AQA · GCSE · Computer Science
Course version: 8525 · Version from Sept 2020
Know that Unicode uses the same codes as ASCII up to 127.
Full specification wording
Character encoding: Know that Unicode uses the same codes as ASCII up to 127.
ASCII assigns a numeric code to each character it represents, and the first 128 of these codes run from 0 to 127.
Checked against the AQA 8525 specification (opens in a new tab) on .
- Point 10 of 10
Study notes
From the checked teaching notes for this specification point.
The idea
ASCII assigns a numeric code to each character it represents, and the first 128 of these codes run from 0 to 127. Unicode was designed so that this same block of code values means exactly the same characters: code 65 is 'A', code 97 is 'a' and code 32 is the space, whether the system calls the scheme ASCII or Unicode. This backward compatibility means text written in plain ASCII can be read as Unicode without any conversion, because the numeric values already agree. Above 127 the two schemes diverge: ASCII stops, while Unicode continues to assign codes to thousands of further characters such as accented letters, Greek symbols and emoji. So the shared range is 0 to 127 inclusive, and the statement is about that overlap only, not about the whole of Unicode.
What earns the marks
- Unicode and ASCII agree on the same code values for characters numbered 0 to 127 inclusive.
- Within that range a given code represents the same character in both schemes, for example 65 for 'A' and 97 for 'a'.
- The agreement gives backward compatibility, so plain ASCII text needs no conversion to be read as Unicode.
- Above 127 the schemes differ: ASCII has no codes there, while Unicode assigns codes to many additional characters.
Common mistakes and how to put them right
Thinking Unicode and ASCII are identical everywhere.
Put it right: They share codes only up to 127, and Unicode extends far beyond that.
Believing ASCII text must be converted before a Unicode system can read it.
Put it right: Codes 0 to 127 already match, so no conversion is needed in that range.
Assuming the shared range is 0 to 128 or 1 to 127.
Put it right: The shared codes are 0 to 127 inclusive, which is 128 values.
Exam tips
- Learn the boundary value 127 and state that the shared range is 0 to 127 inclusive.
- Use a concrete example such as code 65 for 'A' to show the codes match in both schemes.
- Separate the two ideas in your answer: same codes up to 127, different coverage above 127.
Try the lesson
The start of the Character encoding: Know that Unicode uses the same codes as ASCII up to 127. lesson, made from checked teaching notes for this specification point.
Have a go first
A computer stores the character 'A'. In ASCII, 'A' has the code 65. What is the Unicode code point for 'A'?
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