Edexcel GCSE Computer Science (1CP2) Exam Questions

• A They are lost (1)
• The only correct answer is A. The correct answer is They are lost
• B is not correct because RAM is volatile and its contents are lost when the power is switched off, so they are not stored permanently
• C is not correct because RAM is volatile and its contents are lost when the power is switched off, so they are not saved to secondary storage
• D is not correct because ROM is read-only memory that holds the start-up instructions, so the contents of RAM are not written to it

Award one mark for:

• Laser (1)

Allow laser beam

Do not accept read/write head

Do not accept pits

Do not accept lands

Do not accept reflective surface

Do not accept magnet/magnetic

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

• (The ECU) is more reliable/less likely to crash (1) because it only runs the one program/has a single purpose (1)
• (The ECU) cannot be affected by other software/viruses (1) because it cannot run other software/it can only run the program it was made for (1)
• (The ECU) is cheaper (1) because it has limited processing resources/less memory/simple components (1)
• (The ECU) uses less power (1) because it has limited processing resources/a simpler processor (1)
• (The ECU) is smaller (1) because it has fewer components/less memory than a general purpose computer (1)

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

A suitable benefit stated on its own earns one mark.

Do not accept a description or a location given as the reason, e.g. 'because it is part of the car', 'because it is inside the engine', 'because it is embedded'.

Do not accept a description of an embedded system on its own as the benefit, e.g. 'it does one specific job' or 'it is part of the car'.

Do not accept 'it is faster'/'it has a more powerful processor' as embedded systems have limited processing resources.

Indicative content

The role of the CPU and registers

• The control unit decodes the instruction fetched from main memory and controls the other components during the cycle.
• The ALU carries out arithmetic and logical operations during the execute stage, such as adding two values held in registers.
• Registers hold the data, addresses and results that the CPU is working on during the cycle.
• The program counter holds the address of the next instruction to be fetched, so it is incremented after each fetch.
• The memory address register holds the address of the memory location that is about to be read or written.
• The memory data register holds the instruction or data that has been fetched from or is being written to main memory.

The role of the address bus, data bus and control bus

• The address bus carries the address of the memory location that the CPU needs to access from the CPU to main memory.
• The address bus is one-way, so addresses are only sent from the CPU to main memory.
• The data bus carries instructions and data between the CPU and main memory, so it is bi-directional.
• The width of the data bus affects how many bits can be transferred at one time.
• The control bus carries control signals such as read and write signals, so main memory knows whether the CPU wants to read an instruction or write data.
• The control bus carries signals from the control unit to coordinate the components during the fetch-decode-execute cycle.

The role of the clock

• The clock sends regular pulses that synchronise the actions of the CPU and main memory.
• Each clock pulse triggers the next step of the fetch-decode-execute cycle, so the stages happen in the correct order.
• The clock provides a regular timing signal so that the fetch-decode-execute cycle repeats at a steady rate.
• The clock is separate from the control bus; the control bus carries control signals, while the clock provides timing pulses.
• Do not credit the address bus storing addresses, the data bus storing data, or the control bus controlling the computer without naming a control signal; do not credit clock speed affecting performance as a role in the cycle.
• Level 3 responses must cover all three bullets and link them to the fetch-decode-execute cycle; Level 2 answers may identify roles but link them only partly to the cycle.

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)