Files can be compressed before they are stored.
Define the term lossless compression.
Mark scheme
Award one mark for any of the following up to a maximum of two marks:
- Reduces/makes the size of a file smaller (1)
- No data is lost/removed (during compression) (1)
- The original file/data can be recreated/restored exactly (1)
Allow 'the compressed file takes up less storage space' for the first mark.
The second and third bullets are two ways of making the same point: award a maximum of one mark for them, so a response that says no data is lost and that the original file can be restored, but does not say the file is smaller, scores one mark.
Do not accept descriptions of lossy compression, e.g. 'it removes data that is not needed to make the file smaller'.
Ignore reference to download/transmission times, bandwidth and streaming, as these are benefits of compression and not part of the definition.
Example answers and how they were marked
Lossless compression reduces the size of a file without permanently removing any data, so the original file can be restored exactly.
Why: Reduces the size of a file (1) and no data is lost, so the original can be restored exactly (1); maximum of two marks reached.
It makes a file smaller so it downloads more quickly.
Why: Reduces the size of a file (1); the faster download is ignored as a benefit, not part of the definition.
It removes data that is not needed to make the file smaller.
Why: Describes lossy compression, which the do-not-accept line rules out, so the mention of making the file smaller is not credited.