Edexcel GCSE Computer Science (1CP2) Exam Questions

Award one mark for any of the following:

• More files/data can be stored (in the same storage space) (1)
• The files take up less storage space (1)
• The backup is quicker/faster to complete (1)
• Less data needs to be transferred to the backup device (1)

Do not accept 'makes the files more secure' or 'encrypts the files'.

Award one mark for any of the following up to a maximum of two marks:

• A binary digit (1)
• Has the value 0 or 1 (1)
• The smallest unit of data storage (1)
• A single 0 or 1 (1)

Allow binary digit/binary place value for binary digit

Allow a single binary digit for a single 0 or 1

Do not accept a group of 8 bits/half a nibble of 4 bits, which describe a byte or a nibble

Do not accept a binary number/binary on its own

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.

Indicative content

How lossy compression makes the files smaller

• Some of the data in the file is permanently removed, so the file that is stored is smaller.
• The data that is removed is the data that a person is least likely to notice, such as sounds outside the range of human hearing or small differences in colour in a photograph.
• Removing data means a much higher compression ratio is possible than with lossless compression.

The effect on the photographs and audio

• The original file cannot be reproduced exactly when it is decompressed.
• Photographs may show artefacts, such as blocks or noise where there are contrasting colours, so they are lower quality.
• Some of the sound is lost, so parts of the audio guide may be less clear to listen to.
• If the company later wants to use the photographs at a larger size, it cannot recover the lost detail.

The benefits to the company and its visitors

• The smaller images load faster, so each page of the website appears more quickly for a visitor.
• The audio can be streamed, so a visitor can play the guide without waiting for the whole file to download.
• Less bandwidth is used by the web server, so it can cope with more visitors at the same time.
• Less storage space is needed on the server for the photographs and audio files.

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 the effect on the files and the benefits.

Do not accept the idea that lossy compression keeps all of the original data.