O-LevelComputer ScienceData Representation2210/12 · May/June 2023 · Q310 Marks

When keys are pressed on a keyboard, the text is converted to binary to be processed by the computer.

(a)Describe how the text is converted to binary to be processed by the computer.[3]
(b)(i)State what effect this has on the file size.[1]
(b)(ii)Describe how lossless compression compresses the text file.[4]
(b)(iii)Give two reasons why the text file may have been compressed.[2]

Mark scheme

Marking points from the official mark scheme (May/June 2023). The mark or mark type is shown in brackets.

[1] A character set is used
[1] ... such as Unicode/ASCII
[1] Each character has a unique binary value
[1] It reduces the file size
[1] A compression algorithm is used
[1] ... such as RLE/run length encoding
[1] Repeating words/characters/phrases are identified // Patterns are identified
[1] ... and indexed
[1] ... with number of occurrences
[1] ... with their position
[1] To save storage space
[1] To make it quicker to transmit
[1] To make it small enough to attach to an email
[1] To reduce the bandwidth needed to transmit

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Topic: Data Representation, O-Level Computer Science (syllabus 2210). Structured question, 10 marks.
Source: O-Level Computer Science, May/June 2023 Paper 1 Variant 2, question 3.

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