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Cambridge IGCSE Computer Science · 0478
Topic 1: Data Representation — Part 2
Text, Sound & Images
Representing text
Computers use character sets to assign a unique binary code to every character.
- ASCII
- Uses 7 bits per character (128 characters). Limited to English and common symbols.
- Unicode
- Uses 8–48 bits per character. It supports a much wider range, including different languages and emojis, making computers more accessible worldwide.
Exam Traps
- ASCII uses 7 bits (128 characters) — do not write "8 bits" unless you mean extended ASCII outside the syllabus definition.
Sound is analogue (continuous) and must be sampled (snapshots of amplitude taken at regular intervals) to be stored as binary.
- Sample rate
- The number of samples taken per second.
- Sample resolution
- The number of bits used per sample.
Representing images
Digital images are made of a grid of tiny squares called pixels.
- Resolution
- The number of pixels in the image (Width × Height).
- Colour depth
- The number of bits assigned to each pixel to represent its colour.
Impact: Higher resolution and colour depth lead to higher image quality and larger file sizes.
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