Edexcel GCSE Computer Science (1CP2) Exam Questions

Award one mark for any of the following:

• More files/data can be stored (in the same storage space) (1)
• The files take up less storage space (1)
• The backup is quicker/faster to complete (1)
• Less data needs to be transferred to the backup device (1)

Do not accept 'makes the files more secure' or 'encrypts the files'.

Award one mark for any of the following up to a maximum of two marks:

• Reduces the size of a file (1)
• Permanently removes/loses some data (1)
• The original file cannot be recreated/restored exactly (1)

Allow 'some data is deleted/discarded and cannot be recovered' for the second mark.

Do not award the first mark where the response also states that no data is lost.

Do not accept 'removes repeated data' (this describes lossless compression).

Award up to two marks for a linked explanation such as:

• No data/instructions are removed (1) so the program still works/runs correctly after decompression (1)
• The original file can be recreated exactly (1) so all the code/instructions are present when the program is run (1)
• Lossy compression would permanently remove some data (1) so the program would not execute correctly/could crash (1)
• Every instruction is needed for the program to run (1) so the code must not be changed/lost (1)

For both marks, the expansion must follow/associate with the statement.

Allow 'no data/instructions are removed/lost' on its own as the point mark (1); the second mark needs the consequence for the program, e.g. it still works/runs correctly, or all the instructions are present.

Award credit for a contrast with lossy compression only when the loss of data is linked to the program failing/not running correctly.

Do not accept 'lossless is better quality'/keeps the quality without saying that data/instructions are not lost.

Do not accept 'it makes the file smaller'/'downloads faster'/'transmits faster' as a reason for using lossless, as both types of compression reduce file size.

Award up to two marks for a linked explanation such as:

• Lossy compression permanently removes some data (1) whereas lossless compression does not remove any data (1)
• With lossy compression the original file cannot be recreated exactly (1) but with lossless compression it can (1)
• Lossy compression can produce a smaller file/a higher compression ratio (1) whereas lossless compression keeps all of the data so compresses less (1)

For both marks, the expansion must follow/associate with the statement.

Allow 'removes data' for 'permanently removes data'.

A correct statement about only one type of compression, with no contrast, earns one mark.

Do not accept a reversed statement such as 'lossless compression loses data and lossy compression does not'.

Do not accept 'lossy makes the file smaller' on its own, because lossless compression also reduces the file size; the answer must say that data is removed.

Do not accept 'lossy is worse quality' on its own without saying data is removed.