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General Architecture of a Computer

A computer is a programmable device that accepts data as input and process it with a set of instructions and produces the result as output.

A computer consists of the following four parts,

  1. Input Unit.
  2. Output Unit.
  3. Memory Unit.
  4. Central Processing Unit.
architecture of computer
The general architecture of a Computer

Input Unit

  • The input unit accepts data and instructions from user.
  • Digitise received data.
  • Supply digitised data to computer system for processing.

Output Unit

  • Accept processed data from computer.
  • Convert binary data to humanely acceptable form.
  • Supply this result to user.


  • Store data to be processed by the system.
  • Store Intermediate result.
  • Store final result.

Central Processing Unit

  • The CPU retrieves and executes all the instructions of a computer program.
  • It consist of
    • Arithmetic and Logic Unit (ALU).
    • Control Unit.
    • Registers.

Arithmetic Logic Unit

  • The ALU performs all arithmetic and logical operations.


  • These are the temporary storage location within the CPU.
  • The CPU uses several types of registers for specific functions.
  • Eg: Accumulator, PC, IR, etc.

Control Unit

  • The control unit controls and coordinates entire computer system.
  • Fetches instruction from memory.
  • Decodes the instruction.
  • Execute the instruction.
  • Control data transfer between memory and I/O devices.


  • Common communication path.
  • Physical group of signal lines that have a related function.
  • Allows transfer of electrical signals between different components.
  • Most used bus architecture is the three bus architecture. (Data bus, Address bus, Control bus)
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