CPU performance

There are four key factors about CPU architecture that affect its performance:

  • cores
  • clock speed
  • cache size
  • processor type

Cores

A CPU can contain one or more processing units. Each unit is called a core. A core contains an ALU, control unit and registers. It is common for computers to have two (dual), four (quad) or even more cores. CPUs with multiple cores have more power to run multiple programs at the same time.

However, doubling the number of cores will not simply double a computer's speed. CPU cores have to communicate with each other through channels and this uses up some of the extra speed.

As the number of cores increases, the number of channels increases rapidly

Clock speed

The clock speed - also known as clock rate - indicates how fast the CPU can run. This is measured in megahertz (MHz) or gigahertz (gHz) and corresponds with how many instruction cycles the CPU can deal with in a second. A 2 gHz CPU performs two billion cycles a second. A faster CPU uses more energy and creates more heat.

A computer will normally have a maximum clock speed set by default, but it is possible to change this speed in the computer BIOS. Some people increase a CPU clock speed to try to make their computer run faster - this is called overclocking.

There are limits to how fast a CPU can run and its circuitry cannot always keep up with an overclocked speed. If the clock tells the CPU to execute instructions too quickly, the processing will not be completed before the next instruction is carried out. If the CPU cannot keep up with the pace of the clock, the data is corrupted. CPUs can also overheat if they are forced to work faster than they were designed to work.

CPU expert Steve Furber explains why modern CPUs have multiple cores