from system to system. 1.6.2 Configuring Expansion Cards 1.6.2.1 I/O Port Addresses The bus system establishes a connection between the CPU and expansion devices and provides a path for the flow of data. The computer must track and control which device is sending data and which device is receiving data to ensure orderly communication. I/O port address and the address bus establish a method of orderly communication by assigning a unique I/O port address to each device. If the CPU needs to communicate with a device, BIOS routines or device drivers can use I/O addresses to initiate conversations over the external data bus. I/O port addresses are patterns of 1s and 0s transmitted across the address bus by the CPU. The CPU must identify the device before any data is placed on the bus. The CPU uses two bus wires-the Input/Output Read (IOR) wire and the Input/Output Write (IOW) wire-to notify the devices that the address bus is being used to read to or write from a particular device. To allow communication directly between the CPU and a device, each device responds to unique, built-in patterns or code. If the CPU needs to check the error status of a hard disk drive controller, for instance, it activates the IOW wire and puts the correct pattern of 1s and CertGuaranteed. Study Hard and Pass Your Exam 220-301 0s onto the address bus. The controller then sends back a message describing its error status. All I/O addresses define the range of patterns assigned to each device's command set. The device ignores all commands outside its range. All devices must have an I/O address, and no two devices can have overlapping ranges. Basic devices on the address list have preset I/O addresses that cannot be changed. Other devices must be assigned to the open addresses, and they must be configured at installation. I/O addresses have 16 bits and are displayed with a hexadecimal number. These hexadecimal I/O addresses must use capital letters as they are case-sensitive. Table 1.6 lists the standard I/O port address assignments. TABLE 1.6: Standard I/O Port Address Assignments I/O Port Address 000h-00Fh 000h-00Fh 020h-021h 020h-021h 040h-043h 040h-043h 060h-063h 060h-063h 070h-071h 080h-083h 080h-083h 0A0h-0AFh 0A0h-0AFh 0C0h-0CFh 0C0h-0CFh 0E0h-0EFh 0E0h-0EFh 0F0h-0FFh 100h-1FFh 100h-1FFh 200h-20Fh 200h-20Fh 210h-217h 210h-217h 220h-24Fh 220h-26Fh 278h-27Fh 278h-27Fh 2B0h-2DFh 2F0h-2F7h 2F8h-2FFh 2F8h-2FFh 300h-31Fh 300h-31Fh 320h-32Fh 320h-32Fh 378h-37Fh Device DMA chip 8237A First DMA chip 8237A PIC 8259A First PIC 8259A PIT 8253 PIT 8253 PPI 8255 Keyboard controller 8042 Real-time clock DMA page register DMA page register NMI mask register Second PIC 8259A Reserved Second DMA chip 8237A Reserved Reserved Reserved for coprocessor 80287 Unused Available Game adapter Game adapter Extension unit Reserved Reserved Available Parallel printer Second parallel interface EGA Reserved COM2 COM2 Prototype adapter Prototype adapter Hard disk controller Available Parallel interface CertGuaranteed. Study Hard and Pass Your Exam 220-301 378h-37Fh parallel interface 380h-38Fh SDLC adapter 380h-38Fh SDLC adapter 3A0h-3AFh Reserved 3A0h-3AFh Reserved 3B0h-3BFh Monochrome adapter/parallel interface 3B0h-3BFh Monochrome adapter/parallel interface 3C0h-3CFh EGA 3c0h-3CFh EGA 3D0h-3DFh CGA 3D0h-3DFh CGA 3E0h-3E7h Reserved 3E0h-3E7h Reserved 3F0h-3F7h Floppy disk controller 3F0h-3F7h Floppy disk controller 3F8h-3FFh COM1 3F8h-3FFh COM1 The I/O Address are set in two different was for expansion devices depending on whether the device is Plug and Play or not • On non-Plug and Play compatible devices, I/O addresses are often set by changing jumpers, changing DIP switches, or through use of software drivers. DIP switches are like mini-rocker panel switches. Jumpers are small caps that are used to link pairs of pins to close a circuit. Devices using these techniques should have instructions on how to configure the settings and locate the switch block or jumpers. • On Plug and Play systems, Plug and Play compatible expansion cards are self-configuring, and usually no intervention is needed to set I/O addresses for those cards. It is possible for Plug and Play cards to conflict with older ISA cards that do not recognize the Plug and Play devices. If you are confronted with this problem, the I/O Address for the ISA card may need to be reset or the ISA card may need to be replaced with a Plug and Play version. Devices assigned overlapping I/O addresses do not respond to commands correctly and often stop functioning. In addition, I/O overlaps can cause the computer to lock up intermittently. However, I/O overlaps do not arise automatically. They usually arise immediately after a new device is installed. The best way to prevent I/O address overlaps is to document all I/O addresses. 1.6.2.2 Interrupt Request (IRQ) Interrupt Requests (IRQs) are used to control the flow of communication and prevent multiple devices from communicating at the same time. Controlling the flow of communication is called interruption. Every CPU has a wire called the interrupt (INT) wire. If voltage is applied to the wire, the CPU interrupts what it is doing and attends to the device. On older computers, a specific type of chip, called the 8259 chip, is used to assist the CPU to detect which device requesting interrupts; on newer computers the function of the 8259 chip is incorporated into the chipset. Every device that needs to interrupt the CPU is provided with a wire called an IRQ. If a device needs to interrupt the CPU, it applies voltage to the 8259 chip through its IRQ wire. The 8259 chip in turn alerts the CPU, by means of the INT wire, that an interrupt is pending. The CPU then uses a wire called an INTA (interrupt acknowledge) to signal the 8259 chip to send a pattern of 1s and 0s on the external data bus. This information conveys to the CPU which device is interrupting. The 8088 computers used only one 8259 chip, which limited these computers to using only eight IRQs. Because a keyboard and system timer were fixtures on all computers, these IRQs were permanently wired CertGuaranteed. Study Hard and Pass Your Exam 220-301 into the motherboard. The remaining six wires were then made part of the expansion bus and were available for use by other devices. 80286-based computers used two 8259 chips to add 8 more available IRQs. These new wires were run to the extension on the 16-bit ISA expansion slot. However, the CPU has only one IRQ wire, thus one of the IRQs is used to link the two 8259 chips together. This is also referred to as cascading and leaves a total of 15 available IRQs. Table 1.7 lists the computer's typical IRQ assignments. TABLE 1.7: Typical IRQ Assignments IRQ Function IRQ 0 System timer - cannot be changed IRQ 1 Keyboard controller - cannot be changed IRQ 2/9 Available IRQ 3 COM2, COM4 - can be changed IRQ 4 COM1, COM3 - can be changed IRQ 5 LPT2 - can be changed IRQ 6 Floppy disk controller - cannot be changed IRQ 7 LPT1 - can be changed IRQ 8 Real-time clock - cannot be changed IRQ 10 Available IRQ 11 SCSI/available IRQ 12 Available IRQ 13 Math coprocessor - cannot be changed if a math coprocessor is present IRQ 14 Primary IDE controller - cannot be changed IRQ 15 Secondary IDE controller - can be changed As can be seen from Table 1.7: • IRQ 2 and IRQ 9 are wired together and are thus the same IRQ; • Three IRQs are hardwired. These are IRQ 0, IRQ 1 and IRQ 8; • Four IRQs default to specific types of devices but can be changed. These are IRQ 3, IRQ 4, IRQ 5 and IRQ 7; • Four IRQ assignments are common to all computers. These IRQ 6, IRQ 13, IRQ 14 and IRQ 15. Of these four IRQ 6 and IRQ 14 cannot be changed, and IRQ 13 can be changed only if the computer does not have a math coprocessor. IRQ 15 can be changed; • Four IRQs are not specific and are available for use. These are IRQ 2/9, IRQ 10, IRQ 11 and IRQ 12. Like I/O addresses, IRQs are either set automatically if the device is Plug and Play compatible, or manually if the device is non-Plug and Play. Note: Some legacy devices have a limited number of IRQ settings; you might need to change the IRQs of one of the other devices to free an IRQ that can be used by these legacy devices. 1.6.2.3 Direct Memory Access (DMA) As the CPU handles interrupts and accesses I/O addresses, it must move a lot of data, using considerable CPU power and time. To reduce CPU usage, the 8237 chip is installed on the system to work with the CPU. The 8237 chip is also called the DMA chip. The only function of this chip is to move data. It handles all the data passing from peripherals to RAM and vice versa. However, DMA transfers are not automatic. Hardware and device drivers must be designed to take advantage of this chip. Originally, DMA was used only to transfer data between floppy disk drives and RAM; early computers had only four wires and one DMA chip. Any device requiring DMA had to send a request, just like an IRQ. DMA channels use the same rules as IRQs. As with the 8259 chip, DMA availability soon became a problem because an insufficient number of channels that were available. A second cascaded DMA chip was CertGuaranteed. Study Hard and Pass Your Exam 220-301 added for 80286-based computers. Not many devices use DMA, but sound cards, a few SCSI controllers, and some CD-ROM drives and network cards do require DM A. Just as with IRQs and I/O addresses, DMA can be set by either automatically or manually, depending n whether the device is plug and Play compatible or not. Table 1.8 lists the typical DMA channel assignments. TABLE 1.8: The Typical DMA Channel Assignments DMA Channel Function 0 Available 1 Available 2 Floppy disk controller 3 ECP (Enhanced Capabilities Port) parallel/available 4 First DMA controller 5 Second sound card 6 SCSI/available 7 Available 1.6.3 External Expansion Buses IBM created preset combinations of IRQs and I/O addresses for serial and parallel devices. These preset combinations are called ports. The word port simply means a portal or two-way access. The preset combinations are called COM ports for serial devices and LPT (line printer) ports for parallel devices. The purpose of a port is to make installation easier. Modems and printers, therefore, do not require IRQ or I/O settings. When assigned to an active port, they will work. Table 1.9 lists the standard computer ports. TABLE 1.9: The Standard Computer Ports Port I/O Address IRQ COM1 3F8 4 COM2 2F8 3 COM3 3E8 4 COM4 2E8 3 LPT1 378 7 LPT2 278 5 Most computers have rear panel connectors with built-in ports with cable connections either directly to the motherboard or in an expansion slot. In this case, the standard port addresses and IRQs are assigned to them. This makes it possible to install an external device simply by plugging in the port and assigning addresses to the device. If necessary, these ports can be disabled in the CMOS setup, freeing their I/O addresses and IRQs for another device. 1.6.3.1 Serial Ports The original 8088-based IBM computers were equipped with two serial ports: COMl, which was set to IRQ 4, and COM2, which was set to IRQ 3. Although those two IRQs are still the standard for COM ports 1 and 2, many BIOS routines will allow different IRQ assignments or may allow an unused port to be disabled. Because of the limited number of IRQ addresses available, additional COM ports have to share IRQs with the existing ports. Therefore COM3 shares IRQ 4 with COM1, and COM4 shares IRQ 3 with COM2. To enable use of these additional ports, FIG 1.31: A DB9 Serial Port COM3 was assigned I/O address 3E8-3EF, and Connector COM4 was assigned I/O address 2E8-2EF. This CertGuaranteed. Study Hard and Pass Your Exam 220-301 sharing was possible because the IRQ-sharing devices would be unlikely to use them at the same time. The serial port on the computer has a 9-pin male connector. 1.6.3.2 Parallel Ports LPT ports used are for parallel data connections and are also referred to as parallel ports. The original IBM standard LPT port did not provide bidirectional communications and was designed solely for one-way data streams to a printer. The standard addresses are IRQ 7 for LPT1 and IRQ 5 for LPT2, if it is present. Many devices, such as tape dives, SCSI drives, or modems, that can use the parallel port at the back of the computer are manufactured today, reducing costs. These devices use bidirectional communication and, therefore, need an interrupt. The modern parallel port has a 25-pin female connector. On FIG 1.32: The DB25 Parallel Port newer computers Connector USB connections are used rather than the parallel port. The parallel port on the computer has a 25-pin female connector. 1.6.3.3 IEEE 1394 FireWire Serial Interface The IEEE 1394, known also by its Apple trade name of FireWire, is a serial interface for connecting external peripherals or devices to the computer. This is a high-speed serial interface that allows for the connection of up to 62 devices on a chain, at data transfer rates of up to 50 MB per second. This new interface offers several advantages: a hot swap capability, small and inexpensive connectors, and a simple cable design. Currently, few devices and motherboards support IEEE 1394, but it is seen as a viable method for connecting multimedia devices like camcorders and other consumer electronic devices to the computer. Its isochronous transfer method, i.e., it transfers data at a constant rate, makes it a suitable option for multimedia products. Currently, many IEEE 1394 computer FIG 1.33: Fire Wire Cable products are expensive and there is no provision for connecting internal devices. 1.6.3.4 Universal Serial Bus CertGuaranteed. Study Hard and Pass Your Exam 220-301 The newest expansion bus is the Universal Serial Bus (USB). It connects external peripherals such as mouse devices, printers, modems, keyboards, joysticks, scanners, printers and digital cameras to the computer. The USB port is a thin slot and most FIG 1.34: USB Ports included in the Rear Panel newmotherboards Connectors offer two USB ports, located near the keyboard connector. They can also be provided through an expansion card. USB supports isochronous and asynchronous data transfers. Isochronous connections transfer data at a guaranteed constant rate while asynchronous data can be transferred whenever there is no isochronous traffic on the bus of delivery, i.e., it is transfers data intermittently. USB 1.1 supports data transfer rates of 1.5 megabits per second (Mbps) asynchronous transfer rate for devices, such as a mouse or keyboard, that do not require a large amount of bandwidth; and 12 Mbps isochronous transfer rate for high-bandwidth devices such as modems, speakers, scanners, and monitors. The guaranteed constant data-delivery rate provided by isochronous data transfer is required to support the demand of multimedia applications and devices. USB devices can be attached to the computer while the computer is powered and in operation. The new device will usually be recognized by an operating system that has Plug and Play capability, and the user will be prompted for drivers, if required. USB is a new standard, and some early USB ports and chip sets might not properly support some newer devices and some USB devices may require an external power supply. 1.6.4 Cables and Connectors Cables and connectors are a very common source of problems. If a peripheral device that had been working recently does not work, check the cables for loose connections; for bent or broken pins on the connector; and for worn or frayed cables. The following section discusses the various computer cables. 1.6.4.1 Parallel Printer Cables Parallel printer ports and cables are used to connect printers and other external devices such as CD-ROM drives, tape drives, and scanners. Centronics Corporation invented the most common type. It is an 8-bit parallel connection FIG 1.35: A with handshaking signals between the printer and the Centronics Connector computer-these tell the computer when to start or stop sending data. A standard printer cable is CertGuaranteed. Study Hard and Pass Your Exam 220-301 configured with a 36-pin Centronics connector on the printer end and a standard DB25 (25-pin) parallel port connector on the computer end. The original parallel port was designed only to send information to printers and was unidirectional. However, some bidirectional communication was possible by manipulating the handshaking lines. Today, computer manufacturers have developed updated versions that allow better bidirectional communication while maintaining the original Centronics specification. The Institute of Electrical and Electronic Engineers (IEEE) developed the IEEE 1284 standard to oversee the standardization of these ports. 1.6.4.2 Serial Port Cables A serial port allows a computer to send data over long distances by converting parallel data to serial data. Typical computers will have one or two serial ports, usually designated as COM1 and COM2. The serial port on the computer is a 9-pin male connector, shown in Figure 1.36. 1.6.4.3 Keyboard Cables Keyboards are manufactured in two different styles with different cables and connectors. Earlier versions used a 5-pin DIN connector while most new keyboards use a 6-pin mini-DIN connector as used on a PS/2 mouse. Connectors are available to convert the 5-pin DIN connector to a 6-pin mini-DIN connector. Although they have a different number of pins, they use the same wires and pinouts. FIG 1.36: A DB9 Serial Port Connector FIG 1.37: Keyboard Connectors 1.7 Input Devices 1.7.1 The Keyboard the Keyboard is one of the most basic system components on a computer. It is the primary input device and s used for entering commands and data into the system. Since the introduction of the original IBM PC, IBM has created three keyboard designs, and Microsoft has augmented one of them. These designs have become de facto standards in the industry and are shared by virtually all PC manufacturers. These keyboard types are: the 83-key PC/XT keyboard, which was sold with the original IBM PC; the 84-key AT keyboard, which was sold with the AT computer; the 101-key Enhanced keyboard, which replaced the AT keyboard; and the 104key Windows keyboard. In 1986, IBM introduced the 101-key Enhanced keyboard for the newer XT and AT models. Other companies quickly copied this design, which became the standard on Intel-based PC systems until the introduction of the 104-key Windows keyboard in 1995. The 101-key Enhanced keyboard originally used the five-pin DIN keyboard connector to connect to the AT motherboard but was replaced by the six-pin mini-DIN keyboard connector with the advent of the ATX motherboard. With the introduction of Windows 95, a modified version of the 101-key Enhanced Keyboard, called the CertGuaranteed. Study Hard and Pass Your Exam 220-301 104-key Windows keyboard, was introduced. This keyboard was developed by Microsoft and became the de facto industry standard for keyboard layouts. This layout includes left and right Windows (WIN) keys and an Application key that are used for operating system and application-level keyboard combinations. The WIN keys open the Windows Start menu, while the Application key simulates the right mouse button. Several WIN key combinations offer preset macro commands as well. Table 1.10 lists the WIN key combinations used with the 104-key Windows keyboard. TABLE 1.10: WIN Key Combinations Key Combination WIN+R WIN+M Shift+WIN+M WIN+D Operation Opens the Run dialog box Minimize all open applications on the desktop Reverses the WIN+M operation Toggles between minimizing all open applications on the desktop and reversing this operation WIN+F1 Opens Windows Help WIN+E Starts Windows Explorer WIN+F Opens the Find Files or Folders dialog box Ctrl+WIN+F Opens the Find Computer dialog box WIN+Tab Cycles through the taskbar buttons WIN+Break Displays the System Properties dialog box Most older 104-key Windows keyboards have the PS/2 keyboard connector but most newer keyboards connect to the PC via a USB port instead of the standard PS/2 keyboard port. Although most current motherboards still include the standard serial, parallel and PS/2 ports, which are now called legacy ports, socalled legacy-free systems provide only USB ports. To use a USB keyboard, you BIOS must support USB Legacy mode to allow non-USB aware system to recognize the USB keyboard. Most modern computers include USB Legacy mode, although it might be disabled by default in the system BIOS. 1.7.2 Pointing Devices The Windows GUIs necessitate the use of a mouse. The traditional mouse contains a small, rubber ball that rolls as you move the mouse. This ball rests against two rollers: one for translating the x-axis movement and the other for translating the y-axis movement. These rollers are typically connected to small disks with shutters that alternately block and allow the passage of light. Small optical sensors detect movement of the wheels by watching an internal infrared light blink on and off as the shutter wheel rotates. These blinks are translated into movement along the axes. This type of setup, called an opto-mechanical mechanism, is still the most popular type of mouse mechanism. The other major method of motion detection is optical and use optical technology to detect movement, but have no moving parts of their own. The optical mouse can work on almost any surface. Optical mice as well as traditional ball-type mice, are available as corded or cordless models. Cordless balltype mice are usually much larger than ordinary mice because of the need to house both the ball mechanism and batteries, but cordless optical mice are about the same size as corded mice. Cordless mice use either infrared (IR) or radio frequency (RF) receivers to replace the cable. The receiver is plugged into the mouse port, while the battery-powered mouse contains a compatible transmitter. IR devices must have a clear lineofsight between the input device and the receiver, while RF receivers do not require line-of-sight. The connector used to attach your mouse to the computer can be serial, PS/2 or USB. A DB-25 or DB-9 connector was used on most older mice to connect to the serial port on the motherboard. These mice use the system resources allocated to the COM port to which it is connected. In 1987, IBM introduced a dedicated mouse port built into the motherboard of their PS/2 computer. This port is often referred to as a PS/2 mouse port. These ports accept a connector that is identical to the mini-DIN connector. CertGuaranteed. Study Hard and Pass Your Exam 220-301 Note: The PS/2 ports used for both keyboard and mouse connections are physically and electrically interchangeable, but the data packets they carry are not. Therefore, a PS/2 keyboard will not function when connected to the dedicated mouse port and the PS/2 mouse will not function when connected to the keyboard port. On most motherboards, the dedicated mouse port is color coded green while the PS/2 keyboard port is color coded purple. Most modern mice ship with a USB connector that can be connected to any USB port. To use the USB mouse outside of the normal Windows operating system, such as in Windows Safe mode, USB Legacy mode must be enabled in your computer's BIOS. USB Legacy mode enables non-USB-aware systems to recognize a USB keyboard and mouse. Some USB mice are also sold with a USB-to-PS/2 adapter that allows you to connect a USB mouse to the dedicated mouse port. These mice are similar to Serial-PS/2 hybrid mice that are usually shipped with a mini-DIN to DB-9 or DB-25 adapter. These hybrid mice contain circuitry that automatically detects the type of port to which the mouse is connected. Note: The USB-to-PS/2 and mini-DIN-toDB-25 adapters that ship with hybrid mice cannot be used to connect a mouse to an interface that the mouse was not designed for. 2. Storage Devices The computer has a number of different storage devices on which data can be stored. These devices are also referred to as disk drives and come in assorted shapes and sizes. The first disk drives were physically large but small in capacity and were very expensive. Today, disk drives are physically small, large in capacity and are comparatively inexpensive. In addition there are different types of disk drives: hard disk drives, floppy and stiffy disk drives, CD-ROM and DVD drives, and CD-R and DVD-Ram drives. 2.1 Floppy Disk Drives The most basic input device is the floppy disk drive. It was first developed in 1972 by IBM for their System 370 computers. These drives used 8-inch floppy disks. Other companies adapted the same basic design for their computers. The floppy disks came pre-formatted, and only worked on a given operating system or computer. This resulted in high-cost drives and reduced the ability to use FIG 2.1: 5.25-Inch and 3.5-Inch Floppy Disk floppies as a quick means of Drives transporting files from one system to another. When IBM introduced the personal computer in 1981, it came standard with a 5.25-inch floppy disk drive. CertGuaranteed. Study Hard and Pass Your Exam 220-301 The 5.25-inch floppy disk drive was replaced by a 3.5-inch version that was also called a stiffy disk drive. The 3.5-inch floppy disk drive uses the same technology as the 5.25-inch version drive but uses a 3.5-inch disk encased a plastic coat. The floppy disk drive is an inexpensive read/write removable media as the data stored on a floppy disk can be moved from one computer to another, provided both have similar floppy disk drives. All floppy disk drives are connected to the motherboard's external data bus by a 34-lead ribbon cable, shown in Figure 2.3. This cable has a seven-wire twist in lines 10 through 16 to ensure that when two floppy disk drives are attached, the drive-select and motorenable signals on those wires can be inverted to select the primary active drive, designated FIG 2.2: 5.25-Inch and 3.5-Inch Floppy FIG 2.3: The Twisted Disks the A drive Cable by the BIOS. The power connection for a floppy disk drive, is either the large, Molex-type connector on the 5.25-inch floppy disk drive or the mini connector on the 3.5inch floppy disk drive. Once you have physically installed a floppy disk drive, you must run the BIOS Setup program to adjust the proper CMOS settings for the drive type and capacity as well as the correct drive letter. Floppy disk drives are one of the most fragile parts of a computer system. They are highly susceptible to failure because their internal components are directly exposed to the outside world. Often, there is only a small door or slot that separates the R/W heads from dust, grime, and cigarette smoke. Floppy disk drives are also often the victims of inverted disks, paper clips, and other foreign objects that can cause mechanical damage. They are however inexpensive and easy to replace. The only preventive maintenance required on them is to keep them clean. Cleaning kits are available in most computer and discount stores. CertGuaranteed. Study Hard and Pass Your Exam 220-301 If a floppy disk drive does not work, the first thing you should suspect is the floppy disk. Make sure that the disk is not write protected or try another formatted disk. Beware not to test a drive by using a disk that contains important data as the disk drive may destroy any disks placed into it if the drive is faulty. If two or more disks are unreadable, then drive is probably faulty. 