During the execution of a program, the control unit fetches one instruction at a time from the main memory and then executes it. In this execution process, it takes help of ALU, if the instruction execution involves arithmetic or logical operation (like AND, OR, Ex-OR). After execution of the current instruction, the CPU fetches the next instruction for execution. This process continues until the program is completed and the result is output using the output device. In many computers, the control unit and the ALU are integrated into a single block, known as Central Processing Unit (CPU).
Central Processing Unit (CPU) consists of the following features −
CPU is considered as the brain of the computer.
CPU performs all types of data processing operations.
It stores data, intermediate results, and instructions (program).
It controls the operation of all parts of the computer.
CPU itself has the following three components.
Memory or Storage Unit
a control unit
ALU(Arithmetic Logic Unit)
This unit can store instructions, data, and intermediate results. This unit supplies information to other units of the computer when needed. It is also known as an internal storage unit or the main memory or the primary storage or Random Access Memory (RAM).
Its size affects speed, power, and capability. Primary memory and secondary memory are two types of memories in the computer. Functions of the memory unit are −
It stores all the data and the instructions required for processing.
It stores intermediate results of processing.
It stores the final results of processing before these results are released to an output device.
All inputs and outputs are transmitted through the main memory.
This unit controls the operations of all parts of the computer but does not carry out any actual data processing operations.
Functions of this unit are −
It is responsible for controlling the transfer of data and instructions among other units of a computer.
It manages and coordinates all the units of the computer.
It obtains the instructions from the memory, interprets them, and directs the operation of the computer.
It communicates with Input/output devices for transfer of data or results from storage.
It does not process or store data.
This unit consists of two subsections namely,
The function of arithmetic section is to perform arithmetic operations like addition, subtraction, multiplication, and division. All complex operations are done by making repetitive use of the above operations.
The function of the logic section is to perform logic operations such as comparing, selecting, matching, and merging of data.