Edexcel GCSE Computer Science (1CP2) Exam Questions

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

• Carries out arithmetic operations/calculations, such as addition or subtraction (1) so that the result can be stored in a register (1)
• Carries out logical operations, such as comparing two data items (1) to see which one is greater/larger (1)
• Compares two data items (1) to decide whether a condition is true / which path a program takes next (1)

Allow the result of an arithmetic or logical operation being held/stored in a register, but only where the operation is named.

Do not accept answers that say the ALU stores data or results without naming an operation (registers/main memory store data).

Do not accept answers about controlling components, decoding instructions or timing (that is the control unit or the clock).

Do not award credit for 'it processes data' on its own; an arithmetic or a logical operation must be named.

An example on its own, e.g. 'it adds two numbers', does not earn a second mark; the second mark needs a linked development.

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

• Decodes/interprets/translates the instruction (1) to work out what the instruction is/what operation is required (1)
• Sends control signals to the other components (1) so that the correct component carries out the instruction (1), e.g. the ALU/main memory
• Controls the fetch of the instruction from main memory (1) because the address of the next instruction is sent via the address bus (1)
• Controls the fetch of the next instruction from main memory (1) by sending a control signal/read signal to main memory (1)

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

For the decode point, 'decodes the instruction' alone gains 1 mark; a second mark needs the purpose of decoding, i.e. working out what the instruction is/what operation is required.

Do not accept 'it controls the CPU' on its own, without naming a task in the cycle.

Do not accept 'it fetches the instruction from memory' on its own, as this describes the fetch step rather than the control unit's role; credit only if linked to controlling/signalling the fetch.

Do not accept carrying out arithmetic/logical operations, as these are carried out by the ALU, or holding the address of the next instruction, as this is the program counter.

Do not accept storing the instruction in a register (e.g. MAR/MDR), as this is not the role of the control unit.

Indicative content

How data is stored on optical media

• Data is stored as pits and lands burnt or pressed into a spiral track on the disc.
• A laser beam is shone at the disc and the light that is reflected back is measured; pits and lands reflect the light differently.
• The differences in the reflected light are read as binary 1s and 0s.

Benefits of optical discs for selling films

• Optical discs are cheap to mass produce once the master disc has been pressed, so the studio can sell each film at a low price.
• A disc is small and light, so a customer can easily store it, carry it home or give it as a gift.
• A Blu-ray disc can hold a whole high-definition film (up to 50 GB), so a customer can watch the film without an internet connection.
• Artwork can be printed on the disc and its case, which helps the studio sell the film.

Drawbacks of optical discs for selling films

• A DVD holds only about 8.4 GB, so a high-definition film with extra features may not fit on one and the studio would need to sell it on a Blu-ray instead.
• Optical discs are easily scratched, which can cause read errors so the film will not play.
• Many modern devices, such as some laptops, no longer have a disc drive, so some customers would not be able to play the film.
• Discs can be affected by heat and sunlight, so they may deteriorate over time.

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)

Additional guidance

• Level 2 requires points to be linked or developed, for example a benefit or drawback explained in terms of the studio or its customers. An answer that only lists basic, independent points, with no linkage, is limited to Level 1.
• Level 3 requires all three areas and a judgement about whether the studio should keep selling films on optical discs. Do not credit magnetic storage or solid state storage as a description of how optical media stores data; credit these only where they are compared with optical media.