Edexcel GCSE Computer Science (1CP2) Exam Questions

• B Data is permanently removed to reduce the file size (1)
• The only correct answer is B. The correct answer is data is permanently removed to reduce the file size.
• A is not correct because the data removed by a lossy algorithm is not restored after transmission
• C is not correct because that describes lossless compression, where the original file is rebuilt exactly
• D is not correct because dictionary encoding is a lossless method that records repeated patterns once

• D Time slice (1)
• The only correct answer is D. The correct answer is time slice.
• A is not correct because a process is a program that is being run
• B is not correct because round robin is a scheduling method that takes turns, not the period of CPU time itself
• C is not correct because a scheduler decides which process runs next

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

• Breaks messages/data into packets (1)
• Reassembles packets (at the destination) (1)
• Detects errors (1)
• Resends lost/missing packets/requests retransmission of lost packets (1)
• Creates/establishes a connection between two computers/hosts/sets up a connection before data is sent (1)

Do not accept routing packets or using IP addresses, which is the role of IP.

Do not accept encrypting data or providing security.

Do not accept vague answers such as 'transmits data' or 'sends data' without saying how TCP does this.

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.

Award up to two marks for a linked explanation such as:

• Only a limited number of different amplitude values can be stored (1) so each sample is rounded to the nearest available value and the digital wave does not match the analogue wave exactly (1)
• The wave is continuous but only a limited set of values can be represented (1) so amplitude detail/accuracy is lost (1)
• Quiet and loud parts of the sound may be stored as the same value (1) because there are too few values to tell them apart (1)
• The range of amplitudes that can be represented is limited (1) so the loudest/quietest parts of the sound cannot be stored accurately (1)

For both marks, the expansion must follow/associate with the statement.

Do not award marks for answers that say the sound cannot be stored or heard at all.

Do not award answers about the number of samples taken/sample rate, as the number of bits limits the amplitude values, not how often the wave is sampled.

Do not accept 'lower quality'/'less accurate'/'less detail' on its own without a link to the amplitude values that can be stored/the number of bit combinations.

Do not accept 'the file size is smaller' without a link to the accuracy or the range of values that can be stored.

Award up to two marks for a linked explanation such as:

• (Computers) are made of electronic components/switches/transistors that have two states, on/off (1) so binary's two values 0 and 1 can represent these states (1)
• Data stored as binary is more resistant to errors (1) because only two voltage levels/states need to be distinguished, so electrical noise/interference is less likely to be misread as a different value (1)
• Circuits that only need to distinguish two states are simpler/cheaper to manufacture (1) because each component only needs to hold one of two stable states (1)

For both marks, the expansion must follow/associate with the statement.

Do not accept 'computers only understand 0s and 1s' as a reason on its own without saying what the two states are or why binary matches them.

Do not accept 'computers are digital' or 'that is how computers work' without expansion.

Do not accept 'binary is easier to read/write' or 'binary is easier to understand' as a reason for using binary.

Do not award the same point twice if it is repeated in different words, e.g. two answers that both say circuits/components are on or off.

Award up to two marks for a linked explanation such as:

• Data can avoid a busy/congested link (1) because the router can choose another path (1)
• Data can still arrive if a link fails (1) because the router sends it another way (1)
• Data can take the shortest/fastest path (1) because the router compares the routes and chooses the one with the fewest hops/least traffic (1)

For both marks, the expansion must follow/associate with the statement.

Allow other valid benefits with a linked reason, e.g. traffic can be shared across routes/load balanced (1) because the router can send some packets by another path (1)

Do not accept 'the route is always the same' as this is not a benefit of choosing a route.

Do not accept 'routers are fast' or 'packets are sent faster' on its own: the reason must say how the route is chosen, e.g. avoiding congestion or using a routing table.