Central Processing Unit

The Main Parts of a Computer

A computer system consists of a number of different units each of which has its own special function.

Flow Diagram Central Processing Unit (cpu).
  1. Control Unit
    All the computer functions are co-ordinated by this unit, which interprets and carries out the instructions contained in a program.
  2. Immediate access (or main) store
    This consists of a very fast access store. Since the operation is electronic and there are no moving parts, data can be read in nanoseconds (one thousand millionths of a second).
  3. Arithmetic Unit
    This is the operational unit. Here calculations are performed and the logical processes of selecting, sorting and comparing of information take place.
  4. Registers
    These are small stores. They hold the data to be worked on in a calculation and give it up as instructed. Data can be transferred from one register to another.

Input Unit
This reads the information to be stored in the machine and converts it into an electrical form which can later be used in arithmetical calculations.

Backing Store
Data (information) can be permanently stored away here, usually in the form of recordings on magnetic material. It contains the vast mass of data a computer can deal with.

Output Unit
This presents the results of a computer operation, often in printed form as on a payslip. It may be presented on a television screen, tape, disc, cassette or card.

Reproduced from "How it Works" Ladybird Series