The processor, also called CPU or central processing unit, is the brain of a computer. In PCs, it is built into a single chip – a small piece of silicon with a complex electrical circuit, called an integrated circuit – that executes instructions and coordinates the activities of all other units.

A generic CPU includes:

-          The control unit, which examines instructions from memory and execute them;

-          The arithmetic and logic unit (ALU), which performs arithmetic and logical operations;

-          The registers, high-speed units of memory used to store and control data.

The speed of processors is measured in gigahertz. Thus, a CPU running at 4 GHz can make about four thousand million calculations a second. An internal clock sends out signals at fixed intervals to measure and synchronize the flow of data.

A CPU can be 64-bit or 32-bit. This definition describes the size of data units handled by the CPU. The use of a 64-bit processor affects the size of buses and CPU registries. 64-bit systems can access more than 4 GB of addressable memory, while 32-bit systems cannot.

The CPU cache is a small and extremely fast memory used by the CPU. Frequently used data is stored in the CPU cache by the processor to minimize access time. Cache is just like RAM, only faster because it is built into the CPU itself. Both RAM and cache are holding areas for frequently used data. Without them, the CPU would have to keep on reading from the hard disk drive, which would take a lot more time. Basically, RAM minimises interaction with the hard disk, while cache minimises interaction with the RAM.