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OCR H446 1.1.1 CPU performance: clock, cores and cache

Part 6 of 12 · H446 1.1.1 · Structure and function of the processor

OCR H446 1.1.1: CPU performance: clock, cores and cache. Students learn to explain how clock speed, cache and cores may affect performance through mechanisms, workload conditions and bottlenecks.

Students will:

  • explain factors affecting processor performance
  • connect a hardware change to its effect on a workload
  • qualify performance claims rather than assuming every change helps

Inside: 5 explanation cells, 1 multiple-choice question, 2 fill-in-the-blanks cells and 2 written answers. 18 marks, about 25 to 35 minutes.

Series: H446 1.1.1 · Structure and function of the processor, part 6 of 12.

Shared by Coding PathwayVerified teacher

  • 10 cells
  • About 30 minutes
  • CC BY-SA 4.0
  • Shared 31 Aug 2026
  • Updated 3 Sept 2026

Preview

The whole resource, exactly as a class sees it. Answers and marking are held back.

CPU performance: clock, cores and cache

A venue compares Central Processing Units (CPUs) for live ticket checks and overnight reports. No single headline number guarantees performance. For each factor, state what changes, explain how that can affect performance and identify an important limitation.

By the end, you will be able to

  • explain clock speed, number of cores and cache;
  • state when each benefit depends on the workload or another bottleneck;
  • reject ‘twice the specification means twice the speed’.

Explain each performance factor

Explain how a CPU feature affects performance and when the benefit may be limited feature changeperformance mechanismcondition or limitation higher clock speedmore cycles each secondinstructions may progressthrough stages soonerheat, power and otherbottlenecks still mattermore processor coresmore execution resourcesindependent work may runconcurrentlydepends on parallel work,dependencies and overheadlarger or faster cachemore nearby fast storagefewer accesses to slowermain memory may be neededdepends on workload,hit rate and cache latency State the change → explain how it helps → state when it may be limited
FactorHow it can helpWhen the benefit may be limited
Higher clock speedmore clock cycles per secondheat, power, architecture and work per cycle matter
More coresmore instruction streams/tasks may run concurrentlysoftware must expose parallel work; dependencies and overhead remain
More/faster cachemore needed data/instructions can be supplied without slower RAM accessbenefit depends on hit rate, workload and cache latency

Cache is small, fast storage close to the CPU. It is not another name for RAM.

Worked comparison

A clock speed of 3.2 GHz means approximately 3.2 billion clock cycles per second. It does not guarantee 3.2 billion completed instructions per second because an instruction can involve several cycles and processors can do different amounts of work per cycle.

Processor B also has four cores rather than two. A report generator can divide independent customer batches across cores, so throughput may rise. A single dependent validation chain cannot simply be split, and coordination adds overhead. Therefore ‘twice as many cores is twice as fast’ is unsupported.

Multiple choice1 mark

Which is the strongest performance statement?

  • AChanging cache always speeds up every program
  • BClock speed is the only performance factor
  • CMore cores can improve throughput when software has parallel work
  • DCache and RAM are the same component
Fill in the blanks3 marks
A higher clock speed means more gap 1 per second. A larger cache may reduce slower gap 2 accesses. More cores help when work can be processed gap 3.
  • clock cycles
  • RAM
  • concurrently
  • sequentially
Written answer6 marks

Explain how clock speed, number of cores and cache can affect CPU performance.

For each factor, include direction and mechanism. Add at least one condition or limitation.

Students type their answer here.

Written answer5 marks

A school runs one mostly sequential legacy application and repeatedly reads the same small data set. Compare a processor with more cores against one with a larger/faster cache.

Apply both mechanisms to the stated workload and recommend conditionally.

Students type their answer here.

Checkpoint

Complete each statement about how a CPU feature affects performance. There is no answer bank.

Fill in the blanks3 marks
Raising clock speed can increase power use and produce more checkpoint gap 1. Extra cores give limited benefit when a task has many checkpoint gap 2 between its steps. Cache benefit depends partly on the cache checkpoint gap 3, meaning how often required contents are found there.

Consolidate your understanding

Check that every performance claim includes a mechanism, a workload condition and an appropriate qualification.