CPU Performance
Understand CPU Performance for GCSE Computer Science with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA GCSE Computer Science (8525). CPU performance depends on clock speed, the number of cores and the amount of cache.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA specification. Every worksheet comes with a full mark scheme.
Topic overview
Three factors affect how quickly a CPU can process instructions, and each must be explained rather than just named.
Clock speed is the number of cycles the CPU performs each second, measured in hertz. A higher clock speed means more instructions processed per second. A 3 GHz processor performs three billion cycles each second.
The number of cores is how many independent processing units the CPU contains. Each core can process instructions simultaneously, so a quad-core processor can in principle handle four instructions at once — though only if the software is written to use multiple cores. Cache size matters because cache is far faster than main memory, so more cache means fewer slow trips to RAM.
Revision notes
Clock speed
The number of cycles performed each second, measured in hertz.
A 3 GHz processor performs three billion cycles per second. A higher clock speed means more instructions processed in a given time, assuming everything else is equal.
Number of cores
Each core is an independent processing unit that can execute instructions simultaneously.
A quad-core processor can in principle process four instructions at once. But the software must be written to use multiple cores — a program written for one core gains nothing from four.
Cache size
Cache is very fast memory inside the CPU holding frequently used data and instructions.
More cache means more can be held there, so the CPU makes fewer trips to the much slower main memory. This is why cache size affects performance even when clock speed is unchanged.
Key points
- Clock speed is cycles per second in hertz.
- Higher clock speed processes more instructions.
- Cores are independent processing units.
- More cores allow simultaneous processing.
- Software must be written to use multiple cores.
- More cache means fewer trips to main memory.
Worked examples
Example 1
Explain how increasing the number of cores can improve performance. [2 marks]
Working
Example 2
Explain why a larger cache improves CPU performance. [2 marks]
Working
Example 3
A processor has a clock speed of 3 GHz. State what this means. [2 marks]
Working
Common mistakes
Saying more cores always doubles speed.
Only if the software is written to use them.
Naming factors without explaining them.
Each needs its mechanism explained.
Confusing cache with RAM.
Cache is inside the CPU and much faster.
Giving clock speed in bytes.
It is measured in hertz.
Exam tips
- Explain the mechanism behind each factor.
- Mention the software condition for multiple cores.
- Use hertz for clock speed.
- Link cache size to avoiding slow memory access.
Key terms
- Clock speed
- Cycles performed per second, in hertz.
- Core
- An independent processing unit within a CPU.
- Cache
- Fast memory inside the CPU.
- Gigahertz
- One billion cycles per second.
Related topics
Written and reviewed against the current AQA specification. Spotted an error? Let us know.