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# ch06 - CHAPTER 6 INSIDE THE SYSTEM UNIT How computers...

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1 CHAPTER 6 INSIDE THE SYSTEM UNIT How computers represent data. We’re all used to counting with decimal numbers, which consist of 10 digits (0, 1, 2, 3, 4, 5, 6, 7, 8, 9). Computers count with binary numbers , which consist of only two digits (0 and 1). A binary number is called a binary digit, or bit for short. A bit is the smallest unit of information that a computer can work with (Figure 6.1). Think of a bit as being similar to a light switch: it has only two possible states, and is always in one or the other. If there is one light switch, the switch is on, or the switch is off. If there are two light switches, there are four possibilities: both switches are on; both switches are off; the first switch is on, and the second switch is off; or the first switch is off, and the second switch is on. Three switches allow for eight possibilities, and so on—up to eight switches, which results in 256 possible combinations. Representing Characters: Character Codes Character codes translate numerical data into characters readable by humans; American Standard Code for Information Interchange (ASCII)—Eight bits equals one character; used by minicomputers and personal computers; Extended Binary Coded Decimal Interchange Code (EBCDIC)—Eight bits equals one character; used by mainframe computers; Unicode —Sixteen bits equals one character; over 65,000 combinations; used for foreign language symbols. The measurements used to describe data transfer rates and data storage capacity. The basic unit of information in a computer is the bit, a single-digit binary number (either 1 or 0). An eight-bit sequence of numbers, called a byte , is sufficient to represent the basic letters, numbers, and punctuation marks in most European languages. For this reason, the term byte is synonymous with the term character (a letter or number). Larger units of data are described by the terms kilobyte ( K or KB , approximately one thousand bytes), megabyte ( M or MB , approximately one million bytes), gigabyte ( G or GB , approximately one billion bytes), and terabyte ( T or TB , approximately one trillion bytes). Data transfer rates are measured in bits per second ( bps ). Common terms to describe data transfer rates include Kbps (approximately one thousand bits per second ), Mbps (approximately one million bits per second ), and Gbps (approximately one billion bits per second ). The components found inside the system unit, and their uses. Inside the system unit, there is the motherboard, power supply, cooling fan, speaker, internal drive bays, external drive bays, and various expansion cards (such as the sound card and network interchange card). 8 bits = 1 Byte 1024 Bytes = 1 Kilobyte (KB) 1,048,576 Bytes = 1 Megabyte (MB) 1,043,741,824 Bytes = 1 Gigabyte (GB)

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2 The motherboard contains the computer’s central processing unit ( CPU ). A computer’s power supply transforms the alternating current ( AC ) available from standard wall outlets into the direct current ( DC ) needed for the computer’s operation.
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