Edexcel GCSE Computer Science (1CP2) Exam Questions

• A Address bus (1)
• The only correct answer is A. The correct answer is address bus. Do not accept 'address' on its own.
• B is not correct because the control bus carries control signals in both directions between the CPU and other components
• C is not correct because the data bus carries data in both directions between the CPU and main memory
• D is not correct because the system bus is the collection of all three buses

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.

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

• A read/write head moves over the surface of the disk (1) to read/write data by detecting or changing the magnetic alignment of areas of the surface (1)
• The head magnetises areas of the disk surface in different directions (1) so each area represents a binary 1 or 0 (1)
• Data is stored on concentric circles called tracks (1) which are divided into sectors (1)

Allow one mark for tracks/concentric circles on their own.

For the second mark in the first two bullets, the response must refer to the magnetic alignment/charge being detected or changed, not just that the head reads/writes data.

Do not award a mark for 'it is magnetic' or 'it stores data in binary' with no description of how the data is stored.

Do not accept descriptions of optical storage (e.g. a laser, pits and lands) or solid state storage (e.g. electric charges in chips).

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.