2.2 Hard Disk Drives Hard disk drives are mass storage devices and all modern computers have at least one hard disk drive. The first hard disk drives were small in capacity, physically large, and expensive in comparison with the hard disk drives of today. They were about 4 inches tall, 5.25 inches wide, and 8 inches long. The first personal computer to include a hard disk drive was IBM's XT computer of 1981. This computer came with a 10-MB hard disk drive installed in it; but the first hard disk drives were released in the late 1970s. These drives were initially called fixed disks because they were not removable. Hard disk drives are composed of several platters, matched to a collection of R/W heads and an actuator. Unlike floppy disk drives, a hard disk drive is sealed, although it has an aperture with an air filter. As it is sealed, it cannot be contaminated by dust or smoke from the surrounding environment while the aperture allows the air pressure to be equalized between the interior and the exterior of the drive. The aim of the hard disk drive is to access data FIG 2.4: A Hard Disk Drive stored on a flat surface quickly and directly. To do this, two different motions are required. As the disk spins, the R/W heads move across the platter perpendicular to the motion of the disk. The R/W heads are mounted on the ends of the actuator arms. A critical element in hard disk drive design is the speed and accuracy of these actuator arms. 2.2.1 Geometry Hard disk drives are composed of one or more disks or platters on which data is stored. The geometry of a hard disk drive determines how and where data is stored on the surface of each platter, and thus the maximum storage capacity of the drive. In other words, it is the organization of data on the platters. There are five numerical values that describe the hard disk drive's geometry. These are Heads, Cylinders, Sectors CertGuaranteed. Study Hard and Pass Your Exam 220-301 Per Track, Write Precompensation, and Landing Zone. Write precompensation and landing zone are obsolete on modern hard disk drives. The other three values, i.e., the values for cylinders, heads, and sectors per track are known collectively as the CHS values. The capacity of any hard disk drive can be determined from these three values. • Heads, which are the number of Read/Write heads that a hard disk drive has. This number is usually relative to the total number of sides of all the platters on which data can be stored. Thus, if a hard disk drive has four platters and one Read/Write head on either side of each platter, it will have eight heads. Some hard disk drives use voice coil motors to control the actuator arms. These hard disk drives reserve a head or two for accuracy of the arm position. In addition, some hard disk drive manufacturers use a technology called sector translation. This allows them to have more than two heads per platter. However, the maximum number of heads is limited by BIOS to 16. • Cylinders: Data is stored in concentric circles on the surface of each platter. Each concentric circle is called a track. There are hundreds of tracks on the surface of each platter. A set of tracks of the same diameter through each platter is called a cylinder. This is a measurement of drive geometry; the number of tracks is not a measurement of drive geometry. BIOS limitations set the maximum number of cylinders at 1024. • Sectors Per Track: A track is divided into small arcs called sectors with each sector holds 512 bytes of data. BIOS limits the number of sectors per track at 63. • Write Precompensation: All sectors store 512 bytes of data, however, the sectors toward the outside of the platter are physically longer than those closer to the center. Early drives experienced difficulty with the varying physical sizes of the sectors. Therefore, a method of compensation was needed. The write precompensation value defines the cylinder where write precompensation begins. Modern hard disk drives do not have the same problem and hence the write precompensation value is obsolete. • A Landing Zone defines an unused cylinder as a "parking place" for the Read/Write heads. This is found in older hard disk drives that use stepper motors. It is important to park the heads on these drives to avoid accidental damage when moving hard disk drives. The maximum CHS values are: 1024 cylinders; 16 heads; and 63 sectors per track. Therefore, the largest hard disk drive size recognized directly by the BIOS is 504 MB (1024 cylinders × 16 heads × 63 sectors per track × 512 bytes per sector = 528,482,304 bytes or 504 Megabytes). Larger drive sizes can be attained by either bypassing the system BIOS and using one of their own or by change the way the system BIOS routines are read. 2.2.2 Hard Disk Drive Types The original computer design did not include hard disk drives. Hard disk drives were reserved for large mainframe computers and remained highly proprietary in design. Today, there are four types of hard disk drives, each with its own method of installation. 2.2.2.1 ST-506/412 Hard Disk Drives The very first hard disk drives for personal computers used the ST-506/412 interface. It was developed by Seagate Technologies in 1980 and originally appeared with the 5-MB ST-506 drive. The ST-506/412 was the only hard disk drive available for the IBM computer and was the first to be supported by the ROM BIOS CertGuaranteed. Study Hard and Pass Your Exam 220-301 FIG 2.5: The 40-Pin IDE Connector chip on the motherboard. The ST-506/412 uses a 34-connector control cable and two 20-pin connectors to support two hard disk drives. The 34-wire control cable has a twist in it for line 25 through 29 configuration, similar to the floppy disk drive cable; this twist determines which hard disk drive is hard disk drive 0 and which is hard disk drive 1. The drive at the connector end with the twist is designated hard disk drive 0. ST-506/412 hard disk drives were easy to install because the primary input/output (I/O) commands were built into the original IBM AT system BIOS. However, as hard disk drive capacities increased, they required changes in setup to get around the limitations imposed by earlier models. Often, these changes increased the workload on the CPU which resulted in slowing down the processing of data. Hence new methods for overcome the bottlenecks caused by the early hard disk drives were required. 2.2.2.2 Enhanced Small Device Interface (ESDI) Hard Disk Drives One of the methods for overcoming the bottlenecks caused by the ST-506/412 hard disk drive was the Enhanced Small Device Interface (ESDI) which was developed by the Maxtor Corporation and was introduced in 1983. This technology moved many of the controller functions directly onto the hard disk drive itself. This greatly improved data transfer speeds. The installation of ESDI drives was almost identical to the installation of ST-506 drives. Today ESDI drives are obsolete because of their high cost and because of advances in other drive technologies. 2.2.2.3 Integrated Device Electronics (IDE) Hard Disk Drives The Integrated Device Electronics (IDE) drive was developed in the early 1990s and became the standard for computers. The purpose of the IDE was to integrate the drive controller with the drive itself rather than use a separate controller card. The IDE interface uses a 40-pin cable that plugs into the controller and into the hard disk drive. IDE controllers identify the two drives as either master or slave rather than hard disk drive 0 and hard disk drive 1. The IDE hard disk drive can be set to either master or slave be using jumpers. Setting these jumpers serves the same function as the twist in the ST-506 cable. Some hard disk drives use CertGuaranteed. Study Hard and Pass Your Exam 220-301 PIO drive. The official name for IDE PIO (Programmed Input/Output) is a drives is ATA (Advanced Technology Attachment and is based method of transferring data from a on the original IBM AT standard for device hard disk drives. ATA drives use the to another device utilizing the same interface command set as the computer processor and not the memory or original ST-506 drives and are DMA. handled by the system BIOS built into the original IBM AT. However, Because PIO modes utilize the ATA limitations led to its decline as computer processor, using PIO is slower than a viable hard disk drive interface. ATA/IDE supports two drives per DMA. PIO Mode 0 supports a maximum port and PIO modes 0, 1 and 2. transfer 2.2.2.4 Enhanced IDE (EIDE) rate of 3.33 MBps, POI Mode 1 Hard Disk Drives supports a This led to the development of Enhanced IDE (EIDE) which adds a maximum transfer rate of 5.22 MBps, POI number of improvements to the Mode 2 supports a maximum transfer standard IDE drives, including increased data transfer rates; support rate of storage devices such as CD-ROM of 8.33 MBps, POI Mode 3 supports a drives, Zip drives, and tape drives; maximum transfer rate of 11.11 support for up to four IDE devices; MBps, and POI Mode 4 supports a maximum PIO modes 3 and 4, and hard disk transfer drives larger than 528 MB. EIDE dives can use several methods used rate of 16.67 MBps. to overcome the 528-MB hard disk barrier. • Logical Block Addressing (LBA) is a means of addressing the physical sectors on a hard disk drive in a linear fashion. A translating BIOS detects the capacity FIG 2.6: The Hard Drive showing the of Jumpers the drive and manipulates the CHS values so that the cylinder value is always less than 1024. When the computer boots up, an enhanced drive parameter table is loaded into memory. When data is transferred, this table intercepts the request and converts the system's CHS values to LBA values that the computer's BIOS can handle. • A second method for overcoming the 528 MB barrier is the Enhanced CHS standard. This standard allows drives to be manufactured a little faster and more easily than LB A. IBM and other manufacturers support this standard. CertGuaranteed. Study Hard and Pass Your Exam 220-301 • A third method is Fast ATA used by Seagate Technologies. Fast ATA drives will support either LBA or CHS drive translation to break the 528-MB barrier. • Anther method is to use Logical Cylinders, Heads, and Sectors (LCHS), which is a value that the operating system uses to determine the size of the hard disk drive and Physical Cylinders, Heads, and Sectors (computerHS), which is a value used within the device to determine its size. A translating BIOS and the operating system use different algorithms to determine the address of the data. Hard disk drives larger than 8.4 GB require a BIOS that supports enhanced interrupt 13h extensions. There are three methods you can use to enable this function on older computers that do not come with supports for enhanced interrupt 13h extensions. FIG 2.7: Serial ATA Ports You can upgrade the system BIOS to one that supports enhanced interrupt 13h extensions if the motherboard manufacturer has developed one; you can install a hard disk drive adapter card with interrupt 13h support; or you can use a software program from the hard disk drive manufacturer that allows the system to access the drive. Newer EIDE hard disk drives have an Ultra FIG 2.8: The Serial ATA DMA rating. Ultra DMA/33 is a faster drive technology that can be Connector used on virtually all Pentium motherboards. Ultra DMA/66 offers raw data transfers at twice the speed of its older DMA/33 sibling. It requires a compatible system bus on the motherboard or a special controller card, BIOS, CertGuaranteed. Study Hard and Pass Your Exam 220-301 and special IDE ribbon cable that can handle the transfer rates. have one of the 40-pin connectors on an ultra DMA/66 cable is blue while the other is black. Ultra DMA/100 and ultra DMA/133 have also been developed. However, the IDE ribbon cable has a limitation of 133 MBps. Speeds of more than 133 MBps are not possible on a parallel ribbon cable because of signal timing, electromagnetic interference (EMI), and other integrity problems. To overcome this limitation, a newer ATA interface called Serial ATA was developed. Serial ATA is compatible with existing BIOS, operating systems, and utilities that work on Parallel AT A. Thus, Serial ATA supports all existing ATA and ATAPI devices, including CD-ROM and CD-RW drives, DVD drives, tape devices, and any other storage devices currently supported by Parallel AT A. Serial ATA uses much thinner cables with only seven pins. EIDE drives are based on the ATA-5 specification, which has a maximum capacity limitation of 137 GB (65,536x16x255 sectors). This limitation has been overcome by the ATA-6 specification drafted in 2001. ATA-6 augments the addressing scheme used by ATA to allow drive capacity to grow to 144 Petabytes (PB). Any hard disk drives larger than 137GB would conform to ATA-6, however, your motherboard BIOS should also support ATA-6. 2.2.2.6 Small Computer System Interface (SCSI) Hard Disk Drives Small Computer System Interface (SCSI) was introduced in 1979. It is the most robust of the hard disk drive interfaces, and it is popular on network servers and high-performance workstations. Apple adopted SCSI as its expansion bus standard. The original SCSI standard allowed up to seven peripheral devices to be connected in a series to one common bus through a single host adapter connected to the computer bus. These devices could be attached inside or outside the computer. SCSI-2 increased that to 15 devices, and some adapters allow multiple chains for even more SCSI Memory Management devices. The SCSI SCSI host adapters usually have bus functions as a communications pathway their own between the ROM chips. On MS-DOS-based computer system bus and the SCSI device computers, you must ensure that controller. That the appropriate "X=" statements is improves performance, because the card takes over in the EMM386.EXE line of the the low-level config.sys file and the appropriate commands and frees the system bus during "EMMEXCLUDE=" statement is operations that do not in the system.ini file. A missing or involve RAM. A SCSI adapter uses its own BIOS erroneous "EMMEXCLUDE=" and firmware to statement in the system.ini file communicate with the devices attached to it, then can cause intermittent lockup uses a software problems. CertGuaranteed. Study Hard and Pass Your Exam 220-301 interface layer and drivers to communicate with the operating system. This design frees expansion slots and reduces the number of interrupts and memory addresses needed, while cutting down the number of drivers required. The SCSI design has undergone a number of developments since the late 1970s. In June 1986, the ANSI X3.131-1986 standard, known as SCSI-1, was formally published. This has a very loose definition, with few mandates. As a result, manufacturers of SCSI products developed a variety of competing designs. • SCSI-1 supported up to seven devices on a chain plus the host adapter, each of which transferred data through an 8-bit parallel path. Compatibility of SCSI drives was nearly impossible because many SCSI devices had their own custom commands on top of the limited SCSI standard. The wide range of proprietary drivers, operating system interfaces, setup options, and custom commands made true compatibility a real problem. It was, however, popular with Apple and UNIX developers, who could work with a limited range of devices. • The limited acceptance of the SCSI-1 standard, despite its great potential, led to a more robust standard with a range of commands and a layered set of drivers. The result was a high-performance interface that began to take over the high-end market. It became the interface of choice for fast hard disk drives, optical drives, scanners, and fast tape technology. One of the most important parts of the SCSI-2 specification is a larger and mandatory standard command set. Recognition of this command set is required for a device to be SCSI-2 compliant. SCSI-2 also supports; Fast SCSI; Wide SCSI(16-bit); Fast/Wide SCSI; Ultra SCSI SI-2 (32-bit); and backward compatibility with SCSI-1 Fast SCSI-2 uses a fast synchronous mode to transfer data, doubling the data transfer speed from 5 MB/s to 10 MB/s. Wide SCSI doubles that again to 20MB/s. • To increase the pace of development, the SCSI Committee approved a fast-track system for the SCSI-3 standard. A subcommittee handled most of the work, and new subsections were adopted without waiting for the publication of the SCSI definition. This together with the advent of the computerI bus and mature Plug and Play operating systems, has made it easy to install components and has given users excellent control and flexibility. All SCSI-3 cards have ways to support existing SCSI-2 devices. 2.2.3 Installing and Setting Up IDE and EIDE Drives Regardless of their Plug and Play compatibility, all boot devices such as disk drives and CD-ROM drives that are used to boot must be configured at the BIOS and hardware levels because they typically contain the operating system and must run properly before the operating system can be started. There are a number of steps in this procedure. First the hard disk must be physically installed in the computer. This entails setting the jumpers, affixing the hard disk drive in a drive bay and attaching the cables. Once this is done, the geometry of the drive must be entered into the CMOS through the CMOS setup program before the computer will recognize the new device. This information must be entered exactly as specified by the manufacturer. Most new hard disk drives can be detected automatically by the CMOS setup program. The hard disk drive must also be assigned a drive name or letter that is unique. If only one hard disk drive is installed, it must be configured as drive 0, or master. If a second drive is installed, it is recognized as hard disk drive 1, or slave. Many CMOS configurations use the terms C and D. Under all versions of MS-DOS and Windows, hard disk drive 0 is recognized as the C Drive and hard disk drive 1 is recognized as the D drive. A single hard disk drive can also be partitioned into two or more logical drives, each with its own unique drive name and letter. In addition, CD-ROM drives, network drives and tape drives must also be assigned unique drive letters. The CertGuaranteed. Study Hard and Pass Your Exam 220-301 only drive letters that are fixed are the A drives and B drives, which are always the floppy disk drives, and the C drive, the boot drive where the operating system resides. Older hard disk drives would require Low-Level Formatting. During low-level formatting, all the sectors are created and organized to accept data; the proper interleave, i.e., the sector header, trailer information, and intersector and intertrack gaps, are set, and the boot sector is established. Low-level formatting on modern IDE hard disk drives can only be performed by the manufacturer or with a special utility provided by the manufacturer. To continue the hard disk drive installation in MS-DOS, Windows 3.x, Windows 9x, and Windows ME, you will need a bootable floppy disk that contains the fdisk and format programs that are required to prepare the new drive. For Windows NT, Windows 2000 and Windows XP, you can use either a bootable floppy disk or a bootable CD-ROM disk. This bootable disk can be used for partitioning and high-level formatting. The hard disk drive must then be partitioned using fdisk.com program. You can partition the drive as a single logical drive that uses the maximum hard disk drive space or a part of it, or you can partition one physical hard disk drive into a number of logical drives. A computer can have up to 24 logical drives identified as C drive through Z drive. Hard disk drive partitioning allows you to overcome the hard disk drive size limitations imposed by the operating system. When MS-DOS was first designed to use hard disk drives, the largest hard disk drive that could be used was 32 MB because of the way MS-DOS stored files on the hard disk drive. Partitioning was included in MS-DOS 3.3 to allow users to partition larger drives into 32 MB partitions, each of which could then be accessed by MS-DOS. The maximum hard disk drive partition size was increased to 512 MB in MS-DOS 4.0 and 2 GB in MS-DOS 5.0. Windows 98, Windows ME, Windows Making a Bootable Disk To create a bootable floppy disk, NT 4.0, Windows 2000 and Windows XP support you must much larger run the format a: command with drive sizes. However, on some older computers, the /s the physical hard switch in MS-DOS or in a DOS disk drive size limitation of the operating system prompt on might be less a computer that is already server than the limitation set by the BIOS. In this working. This event, hard disk will copy the system files required access will be limited to the largest size that can to boot be recognized by the computer to the floppy disk. the BIOS. You must There are two types of partitions: primary and then copy the format.com or extended. format.exe and • The primary partition is the location where the fdisk.com files to the floppy disk. boot The information for the operating system is stored. To default location for these files is boot from a the C:\DOS hard disk drive, the drive must have a primary directory in MS-DOS and partition. the Primary partitions are for storage of the boot C:\Windows\Command directory sector, which in Windows 9x and Windows ME. CertGuaranteed. Study Hard and Pass Your Exam 220-301 tells the computer where to find the operating system. The primary partition is always identified as drive C. In addition, MS-DOS, Windows 9x and Windows ME can only be installed on the primary partition. • The extended partition is not associated with a physical drive letter. Instead, the extended partition is further divided into logical drives. In a dual boot configuration, Windows NT, Windows 2000, Windows XP, UNIX and LINUX can be installed on a logical partition with a pointer, usually the boot.ini file, on the primary partition indicating the location of the operating system. Once you have partitioned the drive you must perform a high-level format on it to complete the hard disk drive installation process. The high-level format is often referred File Allocation Tables to simply as format because the format.com or The base storage unit for drives is a format.exe sector, program used to perform a high-level format. The each of which can store up to 512 bytes high-level of format creates and configures the file allocation data. A sector can only be assigned to tables and the one root directory. file. Therefore, any part of a sector left unfilled is wasted. The operating system needs to keep track of which sectors are 2.2.4 Maintaining a Hard Disk Drive To minimize the impact of a hard disk drive failure used and which sectors are available for you should data. The operating system also needs to perform comprehensive, backups regularly and you keep track of files that are larger than should 512 save a copy of the boot sector and partition table bytes and are stored on more than one information. sector. The operating system must also should also have a list of the hard disk drive CHS keep parameters; track of the sequential order of the a bootable floppy disk with the fdisk, format, and sectors chkdsk in which the data of these files are command files; and drivers needed to get the stored. operating system The file allocation tables (FAT) are uses running to perform hard disk repairs: to keep track of this information. The most common drive errors begin with "Abort, Retry, Fail, Ignore". These errors are the easiest to fix and can usually be attributed to a bad sector on the drive. When this happens, you should run the ScanDisk program. MS-DOS, Windows 3.x, Windows 9x, and Windows ME contain versions of this program. ScanDisk performs a number of tests on the hard disk drive, including searching for invalid filenames, invalid file dates and times, bad sectors, invalid compression structures, lost clusters, invalid clusters, and cross-linked clusters. In most cases Scan Disk can fix these problems. In addition, Windows 9xand Windows ME-based computers will automatically run Scan Disk any time the operating system is not properly shut down. Connectivity problems occur when the drive is not connected or plugged in properly and usually appears when you boot up a computer. In such an event you will get a "HDD Controller failure" message, or a "No boot device available" message, or a "Drive not found" message. These problems can be solved by inspecting the connectors can cables, including the power cable on the hard disk drive. You could also try removing and reseating the controller if you get a "HDD Controller failure" message. CertGuaranteed. Study Hard and Pass Your Exam 220-301 It is also possible for a drive to lose boot and partition information. This information is stored on sectors and can fail. If the partition table or boot sector is corrupted you could get a "Invalid partition table" message, or a "Corrupt boot sector", message or a "Non-system disk or disk error". The best solution for these problems is to repartitioning the drive and restore the data on the drive from a backup copy. 2.2.5 Setting Up a SCSI Subsystem There are several steps in setting up a SCSI-based system or adding a new SCSI peripheral to an existing system. Start with the SCSI Host Adapter card. These come in a wide variety of sizes, shapes, and configurations. Some offer one connection, whereas others have four. Begin setting up the host adapter card by setting its jumpers, then install the SCSI adapter card in the appropriate expansion slot. Next, record the ID for each device, including the host adapter as it is assigned. Logical Unit Numbers The ID for each device on a chin must be Logical unit numbers (LUNs) unique to that chain. can be used to provide a After the IDs are set, verify the termination for unique identifier for up to each end of the seven subunits on one ID SCSI chain and attach the cables beginning wit number. This the host adapter makes it possible to have a and then moving to the end of the chain. Repeat single SCSI ID support more this process for than one device. These are the external devices. It is advisable to connect used primarily in hard disk the power to one drive arrays to create one large device, power up, and check for problems logical drive out of several proceeding to the next device if no problems or smaller physical drives. conflicts are detected. Finally, load any software required to allow the operating system to recognize the new hardware. 