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GCSE Computer Science/Paper 1/Data Storage: Characters

The relationship between the number of bits per character in a character set, and the number of characters which can be represented, e.g. ASCII, Unicode

Characters: The relationship between the number of bits per character in a character set, and the number of characters which can be represented, e.g. ASCII, Unicode

1.2.4b Data Storage: Characters

Practise exam questions

Data Storage: Characters — Note 4 of 4

What you need to know

The number of bits used per character determines the maximum number of characters a character set can represent. ASCII uses 7 or 8 bits; Unicode uses up to 32 bits, supporting many more characters.

What to know

  • More bits per character = more possible characters BUT larger file sizes.
  • Unicode includes all ASCII characters PLUS characters from other languages (Chinese, Arabic, etc.) and emojis.

Key terms

Exam tipCommon mistake

ASCII

A character encoding system that represents characters using binary codes, originally designed to represent standard English characters.

  • ASCII uses 7 bits (or extended ASCII uses 8 bits) per character, allowing 128 (or 256) different characters.
  • Exam tip: For OCR J277, ASCII is treated as 8 bits per character (extended ASCII) to avoid confusion. So max characters = 2^8 = 256.
Unicode

A character encoding system that assigns unique binary codes to characters from most of the world's languages, including symbols and emojis.

  • Unicode uses between 8 and 32 bits per character, allowing over 4 billion unique characters — enough for every language, plus emojis and symbols.
  • Common mistake: Saying Unicode 'always uses 32 bits'. Unicode uses BETWEEN 8 and 32 bits — it is variable-length.

Exam technique

  • Tip:The formula for how many characters can be represented: 2^n where n = number of bits. E.g. 7 bits = 2^7 = 128 characters. 8 bits = 256.
  • Tip:To represent 150 different characters, you need at least 8 bits (2^7=128 is not enough, 2^8=256 is enough).

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Practise 1.2.4b questions
← Previous noteThe term 'character set'1.2.4b Data Storage: CharactersNext topic →Calculate file sizes of image1.2.4c Data Storage: Images

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Data Storage: Characters

Note 4 of 4

  1. 1Calculate file sizes of text
  2. 2The use of binary codes to represent characters
  3. 3The term 'character set'
  4. 4The relationship between the number of bits per character in a character set, and the number of characters which can be represented, e.g. ASCII, Unicode
Topic overview

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