Text, Sound and Images
Data Representation
This comparison has been set for up to 4 marks, and the mark scheme wants precise statements.
| Feature | ASCII | Unicode |
|---|---|---|
| Bits per character | 7 (or 8 for extended) | 16+ |
| Number of characters | 128 (or 256) | 65 536+ |
| Storage space per character | Small | Large |
| Languages covered | English only | All major world languages |
| Emoji and modern symbols | No | Yes |
| Best use | English text on systems with limited memory | International text, web pages, modern software |
Trade-offs in a single sentence
- stores more characters but uses more memory per character.
- uses less memory but cannot represent international text or emoji.
Mark-scheme language: when comparing, mention the number of bits, the number of characters, and what each can represent. The mark schemes list precise points like these, and a vague verdict like "Unicode is bigger" or "Unicode is better" matches none of them.
Common exam question
Comparing ASCII with Unicode
Question: Explain the differences between the ASCII and Unicode character sets, or give two advantages and one disadvantage of using Unicode rather than ASCII (1–4 marks).
Asked in 2 of the 17 papers. Each mark is one precise point about either set, with a figure where there is one, so each of these pairs can earn two marks: ASCII uses 7 or 8 bits per character, Unicode up to 16 or 32; ASCII has 128 or 256 characters, Unicode 65 536 or over 4 billion; ASCII covers few languages, Unicode many languages and emojis. In the four-mark version at most three marks can come from points about one character set alone, so make at least one point about each of them.
Asked for advantages of Unicode, give any two of more characters, more languages, and emojis or symbols. Its one disadvantage is that each character needs more storage space.