2.3 RAID Arrays Redundant Array of Independent Disks (RAID) is a technique in which data can either be duplicated on multiple drives or have parity, which is a mathematical value that can be used to re-create missing data, written to one or more dives to prevent the failure of any single drive from causing downtime or a loss of data. It is thus a fault-tolerant solution, and like many fault-tolerant solutions, RAID can have a performance impact. RAID can be done via specialized hardware controllers or via software. Hardware solutions are generally faster and more portable; software solutions are cheaper. A group of RAID-configured drives is called a drive array or an array. The structure of an array is usually described as its level, which refers to a specific type or combination of redundancy in use. There are several defined RAID levels: RAID 0; RAID 1; RAID 2; RAID 3; RAID 4; RAID 5; RAID 6; RAID 7; RAID 10; RAID 53 and RAID 0+1. The most common of these are: RAID 0; RAID 1; RAID 5; RAID 10; and RAID 0+1. • RAID 0 is also called striping. It provides increased read and write performance but does not provide redundancy. Data is split into smaller uniform-sized blocks, or stripes, and is written to or read from multiple drives at the same time. Multiple drives with smaller stripes increase the performance, but the failure of any disk drive results in loss of all data. Best performance can be achieved when data is striped across multiple controllers with only one disk drive per controller. This RAID level is used mainly for ultra high-performance databases but should not be used in mission critical environments. RAID 0 requires a minimum of two disk drives. • RAID 1 is also called mirroring. It provides redundancy by duplicating the exact contents of one drive CertGuaranteed. Study Hard and Pass Your Exam 220-301 onto another. If one disk drive fails, the other disk drive has a complete copy of the data. This is a very reliable method of protecting data. It has a small write performance impact, because data must be written twice - once to each disk drive. It also has a read impact, because often information can be read from either or both disk drives at the same time. A variation of this RAID level called duplexing uses a controller for each mirrored disk drive. Duplexing can improve performance while increasing fault tolerance. RAID 1 has a high level of disk drive overhead because one half of the total disk space is used for providing redundancy. This level is commonly used for high-value, moderate performance data like log files. • RAID 2 uses Hamming error correction codes (ECC). It is intended for use with drives which do not have built-in error detection. With RAID 2, each bit of data word is written to a data disk drive with its Hamming Code ECC word recorded on the ECC disk drives. On read, the ECC code verifies correct data or corrects single disk errors. Each data disk requires its own ECC disk therefore this RAID level is very expensive. Currently, RAID 2 is not implemented because practically all modern IDE disk drives and all SCSI disk drives have embedded ECC. This RAID level is not commercially viable. • RAID 3 is similar to RAID 0 in that data is stripes at a byte level across multiple disk drives. Stripe parity, which is generated on writes, is recorded on a single parity disk and checked on reads. Parity is a mathematical value that can be used to re-create missing data. This provides some fault tolerance except when the parity disk fails. Byte level striping requires hardware support to improve efficiency. RAID 3 requires a minimum of three disk drives. • RAID 4 is similar to RAID 3 except that data is striped at the block level across multiple disk drives. Stripe parity is also recorded on a single parity disk. This provides some fault tolerance except when the parity disk fails. The performance of RAID 4 for reads is the same as RAID 0. Writes, however, require that parity data be updated each time. This slows small random writes. RAID 4 requires a minimum of three disk drives. • RAID 5 is also called striping with parity. It is the most common level of RAID. It is similar to RAID 4 with the exception that parity information is distributed among all the disks. If a single disk drive fails, the original data can be re-created by doing the reverse of the parity calculation. RAID 5 exacts a performance impact for writes because of the parity calculation, but yields a performance increase on reads. RAID 5 is commonly used to provide redundancy at a lower effective overhead than RAID 1 and requires a minimum of three disk drives. • RAID 6 is an extension of RAID 5 and allows for additional fault tolerance by using a second independent distributed parity scheme, or two-dimensional parity. Data is striped on a block level across a set of disks as in RAID 5, and a second set of parity is calculated and written across all the disks. Consequently, RAID 6 provides for an extremely high data fault tolerance and can sustain multiple simultaneous disk drive failures. It is ideal for mission critical applications. • RAID 7 is a proprietary solution. It is similar to RAID 4, except that all read/write transfers are asynchronous, independently controlled and cached via a high speed system bus called x-bus. The single parity disk can be located on any of the channels. The operating system responsible for coordinating the asynchronous read/write transfers is resident on an embedded array control processor. • RAID 10 is also called RAID 1+0 or striping plus mirroring, and is a striped array of RAID 1 arrays. It can sustain multiple disk drive failure, as long as they are not in the same mirrored pair, with the same disk drive overhead as RAID 1. With RAID 10, data is striped across RAID 1 arrays to achieve high read/write performance. Recovering form a disk failure in a RAID 10 array requires rebuilding the failed disk from the data on its mirror drive. RAID 10 requires a minimum of four disk drives. • RAID 53 is implemented as a striped array of RAID 3 arrays. It has the same fault tolerance and disk drive overhead as RAID 3 but high performance are achieved because of its RAID 0 striping. CertGuaranteed. Study Hard and Pass Your Exam 220-301 • RAID 0+1 is also called mirroring plus striping. Like RAID 10, it combines the performance and redundancy benefits of RAID 0 and RAID 1. Each disk in a RAID 0+1 array is mirrored, preventing a single drive failure from causing downtime. The failure of a single disk drive, however, will result in the RAID 0+1 array becoming a RAID 0 array as all data on the array that has the failed disk will be lost. Furthermore, recovering from a disk failure requires that the complete RAID 0 that suffered the failure must be rebuilt. RAID 0+1 requires a minimum of 4 disk drives and is commonly used for database storage. 2.4 CD-ROM and DVD-ROM Drives Both the compact disc read-only memory (CD-ROM) and the digital versatile disc read-only memory (DVD-ROM) drive are based on technology from the audio-visual industry, and both have become standard equipment on computers. A compact disc can hold a maximum of approximately 737 MB of data while a DVD disc can hold up to 4.7GB (single layer) or 8.5GB (dual layer) of data on a single side of the disc and twice that amount on double-sided DVD disks. Both CD-ROM and DVD-ROM drives make use of highcapacity optic media in the form of a silvery platter that holds digital data that is read by means of a laser beam. Many new computers come with a DVD-ROM drive that are compatible with compact discs. DVDROM drives require additional decoding hardware, either on the drive itself or on a companion card, to play mpeg videos effectively. Without this additional hardware, the playback of mpeg files will be erratic with lost frames and erratic audio playback. CD-R Platters CD-recordable (CD-R) discs use materials A CD platter is composed of a reflective layer of other than aluminum. They often aluminum have a applied to a synthetic base that is composed of yellow or green cast on the data side. polymers. A layer of transparent polycarbonate Some covers the aluminum. A protective coating of CD-ROM drives, such as the older lacquer is applied to the surface to protect it from IDE dust, dirt, and scratches. CD-ROM drives are not able to read CD-R discs. Data is written to a CD at a press by creating pits and lands on the CD's surface. A pit is a depression on the surface, and a land is the height of the original surface. The transition from a land to a pit or a pit to a land represents a binary character of 1 while continuous lands and continuous pits represent binary 0. The reading of data is based on the speed at which the CD rotates and the reflection of light. The data transfer speed of a CD-ROM drive is expressed in relation to the rotation speed of an audio CD player. The latter can transfer 150 KB of data per second. A 2X CD-ROM drive operates at 300 KB per second, a 4X at 600 KB per second, etc. Table 2.1 lists transfer rates for some common CD-ROM drives. TABLE 2.1: The Transfer Rate of the CD-ROM CD-ROM Speed 4X 6X 8X 12X 16X 24X Transfer Rate 600 KB per second 900 KB per second 1.2 MB per second 1.8 MB per second 2.4 MB per second 3.6 MB per second CertGuaranteed. Study Hard and Pass Your Exam 220-301 32X 4.8 MB per second 40X 6.0 MB per second 48X 7.2 MB per second 52X 7.8 MB per second A single-speed DVD-ROM drive provides a data transfer rate of 1.385MBps, which is roughly equivalent to a 9X CD-ROM. This, however, does not mean that a 1X DVD-ROM drive can read CDs at 9X rates. DVDROM drives spin a disk 2.7 times faster than a CD-ROM drive of the same speed. Therefore, many DVDROM drives list two speeds, one for reading DVD disks and another for reading CD disks. Thus, a DVDROM drive listed as a 16X/40X would indicate the performance when reading DVD disks and CD disks, respectively. 2.4.1 Recordable CD Drives CD-R or CD-RW discs and drives allow you to record or burn your own CDs. This enables you to store large amounts of data at a lower cost than most other removable, random-access mediums. Another benefit of the CD for archiving data is that CDs have a much longer shelf life than tapes or other removable media. The first CD-R recording system appeared on the market in 1988. it was a large piece of equipment that operated at 1X speed only. The main purpose of these early CD-R devices was to produce prototype CDs that could be replicated via the standard stamping process. In 1991, Philips introduced the first 2X recorder (the CDD 521) and then JVC in 1993 followed with their 2X recorders that the first drive that had the halfheight 5.25-inch form factor that most desktop system drives still use today. In 1995, Yamaha released the CDR100 which was the first 4X CD-R. In the same year CD-Rs became cheaper and a surge in popularity of the CD-R device occurred. In 1996, Ricoh introduced the first CD-RW drive, which was fully backward-compatible with CD-R drives and could function as a CD-R drive. Thus, these drives can work with either CD-R or CD-RW discs. Therefore, CD-RW drives have replaced CD-R drives. However, CD-RW discs are more expensive than CD-R discs, are slower than CD-R discs, and are not readable in all CD audio or CD-ROM drives. CD-R media is a write once, read many (WORM) media. Thus, after you fill a CD-R with data, it is permanently stored and cannot be erased. CD-RW discs, on the other hand, can be reused up to 1,000 times, making them suitable for almost any type of data storage task. 2.4.2 Recordable DVD Drives There are currently three competing DVD recordable standards - DVD-RAM, DVD-R/RW, and DVD+R/RW. DVD-RAM, which was introduced in July 1997, is endorsed by Panasonic, Hitachi, and Toshiba and uses a phase-change technology similar to that of CD-RW. DVD-RAM discs cannot be read by most standard DVD-ROM drives because of differences in both reflectivity of the media and the data format. DVD-ROM drives that follow the MultiRead2 specification and can thus read DVD-RAM discs began to come on the market in early 1999. DVD-RAM uses the wobbled land and groove recording method, which records signals on both the lands, i.e., the areas between grooves, and in the grooves that are preformed on the disc. This is unlike CD-R or CD-RW, in which data is recorded on the groove only. The grooved tracks wobble slightly right and left, and the frequency of the wobble contains clock data for the drive. DVD-R, which was originally created by Pioneer and released in July 1997 is a write-once medium similar to CD-R. DVD-R discs can be played on standard DVD-ROM drives. Some recent DVD-RAM drives can also write to DVD-R media. These discs use an organic dye recording layer similar to CD-R. To enable positioning accuracy, DVD-R also uses a wobbled groove recording. Data is recorded within the grooves only. The grooved tracks wobble slightly right and left, and the frequency of the wobble contains clock data CertGuaranteed. Study Hard and Pass Your Exam 220-301 for the drive to read, as well as clock data for the drive. The grooves are spaced more closely together than with DVD-RAM, but data is recorded only in the grooves and not on the lands. Rewritable DVD-R, DVDRW was introduced in November 1999. It is an extension to DVD-R as CD-RW is an extension to CD-R. DVD+R was introduced after DVD+RW and is becoming the premier DVD recordable standard because it is the least expensive and most compatible with existing formats. It was developed and is supported by Philips, Sony, Hewlett-Packard, Mitsubishi Chemical, Ricoh, Yamaha, Verbatim, and Thompson. The major reasons for the development of DVD+R was to provide a lower-cost method for permanent data archiving with DVD+RW drives and to overcome compatibility issues with DVD-ROM and DVD video players that were incapable of reading media created with DVD+RW drives. The basic structure of a DVD+RW or DVD+R disc resembles that of a DVD-R disc with data written in the grooves only. However, the groove is wobbled at a frequency different from that used by DVD-R/RW or DVD-RAM. In addition, the DVD+R/RW groove contains positioning information which makes the DVD+R/RW media more accurate positioning for lossless linking. However, DVD+R/RW drives cannot write to DVD-R/RW and DVD-RAM media. Because DVD+R/RW offers low drive and media prices, provides the highest compatibility with existing formats, it is the most ideal for data storage in personal computers. 2.4.3 Connecting CD and DVD Drives In most cases, there is no difference in attaching a CD-ROM or DVD drive. Depending on the features and design, you may have to install an add-on decoder card with a DVD product to improve performance when playing videos. Both types of drives are peripheral devices and must be connected to the bus of the computer through a controller. Some CD-ROM and DVD drive manufacturers provide a proprietary adapter board made specifically for their product. These boards are supplied with the drive and are not interchangeable. Early CD-ROM drives used either SCSI or a special version of a parallel port while most modern CD-ROM devices are either EIDE or SCSI. In addition, many DVD drives come with a decoder board to improve video and audio playback. Some add-on sound cards have built-in IDE controllers tha could be used to support the CD-ROM. These were very useful on early computers that had support for only two IDE devices. Most sound cards come with a 15-pin female connector known as the Musical Instrument Digital Interface (MIDI) connector while some of the newer sound cards also have a SCSI interface. Modern CD-ROM and DVD drives can be installed on either a SCSI Host Adapter or an EIDE connector. 2.4.4 Installing CD-ROM and DVD Drives Installing an internal drive is a four-step process that involves installing the drive controller or decoder card; installing the drive into a 5.25-inch drive bay in the computer case; attaching the data, audio and power cables; and installing the necessary operating system drivers. The file structure for a CD-ROM or DVD drive is different from the directory used by the MS-DOS file allocation table (FAT). Therefore, you will need a special driver for MS-DOS to be able to recognize this device as a drive. A standard device driver supplied by the manufacturer for BIOS might also be required. Microsoft's mscdex.exe, an MS-DOS resident application, provides the required translation and also specifies the device driver required by the device. This will also necessitate changes to the config.sys and autoexec.bat files. Many CD-ROM drive installation disks will make these changes automatically. Windows 9x, and Windows ME use a CertGuaranteed. Study Hard and Pass Your Exam 220-301 FIG 2.9: CD-ROM Cable 32-bit protected-mode driver called vcdfsd.vxd Connections which replaced mscdex.exe. When adding a new CD-ROM drive in Windows 95, you can use the Add New Hardware Wizard. This wizard will properly identify and set up the CD-ROM drive. Later versions of Windows that support the Plug and Play feature, will recognize the new drive and run the install wizard automatically. 3. Output Devices 3.1 CRT Monitors A monitor operates fundamentally like a TV set, except that it is designed to receive signals from a display adapter card in the computer, rather than a broadcast signal. A variety of design factors and the features of the display adapter card influence the quality of a monitor's display. The CRT (cathode-ray tube) is the main component of a traditional monitor. The rear of the CRT holds a cylinder that contains one or more electron guns. Most color monitors have three electron guns for red, green, and blue (RGB) which allows the visual production of all colors. The wide end of the CRT is the display screen, which has a phosphor coating that can emit light when hit with radiation. When active, the electron guns beam a stream of charged electrons onto the phosphorus coating. When the coating is hit with the right amount of energy, light is produced in a pattern of very small dots. This same technology is used in X-ray imaging, oscilloscopes, and other CRT devices. Similarly, monitors emit X-radiation. There is one dot for each FIG 3.1: A CRT Monitor RGB color, and the dots are grouped in patterns close together. The name for a collection of all dots in a specific location is a pixel, which stands for picture element. The Screen Resolution and Dot Pitch human eye Screen RESOLUTION refers to the degree perceives the of detail offered in the presentation of an collection of image on the screen and is expressed in pixels on the pixels per inch. The greater the number of front of a CRT pixels per inch, the smaller the detail that as a compound can be displayed and the sharper the image, in much picture. Monitor resolution is expressed as the same way the number of horizontal pixels x the as it interprets number of vertical pixels. DOT PITCH the pattern of defines the diagonal distance between the ink dots in a two closest dots of the same color and is CertGuaranteed. Study Hard and Pass Your Exam 220-301 newspaper expressed in hundredths of millimeters. the halftone as a smaller the dot pitch, the greater the photograph. number of dots, and the sharper the image. The image on the screen is not painted all at once. The stream is directed in rows starting in an upper left corner. A series of raster lines are drawn down the face of the screen until the beam reaches the lower right, whereupon the process starts over. A given line must be visible for long enough to allow the formation of a complete image, but must not blur the dots painted in the next pass. The term persistence is used to define how long the phosphors on the screen remain excited and emit light. The time the stream takes to complete a vertical pass is called the vertical refresh rate (VRR) and the time the stream takes to pass once from left to right is known as the horizontal refresh rate (HRR). If the vertical rate is too slow, it can cause flickering and larger CRTs require higher, i.e., quicker, refresh rates. At a resolution of 640 × 480, the minimum refresh rate is 60 Hz; at a resolution of 1600 × 1200, the minimum refresh rate is 85 Hz. Both the monitor and the display adapter produce the refresh rate. The first monitors had fixed refresh rates. In 1986, NEC introduced the first multi-frequency monitor that could automatically adjust the refresh rate to take advantage of the highest rate supported by the display adapter cards of that time. Today, this feature is standard on most monitors. Some older monitors use interlacing. Interlacing refreshes the monitor by painting alternate rows on the screen and then returning to paint the rows that were skipped the first time around. This increases the effective refresh rate but can lead to eye strain. The monitor is the highest consumers of electrical current in the average computer therefore most new monitors provide some level of power-saving technology. The Video Electronics Standards Association (VESA) has established a standard set of power economy controls to reduce power use when the monitor is idle. These are collectively referred to as Display Power Management Signaling (DPMS) modes. DPMS technology uses monitors to gauge activity levels of the display. If there is no change in the data stream from the adapter, as set in either the BIOS or operating system controls, the monitor is switched to inactive status. The goal is to reduce power consumption while minimizing the amount of time required to restore the display to full intensity when needed. Frequently turning a monitor on and off places stress on the components. DPMS reduces the need to use the mechanical switch to turn the device on or off. You should advise clients without power-saving systems in place to turn on the display only when it is first needed and to turn it off at the end of each workday. In most cases, the monitor must be adjusted for a proper picture when the screen resolution or refresh rate is changed or a new display card is added to the system. Table 3.1 lists the typical monitor CertGuaranteed. Study Hard and Pass Your Exam 220-301 adjustments. 3.2 Flat-Panel Displays Flat-panel displays (FPDs) are thin, bright display outputs that are gaining a foothold on desktop computer systems as a replacement for traditional CRT monitors. They require a much smaller desk space because they do not have large cases that house electron guns, nor a heavy glass front. They do not rely on transitory phosphors to create an image and are therefore free from flicker. FPDs have flat screens and there is thus no distorted image at the edge of the viewing area, as there is with curved CRT monitors. They however, have limited optimal viewing angles Most FPDs also lack the range of resolutions of the CRT-based monitors and require a digital graphics adapter card that is tuned to that FPD. Several different types of FPDs are available today, varying in cost, image quality, and several other factors that affect both suitability to different computing applications and user acceptance. • Liquid Crystal Displays (LCDs) form an image by using transparent organic polymers sandwiched between a pair of polarizing filters, with some form of back-lighting. The filters are set at a 90-degree angle to each other. In an uncharged state (no current applied), the crystals are aligned so that light can pass through the top filter. When a current is added, the crystals align to the electric field, blocking the transmission of light. Color light-emitting diode (LED) displays have three adjoining cells, each equipped with a different RGB color filter. • Electroluminescent Displays (ELDs) actually emit light, rather than simply controlling the transmission of a back-light source. The light generation comes from phosphors layered between front and back electrodes. Most ELD products are found in technical applications as well as ATM machines. • Plasma Display Panels (PDPs) work much like the fluorescent lights by energizing an inert gas. Phosphor films are used to produce a color image. This technology is used to manufacture very large FPDs. Like fluorescent lights, PDPs are relatively inexpensive to produce, but lower contrast and brightness, as well as higher relative power consumption, have limited their use for computer applications. 3.3 Display Adapters The monitor is half of a computer's display system and must be matched to a display adapter card, although some entry level motherboards have integrated display adapters built into the motherboard's circuitry. The display adapter has gone through several major evolutions as the nature of computers changed. CertGuaranteed. Study Hard and Pass Your Exam 220-301 • The early 8088-based IBM personal computers used Monochrome Display Adapter (MDA) cards which were matched to the limited capabilities of the early monitors. The MDA offered a simple text based monochrome display, producing an 80-character-wide row of text at a resolution of 720 × 350 pixels. The MDA card was a 1-bit device, with each pixel using 1 bit, valued either 0 or 1 to represent whether a given pixel was on or off. It was equipped with 256 KB of FIG 3.2: An MDA Adapter dynamic RAM (DRAM) but relied on the CPU to process the display image. It also had a 9-pin d-shell, male connector to which the monitor cable was attached. • The MDA was superseded by the Color/Graphics Adapter (CGA) card which provided up to four colors: amber, green, white and black. These colors were in fact different intensities of the monitor's active color. In four-color mode, CGA provided a resolution of 320 × 200 pixels and a resolution of 640 × 200 pixels in two-color mode. Like the MDA, the CGA had 256KB of DRAM but relied on the CPU to process the display and had a 9-pin d-shell, male connector to attach the monitor cable. • The Enhanced Graphics Adapter (EGA) card was an improved version of CGA card and was the first display adapter card that gave the computer the capability to use actual color. The EGA used the same 9-pin d-shell, male connector that was used by the MDA and CGA to attach the monitor cable and had a maximum resolution of 640 × 350 with 16 colors in text-only mode, and a resolution of 640 × 200 with two colors in graphics mode. However, the EGA was not fully backward-compatible with CGA and MDA. • Graphic artists, engineering designers, and the manipulation of photo-realistic images needed more the 16-color display provided by the EG A. In response to this need, IBM offered a short-lived and very complicated engineering display adapter, the Professional Graphics Adapter (PGA). It required three ISA slots, and provided limited three-dimensional manipulation and 60-frames-per-second animation of a series of images. It was, however, very expensive. • One reason for the demise of the PGA was the advent of the Video Graphics Array (VGA). All the preceding cards were digital devices, but the VGA produced an analog signal. That required new cards, new monitors, and a 15-pin female connector. Developers were then able to produce cards that provided the user with up to 262,144 colors and resolutions up to 640 × 480. The VGA card quickly became commonplace for a computer display system. Note: The VGA has a maximum resolution of 640 × 480. This resolution is used when VGA mode is used. • Thereafter the Video Electronics Standard Association (VESA) developed a standard list of display modes that extended VGA to the high-resolution color and photographic quality we know today. This CertGuaranteed. Study Hard and Pass Your Exam 220-301 standard is known as Super VGA (SVGA). The SVGA set specifications for resolution, refresh rates, and color depth for compatible adapters. On Pentium and later computers, an SVGA adapter is the minimum standard for display systems. The lowest resolution needed for SVGA compatibility is 640 × 480 with 256 colors, and most modern adapters usually go far beyond that. The other standard SVGA resolutions are 800 × 600 and 1024 × 768. High-end systems with large monitors are sold at 1600 × 1200 resolution at high refresh rates. The SVGA specification for 256 shades of gray is one of the basic SVGA specifications for true photographic reproduction of monochrome images; it is the number of shades that the human eye can distinguish in a grayscale photo. Color requires the same number of shades for each color in the image to achieve the same level of visual realism. To get 256 shades requires an 8-bit memory address system inside the card. However, an 8-bit display adapter card cannot display all the colors of a full-color picture in color mode, therefore a lookup table is used to figure the closest match to a hue that cannot be represented directly. This method kept the cost of the early SVGA cards low. With the advent of the 80486 processor, 16-bit SVGA cards, which allowed approximately 64,000 colors, were developed. More bits require more memory, more processing requirements, a larger lookup table, and a higher cost. These cards were designed to be used with larger monitors, 15 to 17 inches at 800 × 600 or 1024 × 768 resolution. The new systems were too expensive for average users, but graphics professionals and power users generated a large enough market to fuel development. • In 1991 IBM introduced the Extended Graphics Array (XGA). The XGA was only available as an Micro Channel Architecture (MCA) expansion card. The MCA expansion slot was an IBM propriety expansion slot that IBM developed for their PS/2 computers. The XGA could support 256 colors at 1,024 × 768 pixels or 65,536 colors at 640 × 480 pixels. Its design was optimized for graphical user interfaces (GUIs) such as Microsoft Windows or OS/2, and used interlaced technology. Because the MCA expansion slot was an propriety expansion slot only used on IBM computers, XGA display adapter cards are rare. Most of the early SVGA card used the PCI expansion bus, however, having more cards on a single bus slowed down the performance of these display adapter cards, just when 24-bit display adapters and 3D rendering called for greater demands on the display system. This led Intel to developed the FIG 3.3: An AGP SVGA Adapter Card Accelerated Graphics Port (AGP), a single slot tuned for the display adapter. The AGP removes all the display data traffic from the PCI bus and gives that traffic its own 525-MB-persecond pipe into the system's chip set and, from there, straight to the CPU. It also provides a direct path to the system memory for handling graphics. 