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AQA GCSE Computer Science · 8525
AQA 8525 Check the specification (PDF) (opens in a new tab)
Computers store text using numbers represented in binary. A gives characters agreed codes: when software reads a code, it can identify the character it represents. Characters include letters, digits, punctuation and other symbols, not just the letters of the alphabet.
For text to be exchanged successfully, the systems sending and receiving it must interpret its codes consistently. Otherwise, a number intended to represent one character could be interpreted as something else.
Standard ASCII has 128 different codes. These cover uppercase and lowercase English letters, the digits 0–9, some punctuation and symbols, and control characters. Its character range is useful for basic English text, but it cannot represent the many characters needed by languages worldwide.
For example, standard ASCII cannot represent the accented letter ñ, Greek letters such as Ω, or the characters used to write Arabic and Chinese. It also lacks many mathematical symbols and emojis. A system limited to ASCII therefore cannot faithfully store all of this text as its original characters.
Unicode is an international standard for representing text. It assigns unique numeric codes to characters from many different alphabets and writing systems, as well as a wide range of special symbols. Its purpose is to provide a common standard that supports text across languages, programs and computer systems.
Unicode has a far greater capacity than ASCII. This allows it to represent accented letters, Greek, Arabic and Chinese characters, mathematical symbols, arrows and emojis, alongside ordinary English text.
Consider a message containing ñ, Ω and an emoji. Standard ASCII cannot represent all those characters, whereas Unicode can. The message can retain the intended characters rather than replacing them with approximate alternatives or question marks.
Unicode makes it possible for a website, document or messaging application to contain several languages and special symbols together. This is important for international communication: people can write names and messages using the characters their language actually needs.
Its shared codes also help different systems exchange text consistently when they use Unicode correctly. The main advantage over ASCII is therefore not simply that Unicode has more codes, but that this larger range makes multilingual text and special symbols usable within a common standard.
Unicode is an international character encoding standard for representing text across languages and computer systems.
This wider range allows multilingual documents and messages to preserve their intended characters. Shared codes support consistent text exchange between systems using Unicode correctly.
When comparing Unicode with ASCII, link its larger character range to support for different alphabets and special symbols.
Do not claim that every Unicode character uses 16 bits: the storage required depends on the encoding used.
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Character encoding
A standard that assigns codes to characters so that text can be represented in binary.
Character set
The collection of characters available in a character encoding system.
ASCII
American Standard Code for Information Interchange: a character encoding standard with 128 codes, covering English letters, digits, some symbols and control characters.
Unicode
An international character encoding standard that assigns unique numeric codes to characters from many writing systems and to a wide range of symbols.
Put your knowledge into practice — try past paper questions for Computer Science
Character encoding
A standard that assigns codes to characters so that text can be represented in binary.
Character set
The collection of characters available in a character encoding system.
ASCII
American Standard Code for Information Interchange: a character encoding standard with 128 codes, covering English letters, digits, some symbols and control characters.
Unicode
An international character encoding standard that assigns unique numeric codes to characters from many writing systems and to a wide range of symbols.