Okay, RAID stands for Redundant Array of Inexpensive Disks (or something similar). It’s not a software thing at all; it’s a means of arranging hard drives in such a way that:
[ul][li]The information is broken up or “striped” across several hard drives. Each “read” operation takes time, so reading 2 units of data will take 2 “read cycles” (speaking simply). If you break up your data so that each of two hard drives has one of the data units, you can read them simultaneously, taking only one “read cycle”. Your two hard drives are treated as one big hard drive, which can be read from (and written to) at twice normal speed. This is known as a RAID 0, which is actually a misnomer, since none of the information is really “redundant” (see next item). RAID 0 arrangements can be set up with three or even four drives, with corresponding (but gradually diminishing) improvements in speed.[/li][li]The information is copied (“mirrored”) across several drives, making redundant copies. If you absolutely need your information to be kept safe, it might be worthwhile to install a second hard drive and write the same information to both at the same time. If one drive fails, your machine automatically jumps to the other, and you can replace the defective drive, copy the contents from the working drive, and carry on with no major interruption in service. This is known as a RAID 1.[/li][li]Some combination of the two. RAID 10 (one-zero, not “ten”) uses four hard drives, essentially two identical striped pairs. There are other arrangements like RAID 3 and RAID 5 and whatnot that use various combinations of drives in an attempt to balance speed, safety and expense.[/li][/ul]
Until a few years ago, RAID configurations required SCSI drives, which are fast but expensive. Lately, though, setting up RAIDs with the more common and less expensive IDE hard drives has become possible. If you’re buying a generic (i.e. IDE) hard drive to upgrade your computer, you might consider getting two identical hard drives and a RAID card. Once installed, a RAID 0 stripe gives you high speed, but unless you’re using it for drive-heavy operations like video editing or file serving, it may be more expense, complexity and risk than you actually need. I use a single hard drive to store my Windows junk and main programs, and a pair of drives in a “stripe” (RAID 0) as the “scratch” disk for my video projects. I can capture several hours of video without losing a single frame because my RAID is fast enough to keep up, even at 30 frames/second at high quality. I couldn’t do that on my single “C:” drive. By the same token, I don’t bother installing programs like Microsoft Office on my special “G:” drive (as I said, the drives in the RAID are viewed as a single unit, to which I can assign any letter I want) because that would be a waste.
A RAID0 is risky because if either drive fails, I’m screwed, so I only keep temporary or less-important files on the G: drive. When I finish a video project, I burn it on CD-ROM as soon as possible.
Tom’s Hardware Guide has an excellent introduction to IDE, with Part 2 and Part 3 getting into the nitty-gritty of RAID configuration.