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 8192 (1)
• The only correct answer is C. The correct answer is 8192.
• A is not correct because 1024 is the number of bytes in a kibibyte
• B is not correct because 8000 is the number of bits in 1000 bytes
• D is not correct because 8 388 608 is the number of bits in a mebibyte

Award one mark for:

• 2048 (1)
• 2 × 1024 (1)
• 2^11 (1)

Allow 2048 bytes.

Do not accept 2000, which is the number of bytes in two decimal kilobytes.

Do not accept 1024, which is the number of bytes in one kibibyte.

Do not accept 16, which is the number of bits in two bytes.

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:

• Makes each file smaller (1) so less secondary storage is needed for the videos (1)
• Uses less bandwidth (1) so the video streams without buffering (1)
• Reduces the amount of data sent (1) so users use less of their data allowance (1)
• Can be streamed (1) because the data can be sent as fast as the user watches it (1)

Award one mark for a valid point on its own; the second mark is only awarded when the development is linked to that point.

Do not award a second mark for a development that repeats the point made.

Allow "takes less time to transmit/upload/download" as the development for a smaller file.

Do not accept responses that say compression saves memory/RAM (the videos are stored in secondary storage).

Do not accept compression makes the video more secure or improves its quality.

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.