Unit
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System System Unit
Box -like case that houses the electronic components of the computer such as:
processor memory module expansion cards ports
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Motherboard
Motherboard is the main circuit board inside the System unit which holds:
processor memory expansion slots
Motherboard connects directly or indirectly to every part of the PC.
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Integrated Circuits - IC
IC is a super thin slice of semiconducting material (silicon crystal) packed with microscopic electronic elements, such as transistors, wires, capacitors, resistors that act as electronic switches (gates that open or close the circuit to electronic signals). Bits are represented as electrical pulses that travel over these circuits. Small in size, about one-half-inch square.
Also called a chip, microchip and computer chip.
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Integrated Circuits
Integrated Circuits examples:
Microprocessors Memory Support circuitry
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CPU and Microprocessor
CPU - Central Processing Unit - is a central component of the PC. This vital component is in some way responsible for every single thing the PC does. CPU is a part of a single chip called a microprocessor. Microprocessor usually contains registers and clock.
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Microprocessor (Processor)
Designed to process instructions Largest chip on motherboard Intel: world's largest chipmaker (Pentiums) AMD: Cheaper chips (Athlons)
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Personal computers processors Name Pentium Extreme Dual-core Pentium D dual-core Pentium 4 with HT Technology Pentium 4 Pentium 3 Celeron D Celeron 486DX 386 286 Athlon 64 X2 dual core Athlon 64 FX Sempron Celeron M Pentium M Mobile Celeron Turion 64 Date Introduced 2005 2005 02/05 00/05 99/03 04/05 98/03 89/94 85/90 1982 05 05 04 04 03/04 99/03 05 AMD Intel AMD Manufac turer Intel Clock Speed 3.2 GHz 2.8 -3.2 GHz 2.4 -3.8 GHz 1.3 3.8 GHz 450MHz -1.4 GHz 2.4 3.2 GHz 266MHz 2.8 GHz 25-100 MHz 16 -32 Mhz 6 -12 MHz 2-2.8 GHz 2.6-2.8 GHz 1.5-2GHz 900MHz- 1.6 GHZ 1 2.26 GHz 266MHz-2.8GHz 1.6-2.4GHz Number of Transistors 178 million 230 million 55-178 million 42-125 million 9.5-44 million 26-125 million 7.5-55 million 1.6 million 275,000 134,000 233 million 114 million 68 million 55 million 77-140 million 19 million 114 million
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CPU
CPU contains:
Control Unit Arithmetic Logic Unit.
These two components work together to process data.
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Control Unit
Directs and coordinates most of the operations in the computer. Interprets each instruction and initiates the appropriate action to carry out the instruction. CU repeats a set of four basic operations:
fetching an instruction decoding the instruction executing the instruction storing the result
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Instruction Cycle
fetching - process of obtaining an instruction or data from memory decoding - process of translating the instruction into commands that the computer understands. executing - process of carrying out the commands. storing is the process of writing the result to memory.
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ALU - Arithmetic Logic Unit
Executes the instructions. Performs the following operations:
arithmetic: + - * / comparison: equal to, greater than, less than logical operations: AND, OR, NOT
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Truth Table for AND operator
Expression A AND B A true true false false B true false true false Result true false false false
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Truth Table for OR operator
Expression A OR B A true true false false B true false true false Result true true true false
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Pipelining
With pipelining the CPU begins executing the second instruction before the first instruction is completed.
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Registers
Registers are a mini-storage area for data and instructions, used by the ALU to complete tasks the Control Unit has requested. Data can come from data cache, main memory or the control unit. This makes retrieval for the ALU quick and efficient. Registers are part of the microprocessor.
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Registers
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System Clock
System clock is a small chip used to synchronize and control timing of all computer operations. Each tick is called a clock cycle. A CPU requires a fixed number of clock cycles to execute each instruction. The faster the clock the more instructions the CPU can execute per second. Superscalar processors - processors that can execute more then one instruction per clock cycle.
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Clock Rate (Clock Speed)
Clock speed is the number of pulses emitted from a computer's clock in one second;
It determines the rate at which logical or arithmetic gating is performed in a computer. It is measured in megahertz - MHz or gigahertz - GHz A hertz is one cycle per second 1 MHz - one million ticks per second. 1 GHZ - one billion ticks per second. Today's computers use clock in range: 2GHz 4 GHz
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Heat Sinks
Processors generate a lots of heat. Heat sink - small ceramic or metal component designed to absorb and ventilate heat produced by electrical components.
