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

• C Data is restored to its original format (1)
• The only correct answer is C. The correct answer is data is restored to its original format.
• A is not correct because encryption changes data so that it cannot be read without a key; it does not restore the data
• B is not correct because permanently removing data to reduce the file size is lossy compression, not decompression
• D is not correct because storing data using fewer bits is compression, not decompression

Indicative content

Secondary storage

• Compressed lesson videos take up less space on the school's file server, so more recordings can be stored.
• The cloud backup service has a fixed amount of storage, so compressing the files means more of them can be backed up within it.
• Video files are very large, so without compression a much bigger hard disk would be needed to keep them all.

Sending data over a network

• A compressed video is split into fewer packets, so it takes less time for a student to download it at home.
• Less data is transferred, so the school's internet connection is not used up as quickly and other users are not slowed down.
• A smaller file can be sent as an email attachment, where there is a limit on the size of an attachment.
• Compressed video can be streamed, because the data can be sent as fast as it is played, which reduces buffering.

Drawbacks of compressing the files

• The file has to be compressed before it is stored and decompressed before it is played, which takes time and processing power.
• Lossy compression permanently removes data, so the quality of the lesson recording is reduced and it cannot be restored exactly.
• Lossless compression keeps all of the data, but it does not make the files as small as lossy compression does.

Levels

• Level 0 (0 marks): No rewardable content.
• Level 1 (1–2 marks): Basic, independent points are made, showing elements of understanding of key concepts/principles of computer science. (AO1) The discussion will contain basic information with little linkage between points made or application to the context. (AO2)
• Level 2 (3–4 marks): Demonstrates adequate understanding of key concepts/principles of computer science. (AO1) The discussion shows some linkages and lines of reasoning with some structure and application to the context. (AO2)
• Level 3 (5–6 marks): Demonstrates comprehensive understanding of key concepts/principles of computer science to support the discussion being presented. (AO1) The discussion is well developed, with sustained lines of reasoning that are coherent and logically structured, and which clearly apply to the context. (AO2)

Level 3 responses must cover both secondary storage and sending data over a network.

Do not accept the idea that compression makes the files more secure.