Central Processing Unit (CPU)

CPU itself has following three components.

  • Memory or Storage Unit
  • Control Unit
  • ALU(Arithmetic Logic Unit)

Control Unit : This unit of CPU directs the entire computer system to carry out stored program instructions.This unit controls the operations of all parts of computer but does not carry out any actual data processing operations. 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. The control unit must communicate with both the arithmetic logic unit and main memory.It also communicates with Input/Output devices for transfer of data or results from storage.It does not process or store data.

ALU(Arithmetic Logic Unit): The arithmetic logic unit executes arithmetic and logical operations. Arithmetic operations include addition, subtration, multiplication and division. All complex operations are done by making repetitive use of above operations.The logical operation include compare numbers, letters and special characters using logic functions such as AND, OR and NOT.

Output Unit

The output unit is used to present soft and hardcopy of information.The VDU (Visual Display Unit or Monitor) and printer are common output units.

How CPU communicate with other units while processing

  • The program and the necessary data are entered into the Computer system from an input device, and are stored in main memory where they can be accessed as needed.
  • Now, the CPU retrieves the instructions from the main memory, one by one, and decodes each instruction to determine what operation to be performed.
  • When required by instruction, the CPU also retrieves the necessary data from main memory.
  • The CPU then performs the operation required by the instruction, which might be arithmetic or logical operation. As each instruction is performed, the results are either temporarily saved by the CPU or are stored in main memory.
  • The processing cycle (retrieve instruction, decode and execute instruction, save results) is repeated until all the program instructions have been carried out by the CPU. The final results are then either stored in main memory, or are sent to an output device such as a printer.