How character sets (ASCII and UNICODE) are used to represent text

1.4.1 Data Types

Data Types — Note 10 of 10

Candidates should have an understanding of how characters are represented in a computer and in binary. Candidates should understand the need for a character set and how a computer makes use of a character set. Candidates should be aware of the ASCII and UNICODE character sets and be able to explain the differences between these and how these impact what can be stored. Candidates should be able to use a character set, or part of a character set, to translate characters into binary and vice-versa. (Candidates are not expected to memorise any values in a character set).

What you need to know

A character set maps each character to a unique binary code so that text can be stored and processed. ASCII covers English characters; Unicode covers the characters of almost every language plus symbols and emoji.

What to know

Codes for letters and digits are in sequence, e.g. 'A' = 65, 'B' = 66; 'a' = 97. So if you know one code you can work out others.
More bits per character means more characters can be represented, but text files are larger.

Key terms

Exam tipCommon mistake

Character set: A defined list of characters a computer can recognise, each with a unique binary code.
Exam tip: You may be given part of a character set table and asked to translate characters to binary or back. You do not need to memorise any codes.
ASCII: Originally a 7-bit character set (128 characters) covering English letters, digits, punctuation and control characters. Extended ASCII uses 8 bits (256 characters).
Unicode: A character set that can represent the characters of most of the world's languages, plus symbols and emoji, using up to 32 bits per character. Its first 128 codes match ASCII.
Unicode allows text in different languages to be exchanged and displayed correctly worldwide.
Common mistake: Saying Unicode always uses 32 bits. Unicode encodings such as UTF-8 use a variable number of bytes per character.