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1.1.2CPU performance

OCR GCSE Computer Science (J277) · Computer systems (Paper 1) › Systems architecture

Practise CPU performance. 12 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.

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A CPU has a clock speed of 3.2 GHz. State how many cycles it can carry out each second.
3,200,000,000 (3.2 billion)

Sample questions

Written for this site in the style of OCR exam questions. They are not taken from real past papers.

Question 1Easy3 marks
(a) State what is meant by the clock speed of a CPU.[1]
(b) A CPU has a clock speed of 3.2 GHz. State how many cycles it can carry out each second.[1]
(c) Which one of the following would improve the performance of a CPU?
Tick (✓) one box.[1]
  • Lowering the clock speed
  • Reducing the size of the cache
  • Increasing the number of cores
  • Removing the accumulator
Show the answer and mark scheme
(a)
  • the number of (fetch–execute) cycles the CPU can carry out per second
(b) Answer: 3,200,000,000 (3.2 billion)
  • 3.2 billion / 3,200,000,000
(c) Answer: Increasing the number of cores
Question 2Medium4 marks
(a) Explain how increasing the number of cores can improve the performance of a computer.[2]
(b) Explain why doubling the number of cores does not always double the performance.[2]
Show the answer and mark scheme
(a)
  • each core is a separate processing unit that can fetch and execute instructions independently
  • so more instructions can be processed at the same time / tasks can be run in parallel
(b)
  • some programs are not written to use more than one core
  • some tasks cannot be split up because each step depends on the result of the one before
  • the cores have to communicate / coordinate, which takes time
  • other components may slow the system down, e.g. waiting for RAM
Question 3Hard5 marks
Some users increase the clock speed of their CPU above the manufacturer's setting. This is called overclocking.
(a) Explain one benefit and two possible problems of overclocking a CPU.[3]
(b) Explain why a CPU with a higher clock speed may not always run a program faster than a CPU with a lower clock speed.[2]
Show the answer and mark scheme
(a)
  • benefit: more cycles per second, so instructions / programs are processed faster
  • problem: the CPU produces more heat / needs better cooling
  • second problem: the computer may become unstable and crash / the CPU may be damaged or its lifespan reduced / uses more power
(b)
  • the slower CPU may have more cores that the program can use
  • the slower CPU may have a larger cache, so it waits for RAM less often
  • the program may be slowed by other components, e.g. waiting for data from RAM or secondary storage

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