3.3.1 Hardware Acceleration CertGuaranteed. Study Hard and Pass Your Exam 220-301 The adapters that followed the EGA cards offered more colors and higher resolutions. This required more processing and placed a greater load on the CPU. Therefore newer display adapter cards began to include their own display coprocessors that were tuned the display processing and were equipped with more memory. In addition, many display adapter cards use bus mastering to reduce the amount of traffic on the system bus and to speed display performance. Video coprocessing is also called hardware acceleration. Today, high-performance graphics adapters are the norm. 3.3.2 Video Memory The amount of memory on a display adapter is a major factor in determining the screen resolution and color depth that the card can manage. Just as with system RAM, the video memory must be able to operate at a speed that can keep up with the processor and the demands of the system clock. If the display adapter is too slow at updating the image on the monitor, the user is left waiting or is presented with jerky mouse movements and keystrokes that appear in delayed bursts rather than as typed. • Early video cards used fast page-mode RAM (FPM RAM), a series of chips that were basically the same as the RAM used on the early computer's motherboard. This memory form was fine for MDA and CGA cards, but with the higher resolution, increasing pixel depth, and faster refresh rates of VGA displays and beyond, vendors required improved memory models to get maximum performance out of their video coprocessors. • This led to the development of dual-ported memory in the form of video RAM (VRAM) that can read and write to both of its I/O ports at the same time. It allows the display coprocessor to communicate with the system bus and the monitor simultaneously. This memory is fast, but very expensive but is appropriate for graphics-intensive applications designed for drawing and painting or for computer-aided design (CAD) and 3-D games. • A more cost effective alternate to VRAM is extended data out DRAM (EDO DRAM), which can begin reading a new set of instructions before the preceding set of instructions has been completed. This is a common form of system DRAM that boosts performance to about 15 percent above conventional DRAM. • Samsung developed Window RAM (WRAM), a high-speed variant of VRAM that costs less to produce and boosts performance by about 20 percent beyond VRAM. VRAM and WRAM have become the standard memory types for high-end display adapters used for graphics-intensive applications designed for drawing, painting, CAD and 3-D games. • The midrange display market makes use of synchronous graphics RAM (SGRAM) that is tuned to the graphics-card, offering faster transfers than DRAM, but are not as fast as VRAM and WRAM. • Multibank DRAM (MDRAM) uses interleaving, i.e., it divides video memory into 32-KB parts that can be accessed concurrently, to allow faster memory I/O to the system without expensive dual porting. It is also a more efficient type of chip that is practical to produce in sizes smaller than a full megabyte. 3.3.3 Display Drivers Text-based display adapters used on MS-DOS-based computers did not need software drivers to interface between the operating system and the image on the screen. However, Microsoft Windows, OS/2, and other graphics-rich operating systems do need drivers as well as controls to adjust the refresh rate, resolution, and any special features the card offers. Display drivers, which is a software layer, marries the display system, i.e., the display adapter card and monitor, to the operating environment, to meet these needs. Thus, when installing a new card or operating system for a client, be sure to check the manufacturer's Web site for the latest display drivers. You will reduce the likelihood of problems in using the new addition, and you will find that most new cards incorporate setup routines that can make quick work of getting a new display running. 3.3.4 Troubleshooting Display Systems CertGuaranteed. Study Hard and Pass Your Exam 220-301 In spite of the increasing complexity of display systems, most display problems can be traced to cables improperly connected or damaged; lack of power; incorrect screen resolution; corrupt or incorrect drivers; and memory conflicts with other components. When troubleshooting a display system: • Verify that both the power and monitor-display adapter cables are properly attached. Failure to attach them properly can lead to no picture at all or to an erratic image with incorrect colors. If the monitor cable has been removed and reattached, bent pins could be the problem. Make sure power is reaching both the computer and the monitor and that they are turned on. • Make sure that the adapter is properly seated in the expansion slot by removing it and reinserting it firmly in the expansion slot. • Boot the system. If you get an image during the power-on self test (POST) but the computer does not load the operating system, suspect memory or driver problems. The same is true if the system repeatedly hangs during Windows operation. Try booting in safe mode. If that succeeds, reinstall the drivers and use Device Manager in the Control Panel System utility to resolve any hardware or memory conflicts. • Reset the card to the 640 × 480 resolution in 16-color VGA mode at the 60-Hz refresh rate. If the card works in normal mode, in Windows, at these settings, but fails at higher resolution, color depth, or refresh rates, check the drivers and the capabilities of the display components. 3.4 Printers Printers have replaced the typewriter in the contemporary office. They come in different shapes and sizes, with different printing mechanisms, and different characteristics. There are four major types of printing devices used to get computer output into "hard" copy (paper copies). They are impact printers, sprayed-ink printers, electrophotographic (EP) printers, and plotters. 3.4.1 Impact Printers Impact printers function very much like typewriters, creating an impression on paper by striking an inked ribbon. Impact printers, of which the dot matrix printer and daisy wheel printer are two major type, were the most commons forms of printers in the early days of computer printing. Dot-matrix printers use an array of pins, commonly 9, 17 or 24 pins which are pressed against the ribbon in patterns corresponding to the characters to be produced while daisy-wheel printers use a wheel that has all the letters of the alphabet on different spokes. The printer's controller rotates this wheel until the spoke holding the desired letter is in place. Then, a hammer behind the wheel strikes this letter onto the inked ribbon and the paper, thus making an image. Daisy-wheel printers cannot reproduce graphics and are generally more expensive than dot-matrix printers. Today impact printers are used primarily for printing multipart carbon forms which require that something strike the page to make multiple copies. Troubleshooting a dot-matrix printer usually requires a reference manual because there are so many printers on the market. However, if a reference manual is not available, a thorough inspection of the mechanical parts of the printer will usually uncover the problem. Table 3.2 lists some of the common problems encountered with dot-matrix printers and their possible causes. TABLE 3.2: Possible Causes of Common Dot-Matrix Problems Symptom Possible Cause The printer does not power up at all. No power is getting to printer or the fuse is blown. The printer does not print although power is on. The printer is not online, the printer is out of paper or the printer cable is not connected properly. CertGuaranteed. Study Hard and Pass Your Exam 220-301 The printer does not go online. The printer is out of paper. The paper slips around platen. The printer is not griping the paper properly. Adjust paper-feed selector for size and type of paper. The print head moves but does not print. The ink ribbon is not installed properly or is out of ink. The print head tears the paper as it moves over it. The pins are not operating properly. If any of the pins are stuck, the head will need to be replaced. The paper bunches up around platen. There is no reverse tension on paper. The paper has dimples. The paper is misaligned or the tractor feed wheels are not locked in place. The Paper/Error indicator flashes continuously. There is an overload condition. The printout is double-spaced or The printer configuration switch is incorrectly set. there is no spacing between lines. The printer cannot print ASCII characters above code 127. The printer configuration switch is incorrectly set. The print mode cannot be changed. The printer configuration switch is incorrectly set. 3.4.2 Sprayed-Ink Printers A sprayed-ink printer spray ink onto paper to form images. There are a variety of sprayed-ink printers, but there are two basic types: ink-jet and bubble-jet. The image quality is relatively good with both types of sprayed-ink printer and are relatively fast in comparison to impact printers. Ink-jet printers have replaced dot-matrix printers in the low-end market. They are relatively cheap but, when recommending an ink-jet printer, you must consider the cost of the ink cartridges as well as the cost of the printer itself. If a sprayed-ink printer fails to operate, the first step in determining the source of the problem is to decide if the problem lies with the printer or with the computer. The best place to start is at the printer, with a visual inspection. If a visual inspection of the printer does not turn up an obvious fault, proceed to the printer's self-test program. In most cases, you can initiate this routine by holding down a specified combination of control keys on the printer while you turn it on. If a test page prints successfully, the problem is most likely associated with the computer, the cabling, or the network. Table 3.3 lists some typical problems encountered with sprayed-ink printers and their possible causes. TABLE 3.3: Possible Causes of Common Sprayed-Ink Printer Problems Symptom Possible Cause The power is on but device does not print. The printer is not online or is out of paper. CertGuaranteed. Study Hard and Pass Your Exam 220-301 The printer does not go online after the ink cartridge has been replaced The ink cartridges is installed incorrectly or the printer cable has been disconnected. The printer is plugged in, but all indicator lights are off and the printer appears to be dead. Check the drive mechanisms and motors for signs of binding. They might need to be replaced. Also check the fuse. The print head does not print. The ink cartridges are empty. The paper does not advance. The paper-handling hardware is jammed. Check that the printer is online and inspect the paper-handling motor and gear train. You can do this by setting the printer offline and pressing the form-feed button. 3.4.3 Electro photographic (EP) Printers Electro photographic (EP) printer are commonly known as laser printers, and use a laser as well as high voltage and black carbon toner to form the image on paper. They were developed in the late 1980s by Xerox and Canon, and were designed around the Electrophotographic (EP) process developed by Xerox. Because of their complexity, these printers have a relatively high cost. However, the images produced by EP printers are of the best quality, and are produced at higher speeds. The laser printer has become the dominant printing device. Laser printers follow one basic engine design, similar to the one used in most office copiers. They are non-impact devices that precisely place toner on paper. EP or laser printer contains eight standard assemblies. These are the EP toner cartridge; the laser scanning FIG 3.4: A Laser Printer assembly; the high-voltage power supply (HVPS); the DC power supply (DCPS); the paper transport assembly, which includes the paper pickup rollers and the paper registration rollers; the transfer corona assembly; the fusing assembly; and the printer controller circuitry. CertGuaranteed. Study Hard and Pass Your Exam 220-301 • The EP toner cartridge holds the toner, which is a black, carbon substance mixed with polyester resins and iron oxide particles. The polyester resins and the iron oxide particles make the toner capable of being attracted to the photosensitive print drum and capable of being fused to the paper. The toner has a negative static electrical charge and contains a medium, called the developer or the carrier and which "carries" the toner until it is used by the EP process, as well as the EP print drum. The EP print drum is an aluminum cylinder that is coated with a photosensitive material that can hold a static electrical charge only when it is not exposed FIG 3.5: A Toner Cartridge to light. When it is exposed to light, it discharges. The EP print drum also contains a rubber cleaning blade that keeps the print drum clean by scraping the used toner off the print drum. • The EP photosensitive print drum can hold a charge if it is not exposed to light. An electrical charge is applied by a pair of fine wires and it is usually dark inside an EP printer resulting in the toner being attracted to the print drum. A laser scanning assembly is used to trace a negative of the image onto the drum, causing the drum to discharge its electrical in the area that the laser sweeps over. As the drum rotates, the laser scanning assembly sweeps the laser across the photosensitive drum. • The EP process requires a supply of high-voltage electricity. This is provided by a high-voltage power supply (HVPS) that converts AC current from a household power socket to higher voltages that the printer can use. This high voltage is used to energize both the corona wire and transfer corona wire. Because of its high voltage requirements, a laser printer should not be connected to an uninterruptible power supply (UPS). Furthermore, high voltages create ozone which is a chemically reactive gas that can severely reduce the life of laser printer components. Therefore most laser printers contain a filter to remove ozone gas from inside the printer. This filter must periodically be removed and cleaned with compressed air. • However, the HVPS cannot be used to power the printer's logic circuitry and motors as these components require low voltages of between +5 and +24V of DC current. The DC power supply (DCPS) is used to convert the household electrical current to +5Vdc and -5Vdc for the logic circuitry and +24Vdc for the paper transport motors. • The paper transport assembly moves the paper from a supply bin to the engine where the image is laid on the paper and fixed to it, and then to a hopper for delivery to the user. This assembly consists of a motor and several rubberized rollers that each perform a different function. The feed roller or paper pickup roller is a D-shaped roller that rotates against the paper and pushes one sheet into the printer when activated. This roller works in conjunction with a special rubber pad to prevent more than one sheet from being fed into the printer at a time. Another type of roller that is used in the printer is the registration roller of which h there are two, both of which work together. These rollers synchronize the paper movement with the image formation process in the EP cartridge. Both of these rollers are operated CertGuaranteed. Study Hard and Pass Your Exam 220-301 with an electronic stepper motor that moves accurately in small increments. • The transfer corona assembly consists of: The primary corona, which charges the photosensitive particles on the surface of the print drum; The transfer corona, which uses a high-voltage electrical charge to charge the surface of the paper just before it reaches the toner area, which in turn pulls the toner from the photosensitive drum onto the paper; and A static-charge eliminator strip which drains away the charge imparted to the paper by the transfer corona, preventing the paper from sticking to the EP cartridge and jam the printer. • The fusing assembly is responsible for fusing the plastic toner particles to the paper. It consists of a halogen heating lamp, a Teflon coated aluminum fusing roller, and a rubberized pressure roller. The halogen lamp heats the fusing roller to between 165 degrees C and FIG 3.6: The Fusing 180degrees C. As the paper passes between the Assembly two rollers, the pressure roller pushes the paper against the fusing roller. This permanently fuses the plastic toner particles to the paper. • The printer controller circuitry is a large circuit board with a CPU, memory, BIOS, and ROM modules that contains the printer languages and fonts. It converts signals from the computer into signals for the various assemblies in the laser printer, using the process known as rasterizing. This circuit board is usually mounted underneath the printer. The board has connectors for each of the types of interfaces and cables to each assembly. When a computer prints to a laser printer, it sends a signal through a cable to the printer controller assembly. The controller assembly formats the information into a page's worth of line-by-line commands for the laser scanner. The controller sends commands to each of the components to start the EP print process. Some advanced EP printer models also employ a hard disk drive with a controller, a network adapter, and a SCSI host adapter. 3.4.3.1 Laser Printer Resolution The quality of a laser printer is related to its resolution, which is expressed in dots per inch (pdi). Horizontal resolution is determined by how fine a line can be focused on the drum by the laser while vertical resolution is based on the increment by which the photosensitive drum is turned for each pass of the raster line. In most cases, laser printer resolution is expressed as a single number, indicating that both the horizontal and vertical resolutions are the same. The as with monitors, the higher the resolution, the sharper the detail and the more memory required print the image to the page. 3.4.3.2 Troubleshooting Laser Printer Problems Properly installed laser printers are usually quite reliable. However, due to the combination of mechanical parts and the variety of steps in printing, laser printer problems do occur. Table 3.4 lists the possible causes of some of the problems that can be encountered with laser printers. TABLE 3.4: Possible Causes of Some Laser Printer Problems Symptom Possible Cause CertGuaranteed. Study Hard and Pass Your Exam 220-301 Ghost images appear at regular intervals on the printed page. The photosensitive drum is not fully discharged, or the previous images used too much toner, and the supply of charged toner is either insufficient or not adequately charged to transfer to the drum. Light ghosting appears on the paper. Previous images used too much toner; therefore, the drum could not be properly charged for the image. This is called developer starvation. Dark ghosting appears on the paper. The drum is damaged. The paper is completely black. The primary corona, the laser scanning module, or the main central board has failed. Random black spots or streaks appear on the paper. The drum was not properly cleaned and residual particles remained on drum. Marks appear on every page. The drum is damaged and must be replaced. The printed image is too light and appears in a column-like streak. The toner is low. Memory overflow error. The printer does not have enough RAM or the printing resolution too high. The printed characters are incomplete. The print density is incorrect. Adjust the darkness setting on the toner cartridge. Transparencies are melted. The wrong transparency material is used. The pages are creased. The wrong type of paper is used. The printed characters are warped, over-printed, or poorly formed. There is a problem with the paper or other media or with the hardware. After clearing a paper jam from the tray, the printer still indicates a paper jam. Printer was not reset after clearing the paper jam. Open and close the cover. After clearing a paper jam from the tray, the paper continues to jam. Problem with the pickup area, turning area, and registration area. CertGuaranteed. Study Hard and Pass Your Exam 220-301 3.4.3.3 Printing on Transparencies When printing on transparencies, ensure that only transparencies made of materials approved for laser printers are used. Laser printers generate far more heat than other types of printers, and using the wrong material will result in the transparency being melted and can cause serious damage to the printer. 3.4.4 Printer Cables To communicate with a computer, a printer can use of a serial cable that is attached to a serial port on the rear connector panel of the computer; a parallel cable that is attached to the parallel or LPT port; a SCSI cable that is attached to a SCI Host Adapter; or a USB cable that is attached to a USB port. The parallel cable was the popular printer FIG 3.7: The Centronics Connector cable until recently but most of the new printers use the faster USB cable. The standard DB25 parallel printer cable on one end, which is attached to the computer's parallel port, and a Centronics-compatible D-Shell fitting on the other end. The Centronics-compatible end of the printer cable is attached to the printer. Another common communication method is a network interface. 4. Upgrading and Repairing Computers The two main requirements for a and efficient computer upgrade or repair is knowledge and preparation. You should be familiar with the computer model you are to work on and you should have a good understanding of the problem or the task at hand. 4.1 Documentation Documentation is one key to preparation. If adequate documentation is not readily available, you must collect or create it. The Internet is a valuable tool for collecting documentation as most computer component manufacturers and vendors have Web site that allow you to download the available documentation. You should check these Web sites for updated drivers and information before performing any upgrades or repairs. When you finish a job, you should save the documentation, including an account of what you did and any problems you encountered for future reference. The types of documentation you should assemble before you begin a repair are: • A computer configuration sheet listing the devices already on the machine, hardware settings, the network configuration, and required passwords for the operating system. • Copies of the computer and motherboard documentation. • A list of all installed expansion cards. If possible, include the date on which they were originally installed. • Copies of the operating system documentation, especially if you are not familiar with the system. • A plan of action. Writing down a checklist of tasks and related tools and parts before starting a project can help you keep focused and on target. Remember, plans can always change; but, without a plan, you could find yourself wandering aimlessly through the project and perhaps getting sidetracked or lost. 4.2 Preparing the Work Area You will require an adequate workspace and the correct tools before you perform any work on a computer. The work area must be flat so that small parts do not roll around and possibly get lost or damaged. The work CertGuaranteed. Study Hard and Pass Your Exam 220-301 area must be sturdy. A typical computer weighs about 25 pounds. Printers and other peripherals will add to that weight. The work area must be able to support that weight. In addition, the area must be well lit, clean, and large enough to hold all the disassembled components and all necessary tools. You should make sure that you have all necessary tools and that they are in working order before you begin taking the computer apart. It may also help to lay out some of the more commonly used disassembly tools such as screwdrivers, nut drivers, and antistatic bags so they can be easily found. Three items that will be particularly useful are an egg carton, a pen and notepad. An egg carton is perfect for organizing screws and small parts that might otherwise get lost while a pen and notepad should be used to record anything that may easily be forgotten, such as cable positions, DIP switch settings, and the location from which you removed the components. Table 4.1 describes the hand tools most commonly required when working on a computer. TABLE 4.1: Hand Tools Tool Screwdrivers Description You should have a large flathead screwdriver, a small flathead screwdriver, and a Phillips screwdriver. Avoid magnetic tip screwdrivers as their magnetism can cause problems. Torx driver You would require a torx driver to remove the odd star-shaped screws found on some proprietary computers and components. Sizes T-8, T10 and T-15 should meet the needs of most computers. Nut driver In addition to the screwdriver, you could also use a nut driver that fits over the hexagonal collar on many computer screws. Sizes 3/16-inch, 7/32-inch, and 1/4-inch should meet the needs of most computers. Tweezers These are very convenient for picking up small parts like screws. You might consider the long plastic variety; these do not conduct electricity and hence will not create any short circuits. Needlenose pliers These can be used to pick up dropped items and to hold or loosen screws, nuts, and bolts. Chip removers These are very useful when changing DIP ROM chips, video RAM or RAM chips that are inserted in DIP sockets. Tube or plastic bag A short plastic tube with a cap on both ends will keep loose screws for small parts and small parts from getting lost. Compressed air A can of compressed air is helpful to remove dust. ESD tools An antistatic wristband is an essential tool. Antistatic mats and antistatic bags are also helpful to reduce the risk of ESD. Multimeter A small, digital meter that is capable of measuring AC and DC volts as well as ohms. Flashlight A small bright flashlight can be used to brighten parts of the computer that the normal light cannot penetrate sufficiently. Hemostats These are useful for picking up and holding small parts. Straight hemostats will work most of the time. However, curved ones will get into those small places that the straight ones cannot reach. POST card A Power On Self Test (POST) card can be used to see what the error messages during system start are when no data is being sent to the display. In addition to this hand tools you should also have some software. It is not necessary to carry an entire arsenal of arcane software. Instead, collect the software that supports the computers you normally work on, including the operating system start up disks and common drivers. You should have a bootable floppy disk CertGuaranteed. Study Hard and Pass Your Exam 220-301 for each operating system that you encounter. These should contain the following files: attrib.exe; command.com; defrag.exe; edit.com; emm386.exe; expand.com; fdisk.exe or fdisk.com; format.exe or format.com; himem.sys; label.com; mem.exe; memmaker.exe; mscdex.exe; msd.exe or msd.com; qbasic.exe; scandisk.exe; share.exe; sizer.exe; smartdrv.exe; and sys.com Also make sure that the original operating system disk or CD with the serial number is available. If it becomes necessary to install one or more software components, the computer might require the serial number, installation ID, or the original distribution disk before any additional files can be installed. 