Cores, cache and clock speed Cambridge IGCSE Computer Science (9–1) revision
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In plain words
Three things decide how much work a CPU gets through in a second: how fast it ticks, how many processing units it has, and how much it can keep close at hand.
6 things to know
- The clock sends out a regular pulse that keeps everything in step. Clock speed is the number of fetch–decode–execute cycles each second, measured in hertz. 3 GHz is three billion a second.
- A faster clock means more instructions are processed each second. It also means more heat.
- A core is a processing unit within the CPU that can run its own fetch–decode–execute cycle. A dual-core CPU has two and a quad-core has four.
- More cores means more instructions can be processed at the same time.
- Cache is a small amount of very fast memory inside or close to the CPU. It holds the instructions and data that are used most often.
- A larger cache means the CPU has to wait for slower RAM less often.
Worked example
Two CPUs have the same clock speed. One has 2 cores and the other has 4. Which is likely to perform better, and why might the difference be less than double?
- The 4-core CPU can process four instructions at the same time, compared with two.
- So it is likely to get more done each second.
- But not all software is written to split its work across several cores, so the gain is often less than double.
Tips and tricks
- "Faster" on its own earns nothing. Say what happens: more instructions are processed each second, or at the same time.
- Cache is not RAM. It is smaller, faster, and inside or right beside the CPU.
It lands in your notebook with its questions as flashcards.
Cores, cache and clock speed: 5 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
What is clock speed measured in?
Cycles per second. Modern CPUs run at a few gigahertz.
What is a core?
More cores, more instructions at once.
What is stored in cache?
Keeping them close saves trips to RAM.
Why does a quad-core CPU usually perform better than a single-core CPU with the same clock speed?
Each core runs its own cycle.
What is a disadvantage of a very high clock speed?
Too much heat can damage the CPU, so it needs cooling.
Quiz
5 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
2 questions, 4 marks. Write your answers on paper, then check them.
Cores, cache and clock speed
Cambridge IGCSE Computer Science (9–1) 0984 · 4 marks · papermunch.org
Name ______________________________ Date ______________
Explain how increasing the clock speed can improve the performance of a CPU.[2]
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More fetch–decode–execute cycles are carried out each second, so more instructions are processed each second.
Explain how a larger cache can improve the performance of a CPU.[2]
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More of the frequently used instructions and data can be kept in the cache, which is faster to access than RAM, so the CPU spends less time waiting.
Answers: Cores, cache and clock speed
- 1. More fetch–decode–execute cycles are carried out each second, so more instructions are processed each second.
- 2. More of the frequently used instructions and data can be kept in the cache, which is faster to access than RAM, so the CPU spends less time waiting.