Edexcel GCSE Computer Science (1CP2) Exam Questions

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 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

Fetching and decoding an instruction

• The register that holds the address of the next instruction (the program counter) contains the address of the instruction to be fetched.
• This address is sent to main memory (RAM) and the instruction is copied from main memory into a register inside the CPU.
• The program counter is updated so that it holds the address of the next instruction in the program.
• The control unit decodes the instruction that has been fetched, working out which operation is required and which data or registers are needed.
• The control unit sends control signals to coordinate the other components as the instruction is carried out.
• The control unit decides what happens next, for example after a comparison it decides whether the next instruction is the following one or a jump.

The arithmetic logic unit (ALU) executes an instruction

• The control unit directs the arithmetic logic unit (ALU) to carry out the operation.
• The ALU performs arithmetic operations such as addition, subtraction, multiplication and division, for example adding two values in a program written by the class.
• The ALU performs logical operations such as comparing two values to see if they are equal or whether one is greater than the other.
• The result of the operation carried out by the ALU is passed back and stored in a register.
• The ALU operates on data that has been fetched from main memory; it does not fetch the instruction and it does not decide which instruction is next.

Registers

• Registers are small, very fast memory locations inside the CPU.
• They hold the data, addresses and results that the CPU is working on during the cycle.
• Registers are used in every stage of the cycle, not only when the ALU produces a result.
• Because registers are inside the CPU they can be read and written much faster than main memory during 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)
• A Level 3 answer must link the roles of all three components to the fetch, decode and execute stages. An answer that links only one component to a stage, with the other points listed separately, is Level 1 (1–2 marks); an answer that links two of the components to stages is Level 2 (3–4 marks). A point repeated under more than one heading is credited once only.
• Accept 'the program counter', 'the address register' or 'a register holding the address of the next instruction' as the register that holds the address of the next instruction. Do not accept 'the control unit performs the calculations', 'the ALU controls the timing of the CPU' / 'the ALU sends the clock signal' or 'registers are in main memory (RAM)'.

Indicative content

What an embedded system is

• An embedded system is a computer system that forms part of a larger device, such as the fitness tracker.
• It performs a single, dedicated or specific task rather than being a general purpose computer.
• It is often built around a microcontroller, which contains the processor, RAM and ROM on a single chip.
• Its software is held in ROM so the tracker can run its program as soon as it is switched on.

Functions in the tracker

• Monitoring the heart rate using a sensor and processing the readings so that they can be displayed on the screen.
• Counting steps using an accelerometer and using the count to calculate the distance walked or the calories burned.
• Tracking sleep by monitoring the wearer's movement during the night.
• Controlling the touch screen so that the user can move between displays.
• Managing the battery, for example stopping the charging when the battery is full and saving power when the tracker is idle.
• Sending the collected data to a smartphone using Bluetooth so that it can be viewed in an app. Accept any other specific function of the fitness tracker that an embedded system could control.

Why an embedded system is suitable for this device

• It has low power consumption, so the battery lasts longer between charges, which matters for a device that is worn all day.
• It is small and light, so it can be fitted into a wristband.
• Its dedicated function means it does not need a full operating system, so it is reliable and does not need restarting.
• The program is small and stored in ROM, so the tracker needs only a small amount of memory.
• It can be optimised for its specific tasks, so it responds quickly to the readings from its sensors.
• The low cost per unit keeps the tracker affordable for the customer.

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 what an embedded system is, the functions it performs in the tracker and why it is suitable for the tracker.
• Do not award installing new software/apps, functions the tracker does not perform (such as playing music) or 'it is like a phone'.