2. Clock speed

The clock is a quartz crystal on the CPU chip that sends out regular electrical pulses. The CPU uses these pulses to keep time, fetching a new instruction with every tick of the clock.

Every CPU has its own clock, and these clocks can tick at different rates. The faster the clock ticks, the more instructions are carried out per second. For example, a computer which has a 3 GHz CPU can process 3 billion instructions per second.

So a simple way of improving CPU performance is to increase the clock speed. For example, by increasing the clock speed from 3 GHz to 4 GHz would enable an additional 1 billion instructions to be processed per second.

However, there are drawbacks to increasing the clock speed above the manufacturer's specifications. Every time the clock ticks and the CPU processes an instruction, a small amount of power is used. This generates heat. With billions of ticks per second, the CPU can rapidly build up heat even to the point of melting the components!

Most computer manufacturers put in safeguards that will shut down the CPU (and the computer with it) when the temperature gets too high.

People who want to get the highest possible performance out of their CPUs by increasing the clock speed (overclocking) have to install expensive specialist cooling systems. Complicated heat sinks, water pipes, or even liquid nitrogen cooling can all be bought and installed for the right price.