
A computer system consists of mainly four basic units; namely input unit, storage unit, central processing unit and output unit. Central Processing unit further includes Arithmetic logic unit and control unit.
Fig. 1.2: Basic computer Organization

A computer performs five major operations or functions irrespective of its size and make.
These are:
- it accepts data or instructions as input,
- it stores data and instruction.
- it processes data as per the instructions,
- it controls all operations inside a computer, and
- it gives results in the form of output.
Functional Units:

The functional units of a computer consists of:
- Input Unit
- Storage Unit
- Processing Unit
- Output Unit
Dotted lines (– – – –) indicate flow of instruction.
solid lines (–––––) indicate flow of data.