Factors affecting CPU performance

We looked at a few of these factors already in GCSE. You can see that content here. At A level there are 6 factors we will look at that affect CPU performance:
1. Multiple cores
2. Cache memory
3. Clock speed
4. Word length
5. Address bus width
6. Data bus width

Multiple cores

Multiple cores means multiple processors that are able to process the same amount of data each. It is common to see dual ad quad cores or even more cores in modern processors. It is definitely useful if you are running several applications. Whether or not you will see a substantial boost in the speed of certain applications running on their own depends on whether they have been written to take advantage of multiple cores. It is more complex to design and write programs to take advantage of multiple cores.

Cache memory

Pronounced cash, cache memory is small amounts of superfast memory on or near the processor. There are often levels of cache in a computer with L1 cache the smallest and fastest and L3 the slowest and largest. All cache is faster to access than RAM.
Cache holds recently and frequently used instructions and data. Cache memory is most useful in improving speeds for things like image and sound intensive programs like games and video editors and for programs performing large amounts of complex mathematical analysis.

Clock speed

The clock speed is the number of times the clock switches between 0 and 1 each second. This is measured in hertz (Hz). Modern computers generally have a clock speed of between 2 and 4 GHz meaning over 2 billion clock switches each second. A processor performs operations on the uptick of the clock. Each processor in a multi-core processor can perform the same number of operations so a 2GHz quad core can in effect perform 8 billion instructions per second.

Word length

Word length is the number of bits that are handled at one time by a processor. The higher the word length the faster the processor. Most modern computers use a computer word of 32 or 64 bits.

Address bus width

The width of the address bus determines the number of memory addresses that can be directly accessed. If you have an 8-bit address bus you can reference 256 addresses. To be able to have up to 216 or 65536 addresses the address would have to be sent in 2 parts slowing down the operation of the processor.

Data bus width

The width of the data bus determines the amount of data that can be transferred at one time. In most computers the data bus is the same width as the computer word. If a processor had a 64-bit computer word but only a 32 bit data bus then it would take two trips for each instruction or piece of data.

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