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:

• It controls the motors/rotors (1) so that the drone can take off, hover, turn and land (1)
• It keeps the drone stable/level automatically (1) by taking readings from a sensor (accelerometer/gyroscope/GPS) (1)
• It receives signals from the remote control (1) and changes the speed of the motors to steer the drone (1)
• It monitors the battery level (1) and brings the drone back to the ground before the battery runs out (1)

The development must relate to the function given in the point.

Accept a named function that the embedded system controls, e.g. 'it keeps the drone level', as the first mark (1).

Award the second mark only when the development gives a specific outcome or detail of that function, e.g. 'so that the drone can take off, hover, turn and land' or 'by changing the motor speeds to keep it level'.

Do not award the second mark for a generic outcome such as 'so it works', 'so it can fly' or 'so the drone moves'.

A bare 'it controls the motors so it can fly' therefore earns the first mark only.

Allow any other specific function of a drone that is carried out by the embedded system.

Do not accept 'it flies the drone' / 'it is the drone's brain' / 'it makes the drone work' without a named function being controlled.

Do not accept answers that describe the user or the remote control flying the drone with no function carried out by the embedded system.

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:

• Fewer samples are taken every second (1) so less detail of the sound wave is captured (1)
• Fewer samples are taken every second (1) so the file is smaller/uses less storage space (1)
• The wave is measured less often (1) so parts/changes in the wave between samples are missed (1)

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

The 'fewer samples are taken/measured less often' point can only be credited once; the second mark is for a valid expansion linked to it.

Do not accept restating the question, e.g. 'the time between measurements is longer' or 'the sample interval is longer', as either the point or the expansion.

Do not accept 'the sample rate is lower' as the expansion, as this says the same thing as a longer sample interval.

Do not accept 'the sound is lower quality/less accurate' on its own without saying what is lost, e.g. less detail of the wave captured/parts of the wave missed.

Do not accept answers about using fewer bits per sample or about compression, as these do not follow from the sample interval.

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

• The programmer can control/manipulate the hardware directly (1) because low-level instructions can access registers/memory addresses/hardware features (1)
• The code can be made to work efficiently with a specific device (1) because low-level languages are processor/chipset specific, so the instructions match that hardware (1)
• The code produced is fast to execute (1) because it is optimised for the specific processor/uses few instructions (1)
• The code produced is small (1) so it fits in the limited memory/ROM available in the device (1)

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

Fast execution and small code size are typical advantages of low-level languages; award them only where the linked reason relates to the device.

Do not accept 'it is easier to write/learn/understand' or 'it is faster to write' as a point or as the expansion, because low-level languages are not easier for these.

Do not accept 'it is close to the hardware' or 'it works with hardware' without expansion of what that allows the program to do.

Do not accept 'because it is low-level' as the expansion; the answer must say what the language/hardware allows.

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.