The central processing unit. This is the heart of your computer. It is an electronic device that contains millions and millions of tiny electronic components that have been designed to carry out basic arithmetic and control functions.
A CPU can add or subtract two numbers, move numbers from one memory location to another or control an external device. Each of the actions of a CPU is controlled by an instruction. These are the machine code instructions that are used by software developers to create software programs.
The specification of a CPU is defined in several ways: its speed (for example, 66MHz) roughly defines the number of instructions that it can process each second - 66 million in this case.
The power of a CPU is also defined in its data handling capabilities: a 32-bit CPU can add, subtract or manipulate numbers that are 32-bits wide. A 16-bit processor can only handle numbers that are 16-bits wide, so would take it twice as long to deal with a big number.
Lastly, there are two main families of CPU. The Intel-developed range of CPUs consists of the 80386, 80486 and Pentium. These are used in PCs and are backwards compatible. Other manufacturers, such as AMD, are licensed to manufacture these CPUs, and they work in exactly the same way.
The second main family is the 68000 and PowerPC range manufactured by Motorola. These processors are used in Apple Macintosh computers and are not directly compatible with the Intel range of machines. (See also Numeric Coprocessor.)
