Page 16 - Handout Digital Electronics

2.3 Components and their functions

2.3.1 Input Unit

The purpose of the input unit is to accept data and convert it into an acceptable form, for example
decimal or alphabetic data must be converted to binary data (a series of binary ones and zeros) which
the computer understands. There is now a variety of input devices, but the keyboard and the mouse
are the most widely used these days. Examples of input devices are:

• Keyboard
• Mouse
• Card reader
• Bar code reader
• Voice input and others.

2.3.2 The Control Unit

The purpose of the control unit is to fetch instructions from main memory, decode the instruction and
prompt its execution by any of the other units, for example an arithmetic instruction would be
executed by the Arithmetic unit (AU) and a logic or Boolean instruction would be executed by the Logic
Unit (LU). So, the control unit coordinates the operation of the entire computer system.

2.3.3 The Main Memory

The main memory is made up of two parts:

• Random Access Memory (RAM)
• Read Only Memory (ROM)

RAM is used to store data that is in current use. This type of memory is volatile and will lose all its
contents should there be any interruption in power supply. ROM is used to store data or information
permanently and if their interruption of power, the previous stored information or data is not lost. So,
it is called non- volatile. ROM is programmed and inserted by the manufacturer.

Note that ROM is also randomly accessed but the random is silent in ROM. ROM is used to store
operating system programs (systems software) that used to start up the computer system.

2.3.4 Arithmetic and Logic units (ALU)

The purpose of this unit is to carry out all arithmetic operations such as addition, subtraction, division
and others. The function of the logic unit is processing logic or Boolean operations such as comparing
two numbers to find out whether they are the same or ORing two binary numbers and others.

16