Components of a Computer System

                  By considering the functions performed by various components, a computer can be represented as a collection of logical components as in Figure 1.3. The main hardware components of a modern computer system are the central processing unit (CPU), the main memory, the secondary storage and the In put-Out put devices.

 

System Unit

                  The system unit, or the cabinet houses most of the essential components of the computer system such as the power supply, the motherboard, the CPU chip, specialized chips, the system clock, RAM, ROM, expansion board and bus lines.


Central Processing Unit (CPU)

The central processing unit performs the majority of calculations and controls the operation of a computer. CPUs are rated by the speed at which they can execute instructions. The speed of a CPU is measured in Megahertz (MHz), and is also known as the clock speed. The higher the value of the speed the faster the computer can run programs. The capacity of a Central Processing Unit is expressed in terms of word size. A word is the maximum number of bits that the CPU can manipulate or store at one time.

The CPU consists of two parts: the control unit (CU) and the arithmetic/logic unit (ALU)

Different manufactures are making CPUs today. Some of these popular CPUs available today are the Intel, AMD, Cyrix and Motorola.


Control Unit (CU)

                  The control unit controls and directs the operation of the entire computer system. Although it does perform any actual processing on the data, the control unit acts as a central nervous system for the other components of the computer. It obtains instructions from the program stored in main memory, interprets the instructions, and issues signals, which cause other units in the system to execute them.


Arithmetic-Logic Unit (ALU)

                  The arithmetic-Logic unit performs arithmetic operations such as addition, subtraction, multiplication and division on data. It also performs logical operations, which involve comparison of data. In microcomputers, the entire CPU is typically fabricated on a single chip.


Motherboard

                  The motherboard is the main circuit board inside the computer. It can be considered as the main communication center through which all the components of the computer transmit data back and forth. All the main parts including the central processing unit of the computer are typically plugged in to the mother board. The mother board also provides sockets, called expansion slots, to plug in special electronic circuitboards to enhance the functionality of the computer. These extra circuitboards are called expansion cards, by using which you can customize a computer to suit your needs. One other major function of the mother board is to supply the necessary power to all its expansion cards.

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Data Representation

             Computers use the two-state system to represent data. Such a two state system is referred to as a binary system. In computers these two states are denoted by the digits 0 and 1 and any such value is called a binary digit or bit. In side the computer these two states are typically implemented by using two different voltages.

             The smallest unit of data that can be stored in a computer is a bit. A bit will have the value '0' or '1' . A large collection of such '0's or '1's is what makes up data in a computer.

Smallest Unit           = 1 bit

8 bits                     = 1 byte (B)

1024 bytes             = 1 kilobyte (KB)

1024 kilobytes        = 1 megabyte (MB)

1024 megabyte       = 1 gigabyte (GB)

1024 gigabyte         = 1 terabyte (TB)
(In computer jargon, One Kilo = 1024)

              The capacity of a particular storage device and the space taken up by a file are always measured using these units.

              Letters, numbers and special characters are represented within a computer by means of a binary coded scheme. Three popular binary coding schemes use eight bits to represent characters whereas Unicode uses 16 bits.

Character	ASCII-8	EBCDIC	Character	ASCII-8	EBCDIC
A B C D E F G H I J K L M	0100 0001 0100 0010 0100 0011 0100 0100 0100 0101 0100 0110 0100 0111 0100 1000 0100 1001 0100 1010 0100 1011 0100 1100 0100 1101	1100 0001 1100 0010 1100 0011 1100 0100 1100 0101 1100 0110 1100 0111 1100 1000 1100 1001 1101 0001 1101 0010 1101 0011 1101 0100	N O P Q R S T U V W X Y Z	0100 1110 0100 1111 0101 0000 0101 0001 0101 0010 0101 0011 0101 0100 0101 0101 0101 0110 0101 0111 0101 1000 0101 1001 0101 1010	1101 0101 1101 0110 1101 0111 1101 1000 1101 1001 1110 0010 1110 0011 1110 0100 1110 0101 1110 0110 1110 0111 1110 1000 1110 1001
0 1 2 3 4 !	0011 0000 0011 0001 0011 0010 0011 0011 0011 0100 0010 0001	1111 0000 1111 0001 1111 0010 1111 0011 1111 0100 0101 1010	5 6 7 8 9 ;	0011 0101 0011 0110 0011 0111 0011 1000 0011 1001 0011 1011	1111 0101 1111 0110 1111 0111 1111 1000 1111 1001 0101 1110

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