IGCSE Computer Science Paper 1 Definitions Worksheet: 1.3 Data Storage and Compression and 2.1 Data Transmission Types and Methods (Modules 86–109)
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Key terms
Write what each term means, in your own words.
1
compression saves storage
2
compression saves bandwidth
3
transmission time
4
permanent loss
5
lossy image compression
6
lossy sound compression
7
RLE pixel row
8
RLE decode
9
lossy vs lossless
10
packet
Answer Key
IGCSE Computer Science Paper 1 · Modules 86–109 · Student wording will vary for definitions
1compression saves storage — Compressed files are smaller, so they take up less storage space. This means more photos or songs fit on a device, and less storage needs to be bought.
2compression saves bandwidth — A compressed file has fewer bits to send, so it uses less of the shared network bandwidth. This eases congestion and helps video and audio stream smoothly.
3transmission time — The time a file takes to upload, download or send. A smaller compressed file has a shorter transmission time, so downloads, email attachments and web pages are quicker.
4permanent loss — Data removed by lossy compression is gone for good, so the original quality cannot be restored. Keep the original file, as re-saving or compressing again only lowers quality further.
5lossy image compression — Reduces an image's resolution or colour depth to shrink the file. Detail is lost for good. Recalculate width x height x depth to see the saving.
6lossy sound compression — Lowering the sample rate or sample resolution of a sound so it needs fewer bits. The file gets smaller, but the lost sound detail can never be recovered.
7RLE pixel row — Run-length encoding of a pixel row stores each run of same-coloured pixels as a count then a colour code, in order along the row. E.g. WWWBB becomes 3W2B.
8RLE decode — Repeat each colour code count times along the row to rebuild the pixels, e.g. 3R2B gives RRRBB. Then check the row adds up to the image width.
9lossy vs lossless — Lossy makes smaller files but permanently removes data; lossless keeps all data so the original can be restored, but saves less space.
10packet — A small piece of a larger file. Data is split into numbered packets so they share the network and a lost packet can be resent instead of the whole file.