Symmetric multiprocessing (SMP) is a technology that allows a computer to use more than one processor. The most common configuration of an SMP computer is one that uses two processors. The two processors are used to complete your computing tasks faster than a single processor. (Two processors aren't necessarily twice as fast as a single processor, though.)

In order for a computer to take advantage of a multiprocessor setup, the software must be written for use with an SMP system. If a program isn't written for SMP, it won't take advantage of SMP. Not every program is written for SMP; SMP applications, such as image-editing programs, video-editing suites, and databases, tend to be processor intensive.

SMP in Windows XP

Operating systems also need to be written for SMP in order to use multiple processors. In the Windows XP family, only XP Professional supports SMP; XP Home does not. If you're a consumer with a dual-processor PC at home, you have to buy XP Professional. Windows XP Advanced Server also supports SMP.

In Microsoft's grand scheme, XP Professional is meant to replace Windows 2000, which supports SMP. In fact, XP Professional uses the same kernel as Windows 2000. XP Home is designed to replace Windows Me as the consumer OS, and Windows Me does not support SMP.

The difference between XP Professional and XP Home is more than just $100 and SMP support. XP Professional has plenty of other features not found in XP Home; some you'll use, others you won't care about. Get more information on the differences by reading this article.