IGCSE Computer Science Paper 1 Definitions Worksheet: 1.2 Text, Sound and Images and 1.3 Data Storage and Compression (Modules 43–58)
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Key terms
Write what each term means, in your own words.
1
Unicode vs ASCII
2
analogue to digital
3
sample resolution
4
higher sample rate or resolution
5
colour depth
6
colours = 2^n
7
colour code table
8
higher resolution and colour depth
9
trade-off
10
nibble
Answer Key
IGCSE Computer Science Paper 1 · Modules 43–58 · Student wording will vary for definitions
1Unicode vs ASCII — Unicode supports far more characters than 8-bit ASCII but uses 16 or 32 bits per character, so the same text takes up more storage space.
2analogue to digital — A sound wave is analogue: its amplitude changes smoothly. A computer stores only separate binary numbers, so the wave a microphone captures must be converted into discrete digital values.
3sample resolution — The number of bits used to store each sample of a sound. More bits give more possible volume levels and a more accurate recording. 16 bits per sample is common.
4higher sample rate or resolution — Raising the sample rate or sample resolution records the sound more accurately, but it also makes the audio file bigger. Lowering either does the opposite: less accurate, smaller file.
5colour depth — The number of bits used to store the colour of each pixel. More bits per pixel means more possible colours, such as 1 bit for 2 colours or 24 bits for true colour.
6colours = 2^n — A colour depth of n bits gives 2^n different colours, so each extra bit doubles the number. For example, 2 bits give 4 colours and 8 bits give 256 colours.
7colour code table — A table giving each colour a binary code. Write each pixel's code row by row to encode an image; read the codes back to redraw it. 4 colours need 2 bits.
8higher resolution and colour depth — Raising either one improves image quality (sharper detail, smoother colours) but stores more bits, so the file size gets larger.
9trade-off — Balancing quality against file size: pick the lowest sample rate, resolution or colour depth that still looks or sounds good enough, so the file stays small enough to store or send.
10nibble — A nibble is a group of 4 bits, so half a byte. Two nibbles make 1 byte. One hexadecimal digit fits exactly in one nibble.