Raid allows you to write to both drives at the same time, so the data is stored across both and you get twice the speed, or to save the same data on both giving you a backup image. Here's what Abit have to say about it: http://www.abit.nl/english/techterm/io.htm#15
The link the other guy provided is great. It'll explain a lot for you. The only thing I'd like to add is this...
For most people RAID is a gimmick. If you move around HUGE files all day long then yes, you might find a use for it. If you use your computer for playing games, browsing the WWW, or just general BS. You're not going to really see any benefit from RAID.
It's pretty funny actually. So many people want it, but so few people actually make real world use of it.
If you're a hobbyist video editor you might consider a cheap IDE RAID solution.
UnlimitedSpeed (Jan 21, 2001 02:32 a.m.):
What does it do? im looking at the abit kt7a raid.