Components of Computer

A general purpose computer has three main components:

(i) Input/Output Unit

(ii) Central Processing Unit (CPU)

(iii) Memory Unit

Input/Output Unit

Input/Output devices are required for user to communicate with the computer. Input devices bring data INTO the computer system and output devices bring data OUT from a computer system.

These I/O devices are also known as peripheral devices like keyboard, mouse, printer, etc.


The Central Processing Unit (CPU) is the part of a computer system that carries out the instructions of a computer program in order to perform the basic arithmetic, logical and input/ output operations of the system.

CPU is also known as the brain of the computer. The speed of CPU depends upon the type of microprocessor used and its processing speed is measured in Mega Hertz (MHz).


The microprocessor is fabricated on a single IC (Integrated circuit). IC is thousands of transistors laid side by side to form a circuit.It is commonly made of silicon.

Intel in 1971 launched the first chip “Intel 4004” which was made by scientist Ted Hoff and engineer Frederico Faggin. Some of the popular microprocessors are i5, i3, Core 2 Dual Intel, Dual Core, Pentium IV, etc.

Two typical components of a CPU are the Arithmetic Logic Unit (ALU) and the Control Unit (CU):

Arithmetic Logic Unit

In computing, an Arithmetic Logic Unit (ALU) is a digital circuit that performs arithmetic and logical operations. The ALU is a fundamental building block of the central processing unit of a computer.

An ALU loads data from input registers and control unit tells the ALU that which operation is to be performed on that data and then the ALU stores its result into an output register.

Most ALUs can perform the following operations:

(i) Logical operations (AND, NOT, OR, XOR)

(ii) Arithmetic operations (addition, subtraction, multiplication and division).

(iii) Bit-shifting operations (shifting or rotating a word by a specified number of bits to the left or right, with or without sign extension).

(iv) Comparison operations (=,=)

Control Unit

The control unit coordinates the input and output devices of a computer system. It fetches the instructions which are given in the form of microprograms. It directs the operation of the other units by providing timing and control signals.

In general, a control unit is a central part of the machinery that controls its operation and entire processing.

e.g. in the automobile industry, the control unit helps to maintain various functions of a motor vehicle.

The control unit is the circuit that controls the flow of data through the processor and coordinates the activities of the other units within it. Control unit acts like human nervous system, which does not process data but behaves as a central unit for other data manipulating components.


It is the internal part of CPU. These are used to store intermediate results obtained during the execution of instruction.

Memory Unit

This unit is responsible to store programs or data on a temporary or permanent basis. It has primary memory (main memory) and secondary memory (auxiliary memory). The input data which is to be processed is brought into main memory before processing.

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