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Edexcel GCSE Computer Science (1CP2) Exam Questions

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4 questions · 11 marks

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1Multiple choice1 markStored Program Computers Swap Remove

Identify the function of the control unit in the fetch-decode-execute cycle.

[1 mark]
  • ADecodes instructions
  • BPerforms arithmetic operations
  • CStores data and instructions
  • DTemporarily stores data being processed
Mark scheme
  • A Decodes instructions (1)
  • The only correct answer is A. The correct answer is Decodes instructions.
  • B is not correct because the arithmetic logic unit performs arithmetic operations
  • C is not correct because main memory stores data and instructions
  • D is not correct because registers temporarily store data being processed
Example answers and how they were marked
Full marks1/1

A Decodes instructions

Why: Correct option: the control unit decodes instructions during the fetch-decode-execute cycle (1).

No marks0/1

C Stores data and instructions

Why: Main memory stores data and instructions, not the control unit; this is a common distractor, so no mark.

No marks0/1

B Performs arithmetic operations

Why: Arithmetic operations are performed by the ALU, not the control unit; a common confusion between CPU components, so no mark.

2Explain2 marksPrimary Memory Swap Remove

RAM is used to store data while a computer is running.

Explain one reason why the data in RAM is lost when a computer is switched off.

[2 marks]
Mark scheme

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).

Example answers and how they were marked
Full marks2/2

RAM is volatile memory, which means it needs a constant power supply to keep the data it is holding. When the power is switched off, the data is lost.

Why: Linked point (1) for 'RAM is volatile memory' and reason (1) for needing a constant power supply to hold the data.

Some marks1/2

The data in RAM is lost because RAM is volatile memory.

Why: Point (1) for 'RAM is volatile' but no linked reason about the power supply, and the mark scheme states that 'RAM is volatile' alone earns only the first mark.

No marks0/2

The data is deleted from RAM by the operating system when the computer is shut down so that the memory is free for next time.

Why: No creditworthy point: the answer says the data is deleted without saying why it cannot be kept, which the mark scheme's 'Do not accept' line rules out.

3Explain2 marksPrimary Memory Swap Remove

A technician increases the amount of RAM in a laptop from 8 GiB to 16 GiB.

Explain one benefit of increasing the amount of RAM in a computer.

[2 marks]
Mark scheme

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

  • More applications/programs can be open/run at the same time (1) because more instructions and data can be held in main memory at once (1)
  • Programs run faster (1) because the CPU does not have to wait for instructions/data to be read/transferred from slower secondary storage (1)
  • The CPU waits/idles for less time (1) because instructions and data can be transferred to the CPU more quickly from RAM (1)

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

Do not accept 'more files/photos/documents can be stored' or 'the computer has more storage' - this is a benefit of secondary storage, not RAM.

Do not accept 'the CPU becomes faster' or 'the clock speed increases'.

Example answers and how they were marked
Full marks2/2

More programs can be open at the same time because more instructions and data can be held in main memory at once.

Why: Linked point (1) for more programs running at the same time and reason (1) for more instructions and data being held in main memory at once.

Some marks1/2

Programs will run faster.

Why: Point (1) only; no linked reason such as the CPU not having to wait for data from slower secondary storage.

No marks0/2

There will be more space to save files and documents on the laptop.

Why: Misconception: the benefit given is a benefit of secondary storage, which the mark scheme's 'Do not accept' line rules out.

4Discuss6 marksFetch Decode Execute Cycle Swap Remove

A small robotics company is designing a new robot. The robot's computer uses von Neumann architecture. The engineers are explaining how programs are stored and run.

Discuss how the von Neumann stored program concept and main memory (RAM) are used during the fetch-decode-execute cycle.

Your answer should include:

  • what is meant by the stored program concept
  • the role of RAM in the cycle
  • why the stored program concept is useful.
[6 marks]
Mark scheme

Indicative content

Stored program concept

  • Instructions and data are stored together in the same main memory (RAM).
  • Instructions are fetched one at a time from memory and executed in sequence.
  • The program can be changed by loading different instructions into RAM.
  • The CPU can only execute instructions that are in main memory.

Role of RAM

  • RAM holds the program instructions and the data being used.
  • The address of the next instruction is held in the program counter (PC).
  • The instruction is fetched from RAM using the address bus.
  • The data bus carries the instruction from RAM to the CPU.
  • RAM is volatile, so programs are lost when power is off.
  • RAM is directly accessible by the CPU, unlike secondary storage.

Benefits

  • The same hardware can run many different programs.
  • Programs can be loaded and changed quickly.
  • No need to rewire the computer for a new task.
  • Makes general-purpose computers possible.

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)
Example answers and how they were marked
Full marks6/6

The von Neumann stored program concept means that both the program instructions and the data are stored together in the same main memory, RAM. During the fetch-decode-execute cycle, the CPU fetches an instruction from RAM, decodes it in the control unit, and then executes it. The program counter holds the address of the next instruction, and this address is sent along the address bus to RAM. RAM then returns the instruction along the data bus to the CPU. RAM is volatile, so it only holds the program while the robot is powered on. The stored program concept is useful because the robot's computer can run different programs without changing any hardware; new instructions can simply be loaded into RAM. This makes the computer general-purpose and flexible.

Why: Comprehensive understanding: defines stored program concept, explains RAM role with PC, address bus and data bus, applies to robot, and gives benefits. Sustained lines of reasoning. Level 3.

Some marks3/6

The stored program concept is when instructions and data are stored in RAM. The CPU fetches instructions from RAM. The program counter keeps the address of the next instruction. RAM holds the program. The benefit is that you can change the program without rewiring the computer.

Why: Adequate understanding: correct basic points about stored program concept and RAM, with some linkage, but little development or application to the robot's fetch-decode-execute cycle. Level 2.

Some marks1/6

The von Neumann stored program concept is that the CPU uses RAM to store the program. The fetch-decode-execute cycle fetches, decodes and executes. RAM is random access memory. The benefit is that it is fast.

Why: Basic independent points only; no real linkage or application to the robot. Level 1.

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