Meaning Of CPU & Function

CPU (Central Processing Unit)

Meaning Of CPU & Function:-The Central Processing Unit (CPU) is the brain of any computer system. In a human body, all major decisions are taken by the brain and all other parts of the body function as directed by the brain. Similar to the human brain, in a computer system, all major calculations, manipulation and comparison are made by CPU. The CPU is responsible for activating and controlling the operations performed by all other units of the computer system.

It consists of set of registers, arithmetic logical unit and control unit, which together interpret and educated execute instruction in assembly language. The primary function of the CPU are as follows: –

  • The CPU transfers instruction and input data from main memory to registers, that is internal memory. 
  • CPU executes the instruction in the stored sequence. 
  • When necessary, CPU transfers output data from register to Main memory. 

Central Processing Unit is often called the brain of computer. The CPU is fabricated as a single Integrated circuit (IG)and is also known as microprocessor. A CPU controls all the internal and external devices and performs arithmetic and logical operations. 

The CPU consists of following main sub- systems

  • Arithmetic logical unit (ALU) 
  • Control unit (CU) 
  • Memory Unit (MU) 

Arithmetic Logic Unit (ALU) 

ALU contains the electronic circuitry that executes all arithmetic and logical operations on the available data. 

All calculations, including comparisons, are made by the ALU. The data and instructions, stored in the primary memory, are transferred to the ALU for processing.Result generated in the ALU are transfer to the primary memory. After completion of processing, the final results are sent to and output device, such as printer.

ALU users registers to hold the data that is being processed. 

Most ALUs can perform the following operations:-

  • Logical operation (AND, NOT, OR, XOR )
  • Arithmetic operations (additions, substraction, multiplication and divisions) 
  • Bit- shifting operations (shifting or rotating a word by a specified number of but to the left or right with or without sign extension) 
  • Comparison (=,>,<,=,>,>,=) 

The calculator represent the Central Processing Unit and the clock is carries out the control function for different operation of the computer. The input and output devices are shown for the keyboard Input and the monitor output. The actual block diagram representation, containing the jobs done by each part. 

Control Unit (CU) 

CU coordinates with the input and output devices of a computer. It directs the computer to carry out store program instructions by communicating with the Alu and the registers. It organises it processing of data and instructions. 

The basic function of control unit is to fetch the instruction is stored in the main memory, identify the operation and the devices involved in it and accordingly generate control signals. 

All this is made possible through the control unit. By selecting, interpreting and conforming to the execution of instructions, the control unit is able to maintain order and direct the working of the entire computer system. Although it does not perform any processing on the data, the control unit acts as the central nervous system for all the other components of the computer. It co-ordinates the entire set of jobs done by the computer system.

Control unit of obtains instructions from the program stored in the main memory, interprets the instructions, and issues electrical signal that cause other units of the system to perform their functions. 


Home computers are called as micro computers. In micro computer the input is supplied by using keyboard, mouse or other input devices. These input devices may be is called peripheral devices. 

A computer must receive both data and program to function properly and should be able to solve problem. Feeding of data and program to a computer is facilitated by an input device. When you input information into your computer with the mouse or keyboard you are sending a signal to the CPU. The CPU has a logic unit that can be do basic arithmetic. The control unit direct the computer to execute program that have been stored in memory.  The speed by which a computer execute program is measured in millions of instruction per second where the processor speed is measured in Gigahertz. When the information has been processed, it is output in a human Rebel form to the monitor and speaker. It can also be stored again for letter processing. 


Processing is done inside the computer in an area called as the Central Processing Unit (CPU). 


Storage is basically holding a keeping the information somewhere. Data can be stored on a variety of fixed or removable media. The hard drive is the main form of fixed data storage. Once the computer information is stored in file it is there organised into folder. No data or information on a hard drive can exist outside a file. File can then be organised into folder. When we look at a file in more details, we see the data is represented by string of zeros and ones. 80 or 1 is called a bit and if the smallest unit a computer can process. Aap group aur wait is a bite and can represent a keyboard character on command to the computer.

All data is stored on a computer in bytes. File size is measured using the following:-

Size Number of Bytes
Kilobytes1KB= 210 or 1024
Megabyte1MB= 210 KB or 1048576
Gigabyte1GB= 210 MB or 1073741824

Output is the result of a computer process. Output may be seen on a monitor screen, heard off through speakers or printed on the printer. Output Device are hardware are also considered to the peripheral devices.

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 this is to be proceed is brought into main memory before processing. The needed instruction for processing and any kind of Intermediate result are also stored in primary memory. Together with these the final output is also stored in the primary memory for transferring it to the output unit. Another kind of memory is required as secondary memory of a computer system. This unit is used to permanently store data, program and output. This unit does not deal directly with CPU. 

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Pooja Rastogi

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