The CPU is the 'brain' of the computer.
The Central Processing Unit (CPU) or the processor is the portion of a computer system that carries out the instructions of a computer program, and is the primary element carrying out the computer's functions. The fundamental operation of most CPUs, regardless of the physical form they take, is to execute a sequence of stored instructions called a program. The program is represented by a series of numbers that are kept in some kind of computer memory. There are four steps that nearly all CPUs use in their operation: fetch, decode, execute, and writeback.

There are two makes of computer processors used in digital imaging Personal Computers. About 80% of computers run Intel chips and AMD who account for the bulk of the remaining 20%. Apple make approx 6% of the worlds PCs and also use Intel processors.

In the past, the best way for computer chip makers to improve performance was to turn up the clock speed on the processor. But that generates more heat and consumes more power, which is bad for computers, especially notebooks. So instead the industry has moved to chips with multiple processor cores, which can provide more performance while consuming less power. This means that 2 or more processors are housed within a single chip, effectively multiplying the number of processes that can be carried out simultainiously. Both the clock speed of the processor and the number of cores (processors) will play a part in how well or quickly the processor and hence computer performs.