Logical Structure and Block Diagram of a Computer

on 19 June 2013

The basic logical structure of a computer (also called block structure or block diagram) of a computer was proposed by Von Neumann. According to the logical structure of a digital computer there are four main units or types of components. They are:

  1. Input Unit
  2. Storage Unit
  3. Central Processing Unit (CPU) and
  4. Output Unit
Computer Block Diagram
Block diagram of a Computer

Input Unit

Input unit enables users to interact with the computer system. All data and instructions need to be entered into the computer system through the input unit. The major functions of the input unit are as follows:

  • Accepts the data and instructions from the outside world (users).
  • Converts the data and instructions into a form that a computer can understand.
  • The converted data and instructions are sent to the computer system for further processing.

Examples of some input units are keyboard, mouse, scanner, microphone etc.

Storage Unit

The function of a storage unit is to store data. It can be temporary or permanent data. It basically stores:

  • Data and instructions required for processing.
  • Intermediate results of processing on a temporary basis.
  • Final results needed to be stored permanently or before they are released to an output device.

Examples of storage device are RAM, ROM, hard-disks, CD-ROM, DVD, Pendrive etc.

Central Processing Unit (CPU)

CPU is responsible for activating and controlling the operations of other units of a computer system. It is also referred to as the brain of computer. CPU consists of two main parts:

  1. Control Unit (CU)
  2. Arithmetic Logic Unit (ALU)

Control Unit

Control Unit is responsible for coordinating various operations of a computer. It uses time signals to do that. The control unit determines the sequence in which computer programs and instructions are executed. It also acts as a switch board operator when several users access the computer simultaneously. In simple words, it acts like the supervisor seeing that things are done in proper fashion.

Arithmetic and Logic Unit

The actual processing of the data and instruction are performed by Arithmetic Logical Unit. ALU takes care of various calculations. The major operations performed by the ALU are addition, subtraction, multiplication, division, logic and comparison. Data is transferred to ALU from storage unit when required. After processing the output is returned back to storage unit for further processing or getting stored.

Output Unit

Output unit is responsible for transferring the processed data back to the outside world i.e the user. The processed data must be in the form that user understands. The major functions of the output unit are as under:

  • Accepts results from the processing unit of computer.
  • Converts those results into human acceptable form.
  • Provides the result to outside world.

Examples of output devices are monitor, printer, speaker etc.


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