Edexcel GCSE Computer Science (1CP2) Exam Questions

• A To store data and programs permanently (1)
• The only correct answer is A. The correct answer is to store data and programs permanently.
• B is not correct because storing the data and instructions currently in use is the role of primary storage/RAM, which is volatile, not the role of secondary storage
• C is not correct because calculations on data are carried out by the CPU, not by secondary storage
• D is not correct because secondary storage is not directly accessible by the CPU; data must first be copied into RAM

Award one mark for:

• Embedded (computer) system (1)

Allow embedded computer/embedded device.

Allow dedicated (computer) system.

Do not accept microcontroller/microprocessor controlled system.

Do not accept general purpose computer/PC/laptop.

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

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)'.