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Technology Guide


TG1.1 TG1.2 TG1.3 TG1.4 TG1.5
What Is a Computer System? The Evolution of Computer Hardware Types of Computers The Microprocessor and Primary Storage Input/Output Devices





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Technology Guide 1 Hardware

TG1.1What Is a Computer System?
Computer hardware is composed of the following components: central processing unit (CPU), input devices, output devices, primary storage, secondary storage, and communication devices. (These devices are described in Technology Guide 4.) Each of the hardware components plays an important role in computing. The input devices accept data and instructions and convert themto a form that the computer can understand. The output devices present data in a form people can understand. The CPU manipulates the data and controls the tasks done by the other components. The primary storage (internal storage) temporarily stores data and program instructions during processing. It also stores intermediate results of the processing. The secondary storage (external) stores dataand programs for future use. Finally, the communication devices provide for the flow of data from external computer networks (e.g., Internet, intranets) to the CPU, and from the CPU to computer networks. A schematic view of a computer system is shown in Figure TG1.1.

ASCII. Today’s computers are based on integrated circuits (chips), eachof which includes millions of subminiature transistors that are interconnected on a small (less than l-inch-square) chip area. Each transistor can be in either an “on” or an “off” position. The “on-off” states of the transistors are used to establish a binary 1 or 0 for storing one binary digit, or bit. A sufficient number of bits to represent specific characters—letters, numbers, and specialsymbols—is known as a byte, usually 8 bits. Because a bit has only two states, 0 or 1, the bits comprising a byte can represent any of 28, or 256, unique characters. Which character is represented depends upon the bit combination or coding scheme used. The two most commonly used coding schemes are ASCII (American National Standard Code for Information Interchange), pronounced “ask-ee,” and EBCDIC(Extended Binary Coded Decimal Interchange Code), pronounced “ebsa-dick.” EBCDIC was developed by IBM and is used primarily on large, mainframe computers. ASCII has emerged as the standard coding scheme for microcomputers. These coding schemes, and the characters they present, are shown in Figure TG1.2. In addition to characters, it is possible to represent commonly agreed-upon symbols in a binary code.For example, the plus sign (+) is 00101011 in ASCII. The 256 characters and symbols that are represented by ASCII and EBCDIC codes are sufficient for English and Western European languages but are not large enough for Asian and other languages that use different alphabets. Unicode is a 16bit code that has the capacity to represent more than 65,000 characters and symbols.

Output Devices InputDevices Bus Mouse Central Processing Unit Control Unit Arithmetic-Logic Unit Bus

Primary Storage

Communication Devices Bus


Figure TG1.1 The components of computer hardware. A “bus” is a connecting channel.

Secondary Storage

External Network




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TG1.1 What Is a Computer System?
Character A B C D E F G H I J K LM N O P Q R EBCDIC Code 11000001 11000010 11000011 11000100 11000101 11000110 11000111 11001000 11001001 11010001 11010010 11010011 11010100 11010101 11010110 11010111 11011000 11011001 ASCII Code 10100001 10100010 10100011 10100100 10100101 10100110 10100111 10101000 10101001 10101010 10101011 10101100 10101101 10101110 10101111 10110000 10110001 10110010 Character S T U V W X Y Z 0 1 2 3 4 5 6...
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