Originally Posted by jailbait
Operating systems began supporting multi processors about 1965 - 1970. So any older operating system probably supports multi processors. The main exception is Windows which did not begin supporting multi-processors until (I think) 2006.
The Windows NT line was developed to be able to use multiple processors from the beginning, so anything built off it would be able to also (2000, XP, 2003, Vista, etc). The consumer line of Windows was never written to handle multiple processors (1, 2, 3, 95, 98, ME). They can run on a computer with multiple processors, or a chip with multiple cores, but they can't use anything more than the first. So, you could run Win 95 on a quad-core chip, but three cores would never see any action.