Switches are used to control the voltage in an electrical circuit and lamps
can be used to indicate the presence or absence of voltage. Some switches are called *momentary*
because the voltage disappears when the input "stimulus" disappears. Others are
called *latches* because the voltage remains even after the input stimulus has gone.

By grouping a number of electrical circuits together, the presence or absence
of the voltages can be used to *represent* numbers. We humans prefer to
use numbers based on the decimal (base 10) system whilst computers work with
the simpler binary (base 2) system.

A single digit in the binary system is called a *bit* and can only represent
the deciaml numbers 0 and 1. Eight bits, when grouped together, are called a *byte*
and can be used to represent any decimal number between 0 and 255.

The next common grouping is sixteen bits. This is called a *word* and can
represent decimal numbers between 0 and 65,535.

After the word is the *double-word* which is 32 bits - the basis of all modern
home computer systems (0 - 4,294,967,295).