A-Level Computer Science Revision — Character Encoding
Revise Character Encoding for A-Level Computer Science with a topic explanation, worked example and common mistakes. Check the board notes for specification differences.
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What is Character Encoding?
Character encoding is a system that assigns a unique numerical value to each character. This allows computers to store and transmit text. The most common character encodings are ASCII and Unicode.
Board notes: Covered by AQA, Edexcel, and OCR. Students should understand the need for character encoding and be familiar with ASCII and Unicode.
Step-by-step explanationWorked examples
Worked example
The character 'A' is represented by the decimal value 65 in ASCII. In binary, this is 01000001. The character 'a' is 97 (01100001). This is why 'a' comes after 'A' when sorting strings.
Practise this topic
Start with low-focus cards for Character Encoding, then move into full exam-style practice when you want the heavier session.
Common mistakes
- 1Confusing characters with their encoded representations.
- 2Not understanding the difference between ASCII and Unicode.
- 3Thinking that Unicode is a 16-bit encoding (it is a variable-width encoding).
Character Encoding exam questions
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Frequently asked questions
What is the advantage of Unicode over ASCII?
ASCII can only represent 128 characters, which is enough for English but not for other languages. Unicode can represent over 140,000 characters, covering almost all of the world's writing systems.
What is UTF-8?
UTF-8 is a variable-width character encoding that is backward-compatible with ASCII. It is the most common character encoding on the World Wide Web.