4.3 Disassembling a Computer Disassembling a computer is a straightforward task. In most cases, you only need to remove the outer cover of the case to gain access to the RAM, expansions cards, drive bays, and the CPU. This usually requires the loosening of four or six screws at the back of the computer case. However, not all covers are the same. Some have removable side panels and some have motherboard trays that slide out the rear end of the computer to provide better access to the components. The user manual that came with the computer is a useful tool when it comes to finding out how remove the cover. You should also remove the power cables that are attached to the back of the computer. The extent to which you have to disassemble a computer depends on the specific upgrade or repair. 4.3.1 Removing the Expansion Cards Expansion cards are the easiest computer components to remove once the case is opened as you will then have easy access to the expansion cards. However, before proceeding, ensure that you antistatic wrist strap is plugged into the ground plug of a wall power outlet socket. There are four major steps in removing the expansion cards: • Remove any internal cables or connectors attached to the expansion card, or that may interfere with the removal. Use your pen and notepad to diagram their installed positions us the pen make identifying marks on the cables to make sure they align correctly when reinstalled. • Remove mounting screw that holds the expansion card in place. • Gently rock the expansion card back and forwards in the direction of the expansion bus. If the expansion card does not come out easily, check to see that the card is not being obstructed. • Once the expansion card is removed, place it in an antistatic bag to help prevent ESD damage while the board is out of the computer. Place the board aside and out of the way before continuing. 4.3.2 Removing the Power Supply Before you removing the power supply from a computer you must first disconnect the power supply connectors from the internal devices from the motherboard. This is a simple matter of grasping the connector, and not the wires, and gently wiggle it out of its receptacle. Yu must also remove the cable and connector that run from an AT power supply to the power switch at the front of the case. This may necessitate the removal of the front cover of the computer case. The AT power supply has two connectors to the motherboard. You should document the positioning of these connectors before removing them to make sure they are connected correctly when you put them back when you are done. Remember the black wires from the two connectors are placed side by side. Once all the power supply connectors are disconnected, you can remove the power supply. This usually requires the removal of four mounting screws at the back of the computer that hold the power supply in place. However, some power supplies are installed on tracks or into slots in the case and need only to be slid out or lifted out. 4.3.3 Removing the Disk Drives Removing a drive is usually a simple task of removing the power connectors, the cables, and the four screws that hold the drive n place and sliding it out the back end of the drive bay. When removing the EIDE cable make a note of the position of the cable and mark the cable itself to ensure correct fitment when you replace it. Remember that the number one pin, marked with a red line is inserted on the side of the power connector. CertGuaranteed. Study Hard and Pass Your Exam 220-301 Once the cable and the power connector is removed, you just need to remove the drive itself. However, some disk drives are installed on rails that are attached to the drives with screws. These rails allow the drive to be slid into the computer's drive bays like a drawer. The drives are then secured with at least two screws on each side. Other computers have a special drive carrier that holds the drive in place and can be easily removed without tools. On some high-end computer systems you can remove the drives while the computer is still running. This is known as a hot-swap. You should thus consult the computer's documentation to see exactly how to remove the type of drive you are working with. 4.3.4 Removing the Motherboard The motherboard is usually the most difficult component to remove as most of the other components must be removed, including all the expansion cards, before the motherboard can be removed. Fortunately, the only time you would need to remove the motherboard is when it must be replaced or upgraded. All the connectors on the motherboard must also be removed before the motherboard can be removed. This includes the EIDE cables, the floppy drive cable, the power connectors, and the front panel connectors. Make a note of where the various cable fit, and their position, especially of the front panel connectors as this will ease the fitment of these connectors and cables when the motherboard is reinstalled. However, if an upgraded motherboard is installed, you will have to consult the motherboard user manual to determine the correct fitment of the cables and connectors. The motherboard is held away from the metal motherboard tray by means of plastic stand offs or spacers and is secured and grounded by means of mounting screws. To remove the motherboard, you must remove the screws FIG 4.1: The Front Panel Connectors holding the motherboard to the mounting brackets. Then, you must slide the motherboard to the side to release the spacers from their mounting holes in the case. 4.4 Upgrading a Computer The task most frequently performed by a computer technician is upgrading old systems to the latest technologies. This ability to expand and upgrade a computer can prolong the life and utility of a computer system. Sometimes the addition of a new software program can lead to hardware conflicts and necessitate an upgrade. Before you begin to upgrade any computer, you must document the system. If the component you are installing is a replacement part, you can simply set the jumpers or DIP switches the same as they were on the component that was removed. However, if you are installing a new type of component, you must first identify available system resources that can be assigned to the new component. The best way to determine the computer system's available resources is by using hardware configuration discovery utilities. These software programs that interface with the system BIOS as well as the various pieces of hardware in the computer and display which IRQ, DMA, and I/O port addresses are being used. Most operating systems include some way of determining this information. MS-DOS, Windows 3.x, and Windows 95 included a tool named msd.exe. Windows 98, Windows 2000 and Windows XP has a graphical utility called the Device Manager while Windows NT includes a program known as NT Diagnostics. All these utilities perform the CertGuaranteed. Study Hard and Pass Your Exam 220-301 same function. msd.exe has an advantage over the other utilities in that it can be included on a bootable floppy disk. Thus, in the event that a resource conflict is preventing your system from booting properly, you can boot to the DOS floppy and troubleshoot your problem. When you run msd.exe, it displays information about the computer's memory, I/O ports, IRQs that are being used, and many other PC resources that you want to see. However, you should not rely completely on the report you get from MSD if you're running it under Windows 3.x or Windows 95 as msd.exe reports the information that it gets from Windows. This may be incorrect and could prove to be problematic. For best results, run MSD should be run MS-DOS mode. In addition to system resources, you must also ensure that there is adequate physical space available for the device. If you are installing an additional disk drive you will require an open drive bay. If you are installing an expansion card, you will require an open slot of the same type as the expansion card you are installing. 4.4.1 Upgrading the Memory Memory is the most commonly upgraded component in a computer system. As programs and hardware get faster and are required to process more graphics and animation, the computer would require more memory. Fortunately, memory upgrades are simplest upgrades to perform. All that is usually required is purchasing the correct memory module that is supported by the motherboard. The best source of information is the documentation that comes with the computer's motherboard. This usually lists the type of memory required, the proper population scheme, and the location on the motherboard. Some motherboards have two types of memory slots but can often only support the use of one type of slot at a time. Installing RAM is an easy process: • Turn off the computer, disconnect all external devices, including the AC connector and the monitor power monitor, and open the computer case. • Attach and ground the antistatic wrist band. • Locate the RAM slots and determine that you have the correct size, speed, and quantity of RAM. If you are adding SIMMs, make sure that the notch in bottom end of the SIMM is aligned with the slot and insert the SIMM into the slot at a 45-degree angle and then snap it into the upright position. Once in the upright position the two metal retaining clips should snap into position. These clips must be opened before you remove the SIMMs. If you are adding DIMMs or RIMMs, flip the plastic retaining clips on the memory slot outward and make sure that the notch in bottom end of the DIMM or RIMM is aligned with the slot. Insert the DIMM or RIMM upright in the slot and push down firmly. When seated correctly, the plastic retaining clips should snap close. Removing the DIMM or RIMM is a simple task of flipping these plastics clips outward. • Once the RAM is installed replace the computer case, nect the power, monitor, and any other needed external devices, and start the computer. The computer should recognize the new memory and either make the correction or automatically go to the CMOS Setup program. In many cases, you need only exit Setup to save the changes. 4.4.2 Upgrading the CPU CertGuaranteed. Study Hard and Pass Your Exam 220-301 Another popular component for upgrade is the CPU. In many cases, upgrading a CPU is a simple matter of removing the old one and inserting the new one. However, you must first determine whether the motherboard's Front System Bus (FSB) can support the clock frequency of the new CPU and what type of socket the motherboard supports. The documentation that came with the motherboard usually contains a table that defines which CPUs are compatible. If you are unable to find the documentation, or if the processor that you want to install is not listed, consult the motherboard manufacturer's Web site or their technical support department. Remember to check for any required jumper settings and BIOS upgrades at the same time. FIG 4.2: A ZIF Socket Although there a numerous different CPU families manufactured by companies such as Intel, AMD, and VIA, CPU generally come in only 3 types of packages: Dual Inline Package (DIP); Pin Grid Array (PGA), and Single-Edge Connector (SEC). • The 80086, 80086, and the early 80286 CPUs came in the Dual Inline Package (DIP) and are inserted into a DIP slot on the motherboard. Replacing these CPUs require the removal of the old CPU chip and the insertion of the new chip. Be sure not to bend the pins when inserting the chip as this may cause the chip to malfunction and might destroy the chip and the motherboard, and be sure to align the chip correctly. There is usually a notch on one end of the chip and one on the DIP socket that must be placed over each other. • Almost all the other CPUs, except for most of the Pentium II CPUs and some of the Pentium III CPUs, come in the Pin Grid Array (PGA) package. Almost all of these CPUs come with a heat sink and fan and are inserted into either a Low-Insertion-Force (LIF) socket or a Zero-Insertion-Force (ZIF) socket on the mother board. To remove the old CPU from a Low-Insertion-Force (LIF)socket, first remove the CPU fan's power connector, making a note of where the connector fits, and then remove the heat sink and fan assembly. Removing the actual CPU requires the use of special tools designed for this purpose. However, a flathead screwdriver or a plate cover for an expansion card slot will also do the job if you pry evenly around the CPU. The LIF socket has a notch on one of its corners, matching a notch on one of the corners of the CPU. These notches should be lined up together. Once aligned correctly, make sure that all the pins are lined up correctly and press the CPU into the PGA socket firmly and evenly. CertGuaranteed. Study Hard and Pass Your Exam 220-301 Attach the heat sink and fan, using the thermal past if required, and connect the CPU fan's power connector to the appropriate power connector on the motherboard on from the power supply. • Removing the old CPU from a ZeroInsertion-Force (ZIF) socket is much easier as the ZIF socket has a lever arm that allows for simple removal and installation of CPUs. ZIF sockets were introduced during the early 1990s as a safe means of providing a user-friendly CPU upgrade. The first ZIF socket had 169 pins and was used on 486SX systems. FIG 4.3: The Pentium II These systems were sold with a 486SX chip already installed in a PGA socket and provided a ZIF socket for a 486 OverDrive chip. To remove the CPU you must first remove the CPU fan's power connector, making a note of where the connector fits and then remove the heat sink and fan assembly. Next, shift the lever arm away from the catch that hold it in position, and move the arm into the upright position. This frees the CPU and it can be lifted out of the socket. Installing the new CPU is equally easy. Some ZIF sockets have a notch on one of its corners while others have a missing pin hole. These are matched to a notch on one of the corners of the CPU or a missing pin on the CPU. These should be lined up together. Once aligned correctly the CPU will slip into the ZIP socket. Shift the lever arm into the locked position, reattach the heat sink and fan assembly and connect the CPU fan's power connector to the appropriate power connector on the motherboard on from the power supply. • Most of the Pentium II processors and some of the Pentium III came in the Single-Edge Connector (SEC) cartridge package that fits into a slot on the motherboard, called the Slot 1. The removal of these CPU requires the unseating of two plastic retaining pins on the siding guides that fit over the side of the CPU, removing the CPU fan's power connector, making a note of where the connector fin in, and then pulling the CPU upward out of the slot. To install the new CPU, ensure that the notch on the bottom end of the CPU is aligned with the FIG 4.4: The SEC Guides slot, slide the CPU into CertGuaranteed. Study Hard and Pass Your Exam 220-301 the slot via the guides and press firmly into place. Once inserted, reseat the plastic retaining pins to secure the CPU in position and reconnect the CPU fan's power connector. Note: If you are working with a dual- or multi-CPU motherboard, the CPUs must be of the same type and speed if more than one is to be installed. In addition, on Pentium II and later systems, most dual- and multi-CPU motherboards have a special card that must be inserted in any empty CPU socket, and the correct slot must be used for a single CPU configuration. When adding an additional CPU to dual- or multi CPU motherboard on a Windows NT, Windows 2000 or Windows XP system, the hardware abstraction layer (hal.dll) must be upgraded. This file allows the operating system to access and spread the processing load across all of the CPUs in a multi-CPU configuration. 4.4.3 Upgrading the Motherboard Upgrading the motherboard is one way to completely overhaul a computer. Installing a new motherboard is a major task and requires complete disassembly, reassembly, and setup of the computer and all its devices. You will put everything covered so far in this lesson into practice when you replace a motherboard. In most cases it may also necessitate a RAM and/or CPU upgrade if the existing RAM and CPU is incompatible with the new motherboard. 4.5. Troubleshooting Computer Problems Troubleshooting is perhaps the most difficult task of a computer technician. Frequently, the problems reported are just symptoms, not the cause. It takes investigation to pinpoint the real cause. After you diagnose a problem, you must develop a plan of action to correct the problem. To efficiently and effectively troubleshoot a problem, you must approach the problem in an organized and methodical manner, eliminating as many possible causes so that you can focus on the real cause of the problem. To do this, you must be organized. The first part in approaching a troubleshooting problem is to completely understand the problem in its entirety. This requires gathering information from the client or the computer operator. Ask a few specific questions to help identify the problem and list the events that led up to the failure. It is often a good idea to examine the computer and verify the client's statements as much as possible. Access to documentation that came with the computer system can also be a valuable source of troubleshooting information as they often contain a list of compatible replacement parts and exploded diagrams of the model being repaired. If the client does not have a copy of the documentation that came with the computer, check the computer manufacturer or vendor's Web site. Also check if the Web site has a Frequently Asked Questions section, this may contain several pieces of information that can be very valuable and might even lead to a possible solution if there is a specific question or problem that relates to your situation. Next, attempt to isolate the problem by eliminating any obvious possible causes working from the simplest possible cause to the more complex. Table 4.2 provides 14 possible categories you can use to isolate the problem. TABLE 4.2: Isolating the Problem Category Electrical power Symptom Possible Cause Computer will not boot Intermittent errors POST Intermittent lock ups Power connectors Plugs and cords Power supply CertGuaranteed. Study Hard and Pass Your Exam 220-301 Devices not working or not detected Fuse box Wiring Electric utility Connectivity Device not working or not detected Intermittent errors on a device Device failure or failure to boot External cables Internal cables Properly seated cards SCSI chain Front panel wiring Boot Computer will not boot Consistent errors on POST Boot ROM All products on the hardware abstraction layer list CMOS CMOS battery Flash ROM Beep errors CMOS text errors, hard disk drive, floppy disk drive, and video errors Memory Computer will not boot Parity errors General Protection Fault with consistent addresses HIMEM.SYS errors Mass storage Error messages: Missing Operating System File Not Found No Boot Device Abort, Retry, Fail Input/output (I/O) System locks up Device not responding Bizarre behavior from a device Operating system Error messages: Missing Operating System Bad Or Missing Command Interpreter Insert Disk With COMMAND.COM Stack Overflow Insufficient File Handles Improper RAM type and setup RAM CMOS settings Motherboard jumper settings Hard disk drives, floppy disk drives, CD-ROM drives Zip drives, tape drives Partitions File structure File allocation tables Directory structure Filenames and attributes IRQ settings I/O address DMA settings Serial port settings Parallel port settings SCSI settings Card jumper settings BUFFERS FILES File Control Blocks Stacks IO.SYS/MSDOS.SYS Set statements Paths and prompts External MS-DOS commands CertGuaranteed. Study Hard and Pass Your Exam 220-301 Multiboot CONFIG.SYS Applications Application does not work properly Application-specific errors Application-specific General Improper installation Improper configuration Software incompatibilities Protection Faults Lock ups only in specific application Device drivers Device lock ups on access Intermittent lock ups Computer runs in safe mode only Memory management Not Enough Memory error Missing extended memory specification and Expanded Memory Specification Device lock ups General Protection Faults at KRNL386.EXE General Protection Faults at USER.EXE or GDI.EXE Configuration/ Programs refuse execute command setup Missing options in program Missing program or device Viruses Computer is slow Failure to boot or intermittent lock ups Storage problems Operating-system problems Mysterious symptoms Network Logon errors Communication errors All devices in the Windows Registry, .ini files, CONFIG.SYS, SYSTEM.INI, called in AUTOEXEC.BAT Improper versions Improper configuration HIMEM.SYS settings EMM386.EXE settings MSDOS.SYS options SYSTEM.INI/WIN.INI Virtual memory Windows resource usage Upper Memory Block management Files used for initialization Basic layout of initialized files Virus problems User password problem Expired password Cable or NIC problems Intermittent problems are the most difficult ones to isolate. The only way to resolve them is to re-create the set of circumstances that causes the failure. Note: For a totally random, intermittent problem, and for intermittent reboots, always suspect a faulty power supply. Once you have isolated the cause you should be able to identify the problem by eliminating the possible causes. Once you have located the problem, either repair or replace the defective part. If the problem is software-oriented, be sure to record the software setting be attempting to reinstall or update the software system. Make sure that your repair has solved the problem. This involves two steps: making sure that the problem no longer exists; and make sure that the repair did not create other problems CertGuaranteed. Study Hard and Pass Your Exam 220-301 Finally, document the problem and the repair. This will be quite useful when encountering a similar problem in the future. 5. Portable Computers There are various different types of portable computers that are classified according to size and function. There are three basic types of portable computers: laptops; notebooks; or subnotebooks which are also called palmtop or handheld computers or personal digital assistants (PDAs). Most modern portable computers standard connectors for desktop keyboards, pointing devices, and monitors. The first portable computers were called luggables and were nothing more that a traditional computer in a slightly smaller case equipped with a small CRT display. The advent of the flat-panel display in the 1980s allowed the portable computer to take on the current slim design. • With the advancements in battery technology and the advent of functional, large-screen, liquid crystal displays (LCDs) in the 1980s, the first truly portable computers were produced. These portable computers are called laptops computers and feature integrated AT-compatible computer motherboards that includes I/O and video controller functions. They usually feature a folding LCD display and a builtin keyboard and pointing device. They also use an external power supply and a removable, rechargeable battery. Today's laptops have fairly large hard disk drives, a CD-ROM drive or DVD drive, and a floppy disk drive. These are the heavier portable computers that offers most of the features on a desktop computer. • Advances in integrated circuit (IC) technology allowed the size of computer components to be reduced even further resulting in the emergence of the notebook Computer. Notebooks are roughly 8.75 inches deep × 11 inches wide × 2.25 inches thick. The reduction in size results in the notebooks having smaller and less capable displays and keyboards. However, a variety of items, such as the docking port, designed to overcome some of the notebook's shortcomings have appeared on the market. Docking ports, also known as docking FIG 5.1: A Laptop Computer stations, are specialized cases into which an entire notebook computer can be inserted. This allows the notebook to be connected to desktop I/O devices such as full- CertGuaranteed. Study Hard and Pass Your Exam 220-301 sized keyboards, CRT monitors, and network connections. At minimum, a docking station provides an alternating current (AC) power source for the notebook. However, docking stations are proprietary devices designed for use with specific notebook models. • Subnotebook computers are also known as palmtops, handheld computers or PDAs and are even smaller than the notebook computers. These computers are 7 inches wide × 4 inches deep × 1 inch high. Due to their size, they have very limited functionality and use a pen-like stylus and handwriting interpretation software to perform operations. 