ASCII

ASCII stands for American Standard Code for Information Interchange. It is a character set designed for English text: every character has its own unique code, and each code is stored in 8 bits, which is one byte.

Because every code is 8 bits long, ASCII has 2 to the power 8 = 256 possible codes. These cover:

• upper-case and lower-case English letters
• the numerals 0 through 9
• punctuation marks, including commas and question marks
• symbols such as +, @ and %
• the space character
• control characters

Control characters are included in the set even though they never appear as visible symbols. They tell the computer to do a job, for example sounding a beep or moving to a tab stop, and each one still has its own code.

Why ASCII is useful

Using one byte per character keeps text files small, so they take up little storage and are quick to send between computers.

Where ASCII runs out

The 256 codes are designed for English text, so they soon run out. There are none left for the alphabets of other languages, for many mathematical and technical symbols, or for emoji, so ASCII cannot represent that text. ASCII is a list of characters and their codes, not a font or a keyboard layout.

In exam questions, an ASCII code is written as an 8-bit binary value, for example 00100001.