Edexcel GCSE Computer Science (1CP2) Exam Questions

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

• Program instructions are stored in main memory/RAM (1)
• The data used by the program is stored in main memory/RAM (1)
• The CPU fetches/reads instructions from main memory to execute them (1)
• The program can be run without the instructions being input again (1)

Allow 'the program is stored in memory' for one mark.

Do not accept answers about programs being stored on secondary storage, such as a hard disk or USB memory stick.

Do not accept answers that only describe the von Neumann architecture (e.g. having a CPU and memory) without stating that instructions are stored in main memory.

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 description such as:

• Data is stored on (flash) memory chips/cells (1) as a pattern of electrical charges (1)
• A current/voltage forces electrons through a barrier (1) so that they are trapped (or not trapped) to hold/represent a value (1)
• Cells with a trapped charge and cells with no trapped charge (1) represent 1s and 0s/binary (1)
• The trapped charge remains when the power is turned off (1) so the data is not lost/it is non-volatile (1)

Do not accept responses that describe magnetic storage, e.g. magnetised platters, spinning disks or read/write heads, or optical storage, e.g. lasers, pits and lands.

Do not award a mark for 'it is solid state' or 'it has no moving parts' without a description of how the data is stored.

Do not award a mark for restating the stem, e.g. 'a laptop uses an SSD' or 'an SSD uses flash memory'.

'Data is stored as electrical charges' on its own, with no reference to memory chips/cells or to how the charge is held, earns a maximum of one mark (1).

A response that only describes electrons being trapped, with no link to how the value/data is represented, earns one mark (1). The second mark needs a link such as trapped and not trapped charge representing 1s and 0s, or the trapped charge being kept so the data is not lost.

Indicative content

the role of RAM in the stored program concept

• In the von Neumann stored program concept, a program's instructions and the data it uses are held together in main memory.
• RAM holds the instructions and data of the program that the CPU is currently processing.
• The CPU fetches each instruction from RAM during the fetch-decode-execute cycle, so a program must be in RAM before it can be run.
• RAM is directly accessible by the CPU, so instructions can be fetched quickly enough for the CPU to keep working.

what happens to a program when it is opened

• When a program is opened, a copy of its instructions and data is transferred from secondary storage, such as the hard drive, into RAM.
• The operating system loads the program into RAM so that the CPU can start fetching and executing its instructions.
• When the program is closed, it is removed from RAM, and the space it used is free for another program.
• If a computer does not have enough RAM, the program may not open, or another open program has to be closed first.

why the CPU cannot execute a program directly from secondary storage

• Secondary storage, such as a hard disk drive, is much slower to access than RAM.
• The CPU can process instructions much faster than secondary storage can supply them, so the CPU would have to wait and would not be working at full speed.
• RAM is fast electronic memory with no moving parts, so data can be read from it in a fraction of the time taken by a magnetic hard disk drive.
• Running the school's programs directly from secondary storage would make the computers in the IT room very slow to use.

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 cover both the role of RAM in the stored program concept and the speed difference between RAM and secondary storage, with a reason such as the CPU having to wait for instructions.
• Answers that make only basic, independent points, such as what RAM is, that a program is copied into RAM when it is opened, or that RAM is faster than a hard drive, without linking them to explain why the CPU would have to wait for instructions, are limited to Level 1.
• Do not accept statements that RAM is permanent storage, that RAM replaces secondary storage, or that secondary storage is read-only.