AQA · GCSE · Computer Science
Course version: 8525 · Version from Sept 2020
Character encoding: Unicode.
Unicode is a character set designed to represent characters from many of the world's writing systems, not just English.
Checked against the AQA 8525 specification (opens in a new tab) on .
- Point 6 of 10
Study notes
From the checked teaching notes for this specification point.
The idea
Unicode is a character set designed to represent characters from many of the world's writing systems, not just English. Each character is assigned a unique code point, written in the form U+ followed by a hexadecimal number, for example U+0041 for the capital letter A. Unicode can represent far more characters than 7-bit ASCII, including accented letters, Greek, Arabic, Chinese characters and symbols. To store Unicode text, an encoding such as UTF-8 or UTF-16 converts code points into binary. UTF-8 is variable length: it uses one byte for basic ASCII characters and more bytes for others, which saves space for English text while still allowing a huge range of characters. The key idea is that Unicode provides a large, universal character set, and an encoding decides how those code points are stored as binary.
What earns the marks
- Unicode is a character set covering characters from many languages and symbol sets.
- Each character has a unique code point, often written as U+ followed by a hexadecimal value.
- Unicode represents far more characters than 7-bit ASCII, including non-Latin scripts and symbols.
- An encoding such as UTF-8 or UTF-16 converts Unicode code points into binary for storage.
- UTF-8 is variable length, using one byte for basic ASCII characters and more bytes for others.
Common mistakes and how to put them right
Treating Unicode and UTF-8 as the same thing.
Put it right: Unicode is the character set of code points, while UTF-8 is one encoding that stores those code points as binary.
Assuming Unicode uses a fixed number of bits per character.
Put it right: Encodings such as UTF-8 are variable length.
Thinking Unicode is just an extended ASCII with 256 codes.
Put it right: Unicode has a far larger range of code points covering many writing systems.
Exam tips
- Distinguish clearly between the character set (Unicode) and the encoding (for example UTF-8) in your answer.
- Give a concrete example of a character Unicode can represent that 7-bit ASCII cannot, such as an accented letter or a non-Latin character.
- Explain the benefit of variable-length UTF-8: it stores common ASCII characters in one byte while still supporting a wide range of characters.
Try the lesson
The start of the Character encoding: Unicode. lesson, made from checked teaching notes for this specification point.
Have a go first
A school in Japan and a school in Wales need to exchange text files containing Japanese and Welsh characters. Which character set allows both schools to represent the same characters in the same way?
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