Symmetric Multiprocessing, or SMP, is the term used to describe a computer system that is equipped with more than one processor, and also equipped with an operating system capable of distributing load evenly over those processors. There is Asymmetric Multiprocessing.
Asymmetric systems dedicate individual processors to specific tasks.
For example, one processor may be dedicated to disk operations, another to video operations, and the rest to standard processor tasks. These systems don't have the flexibility to assign processes to the least-loaded CPU, unlike an SMP system. No mainstream OS supports Asymmetric Multiprocessing. 3.1 Through 4.0 Workstation supports up to two processors. Through 4.0 Server supports up to four processors.