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Edexcel GCSE Computer Science (1CP2) Exam Questions

Build a practice paper from 693 exam-style questions, each with its mark scheme and example answers. Print it, or answer it on paper and then open the mark schemes. Or browse the questions by topic.

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3 questions · 5 marks

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1Multiple choice1 markStored Program Computers Swap Remove

Identify the bus that carries addresses in one direction only, from the CPU to main memory.

[1 mark]
  • AAddress bus
  • BControl bus
  • CData bus
  • DSystem bus
Mark scheme
  • 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
Example answers and how they were marked
Full marks1/1

A Address bus

Why: Correct option: the address bus carries addresses in one direction only, from the CPU to main memory (1).

No marks0/1

C Data bus

Why: The data bus carries data in both directions, so it is not the bus that carries addresses in one direction only from the CPU to main memory; no creditworthy point.

No marks0/1

B Control bus

Why: The control bus carries control signals in both directions, not addresses in one direction only; this is the common control/address bus confusion, so no mark.

2Short recall2 marksEmbedded Systems Swap Remove

An embedded system is a computer system built into another device to perform a specific function.

Give two examples of devices that contain an embedded system.

[2 marks]
Mark scheme

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).

Example answers and how they were marked
Full marks2/2

A microwave oven and a washing machine.

Why: Two creditworthy devices, a microwave oven (1) and a washing machine (1).

Some marks1/2

A dishwasher and a laptop computer.

Why: Dishwasher credited (1); laptop is a general purpose device, so not accepted.

No marks0/2

A desktop computer and a smartphone.

Why: Both are general purpose devices, so neither earns a mark.

3Explain2 marksFetch Decode Execute Cycle Swap Remove

The control unit is part of the CPU.

Explain the role of the control unit in the fetch-decode-execute cycle.

[2 marks]
Mark scheme

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

  • Decodes/interprets/translates the instruction (1) to work out what the instruction is/what operation is required (1)
  • Sends control signals to the other components (1) so that the correct component carries out the instruction (1), e.g. the ALU/main memory
  • Controls the fetch of the instruction from main memory (1) because the address of the next instruction is sent via the address bus (1)
  • Controls the fetch of the next instruction from main memory (1) by sending a control signal/read signal to main memory (1)

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

For the decode point, 'decodes the instruction' alone gains 1 mark; a second mark needs the purpose of decoding, i.e. working out what the instruction is/what operation is required.

Do not accept 'it controls the CPU' on its own, without naming a task in the cycle.

Do not accept 'it fetches the instruction from memory' on its own, as this describes the fetch step rather than the control unit's role; credit only if linked to controlling/signalling the fetch.

Do not accept carrying out arithmetic/logical operations, as these are carried out by the ALU, or holding the address of the next instruction, as this is the program counter.

Do not accept storing the instruction in a register (e.g. MAR/MDR), as this is not the role of the control unit.

Example answers and how they were marked
Full marks2/2

The control unit decodes each instruction, working out what it means, so that the CPU knows which component should carry it out.

Why: Linked point (1) and reason (1): decodes/interprets the instruction, and works out what it is/what operation is required.

Some marks1/2

It decodes the instruction that has been fetched from main memory.

Why: Decode point only (1); it does not explain the purpose of decoding, i.e. working out what the instruction is/what operation is required.

No marks0/2

It adds the two numbers together and stores the result in a register.

Why: Misconception: arithmetic is carried out by the ALU, which the mark scheme's Do not accept line covers.

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