Definition of ASCII

ASCII stands for American Standard Code for Information Interchange.

Computers can only understand numbers, so an ASCII code is the numerical representation of a character such as 'a' or '@' or an action of some sort.

ASCII was developed a long time ago and now the non-printing characters are rarely used for their original purpose.
Below is the ASCII character table and this includes descriptions of the first 32 non-printing characters. ASCII was actually designed for use with teletypes and so the descriptions are somewhat obscure.

Extended ASCII

As people gradually required computers to understand additional characters and non-printing characters the ASCII set became restrictive. As with most technology, it took a while to get a single standard for these extra characters and hence there are few varying 'extended' sets.

The most popular is presented below: