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

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.

Key points

• Definition:ASCII: a character encoding system that represents characters using binary codes, originally designed to represent standard English characters.
• Definition:Unicode: a character encoding system that assigns unique binary codes to characters from most of the world's languages, including symbols and emojis.
• ASCII uses 7 bits (or extended ASCII uses 8 bits) per character, allowing 128 (or 256) different characters.
• Unicode uses between 8 and 32 bits per character, allowing over 4 billion unique characters — enough for every language, plus emojis and symbols.
• 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.
• Exam 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.
• Common Mistake:Saying Unicode 'always uses 32 bits'. Unicode uses BETWEEN 8 and 32 bits — it is variable-length.
• Exam Tip:For OCR J277, ASCII is treated as 8 bits per character (extended ASCII) to avoid confusion. So max characters = 2^8 = 256.
• Exam Tip:To represent 150 different characters, you need at least 8 bits (2^7=128 is not enough, 2^8=256 is enough).