Edexcel GCSE Computer Science (1CP2) Exam Questions

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

• Microwave (oven) (1)
• Washing machine (1)
• Dishwasher (1)
• Digital camera (1)
• Satellite navigation/satnav system (1)
• Traffic light(s) (1)
• Central heating controller/thermostat (1)
• Digital watch/fitness tracker (1)
• Vending machine (1)
• Car (as it contains embedded systems) (1)

Allow any other device that contains an embedded system.

Do not accept general purpose devices such as a laptop, desktop computer, tablet or smartphone (these can run many different programs).

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:

• The read/write head moves over the surface of the platter (1) and detects whether each area of the disk is magnetised (1)
• The platter spins/rotates (1) so the read/write head can pass over the whole surface/tracks of the disk (1)
• The pattern of magnetised and non-magnetised areas detected by the read/write head (1) is read as binary 1s and 0s (1)
• The drive head detects the direction of magnetisation of each area (1) so the data can be read as binary (1)

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

Allow one mark for stating that data is read magnetically / that the read/write head detects the magnetisation of the disk without a linked reason.

Do not accept answers that describe how data is written to the disk, such as the head magnetising the platter, rather than how it is read.

Do not accept 'a laser reads the pits and lands' - this describes optical storage, not magnetic storage.

Indicative content

Stored program concept

• The stored program concept means that the program instructions and the data the program is using are both held in the same main memory (RAM).
• The CPU fetches an instruction from main memory, the control unit decodes it and the instruction is executed, and this is repeated in the fetch-decode-execute cycle.
• The program is stored as a set of binary instructions, so a different program can be run on the college's new computers by loading different instructions into RAM rather than by changing any hardware.
• Instructions are usually carried out one at a time, in the order in which they are stored, which is suitable for the computers in the IT suite that each run one piece of software at a time.

Main memory (RAM)

• Main memory (RAM) holds the instructions and the data that the CPU is currently using.
• RAM is directly accessible by the CPU, so the required instruction or item of data can be fetched quickly during the fetch stage of the cycle.
• RAM can be read from and written to while a program is running, so the results produced by the students' work can be stored back into memory.
• RAM is volatile, so its contents are lost when the power is turned off, and the college's computers will have empty RAM each time they are started.

CPU components

• The control unit decodes each instruction and coordinates the timing and control of the other parts of the CPU, so it directs the fetch-decode-execute cycle.
• The arithmetic logic unit (ALU) carries out arithmetic operations and logical comparisons on the data, for example working out a student's total mark in a spreadsheet.
• Registers are small, fast storage locations inside the CPU that hold the address of the next instruction, the instruction being decoded and the data being worked on.
• The clock sends a regular signal that synchronises the actions of the CPU, so each step of the cycle is carried out in time with the clock.

Buses

• The address bus is one way, from the CPU to main memory, and carries the address of the memory location that the CPU wants to read from or write to.
• The data bus carries the instruction or the data between the CPU and main memory, so it is used to bring an instruction to the CPU in the fetch stage.
• The control bus carries control signals such as read and write, so the CPU can tell main memory whether it is reading an instruction or writing data.

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 the role of main memory (RAM) and the role of the CPU components or the buses during the fetch-decode-execute cycle, as well as the stored program concept.
• Do not accept RAM described as being inside the CPU, or as non-volatile, or any point about how clock speed affects performance, because the question excludes it.