3. The ALU

A general purpose computer has to have a means of doing calculations and comparisons. The ALU carries out this task.

ALU stands for Arithmetic and Logic Unit.  It is where the computer processes data by either manipulating it or acting upon it.  It has two parts:

1. Arithmetic part - does exactly what you think it should - it does the calculations. For example the control unit gives it two numbers and the instruction to add them together.

A+B = C

The ALU then returns the answer to the control unit.

The ALU can do all the standard arithmetic operations (+ - \ and *). It can also carry out more advanced calculations if required.

2. Logic part - it makes comparisons between two numbers A and B and tells the control units whether A is 'greater than' B for example. It then returns the answer to the control unit.

Common logic comparisons are:

'Greater than'

'Less than'

'Equal to'