1.2.1.1 Processor

This is a single ``chip'' or IC (integrated circuit) in most computers. Some high-end computers do have multiple processor ICs. Examples of a processor includes Intel Pentium 4 and AMD Athlon.

The term CPU (central processing unit) is a bit outdated in PCs. This is because processor ICs include many components that, traditionally speaking, do not belong in a CPU. Such components include DMA controllers, interrupt controllers, timers and etc.

The capability of a processor is usually measured in two orthogonal properties. The first one is the ``clock rate'', and it is measured in GHz (giga Hertz) . One GHz means the clock of a processor cycles one billion (1,000,000,000) times per second. It is a rough estimate of the number of instructions that can be performed in a second. Normally, the higher the clock rate, the faster the processor. In other words, a 4GHz processor is faster than a 3GHz processor, assuming everything else is identical.

The second property is the width of data path in the ALU (arithmetic and logic unit) . This measures how big of a number the processor can compute for each clock cycle. As of 2006, we are currently transitioning from 32-bit processors to 64-bit processors. At the same clock rate, a 64-bit processor is not twice as fast as a 32-bit processor! Many factors determine the gain of a 64-bit processor compared to a 32-bit processor.

As much as a processor can crunch data (add, subtract, multiply, divide, compare, and etc.), it has very little ability to store data.