5.1 Portable Computer Components 5.1.1 The PCMCIA Bus The Personal Computer Memory Card International Association (PCMCIA) established several standards for credit-card-sized expansion cards that can be inserted into small slots on portable computers, providing laptops and notebooks with the some form of expandability. These expansion cards are referred to as PCMCIA cards or PC cards and use the PCMCIA bus. The PCMCIA standards have provided portable computers with the ability to add memory expansion cards, network interface cards, SCSI devices, modems, faxes, and many other devices that were previously unavailable to laptop and notebook computer users. There are four PCMCIA standards: type I, type II, type III and type IV. These standards are discussed in Table 5.1. TABLE 5.1: PCMCIA Standards PCMCIA Standard Type I Description The first PCMCIA standard which work only with memory expansion cards. The Type I PCMCIA Card slot accepts cards that are 3.3 mm thick. Type II This standard support most types of modem or network adapters and Type II PCMCIA Card slot accepts cards that are up to 5 mm thick. Most portable computers have two of these slots Type III This standard was introduced in 1992 and was designed primarily for computers with removable hard disk drives. The Type III PCMCIA Card slot accepts cards that are 10.5 mm thick but are compatible with Type I and Type II cards. Type IV Type IV slots are intended to be used with hard disk drives that are thicker than the 10.5 mm Type III slot. The PCMCIA card is the size of a credit card and is sealed in a metal case. One end of the card contains the interface that fits into the PCMCIA card slot while the other end might contain a connector for the external device that is to be attached to the portable computer. PCMCIA cards support only one IRQ which may present a problem if you need to install two devices that require interrupts in a PCMCIA bus. Portable computers use Socket Services and Card Services to make the PCMCIA card hot swappable i.e., allows the PCMCIA card to be installed or removed while the portable computer is in operation. • Socket Services is a BIOS-level software that replaces the BIOS as the interface between the CPU and the PCMICIA card detects when a PCMCIA card is inserted into a PCMCIA card bus and detects what type of card it is. CertGuaranteed. Study Hard and Pass Your Exam 220-301 • Card Services software serves as the interface between the application and Socket Services. It tells the application what IRQ and I/O ports the PCMCIA card is using. Thus, the application does not access the hardware attached to a PCMCIA card directly. 5.1.2 Portable Computer Display Systems Portable computers have a flat LCD screen that consumes much less power than a standard CRT monitor and is approximately half an inch thick. The display is usually the most expensive component in a portable computer system. Often it is more economical to replace the entire computer than to replace the screen. The size of the pixels on an LCD panel cannot be changed therefore an LCD display can only operate at a specific resolution. The color displayed by each pixel of a LCD display is controlled by transistors. There are two major types of LCD displays used on portable computers, defined by their arrangement of transistors. These are passive-matrix displays and active-matrix displays. • Passive-Matrix Displays, which are also called dual-scan displays consist of a single row of transistors running down the edge of the x-axis of the screen and single row of transistors running down the edge of the y-axis of the screen. The number of transistors in these two rows determines the screen's resolution. The two transistors that intersect on the x- and y-axis control each pixel on the screen. If a transistor fails, the entire line of pixels is disabled, leaving a black line across the screen. These displays cannot be repaired. With passive-matrix displays, half the screen is drawn and redrawn at a time. This increases the refresh rate. However, passive-matrix displays tend to be dim because they work by modifying the properties of reflected light rather than generating their own light. For this reason they cannot be viewed from an angle. Passive-matrix displays are also prone to ghost images. The standard sizes for the passive-matrix display screen is 10.5 inches with a resolution of 640 × 480 and 12.1 inches with a resolution of 800 × 600. • Active-Matrix Displays, which are also known as thin film transistors (TFTs), have a transistor for every pixel on the screen rather than just at the edges of the x- and y-axis. Electrodes apply voltages at the perimeter of the grid to address each pixel individually. Because each pixel is powered individually, the active-matrix displays generate their own light and are thus have a much brighter and vivid picture than their passive-matrix counterparts. In addition, the failure of a transistor causes individual dead pixels which are less noticeable than the black line caused by a transistor failure of the passive-matrix display screen. However, because the active-matrix displays have 480,000 transistors instead of 1,400 on an 800 × 600 screen, they are more expensive than passive-matrix displays and require more power and consequently drains the batteries faster. Although the resolution of an LCD display is limited by the number of transistors, its resolution can be enhanced by using virtual screens. This is accomplished by the display drivers and amount of installed video memory and is a memory-swapping technique whereby a larger display is held in video memory while the actual screen displays the portion that fits onto the actual screen. The cursor can be used to move the viewing area to display the other portions of the image. Furthermore, the color depth of an LCD display is affected by video memory with LCD displays operating in 16-bit or 24-bit color mode requiring more video memory. However, portable computers usually have integrated display adapters that are built into the motherboard. This makes an upgrade of the display system virtually impossible. Most portable computers allow connection to an external monitor to increase video capabilities. 5.1.3 Portable Computer Processors Special CPUs are designed use in portable computers as the portable computer dose not have the space to accommodate the large heat sink and fan used to dissipate the heat generated by the CPU in desktop computer systems. CPU manufacturers have addressed this problem in the packaging of the CPU, with Intel developing a Tape Carrier Package. This method of packaging reduces the size, power consumption, and CertGuaranteed. Study Hard and Pass Your Exam 220-301 heat generated by the CPU. A Pentium CPU mounted on a motherboard using Tape Carrier Packaging is much smaller and lighter than the pin grid array (PGA) used in desktop computer systems. The Tape Carrier Packaging CPU is bonded to a piece of polyamide film, called tape, using tape automated bonding. The film is laminated with copper foil etched to form the leads that connect the processor to the motherboard. When the leads are formed, they are gold-plated to prevent corrosion, bonded to the processor chip itself, and then the entire assembly is coated with a protective resin. After being tested, the tape is cut to the proper size and the ends are folded into a gull wing shape that allows the leads to be soldered to the motherboard while the processor is suspended slightly above it. A thermally conductive paste is inserted between the processor chip and the motherboard, allowing heat to be dissipated through a heat sink on the underside of the motherboard. As Tape Carrier Packaging CPU is soldered to the motherboard, they cannot be upgraded. Some manufacturers have however retained the PGA packaging on portable computer CPUs. 5.1.4 Memory As with desktop computer systems, adding memory is one of the most common upgrades performed on portable computers. Some portable computers use memory cartridges that looks like PCMCIA cards, but plug into a dedicated IC memory socket. Others use memory modules that are similar to SIMMs and DIMMs in that they use the same types of DRAM as used n these memory modules. Some modern high-end portable computer systems include SRAM cache memory. The two most common types of memory modules for portables computers are the Small Outline Dual Inline Memory Module (SODIMM), which is often used in Laptops and Notebooks; and the Micro Dual Inline Memory Module (MicroDIMM), which is used in Subnotebooks. 5.1.4.1 The Small Outline Dual Inline Memory Module (SODIMM) Small Outline Dual Inline Memory Modules (SODIMMs) are so named because they are smaller and thinner than regular DIMMs. There are three types of SODIMMs - the 72-pin SODIMM, the 144-pin SODIMM, and the 200-pin SODIMM. • The 72-Pin SODIMM consists of a number of DRAM chips that are attached to a printed circuit board. The gold or tin pins, of which there are two rows of 36 pins each, at the bottom of the SODIMM provide a connection between the module and the memory slot on the motherboard. The pins on the front and back of a SODIMM are not connected and thus provides two lines of FIG 5.2: 72-Pin SODIMM communication paths between the module and the motherboard. The 72-pin SODIMM is 32-bit wide and must be installed in pairs in a 64-bit portable computer system. 72-pin SODIMMs use either FPM DRAM chips or EDO DRAM chips and are approximately 2.375" long and 1" high, though their height may vary. They have a notch at the bottom right corner to ensure their correct orientation when installed. CertGuaranteed. Study Hard and Pass Your Exam 220-301 • The 144-Pin SODIMM is similar to the 72Pin SODIMM but has two rows of 72-pins making a total of 144 pins and are 64-bit wide. They can thus be inserted singularly in 64-bit portable computer systems. 144-pin SODIMMs use EDO DRAM chips, PC66 SDRAM chips, PC100 SDRAM chips, or PC133 SDRAM chips and are approximately 2.625" long and 1" high, though their height may vary. They have one small off center notch within the row of pins to ensure their correct orientation when installed. FIG 5.3: 144-Pin SODIMM • The 200-Pin SODIMM is similar to the 144-Pin SODIMM but has two rows of 100-pins making a total of 200 pins and are 64bit wide. They can thus be inserted singularly in 64-bit portable computer systems. 200-pin SODIMMs use DDR266 SDRAM chips and are available in PC2100 DDR SDRAM. 200-pin SODIMMs are approximately 2.625" long and 1" high, FIG 5.4: 200-Pin SODIMM though the heights may vary. Like 144-pin SODIMMs, 200-pin SODIMMs have one small notch within the row of pins to ensure their correct orientation when installed; however, the notch on the 200-pin SODIMMs is closer to the left side of the module. 5.1.4.2 The 144-Pin Micro Dual Inline Memory Module (MicroDIMM) The Micro Dual Inline Memory Module (MicroDIMM) has 144 pins and consists of a number of DRAM chips that are attached to a printed circuit board. They are called MicroDIMMs because they are smaller than both regular DIMMs and SODIMMs. The gold or tin pins on the bottom of the CertGuaranteed. Study Hard and Pass Your Exam 220-301 FIG 5.5: MicroDIMM provide a MicroDIMM connection between the module and a memory slot on the motherboard. The pins on the front and back of a MicroDIMM are not connected, providing two communication paths between the memory module and the system. A 144-pin MicroDIMM is 64-bit wide and can thus be installed singularly in 64-bit portable computer system. 144-pin MicroDIMMs use PC100 SDRAM chips, PC133 SDRAM chips or DDR266 SDRAM chips and are approximately 1.545" long and 1" high, though their heights may vary. Unlike SODIMMs, MicroDIMMs do not have any notches along their bottom edge. 5.1.5 Hard Disk Drives Despite its different size and packaging, the technology used in a portable computer's hard disk drive is similar to that of the hard disk drive used in desktop computers. EIDE drives are standard in portable computers with the exception of the Macintosh computer, which uses SCSI drives. The internal hard disk drives are 12.5 mm or 19 mm tall, and use 2.5inch platters. Some hard disk drive manufacturers use a caddy to hold the drive and make connections to the motherboard. This makes upgrading as simple as inserting a new hard disk drive into the caddy and then mounting it in the computer. Other systems require purchase of a specifically designed drive, complete with the proper connections built into it. However, the system BIOS FIG 5.6: A Laptops' Hard Disk Drive of the portable computer determines its upgradeability. Portable computer systems manufactured before 1995 might offer only limited hard disk drive-size options and BIOS chips made before EIDE hard disk drives became the standard can only support a maximum hard disk drive size of 528 MB. A flash BIOS upgrade might be available for these systems to provide additional hard disk drives. Another option for expanding hard disk drive space is use of a portable PCMCIA hard disk drive that fits into a Type III PCMCIA Card slot. External drives are also available and can be connected using a PCMCIA SCSI host adapter or specialized CertGuaranteed. Study Hard and Pass Your Exam 220-301 parallel port drive interfaces. 5.1.6 Removable Media Portable computer systems are also equipped with other types of removable storage media that can provide access to large amounts of data. These include CD-ROM drives, DVD drives and Zip drives, as well as floppy disk drives. Some portable computers use swappable drive bays that allow you to remove the floppy disk drive and insert a DVD drive when you need to access data on a DVD disc. In addition, the swappable dive bay can accept other portable devices such as an extra battery. 5.1.7 Keyboards The portable computer keyboard is integrated into a one-piece unit and is therefore difficult to repair or replace. Unfortunately, the keypad is almost always the first component to fail in a portable computer. The keyboards on modern portable computers are approaching the size and functionality of desktop computer systems. This has created more space for manufacturers to utilize in the overall design. 5.1.8 Pointing Devices The portable computers comes with built-in pointing devices. Most of these pointing devices are either: trackball, trackpoint, or touchpad. • A Trackball is a small ball of approximately half an inch in diameter that is partially embedded in the keyboard below the spacebar. These devices are accurate and serviceable, but tend to gather dirt and dust, which dramatically reduces performance. • The Trackpoint was developed by IBM. It is a small, rubberized button of approximately a quarter inch in diameter that located in the keyboard, above the 'B' button and between the 'G' and 'H' buttons (indicated in Figure 5.1), and is nudged in any direction a rather like a joystick. • The most recently developed pointing device for the portable computer is the Touchpad, which is also known as the trackpad. It is an electromagnetically sensitive pad measuring about 1 inch × 2 inches located below the spacebar. It responds to the movement of a finger across its surface to move the cursor. Tapping the pad simulates mouse clicks. 5.1.9 USB Ports The addition of USB technology to portable computers has made it much easier to add new devices or share them with other computers. In addition, there are PCMCIA USB cards that can add USB functionality to older portable computers. 5.1.10 Wireless Adapters Major notebook computer makers, including Dell, IBM, and Toshiba, are now integrating built-in IEEE 802.11b or dual-band IEEE 802.11a/b wireless network adapters and antennas into some of their portable computers. These portable computers use a mini-PCI interface for the wireless network adapter and place the antenna inside the screen housing. These wireless network adapters can be used to access a traditional Ethernet network via a wireless access point (WAP), or can be used for direct communicate between two portable computers. External PCMCIA network adapter cards can be attached to FIG 5.7: A PCMCIA portable computers Network Adapter that do not have integrated network adapters to provide them with the same functionality. CertGuaranteed. Study Hard and Pass Your Exam 220-301 5.1.11 Batteries and AC Adapters Portable computers use batteries and AC adapters to supply power to their components. The AC Adapters converts the AC current from an electrical wall socket to DC current that can be used by the portable computer. However, to be truly portable, the portable computer requires a battery that can b used when no AC power point is available. The portable computer is specifically designed to use less power that a conventional desktop computer and hence has a LCD display rather than the power hungry CRT monitor. There are many different sizes and shapes of batteries used to power portable computers. These batteries fall into three main categories: Nickel-Cadmium (NiCad) Batteries; Nickel Metal Hydride (NiMH) Batteries; and Lithium Ion (LiOn) Batteries. A fourth type of battery, the Lithium Polymer battery is currently in development but has not been released. • Nickel-Cadmium (NiCad) Batteries are the oldest of the three technologies. They have a short life and are sensitive to improper charging and discharging. After being charged, NiCad batteries hold a charge very well. How-ever, their life can be severely shortened if they are not fully discharged before recharging or if they are overcharged. • Nickel Metal Hydride (NiMH) Batteries have a longer life than NiCad batteries and are less sensitive to improper charging and discharging. They are also more expensive than NiCad batteries and tend to loose their charge when not in use. In addition, they cannot be recharged as many times as NiCad batteries. • Lithium Ion (Li-Ion) Batteries cannot be overcharged and hold a charge well when not in use. In addition, they last longer than the other two types of batteries. They are also proficient at handling the heavy-duty power requirements of the modern higher-end portable computers. They are FIG 5.8: A Li-Ion Battery however the most expensive of the three battery technologies and can only be recharged 300 times. In addition to AC adapters and batteries, micro fuel cells have also been developed for portable computers. A fuel cell is a device that converts hydrogen found in methanol into electricity through an electro-chemical reaction. The micro fuel cell is approximately the size of a cigarette lighter and can provide portable computers with electrical power for up to 10 hours. These fuel cell do not require recharging but do require a refill of fuel. 5.2 Power Management To increase battery life, power management can be used to shut down portable computer components that do not need to run continuously. Most portable computers include power-saving modes that suspend the system operations when the computers are not in use. These power-saving modes are generally called suspend mode and hibernate. • In Suspend Mode the entire system except the RAM is shut down after a certain period of inactivity. As power is supplied to the RAM, the data contained in memory is retained and the portable computer system can be reactivated almost immediately. • In Hibernate Mode the entire contents of memory is written to special swap file before the system is completely shuts down. When the portable computer system is reactivated, the swap file is read back to memory. The hibernate mode takes a little longer to reactivate than the suspend mode, but it conserves more battery life. CertGuaranteed. Study Hard and Pass Your Exam 220-301 There are currently two standards that define the interface between the power-management policy driver and the operating system,. The first is the Advanced Power Management (APM) standard which was jointly developed by Intel and Microsoft. This interface is usually implemented in the system BIOS. The second standard is called the Advanced Configuration and Power Interface (ACPI) and was developed Intel, Microsoft, and Toshiba. This standard places the power-management functions under the control of the operating system. 6. Network Systems 6.1 Basic Networking A network is defined as a group of two or more computers linked together for the purpose of communicating and sharing information and other resources, such as printers and applications. Most networks are constructed around a cable connection that links the computers. This connection permits the computers to communicate via the wires in the cable. More recently, a number of wireless network solutions, including infrared ports, Bluetooth radio links, have been developed. For a network to function it must provide connections, communications, and services. • Connections are defined by the hardware or physical components that are required to connect a computer to the network. This includes the network medium, which refers to the hardware that physically connects one computer to another, i.e., the network cable or a wireless connection; and the network interface, which refers to the hardware that attaches a computer to the network medium and is usually a network interface card (NIC). • Communications refers to the network protocols that are used to establish the rules governing network communication between the networked computers. Network protocols allow computers running different operating systems and software to communicate with each. • Services define the resources, such as files or printers, that a computer shares with the rest of the networked computers. 6.1.1 Network Definitions Computer networks can be classified and defined according to geographical area that the network covers. There are four network definitions: a Local Area Network (LAN), a Campus Area Network (CAN), a Metropolitan Area Network (MAN), and a Wide Area Network (WAN). There are three additional network definitions, namely the Internet, an intranet and an Internetwork. These network definitions are discussed in Table 6.1. TABLE 6.1: Network Definitions Definition Description Local Area Network (LAN) A LAN is defined as a network that is contained within a closed environment and does not exceed a distance of 1.25 mile (2 km). Computers and peripherals on a LAN are typically joined by a network cable or by a wireless network connection. Campus Area Network (CAN) A CAN is limited to a single geographical area but may exceed the size of a LAN Metropolitan Area Network (MAN) Wide Area Network (WAN) A MAN is defined as a network that covers the geographical area of a city that is less than 100 miles. A WAN is defined as a network that exceeds 1.25 miles. A WAN often consists of a number of LANs that have CertGuaranteed. Study Hard and Pass Your Exam 220-301 been joined together. A CAN and a MAN is also a WAN. WANs typically connected numerous LANs through the internet via telephone lines, T1 lines, Integrated Services Digital Network (ISDN) lines, radio waves, cable or satellite links. Internet The Internet is a world wide web of networks that are based on the TCP/IP protocol and is not own by a single company or organization. Intranet An intranet uses that same technology as the Internet but is owned and managed by a company or organization. A LAN or a WAN s usually an intranet. Internetwork An internetwork consists of a number of networks that are joined by routers. The Internet is the largest example of a internetwork. Of these network definitions, the most common are the Internet, the LAN and the WAN. 6.1.2 Benefits of Networks Networks provide a number of benefits, primary of which is its ability to share resources. Table 6.2 discusses some of the resources that can be shared on a LAN. TABLE 6.2: Benefits of Shared Network Resources Resource Data Sharing Benefit The sharing of data files that reside in a common location makes multiple-user access easier. It also makes it easier to maintain data integrity when there is a single, central database. Large customer databases and accounting data are ideal for a LAN system. Peripherals Sharing Sharing peripheral devices such as printers, faxes and modems, allows more than one user to utilize the peripheral device. This reduces the overall cost of having to provide all user with their own peripheral devices. It also allows a user to access multiple devices, providing redundant resources in case one device fails. Software Sharing Sharing a single copy of an application can be cost-effective and allows easier maintenance and upgrading. Storage Larger, faster disk systems can be provided for users to store the files on. This provides cost-effective and easy backups. Electronic Mail Networks allow users to send electronic messages to other network users cost-effectively and quickly. 6.1.3 Types of Networks These network definitions can divided into two types of networks, based on how information is stored on the network, how network security is handled, and how the computers on the network interact. These two types are: Peer-To-Peer (P2P) Networks and Server/Client Networks. The latter is often also called Server networks. • On a Peer-To-Peer (P2P) Network, there is no hierarchy of computers, instead each computer acts as either a server which shares its data or services with other computers, or as a client which uses data or services on another computer. Furthermore, each user establishes the security on their own computers and determines which of their resources are made available to other users. These networks are typically limited to between 15 and 20 computers. Microsoft Windows for Workgroups, Windows 95, Windows CertGuaranteed. Study Hard and Pass Your Exam 220-301 98, Windows ME, Windows NT Workstation, Windows 2000, Novell's NetWare, UNIX, and Linux are some operating systems that support peer-to-peer networking. • A Server/Client Network consists of one or more dedicated computers configured as servers. This server manage access to all shared files and peripherals. The server runs the network operating system (NOS) manages security and administers access to resources. The client computers or workstations connect to the network and use the available resources. Among the most common network operating systems are Microsoft's Windows NT Server 4, Windows 2000 Server, and Novell's NetWare. Before the release of Windows NT, most dedicated servers worked only as hosts. Windows NT allows these server to operate as an individual workstation as well. 6.1.4 Network Topologies The layout of a LAN design is called its topology. There are three basic types of topologies: the star topology, the bus topology, and the ring topology. Hybrid combinations of these topologies also exist. • In a network based on the star topology, all computers and devices are connected to a central point called a hub. These hubs collect and distribute the flow of data within the network. Signals from the sending computer go to the hub and are then transmitted to all computers on the network. Large networks can feature several hubs. A star network is easy to troubleshoot because all information goes through the hub, making it easier to isolate problems. More advanced star topologies FIG 6.1: The Star Topology use switches rather than hubs. A switch serves the same purpose as a hub but transmits the signal to the intended recipient rather than to all computers on the network. • In a network based on the bus topology, all computers and devices are connected in series to a single linear cable called a trunk. The trunk is also known as a backbone or segment. Both ends of the trunk must be terminated to stop the signal from bouncing back up the cable. Because a bus network does not have a central point, it is FIG 6.2: The Bus Topology more difficult to troubleshoot than a star network. Furthermore, a CertGuaranteed. Study Hard and Pass Your Exam 220-301 break or problem at any point along the bus can cause the entire network to go down. • In a network based on a ring topology, all computers and devices are connected to cable that forms a closed loop. On such networks there is no terminating ends; therefore, if one computer fails, the entire network will go down. FIG 6.3: The Ring Topology Each computer on such a network acts like a repeater and boosts the signal before sending it to the next station. This type of network transmits data by passing a "token" around the network. If the token is free of data, a computer waiting to send data grabs it, attaches the data and the electronic address to the token, and sends it on its way. When the token reaches its destination computer, the data is removed and the token is sent on. Hence this type of network is commonly called a token ring network. 