Edexcel GCSE Computer Science (1CP2) Exam Questions

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

• (Storage that is) non-volatile / keeps its data when the power is turned off (1)
• (Storage that is) used to store programs and data/files (for later use) (1)
• (Storage that is) not directly accessible by the CPU / not directly accessed by the CPU (1)

Allow both the non-volatile point and the stores programs and data point from one sentence if each idea is clearly stated, e.g. 'non-volatile storage that holds programs and data'.

Allow accessed via the CPU / must be copied into RAM before the CPU can use it for the third point.

Do not accept volatile / loses its data when the power is turned off.

Do not accept a description of primary storage, such as RAM or ROM.

Do not accept capacity.

Do not accept an example device on its own (e.g. hard disk drive).

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

• Decodes each (fetched) instruction (1) to work out which operation is needed / which components should carry it out (1)
• Coordinates/directs the other components (1) by sending control signals along the control bus (1)
• Fetches the next instruction (1) by sending its address to main memory along the address bus (1)
• Sends a read/write control signal to main memory (1) so that the instruction or data is transferred during the fetch/execute stage (1)

Do not accept answers about synchronising the CPU or timing the cycles (that is the role of the clock).

Do not accept answers about carrying out arithmetic or logical operations (that is the ALU).

Do not accept answers about holding data or the results of instructions (that is registers/main memory).

Do not accept generic answers that only say the CU controls the CPU or processes instructions, with no linked development.

Only award one mark for a response that only repeats that the CU sends control signals; the second mark needs a linked outcome such as coordination, a memory read/write, or fetching an instruction.

Do not accept 'during the decode stage' as the development for the decoding point, as it restates the question.

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

• RAM is volatile (memory) (1) because it needs a constant/continuous power supply to hold/store the data it contains (1)
• Data is held in RAM as electrical states/charges (1) so when the power supply is removed these states cannot be kept/refreshed and the data is lost (1)
• RAM is used as short-term storage for the data and instructions currently in use (1) because it can only hold them while the computer has power (1)

For both marks, the expansion must follow/associate with the statement and must link the loss of the data to the power supply being removed.

Accept 'RAM is volatile' on its own for the first mark; the second mark is only awarded for a linked reason about the power supply.

Do not accept 'RAM is temporary/short-term memory' or 'RAM is cleared when the computer is switched off' on its own for both marks, as neither gives a reason.

Do not accept answers that say the data is deleted/cleared/erased by the computer or the operating system, or that the data is saved/moved to secondary storage, without saying why the data cannot be kept (e.g. because RAM needs power/is volatile).

Indicative content

How RAM is used when editing video

• The editing software and the video project being worked on are loaded into RAM so that the CPU can access them quickly.
• RAM holds the frames, effects and timeline data that the CPU is processing as part of the fetch-decode-execute cycle.
• The CPU fetches the instructions and the video data it needs from RAM, which is much faster than fetching them from secondary storage.
• Having more RAM means that more of the 4K video project and its effects can be held in memory at the same time.
• RAM is also used by the operating system and any other open software, so not all of the RAM is available to the editing software.

Why too little RAM causes poor performance

• If there is not enough RAM, the operating system uses virtual memory on secondary storage for data that will not fit in RAM.
• Virtual memory is much slower than RAM, so the editor waits longer for 4K video to load and for effects to be applied.
• Data has to be swapped between RAM and virtual memory, which is extra work that slows the computer down.
• The editing software may freeze or close if it runs out of memory while working on the 4K video.
• Playback of the 4K video is not smooth because the frames cannot all be held in RAM ready for the CPU.

Why adding more RAM may not always improve performance

• If the computer already has enough RAM for the editing software, the extra RAM will not be used and performance will hardly change.
• The clock speed and the number of cores of the CPU decide how quickly instructions are processed, so a slow CPU will still limit how quickly the video is edited.
• A slow secondary storage drive will still limit how quickly the 4K video files can be loaded into RAM.
• Adding RAM only improves performance if a shortage of RAM was the reason for the computer being slow.

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 3 responses must explain how RAM is used when editing video and give a developed reason why adding more RAM may not always improve performance; responses that only explain how RAM is used, or only why too little RAM causes poor performance, are limited to Level 2.
• Accept 'paging' or 'swap file' as equivalent to virtual memory, but do not accept 'cache' or 'ROM'; do not credit statements that adding RAM increases the CPU clock speed or makes the CPU faster, or that 'RAM is volatile' explains poor performance, as these are not linked to the question asked.