Edexcel GCSE Computer Science (1CP2) Exam Questions

• 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

• 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 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:

• Repeated words/patterns are found (1) and stored once in a dictionary with a code (1)
• Each repeated word/pattern is replaced by a shorter code (1) so fewer bits are needed to store the text (1)
• No data is removed (1) so the original text can be recreated exactly (1)
• The compressed file is smaller (1) but all the original characters can still be restored (1)

Do not accept answers that say data is permanently removed or quality is reduced.