6.1.5 Network Operating System The Network Operating System (NOS) consists of a related group of programs that run on networked computers. Some programs provide the ability to share files, printers, and other devices across the network while other programs allow the client computers to access and use those resources. The NOS can be a special program that is installed on the computer's operating system, such as Artisoft's LANtastic or Novell's NetWare, or it can be an integral part of the operating system. Linux, Windows 9x, Windows ME, Windows NT and Windows 2000 are examples of the latter. 6.2 The Network Interface Card (NIC) The Network Interface Card (NIC) is used to link a computer to the network cable system. They provide the physical connection between the computer's expansion bus and the network cabling. The NIC boosts the computer's digital signals that transmit data so that they can be transmitted across a network cable. The NIC CertGuaranteed. Study Hard and Pass Your Exam 220-301 must also change the form of data from a wide parallel stream of 8 bits, 16 bits, or 32 bits, depending on the expansion bus, to a narrow serial stream of 1 bit in and out of the network port Thus, the NIC takes data from the computer, packages it for transmission, and acts as a gatekeeper to control access to the shared network cable. Because the NIC functions as an interface between the computer and the network cabling, it must control the flow of data to and from RAM inside the computer as well as the flow of data in and out of the network cable system. In addition, the NIC must buffer the data between the computer and cable because the computer is typically much faster than the network. This means it must temporarily store the data coming from the computer until it can place it on the network. The NIC is installed in the same as any other expansion card. Its setup requires certain system resources, i.e., IRQ and I/O port address, as well as software. Most NICs have connectors for either thin Ethernet or twisted-pair cabling while some NICs have both connector types. The latter NICs are called FIG 6.4: A NIC Combo Card combo cards. Thin Ethernet uses a round coaxial or BNC (bayonet-Neill-Concelman) connector, and UTP uses an RJ45 connector that similar to a telephone jack. 6.3 Network Cabling Most networks use cables to physically connect computers and devises. There are three main types of network cables: twisted-pair cable; coaxial cable; and fiberoptic cable, which is called the Fiber Distributed Data Interface (FDDI ). 6.3.1 Twisted-Pair Cable Twisted-pair cable consists of two insulated strands of copper wire twisted around each other to form a pair. One or more twisted pairs are used in a twisted-pair cable. The purpose of twisting the wires is to eliminate electrical interference from other wires and outside sources. Furthermore, twisting the wires cancels any electrical noise from the adjacent pair. The more twists per linear foot, the greater the effect. Twisted-pair wiring comes in two types: shielded twisted pair (STP) and unshielded twisted pair (UTP). STP has a foil or wire braid wrapped around the individual wires of the pairs while UTP does not. The STP cable uses a woven-copper braided jacket, which is a higher-quality and FIG 6.5: A RJ-45 more protective Connector jacket than UTP. However, UTP is the more common type of twisted pair cable CertGuaranteed. Study Hard and Pass Your Exam 220-301 and can be divided further into five categories: • Category 1, which is the traditional telephone cable and can carry voice signals but not data; • Category 2, which is certified UTP for data transmission of up to 4 megabits per second (Mbps); • Category 3, which is certified UTP for data transmission of up to 10 Mbps; • Category 4, which is certified UTP for data transmission of up to 16 Mbps; • Category 5, which is certified for data transmission of up to 100 Mbps; and • Category 6, which supports transmission speeds up to 155 Mbps. Twisted-pair is readily available, easy to install, and inexpensive but is sensitivity to electromagnetic interference (EMI), is susceptibility to eavesdropping, lacks of support for communication at distances of greater than 100 feet, and requires of a hub to support networks consisting of more than two computers. 6.3.2 Coaxial Cable Coaxial cable is made of two conductors that share the same axis; the center is a copper wire that is insulated by a plastic coating and then wrapped with a wire braid. The wire braid around the insulation serves as electrical shielding for the signal being carried by the inner conductor. A tough insulating plastic tube outside the outer conductor provides physical and electrical protection. Coaxial cable is either thin (ThinNet) and thick (ThickNet). Of the two, ThinNet is the easiest to use and is about a quarter (.25) inch in diameter. ThinNet can carry a signal about 605 feet (185 meters) before signal FIG 6.6: ThinNet Coaxial Cable strength begins to deteriorate. ThickNet, on the other hand, is about .38 inches in diameter. This makes it a better conductor, and it can carry a signal about 1640 feet (500 meters) before signal strength begins to deteriorate, however, the thicker diameter of ThickNet makes it more difficult to work with. Coaxial cable is more expensive than twisted-pair cable but is more resistant to EMI and can transmit signals further. CertGuaranteed. Study Hard and Pass Your Exam 220-301 6.3.3 Fiberoptic Cable Fiberoptic cable is made of lightconducting glass or plastic fibers and carries data signals in the form of modulated pulses of light. The plastic-core cables are easier to install but do not carry signals as far as glass-core cables. Multiple fiber cores can be bundled in the center of the protective tubing. Fiberoptic cable is immune to EMI and eavesdropping and thus provides a reliable and secure transmission media. It also supports very high bandwidths which means it can carry thousands of times more data than twisted-pair or coaxial cable. 6.3.4 Cable Specifications Cable specifications are based on three factors: speed, bandwidth, and length. Cables specifications are designated with names that FIG 6.7: Fiberoptic Cable Connectors indicate their maximum transmission speed or bandwidth in Mbps, which is one of 1, 5, 10, or 100; their bandwidth, which is either base or broad, depending on whether the cable is baseband or broadband; and the cable length or cable type. If the latter is expressed as is a number, it is the maximum length of the cable segments in hundreds of meters; if it is expressed as a letter, it represents cable type: T for twisted-pair and F for fiberoptic. Table 63 lists the common types of cables and their specifications. TABLE: 6.3: Network Cable Specifications Name Description Type Segment Speed 10BaseT Common cable being phased out in favor of 100BaseT UTP 0.5 to 100 meters 10 Mbps 10Base2 10Base5 Ethernet ThinNet Thick Ethernet Coaxial Coaxial 185 meters 500 meters 10 Mbps 10 Mbps 100BaseT Common UTP 0.5 to 100 meters 100 Mbps Several devices have been developed extend the network and to overcome the restriction imposed by the maximum network cables length. Table 6.4 discusses several of these devices. TABLE 6.4: Network Devices Device Description CertGuaranteed. Study Hard and Pass Your Exam 220-301 Repeaters Bridges Routers The repeater is to extend the length of a network beyond its normal cable lengths and works like an amplifier, increasing or boosting the signal to allow transmissions over longer distances. Repeaters are used to connect network segments and can also be used to connect segments that use different types cable. Bridges serve he same function as repeaters, but can also be used isolate network traffic or problems. Should any problems occur within one segment, the bridge will isolate that segment and not affect other segments on the network, thereby reducing the load on the network as a whole. Routers provide interconnectivity between dissimilar LANs. They work like repeaters but are able to select the best route from one LAN to another based on traffic load. Routers determine the flow of data based on such factors as lowest cost, minimum delay, minimum distance, and least congestion. Routers are generally used to create a WAN. Gateways Gateways provide all the connectivity of routers but resides on a dedicated computer that acts as a translator between two completely dissimilar systems or applications. Because gateways are both translators slower than bridges or routers. Gateways also provide access to special services such as e-mail or fax functions. 6.5 LAN Communication Ethernet is implemented using the bus topology and uses a system known as Carrier Sense Multiple Access with Collision Detection (CSMA/CD) to control network communication. The bus topology allows the connection of more than one computer to the cable. The NIC listens to the cable for a quiet period during which it can send messages and detects whether messages have collided in transit. In such an event, neither message will arrive at its destination and both will be retransmitted. Ethernet transmits data at 10 Mbps. Fast Ethernet works on the same principles as Ethernet but operates at 100 Mbps. A token ring network transmits data by passing a "token" around the network. If the token is free of data, a computer waiting to send data grabs it, attaches the data and the electronic address to the token, and sends it on its way. When the token reaches its destination computer, the data is removed and the token is sent on. Token rings transmit data at 4 or 16 Mbps. 6.5.1 Network Protocols A network protocol is a set of rules and conventions that computers use to communicate over a network. and allows computers running different operating systems to communicate with each other. Networking protocols are grouped into protocol families or protocol suites according to their functions. There are five standard network protocols • Transmission Control Protocol/Internet Protocol (TCP/IP ), which is a set of standard protocols and services developed by the US Department of Defense in the early 1970s as part of an effort to link government computers. This project led to the development of the Internet and is the foundation of the Internet. It is also the most widely used networking protocol; • Networked Basic Input/Output System/NetBIOS Enhanced User Interface (NetBIOS/NetBEUI), which is a LAN protocol developed by IBM and refined by Microsoft. IBM developed NetBIOS as a way to permit small LAN networks of less than 10 computers to share files and printers efficiently. NetBIOS is the original edition; NetBEUI is an enhanced version for more powerful networks based on CertGuaranteed. Study Hard and Pass Your Exam 220-301 32-bit operating systems. This protocol is non-routable; • AppleTalk, which is the core protocol of the Apple Mac operating system and was developed by Apple. It is used to communicate on Apple Mac computers and is routable; • Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX), which is the Novell NetWare core protocol developed by Novell in the early 1980s and is used to communicate on Novell NetWare networks; and • Data Link Control (DLC) protocol, which is the oldest of these standard protocols and was develped by IBM to connect token-ring-based workstations to IBM mainframe computers. Printer manufacturers have adopted the protocol to connect remote printers to network print servers. This is also a non- routable protocol. 6.6 Troubleshooting Basic Network Problems Table 3.5 discusses some of the possible causes of generic network problems and suggest some means of overcoming them. TABLE 6.5: Some Cause and Solutions to Generic Network Problems Symptom Probable Cause Reduced bandwidth This is called a bottleneck and occurs when the network does not transmit as much data as it should because of some constraint that limits the rate at which a task can be completed. If a task uses the processor, network, and disk resources, and spends more of its time transferring data to and from the disk, you could have a memory bottleneck. A memory bottleneck might require additional RAM. Loss of data If data transfers are incomplete or inaccurate, check to ensure that all network cabling and connectors are intact. Slow loading of programs and files Fragmentation occurs when the operating system saves, deletes, and moves data this lows down the reading files and loading of programs. You must defragment the drive to overcome this problem. If slow loading persists after defragmentation, check for memory bottlenecks. Traffic overloads A hardware or software failure can bring a LAN to a halt, or the failure can result in more data traffic than the network is designed to handle. You might receive an error message or you might not see any signs other than poor network performance. You must have a system in place that can monitor and manage network traffic. To resolve this problem, you will need to reduce the traffic on the LAN or expand its capabilities. Common mode failures Some LAN component failures affect other components. This is known as mode a common failure. For example, the on-board logic of an NIC might jumble the data format. The NIC will hand the result to the NOS, which might not detect the error. If the NOS puts that data into a file, the file will become corrupt. 6.7 Advanced Networks 6.7.1 Modems A modem is a peripheral device that allows computers to communicate with each using over conventional CertGuaranteed. Study Hard and Pass Your Exam 220-301 telephone lines, Integrated Services Digital Network (ISDN) lines or cable lines. ISDN modems offer a high-speed digital alternative to the analog modem that uses the conventional telephone line. Most ISDN modems can simultaneously use two lines with a bandwidth of 64 K bits per second (bps) each, allowing transfers of up to 128 bps. While the maximum bandwidth that can be supported by the copper wires of a telephone cable that modems use is 56 Kbps. The movement of data from one computer to another over the telephone line is a multistep process. Only analog signals can be transmitted over the telephone line but the computer uses only digital signals. The analog signal from the telephone must thus be converted to a digital so that the CPU can process it, and the digital signal from the computer must be converted to analog before it can be transmitted across a telephone line. A modem acting as an analog-to-digital converter, rendering the analog signal in the digital format used buy the CPU, and converting a signal from the computer to analog so that it can be transmitted over the telephone line. There are two types of analog modems, internal modems and external modems. Some internal use the computer system's CPU to convert the analog signal to a digital signal and vice versa. • The original modems had a cradle onto which the telephone handset was placed. The cradle had a FIG 6.8: An External Modem built-in speaker and a microphone to send and receive The RS-232 Port tones acoustically. The modern external modem has The RS-232 serial port is used for loweither a built-in a speaker and a microphone, or built-in speed data communication between two audio connectors for a speaker and a microphone, to telecommunications. allow vocal communication by the user rather than to send and receive acoustic tones. It has two telephone ports, one to connect the telephone line to the wall jack and the other to pass the telephone signal to a telephone for regular voice FIG 6.9: An Internal PCI Modem Adapter Card conversations when the modem is not in data mode. The external modem also has a RS-232 serial port on the back of the modem that is used to pass data to and from a serial port on the computer. • The internal modem is a single expansion card CertGuaranteed. Study Hard and Pass Your Exam 220-301 that the entire modem, including the audio ports and the telephone ports, is built into. This configuration offers lower cost than that of an external modem, but it is more prone to compatibility problems. Some internal modems, especially those using Conexant chipsets, rely on the CPU to convert the analog signal to a digital signal and vice versa. Modem is connected to the telephone service provider using two wires in a standard telephone jack. There are however, two versions of the telephone jack: The RJ-11 jack and the RJ-12 jack. • The RJ-11 has only two wires, which make up one line. Therefore, only one signal can be sent or received at a time. The latter is referred to as a Half-duplex. • The RJ-12 uses four wires to make up two lines; it can be used to simultaneously send and receive. This is referred to as a Full-duplex. Most modems offer fax capability. Such a modem is called a fax modem and can send, receive and store faxes, both incoming and outgoing, for reference or online reading. Most allow direct faxing of a document from a word processor, generally by using the print command to send the pages to the modem, where they are converted on the fly to the bitmap form used to send and receive fax transmissions. 6.7.1.1 Modem Speeds Modem speed is measured in baud and bits per second (bps). • The modem's Baud Rate refers to the speed at which a modem can transmit data. Technically, the baud is the number of voltage or frequency changes that can be made in one second. A modem working at 2400 baud, has 2400 cycles per second on the basic carrier frequency. Due to restrictions imposed by the physics of the wiring, a dial-up phone line can only go up to 2400 cycles, a baud rate of 2400. • The actual modem speed is the rate at which data is transmitted is measured in Bits per Second (bps) and depends on the modem's modulation. If a modem modulates one bit for each baud cycle, then the modem speed is 2400 bps. If a 2400-baud modem modulates two bits for one cycle of time, the modem is said to have a speed of 4800 bps. If four bits are modulated with one cycle of time, then a modem speed of 9600 bps is achieved. Modem speed standards are designated by the Comité Consultatif International Télégraphique et Téléphonique (CCITT), an international body that develops fax and modem standards. Table 6.6 lists the standard modem speeds designated by the CCITT. TABLE 6.6: CCITT Defined Modem Speeds CCITT Term V.21 V.22 V.22bis V.23 V.29 V.32 V.32bis V.32fast Bits per Second 300 1200 2400 1200 bps in one direction and 75 bps in the other 9600 4800 and 9600 14,400 28,800 CertGuaranteed. Study Hard and Pass Your Exam 220-301 V.34 28,800 V.42bis 38,400 V.90 56,600 V.92 56,600 6.7.1.2 Modem Communication 6.7.1.2.1 Modem Protocols Like LAN communication, network communication across a modem relies on protocols. To ensure clear and clean communication without any errors, the device on each end must follow a very strict set of rules. If either device violates any of the rules, the communication will fail. This set of rules is called the File Transfer Protocol (FTP). There are five basic protocols used by modems: ASCII; Xmodem; Ymodem; Zmodem and Kermit. • The ASCII protocol uses the standard American Standard Code for Information Interchange (ASCII) character set. This protocol has no error-checking or compression features and is used with simple character-based data. It is not a good protocol for transferring program files. • The Xmodem protocol includes error detection, which makes it more suitable for transferring program files. It transfers 128-byte blocks of data and one checksum character. The latter is used for errorchecking. The receiving computer calculates a new checksum and compares it to the one transmitted. If they are the same, the receiving computer transmits an ACK. If they are different, it sends back an NAK, and the transmitting computer then retransmits the data block. This protocol uses parity error checking, which is not perfect. If two errors were to occur the second error would cancel the first, and no error would be reported. The result can be a corrupted file or random characters on the display. • The Ymodem protocol is basically a faster version of the Xmodem protocol. It transfers data in 1024byte blocks. • The Zmodem protocol is an improvement on Xmodem and Ymodem, adding a few new features, including crash recovery, automatic downloading, and a streaming file transfer method. • The Kermit protocol is rarely used today. It was the first of the synchronous protocols for uploading and downloading data to and from a mainframe computer. 6.7.1.2.2 Handshaking Because all modems and computers are not exactly the same, there must be means by which the two machines determine how to communicate, i.e. the two machines must determine the transmission speed, how the data will be packaged, and which device will control the transfer. This occurs in that short burst of information between the two modems when analog modems or fax machines begin to communicate and is called handshaking. Connections between a sending device, sometimes referred to as DCE, and a receiving device, DTE, are called handshaking signals. They ensure that each sending and receiving device is in sync with the other. The flow control of data between modems is handled by the modems themselves. However, the local flow control between modem and COM port can be set by the user. There are two types of flow control: Hardware Flow Control and Software Flow Control. • Hardware Flow Control takes advantage of some of the extra wires in the serial connection between the modem and the COM port. These wires are used to let the other device know that the DCE is ready to send or receive data. The wires are named RTS and CTS and hardware handshaking is sometimes referred to as RTS/CTS. • Software Flow Control uses special characters known as XON and XOFF to let the other device know that the DCE is starting to send data or that the data transmission is finished. Software handshaking is slower and not as dependable as hardware handshaking. Only some very old modems use software handshaking. 6.7.1.2.3 Modem Standards CertGuaranteed. Study Hard and Pass Your Exam 220-301 Like all other communication devices, modems use standards to ensure proper communication between the two machines. Some modems offer various forms of hardware error detection and correction. Such features usually require matching firmware in the modems at both ends. When modem communication was first used, there were no standardized communication conventions. At that point, proprietary modems were the norm and compatibility was a great problem. The only way one could ensure data transmission then was by using identical modems at the sending and receiving ends of the transmission. The modern modems comply with several standards. There are two sources for these standards: • Manufacturers have placed specifications of their modem functions in the public domain. These specifications can now be copied and used by any manufacturer. If enough manufacturers use a specification, it becomes a standard on its own merits. • Standards committees are formed when there is enough interest expressed by users, vendors, or regulatory committees to develop a set of rules for a class of data or modems. 6.7.1.3 Modem Commands like MS-DOS, modems need commands to tell them what to do and to allow programmers to incorporate the use of modems into their software. Unfortunately, there are no true standard command sets for modems because manufacturers but there is one set of commands, the AT command set developed by Hayes in the 1980s, that has been accepted as a de facto standard. Most modems today are Hayes-compatible. These commands are very useful as diagnostic tools. To use these commands, make sure the communication software is loaded and the computer is in terminal mode. Unless the modem is in online mode, i.e., it is set to autoconnect, it will be in command mode and ready to accept AT commands. Table 6.7 lists some of the more useful AT commands. TABLE 6.7: Some AT Commands Command AT Function This reports if the modem is plugged in and turned on. The mode should respond with OK. ATE1 Echoes the command on the screen. Some modems will not run correctly when the echo is on. ATE0 This turns off the echo to the screen. ATH This takes the telephone off the hook. Should elicit a reply of OK or 0 from the modem, or a dial tone and an OH indicator if it is an external modem. ATM1 This turns the speaker on for the dial tone. ATL0 is the lowest volume setting and ATL2 is medium volume. ATM0 This turns the speaker off. ATD This takes the phone off the hook and dials a number if one is included with the command. ATQ0 This is a troubleshooting aid and enables result codes. Type ATV1 prior to this command and you will get back verbose result codes. ATQ1 This disables result codes. ATH This hangs up the modem. ATH0 This is the same as ATH. ATX This resets the modem to a predefined state. You can configure your own reset state or will be reset to the factory default setting. 