Edexcel GCSE Computer Science (1CP2) Exam Questions

• B To reduce the time taken to transmit a file (1)
• The only correct answer is B. The correct answer is to reduce the time taken to transmit a file.
• A is not correct because compression reduces file size, which can reduce the number of packets sent
• C is not correct because lossy compression can reduce the quality of a file
• D is not correct because encryption, not compression, can make a file harder to open

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:

• 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:

• Statements are written in English-like words/use maths symbols (1) so the programmer can understand more easily what each one does (1)
• The language uses meaningful names for variables/structured constructs such as loops (1) so the code is easier to read/follow (1)
• One statement translates into several machine code instructions (1) so there are fewer instructions to learn/understand for the same task (1)

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

Do not accept 'it is easier' / 'it is simpler' on its own, without saying what is easier/simpler.

Do not accept 'the computer understands it directly' / 'it does not need translating'.

Do not award answers about the program running faster or using less memory, as these are not about ease of learning.

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

• Terminators absorb the signal at the ends of the cable (1) so it is not reflected back along the bus (1)
• Terminators prevent signals reflecting/bouncing back (1) so the reflected signal does not corrupt data on the cable (1)
• Terminators absorb the signal (1) so it does not collide/interfere with data being sent by other devices (1)
• Terminators stop the signal reflecting back down the cable (1) so data can be transmitted and received without errors (1)

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

Allow 'interfere'/'corrupt' only where the answer says the reflected signal mixes with/collides with data on the cable.

Do not accept 'to stop the signal' on its own, as stopping the signal is not the same as stopping it reflecting back along the cable.

Do not accept 'to terminate the cable/network', 'to end the cable' or 'to stop the cable breaking'.

Do not award responses that only repeat the stem, e.g. 'because there is a terminator at each end'.

Indicative content

How each translator deals with a syntax error

• An interpreter stops as soon as it finds a syntax error and displays an error message.
• With an interpreter, the lines before the error have already been executed, so the student can see how far the program got before it stopped.
• A compiler reports errors at the end of translation, so the student gets a list of all the syntax errors in the program in one go.

How much of the program is translated at a time

• An interpreter translates one line at a time and executes each line immediately.
• A compiler translates the whole program in one go before any of it is run.
• A compiler produces object code, so after every change the whole program must be compiled again before the student can run it.
• An interpreter produces no object code, so the student does not have to wait for the whole program to be translated before it runs.

How this affects the student's testing

• An interpreter suits this student because the program can be run straight away after each small change.
• The interpreter stops at the first error found, so the student fixes that error and runs the program again, but may only find the next error on the next run.
• Reporting every error at the end of compilation means the student can fix several errors at once, but cannot run the program until the whole program compiles.
• The student should use an interpreter while testing, and compile the finished program once it works.

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 relate the way each translator works to the student's testing, not just describe the two translators.

Do not accept answers about run-time or logic errors where no comparison of the translators is made.