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Data Representation
Data and instructions inside the computer are represented digitally. Computer understands only two discrete states:
flow of the current no flow of the current
These two states are represented by using numbers:
0 represents no flow of the current 1 represents flow of the current
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Binary System
Binary system uses two unique digits 0 and 1. Each digit "on" and "off" is called a bit. Bit is the smallest unit of data the computer can handle
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Binary digits
1 bit - 2 unique combinations 2 bits - 4 unique combinations 3 bits - 8 unique combinations 8 bits -256 unique combinations
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Byte
Byte - 8 bits grouped together Byte is a basic storage unit in memory 1 byte can represent 256 individual characters. Combination of 0's and 1's is unique for each character.
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Coding Schemes
Combinations of 0s and 1s used to represent characters are defined by patterns called coding schemes. Three coding schemes:
ASCII, American Standard Code for Information EBCDIC, Extended Binary Coded Decimal Interchange Code. Unicode
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ASCII
Used on PC computers and minicomputers. Uses 8 bits to represent a character. Provides codes for 256 characters, including letters, punctuation symbols, and numerals. Sufficient to represent English and Western European languages.
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EBCDIC
Uses 8 bits to represent a character. Used on mainframe computers.
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Unicode
Uses 16 bits to represent a character. 16 bits - 65,000 unique combinations of 0's and 1's. Is large enough to represent Asian and other languages besides English and Western .
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Storage European Units
bit byte - 8 bits kilobyte - KB or K - 1024 bytes ~ 1000 megabyte - MB ~ 1 million bytes gigabyte - GB ~ 1 billion bytes terabyte - TB ~ 1 trillion bytes 210 220 230 240
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Main Memory
Memory is a temporary storage for data, instructions and information. It provides fast access to data and instructions for the CPU. Memory stores three basic items:
portion of operating system instructions portion of application programs data being processed
Data is lost when the power is switched of.
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Memory Addresses
Memory chips are installed on the motherboard. Memory is divided into 1 byte areas. Memory address is a precise location in memory and is identified by unique number.
memory location
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RAM - memory
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Memory Types
Main memory - Random Access Memory (RAM) Virtual Memory Read-Only Memory (ROM) CMOS
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RAM- Random Access Memory
Temporary (volatile) space for data, application software and operating system currently in use Located as a set of chips on the motherboard Less storage than hard disk Capacitors are used to hold bits Capacity is measured in MB (512 MB - 2GB) Speed is measured in nanoseconds
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RAM Types
There are several kinds of RAM. Each type has a different design and different data transfer speeds.
DRAM
Types of DRAM:
SDRAM
-dynamic RAM, must be re-energized constantly or it loses its contents. It's the basic and cheap type of RAM. It uses transistors and capacitors
synchronous DRAM, faster then DRAM because is synchronized to the system clock. fast and cheap DIMMS small circuit board containing several chips DDR SDRAM double data rate SDRAM faster than SDRAM DDR2 SDRAM faster tan DDR SDRAM
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RAM Types
SRAM - static RAM
is faster and more reliable than any form of DRAM. It uses more transistors to store a single bit but no capacitors. This eliminates the need to reenergize it. SRAM is expensive so is only used in cache, where the system requires the fastest possible storage.
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Cache
Cache is a high-speed storage mechanism (faster than RAM), that the processor can access more rapidly than main memory. used for temporary storage of frequently used instructions and data. when processor needs an instruction it searches cache first. cache is located on and next to the CPU chip. there are several types of cache:
level 1, level 2 and level 3
It is built from SRAM chips.
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Level 1 Cache
Level 1 (L1)cache also called internal or primary cache is built into the processor. It has smaller capacity - ranging from 8KB to 128 KB (most common size is 32KB-64KB)
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Level 2 Cache
Level 2 (L2), external or secondary cache is slower than L1 cache, but has larger capacity from 64KB to 16MB (most common size is 512KB-2MB). On older computers L2 was not part of the processor chip. (separate chip on the motherboard). Current processors include advanced transfer cache ( L2) built directly on the processor chip.
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Level 3 Cache
level 3 cache
Modern processors use larger and multilevel cache structures. Never CPU's have level 3 cache. It holds between 2MB 4MB
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Cache
Cache helps speed processing times when the processor requests data, instructions or information. Processor Chip
L1 cache part of processor L2 cache part of processor L1 cache fastest access slower access than L1 cache
L3 cache separate chip between processor and RAM
slower access than L1 and L2 cache
RAM
slower access than L1, L2, L3 cache
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Virtual Memory
Disk based If there is not enough RAM to hold the data and instructions the operating system will use the area of the hard disk called virtual memory to store the data and parts of programs while they are needed by the processor. Works with RAM, but is slower
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ROM Read-only Memory
ROM
memory chip that stores data and instructions that ...