6.7.1.4 Troubleshooting Modem Problems Table 6.8 provides a guidelines to determine if the modem is faulty, or if something is the cause of the problem. TABLE 6.8: Troubleshooting Modem Problems CertGuaranteed. Study Hard and Pass Your Exam 220-301 Possible Cause Possible Solution The modem no longer works after installing new hardware on the computer. Check for IRQ and I/O conflicts. The modem no longer works after installing new software on the computer. Check for IRQ and I/O conflicts. Cards that were configured for software can be inadvertently changed by corrupted software or by the installation of new software. The operating system or an application does not detect the modem. Modem works sporadically. Make sure the software is checking the correct port. Reconfigure or reinstall the software as there might be a corrupt driver. Try another modem type. Check the phone lines. Modem does not hang up the phone line. A power surge can cause this problem. If manual disconnect and reconnect allows the modem to disconnect, but it does not automatically drop the connection continuously, replace or repair the modem. 6.7.2 The Internet The Internet, commonly known as "the Net," is the most extensive WAN. This relatively new communication technology has begun to affect our lives as significantly as television and the telephone. Most LANs make use of passwords and other forms of security, but the Internet is one of the most open networks in the world. The Internet is in essence a collection of services and common Internet uses include communication; locating lost friends and family; researching information for school or work; locating businesses, products, or services; and transferring data. 6.7.2.1 The World Wide Web (WWW) The internet connects a large collection of hyperlinked Web sites The Uniform Resource known as the World Wide Web (WWW). Each Locator (URL) The Uniform Resource Locator Web site within the Web has a unique address called a Uniform (URL) is the World Wide Web's address Resource system and Locator (URL) and can be accessed for information. Most Web must be specified in a browser sites have pages that provide information to when a user clients using the wants to access a Web site. Each Hypertext Transfer Protocol (HTTP). Pages can URL also be begins with the character sequence hyperlinked so that, when a user clicks on a text http://. The rest of the URL is the string or image name that has been coded as a link, they are shown the of the specified site. contents of the linked page. All Web pages use some derivative of Standard Generalized Markup Language (SGML) to code pages so the browser can "read" the instructions on how to display and link material on the pages. A committee of government and industry experts in networking, information systems, and publishing designed this standard. A loose form of an SGML application, Hypertext Markup Language (HTML) was designed to tag the content of Web pages. If you choose to view the source code of a Web page in your browser, you can see the CertGuaranteed. Study Hard and Pass Your Exam 220-301 markup that tells what each portion of the page is, if it has hyperlinks, and any special information on how to display it. Some purists lament how open the design of HTML is, but that openness allows for additional plug-ins that let browsers handle animation, sound, streaming video, and other enhancements to the Web experience. Another SGML derivative that can be used to code pages is the eXtended Markup Language (XML). This has less tags than HTML and is a much tighter form of SGML but is ideal for cross-platform coding. 6.7.2.2 Internet Browsers A browser uses URLs to locate and parse pages on a Web site and is the most common Internet application used the end user. The two most popular Internet browsers are Microsoft Internet Explorer and Netscape Navigator. These programs "open" Web pages for viewing, can access and download remote files using FTP, and perform other routine online tasks. 6.7.2.3 Electronic Mail Electronic mail, which is commonly known as e-mail, is the most commonly used function of the Internet. It allows users to send and receive messages and files electronically all over the world. Electronic mailing lists allow users to join group discussions with people who share their interests. Like regular mail, e-mail is also sent to an address called and e-mail address. To make use of e-mail, one must have access to an e-mail server, an account on that server, and a program to send and receive messages. Microsoft Windows includes Microsoft Outlook Express as an e-mail client. Several other e-mail servers, like Eudora and Hotmail, are available on the Internet and can be accessed via the Internet browser. Virtually all Internet Service Providers (ISPs) offer e-mail as part of their packages, and free accounts are available online as well. To set up an account, you will need to know the address information for both the inbound and outbound mail servers, as well as the account address. The account will have a password that can usually be stored so the user does not have to enter it each time mail is sent or received. 6.7.2.4 FTP FTP is a special application used for uploading and downloading files to and from the Internet. Programs like Win-FTP and Cute FTP offer an easy-to-use interface for moving files to a remote computer and are popular with Webmasters. Most new browsers support downloading files via FTP automatically. 6.7.3 TCP/IP TCP/IP is the network protocol used by computers to communicate over the Internet. TCP/IP has also become a common protocol for LANs. Regardless of which operating system or software you use, your commands travel through the Internet in TCP/IP format. The services of the Internet and the Web could not be provided without TCP/IP. On a TCP/IP network, each computer must have a unique 32-bit address called an IP Address. These addresses designates the location of its assigned device, usually the NIC, on the network and are expressed as four decimal values of 4 bytes each, separated with periods. Each decimal value can have up to 256 values, ranging from 0 though 255. IP addresses are divided into 4 classes: • Class A addresses are assigned to networks with a very large number of hosts. Class A addresses range from 0.0.0.0 through 126.255.255.255. • Class B addresses are assigned to medium-sized to large-sized networks. Class B addresses range from 128.0.0.0 through 168.255.255.255 and 170.0.0.0 through 191.255.255.255. Note: IP addresses with a first octet of 127, i.e. 127.0.0.0 through 127.255.255.255 are reserved for diagnostics purposes and do not fall in the Class A address range or the Class B address range. • Class C addresses are used for small LANs. Class C addresses range of 192.0.0.0 through 223.225.225.225. • Class D addresses are reserved for multicast transmissions. This is commonly used for multimedia CertGuaranteed. Study Hard and Pass Your Exam 220-301 presentations across the Internet. Class D addresses range from 224.0.0.0 through 239.255.255.255. IP addresses are, however, difficult to remember, therefore the Internet uses a user-friendly URL naming convention called The Domain Name System (DNS). DNS is the hierarchical naming system used for identifying domain names on the Internet and on private TCP/IP networks. DNS maps DNS domain names to IP addresses, and vice versa. This allows users, computers, and applications to query a DNS server, which is a computer that matches domain names to IP addresses, to specify remote systems by their domain names rather than by IP addresses. On the Internet, the domain suffix usually gives a general idea of the site's purpose. Table 6.9 lists some of the common Internet domains. TABLE 6.9: Some Common Internet Domains Suffix .com .net .edu Description Commercial organizations Internet core networks (also used by some Internet-related enterprises) US educational institutions. Some non-US educational institutions use the .ac before the two letter country code as in www.oxford.ac.uk .org Non-profit organizations .gov US Government non-military institutions. Other non-US governments have the two-letter country code follow .gov as in www.gov.cu .mil U.S. government armed services .xx Two-letter country code, for example, .au for Australia, .za for South Africa. This suffix is preceded by .co as in .co.au to denote a commercial organization in that country, or by .ac as in .ac.za to denote educational institutions in that country. 6.7.3.1 Testing IP Configurations There are a number of utilities that can be used to test the IP configuration of a computer on a network. Of these utilities, the IPConfig utility and the Packet Internet Groper (ping) utility is the most useful. 6.7.3.1.1 The IPConfig Utility The IPConfig utility is a command-line utility that can be used to display the TCP/IP configuration of your computer. It can also display the IP configuration, and parameters for the network connection on your computer. This information can be used to verify that the client computer is configured with the correct DNS server IP addresses. TABLE 6.10: IPConfig Switches Switch /all /release <adapter> /renew <adapter> /flushdns Function Displays the configuration all network interfaces. Releases the IP address for a specified network adapter card. Renew the IP address for the specified network adapter card. Clears all entries from the DNS Resolver Cache on the local computer. /registerdns Renews the local computer's DHCP lease and reregisters DNS names. /displaydns Displays the contents of the DNS Resolver Cache on the local computer. /showclassid Displays all the DHCP class IDs allowed for the specified network adapter adapter card. /setclassid Modifies the DHCP class ID for the specified network adapter adapter card /? Displays a list of all the IPConfig switches and their functions 6.7.3.1.2 The Ping Utility CertGuaranteed. Study Hard and Pass Your Exam 220-301 The ping utility is another command-line utility that is useful when installing or troubleshooting an Internet connection. It can be used to test low-level communication over a TCP/IP network to a specified IP address in the form of an echo request and reports whether the target is present and how long it takes to get a reply. You can also use this utility to check the computer's NIC by specifying the loop back address 127.0.0.1. If the ping utility fails, it returns an error message. As shown in Table 6.11, you can receive various messages when you use the ping utility. FIG 6.8: The Ping Utility TABLE 6.11: Ping Error Messages Error Message Problem Destination host There is an IP routing problem between your computer and unreachable the remote host Unknown host hostname None of the client's name resolution mechanisms recognize the name that you typed - check that you typed the host name correctly. Request timed out The name resolution mechanisms have recognized the name, but the remote host did not receive the request or did not respond to it - check connectivity to the remote host In all versions of the Microsoft Windows operating system, this utility can be run from a DOS prompt or command prompt window, which can be accessed by typing command or cmd in the Run dialog box. The syntax is ping -<switch> <IP Address>. The switches that can be used with the ping utility is discussed in Table 6.12. TABLE 6.12: Ping Switches Switch -a -f -i -j -k -l -n -r -s -t Function Resolves IP addresses to domain names. Sets a "Don't Fragment" flag in outgoing packets. <TTL> Specifies the Time to Live (TTL) for outgoing packets. <host-list> Loose source routing along host-list. <host-list> Strict source routing along host-list. <size> Sends packets to the specified size set in the brackets. <count> Sets the number of echo requests to the value given within the brackets. <count> Records the route for count hops. <count> Time stamp for count hops. Pings the specified address until stopped. You can view statistics and then continue pinging by pressing CTRL+BREAK, or you can stop the CertGuaranteed. Study Hard and Pass Your Exam 220-301 ping completely without viewing statistics by pressing CTRL+C. -v <TOS> Specifies type of service (TOS). -w Sets the length of the wait periods in milliseconds for a response before showing a timeout error. You may need to set this if the host is slow in responding. 6.7.4 Connecting to the Internet Before setting an Internet connection, you must first determine how the computer will access the Internet. This was once a simple matter of choosing a modem but today there are faster alternatives to the analog modem, such as ISDN, Digital Subscriber Line (DSL) and Asymmetric DSL (ADSL). A customer planning to use ISDN will require an ISDN TA while customers planning to use DSL or ADSL will require a satellite and cable connections. Some connections, such as DSL and cable, always online while most modems and ISDNs make use of dial-in service. A practice that is becoming more common is adding a firewall between a computer and the Internet to improve security. A firewall may be another computer or a stand-alone device, or a software program that acts as a gateway to the Internet, monitoring incoming traffic. It can help prevent the introduction of a virus or attempts to hack into the protected system or network. You also need to consider which browser(s) to install. Some ISPs provide only the connection or gateway to the Internet and not the software required to access the Internet. Others provide their own browser software package. Most ISPs allow you to choose which browser you want to use. 6.8 Wireless Networks Conventional Ethernet networks require cables connected computers via hubs and switches. This has the effect of restricting the computer's mobility and requires that even portable computers be physically connected to a hub or switch to access the network. An alternative to cabled networking is wireless networking. The first wireless network was developed at the University of Hawaii in 1971 to link computers on four islands without using telephone wires. Wireless networking entered the realm of personal computing in the 1980s, with the advent to networking computers. However, it was only in the early 1990s that wireless networks started to gain momentum when CPU processing power became sufficient to manage data transmitted and received over wireless connections. Wireless networks use network cards, called Wireless Network Adapters, that rely radio signals or infrared (IR) signals to transmit and receive data via a Wireless Access Point FIG 6.9: A PCI Wireless Adapter Card (WAP). The WAP uses has an RJ-45 port that can be attached to attach to a 10BASE-T or 10/100BASE-T Ethernet hub or switch and contains a radio transceiver, encryption, and communications software. It translates conventional Ethernet signals into wireless Ethernet signals it broadcasts to wireless network adapters on the network and performs CertGuaranteed. Study Hard and Pass Your Exam 220-301 the same role in reverse to transfer signals from wireless network adapters to the conventional Ethernet network. WAP devices come in many variations, with some providing the Cable Modem Router and Switch functions in addition to the wireless connectivity. Note: Access points are not necessary for direct peer-to-peer networking, which is called ad hoc mode, but they are required for a shared Internet connection or a connection with another network. When access points are used, the network is operating in the infrastructure mode. 3.8.1 Wireless Network Standards In the absence of a industry standard, the early forms of wireless networking were single-vendor proprietary solutions that could not communicate with wireless network products from other vendors. In 1997, the computer industry developed the IEE 802.11 wireless Ethernet standard. Wireless network products based on this standard are capable of multivendor FIG 6.10: A Wireless Access interoperability. Point (WAP) The IEEE 802.11 wireless Ethernet standard consists of the IEEE 802.11b standard, the IEEE 802.11a standard, and the newer IEEE 802.11g standard. Note: The Bluetooth standard for short-range wireless networking is designed to complement, rather than rival, IEEE 802.11-based wireless networks. 3.8.1.1 The IEEE 802.11 Standard IEEE 802.11 was the original standard for wireless networks that was ratified in 1997. It operated at a maximum speed of 2 Mbps and ensured interoperability been wireless products from various vendors. However, the standard had a few ambiguities allowed for potential problems with compatibility between devices. To ensure compatibility, a group of companies formed the Wireless Ethernet Compatibility Alliance (WECA), which has come to be known as the Wi-Fi Alliance, to ensure that their products would work together. The term Wi-Fi is now used to refer to any IEEE 802.11 wireless network products that have passed the Wi-Fi Alliance certification tests. 3.8.1.2 The IEEE 802.11b Standard IEEE 802.11b, which is also called 11 Mbps Wi-Fi, operates at a maximum speed of 11 Mbps and is thus slightly faster than 10BASET Ethernet. Most IEEE 802.11b hardware is designed to operate at four FIG 6.11: Wi-Fi speeds, using three Certified different data-encoding methods depending on the speed range. It operates at 11 CertGuaranteed. Study Hard and Pass Your Exam 220-301 Mbps using quatenery phase-shift keying/complimentary code keying (QPSK/CCK); at 5.5 Mbps also using QPSK/CCK; at 2 Mbps using differential quaternary phase-shift keying (DQPSK); and at 1 Mbps using differential binary phase-shift keying (DBPSK). As distances change and signal strength increases or decreases, IEEE 802.11b hardware switches to the most suitable data-encoding method. Wireless networks running IEEE 802.11b hardware use the 2.4 GHz radio frequency band that many portable phones, wireless speakers, security devices, microwave ovens, and the Bluetooth short-range networking products use. Although the increasing use of these products is a potential source of interference, the short range of wireless networks (indoor ranges up to 300 feet and outdoor ranges up to 1,500 feet, varying by product) minimizes the practical risks. Many devices use a spread-spectrum method of connecting with other products to minimize potential interference. IEEE 802.11b networks can connect to wired Ethernet networks or be used as independent networks. 3.8.1.3 The IEEE 802.11a Standard IEEE 802.11a uses the 5 GHz frequency band, which allows for much higher speeds, reaching a maximum speed of 54 Mbps. The 5 GHz frequency band also helps avoid interference from devices that cause interference with lower-frequency IEEE 802.11b networks. IEEE 802.11a hardware maintains relatively high speeds at both short and relatively long distances. Because IEEE 802.11a uses the 5 GHz frequency band rather than the 2.4 GHz frequency band used by IEEE 802.11b, standard IEEE 802.11a hardware cannot communicate with 802.11b hardware. A solution to this compatibility problem is the use of dual-band hardware. Dual-band hardware can work with either IEEE 802.11a or IEEE 802.11b networks, enabling you to move from an IEEE 802.11b wireless network at home or at Starbucks to a faster IEEE 802.11a office network. 3.8.1.4 The IEEE802.11g Standard IEEE 802.11g is also known as Wireless-G and combines compatibility with IEEE 802.11b with the speed of IEEE 802.11a at longer distances. This standard was ratified in mid-2003, however, many network vendors were already selling products based on the draft IEEE 802.11g standard before the final standard was approved. These early IEEE 802.11g hardware was slower and less compatible than the specification promises. In some cases, problems with early-release IEEE 802.11g hardware can be solved through firmware upgrades. 3.8.2 Wireless Network Modes Wireless networks work in one of two modes that are also referred to as topologies. These two modes are ad-hoc mode and infrastructure mode. The mode you implement depends on whether you want your computers to communicate directly with each other, or via a WAP. • In ad-hoc mode, data is transferred to and from wireless network adapters connected to the computers. This cuts out the need to purchase a WAP. Throughput rates between two wireless network adapters are twice as fast as when you use a WAP. However, a network in ad-hoc mode cannot connect to a wired network as a WAP is required to provide connectivity to a wired network. An ad-hoc network is also called a peer-to-peer network. CertGuaranteed. Study Hard and Pass Your Exam 220-301 • In infrastructure mode, data is transferred between computers via a WAP. Because a WAP is used in infrastructure mode, it provides connectivity with a wired network, allowing you to expand a wired network with wireless capability. Your wired and wirelessly networked computers can communicate with each other. In addition, a WAP can extend your wireless network's range as placing a WAP between two wireless network adapters doubles their range. Also, some WAPs have FIG 6.12: A WAP Router a built-in router and firewall. The router allows you to share Internet access between all your computers, and the firewall hides your network. Some of these multifunction access points include a hub with RJ-45 ports. 3.8.3 Security Features Because wireless networks can be accessed by anyone with a compatible wireless network adapter, most models of wireless network adapters and WAPs provide for encryption options. Some devices with this feature enable you to set a security code known as an SSID on the wireless devices on your network. This seven-digit code prevents unauthorized users from accessing your network and acts as an additional layer of security along with your normal network authentication methods, such as user passwords. Other wireless network adapters and WAPs use a list of authorized MAC numbers to limit access to authorized devices only. All Wi-Fi products support at least 40-bit encryption through the wired equivalent privacy (WEP) specification, but the minimum standard on newer products is 64-bit WEP encryption. Many vendors also offer 128-bit or 256-bit encryption on some of their products. However, the WEP specification is insecure. It is vulnerable to brute-force attacks at shorter key lengths, and it is also vulnerable to differential cryptanalysis attacks, which is the process of comparing an encrypted text with a known portion of the plain text and deriving the key by computing the difference between them. Because WEP encrypts TCP headers, hackers know what the headers should contain in many cases, and they can attempt to find patterns in a large body of collected WEP communications in order to decrypt the key. The attack is complex and difficult to automate, so it is unlikely to occur for most networks, especially at key lengths greater than 128 bits. Furthermore, WEP does not prevent an intruder from attaching a hidden WAP on the network and using it to exploit the network. New network products introduced in 2003 and beyond now incorporate a new security standard known as Wi-Fi Protected Access (WPA). WPA is derived from the developing IEEE 802.11i security standard, which will not be completed until mid-decade. WPA-enabled hardware works with existing WEP-compliant CertGuaranteed. Study Hard and Pass Your Exam 220-301 devices, and software upgrades might be available for existing devices. 3.8.4 Bluetooth Bluetooth is a low-speed, low-power standard originally designed to interconnect notebook computers, PDAs, cell phones, and pagers for data synchronization and user authentication in public areas, such as airports, hotels, rental car pickups, and sporting events. Bluetooth is also used for a wide variety of wireless devices on computers, including printer adapters, keyboards and mice, DV camcorders, and data projectors. These devices use the same 2.4GHz frequency range that IEEE FIG 6.13: A Bluetooth PCMCIA Card 802.11b and IEEE 802.11g devices use. However, to avoid interference with IEEE 802.11, Bluetooth uses a frequency hopping spread spectrum signaling method, which switches the exact frequency used during a Bluetooth session 1,600 times per second over the 79 channels Bluetooth uses. Unlike IEEE 802.11, which is designed to allow a device to be part of a network at all times, Bluetooth is designed for ad hoc temporary networks in which two devices connect only long enough to transfer data and then break the connection. The IEEE has developed 802.15.2 for enabling coexistence between 802.11b/g and Bluetooth. It can use various time-sharing or time-division methods to enable coexistence. However, these specifications are not yet part of typical 802.11b/g implementations. Appendix A: The Intel Range of CPUs Intel 8088 Clock Speed: 4.77 MHz FSB Speed: 4.77 MHz Introduction: 1979 Transistors: 29,000 Package: DIP CertGuaranteed. Study Hard and Pass Your Exam 220-301 Intel 80286 Clock Speed: 8-12 MHz FSB Speed: 8-12 MHz Introduction: 1982 Transistors: 134,000 Package: PGA Socket: 70 Pin Intel 80386/386DX Clock Speed: 16-33 MHz FSB Speed: 16-33 MHz Introduction: 1985 Transistors: 275,000 Package: PGA Socket: 132 Pin Intel 386SX Clock Speed: 16-20 MHz FSB Speed: 16-20 MHz CertGuaranteed. Study Hard and Pass Your Exam 220-301 Introduction: 1988 Transistors: 275,000 Package: PGA Socket: Intel 486DX Clock Speed: 25-50 MHz FSB Speed: 25-50 MHz L1 Cache: 8 KB Introduction: 1989 Transistors: 1.2 Million Package: PGA Socket: Socket 3 Intel 486SX Clock Speed: 33-66 MHz FSB Speed: 16-33 MHz L1 Cache: 8 KB Introduction: 1991 Transistors: 1.185 Million Package: PGA Socket: Socket 3 Intel 486DX2 CertGuaranteed. Study Hard and Pass Your Exam 220-301 Clock Speed: 33-66 MHz FSB: 16-33 MHz L1 Cache: 8 KB Introduction: 1991 Transistors: 2 Million Package: PGA Socket: Socket 3 Intel 486DX4 Clock Speed: 75-100 MHz FSB Speed: 25-33 MHz L1 Cache: 16 KB Introduction: 1992 Transistors: 2.5 Million Package: PGA Socket: Socket 3 Intel Pentium Clock Speed: 60-166 MHz FSB Speed: 33-66 MHz CertGuaranteed. Study Hard and Pass Your Exam 220-301 L1 Cache: 16 KB Introduction: 1993 Transistors: 3.3 Million Package: PGA Socket: Socket 7 Intel Pentium Pro Clock Speed: 150-200 MHz FSB Speed: 50-66 MHz L1 Cache: 256 KB L2 Cache: 256 KB - 1 MB Introduction: 1995 Transistors: 5.5 Million Package: PGA Socket: Socket 8 Intel Pentium-MMX Clock Speed: 133-166 MHz FSB Speed: 66 MHz L1 Cache: 32 KB Introduction: 1996 Transistors: 4.5 Million Package: PGA Socket: Socket 7 Intel Pentium II CertGuaranteed. Study Hard and Pass Your Exam 220-301 Clock Speed: 233-450 MHz FSB Speed: 66-100 MHz L1 Cache: 32 KB L2 Cache: 512 KB Introduction: 1997 Transistors: 7.5 Million Package: SEC Socket: Slot 1 Intel Pentium Xeon Clock Speed: 400 MHz-3.06 GHz FSB Speed: 100-533MHz L1 Cache: 8-32 KB L2 Cache: 256 KB-2 MB L3 Cache: 0-1 MB Introduction: 1998 Transistors: 7.5 - 140 Million Package: SEC and PGA Socket: Slot 2 , Socket 603 and Socket 604 Pentium Celeron CertGuaranteed. Study Hard and Pass Your Exam 220-301 Clock Speed: 850 MHz-2.4 GHz FSB Speed: 66-400 MHz L1 Cache: 8-32 KB L2 Cache: 256-512 KB Introduction: 1998 Transistors: 7.5 - 44 Million Package: SEC and PGA Socket: Slot 1, Socket 370 and Socket 478 Pentium III Clock Speed: 450MHz - 1.33GHz FSB Speed: 100-133MHz L1 Cache: 32KB L2 Cache: 256-512 KB Introduction: 1999 Transistors: 9.5 - 28 Million Package: SEC and PGA Socket: Slot 1 and Socket 370 Pentium 4 Clock Speed: 1.3-3.06GHz FSB Speed: 400-800MHz CertGuaranteed. Study Hard and Pass Your Exam 220-301 L1 Cache: 8 KB L2 Cache: 256 - 512 MB Introduction: 2000 Transistors: Package: PGA Socket: Socket 423 and Socket 478 CertGuaranteed. Study Hard and Pass Your Exam ...
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