Factors affecting CPU performance

Factor	How it affects CPU performance
Clock speed	As the clock speed is the number of instructions that can be performed per second a higher clock speed means that the computer can execute more instructions in the same time and will be faster. Modern computers tend to have clock speeds of 2 to 4 GHz meaning 2 to 4 billion instructions per second.
Number of cores	A processor can have multiple cores. There are dual core processors with 2 cores and quad cores with 4 and even some more powerful processors. Each core can process its own set of instructions. This can be useful if you have multiple applications open as they can run more efficiently on separate cores or if an application has been written to take advantage of multiple cores. An application that has not been written to take advantage of multiple cores will run fastest on the CPU with the highest clock speed regardless of the number of cores.
Cache size	The CPU has small but very fast storage locations that are often onboard the CPU itself. These are use to store frequently used data and instructions. If the computer looks for a piece of data or an instruction it first looks in the cache. If it finds it then it can be returned much quicker than by having to fetch it from RAM. If not it will place a copy in the cache for next time after fetching it from RAM. Therefore the more cache the faster processing will be. Level 1 cache is the smallest fastest and most expensive. L1 and L2 cache are uniue to each core while L3 cache is shared between all cores.

Comparing CPU perfomance

You are likely to be asked to compare a number of different CPUs like those below.

Computer A and C can both complete a total of 6GHz of instructions while Computer B can only complete 2.8GHz.
Computer A has more cache than Computer C so would be faster for programs that perform a lot of repetitive steps.
If a program was not written for multiple cores, it would run fastest on Computer C.

Knowledge check

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