Edexcel GCSE Computer Science (1CP2) Exam Questions

• B To reduce the time taken to transmit a file (1)
• The only correct answer is B. The correct answer is to reduce the time taken to transmit a file.
• A is not correct because compression reduces file size, which can reduce the number of packets sent
• C is not correct because lossy compression can reduce the quality of a file
• D is not correct because encryption, not compression, can make a file harder to open

Award one mark for each of:

• 5 × 1024^3 / 5 × 1024 × 1024 × 1024 / 5 × 2^30, for the number of bytes (1)
• A fully correct expression with × 8 to convert bytes to bits, in any order, e.g. 5 × 1024^3 × 8, 8 × 5 × 2^30 (1)

Accept 5 × 1 073 741 824 × 8.

Accept 5 × 2^33 or 42 949 672 960 as a fully correct expression (2 marks).

Do not accept 5 × 1000^3 × 8, which uses decimal multiples.

Do not accept ÷ 8, which converts bits to bytes.

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

• Lossy compression permanently removes/discards some of the data (1) whereas lossless compression keeps all of the original data so the file can be restored/rebuilt exactly (1)
• Lossy compression cannot reproduce/recreate the original file exactly (1) whereas lossless compression can decompress the file back to its original form (1)
• Lossy compression can make a file smaller than lossless compression (1) because more of the original data is removed/discarded (1)
• Lossy compression is used for images/sound/video (1) whereas lossless compression is used where all the original data must be kept, such as program files (1)

Allow one mark for a correct statement about one type of compression only, e.g. 'lossy compression permanently removes some data', with no comparison or development.

Do not accept 'lossy compression loses quality' on its own unless it states that data/information is removed or lost permanently.

Do not accept 'lossy is better' or 'lossless is safer' with no described difference.

Do not award a smaller file size on its own; it must be linked to data being removed or to no data being lost.

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

• The file size is reduced (1) so the documents take less time to transmit/send (1)
• The compressed files are smaller (1) so they are more likely to be within the email attachment size limit (1)
• Less data is sent (1) so less bandwidth/data allowance is used (1)
• Fewer packets are needed (1) so the documents are received more quickly (1)

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

Do not accept 'it saves storage space' on its own without linking to sending the documents.

Do not accept 'it makes the file smaller' as both the point and the reason.