stands for Arithmetic/Logic Unit

This is the part that executes the computer's commands.
A command must be either a basic arithmetic operation:
 +          -                *             /
add, subtract, multiply, divide

or one of the logical comparisons:
        >                    <              =         not =.
greater than, less than, equal to, not equal to

Everything else has to be broken down into these few operations. Only one operation is done in each Machine Cycle.

The ALU can only do one thing at a time but can work very, very fast.