RAID devices are special. Hard disk are generally IDE devices or faster and more expensive SCSI devices. Until a few years ago RAID card only supported SCSI drives. However, more recently RAID IDE cards have come on to the market. But what is RAID? It's quite simple. A RAID controller is usually a PCI card. It connects to hard disks, and you have the option of running the drives in different modes, RAID 0, 0+1, 1, or 5.

RAID 0, requires two identical hard drives (or an even number). When data is read or written, the work is split between the drives. Consequently data is read or written double (or even more) the speed. Consequently you can buy two cheap IDE drives and get fantastic performance. The downside of RAID 0 Stiped, is if one drive fails the whole array could fail. This happened with me once. An error meant I couldn't start Windows to read data. So I had to get another hard disk, install Windows, back-up as much data as I could, and then format the RAID array. With RAID you have the option of viewing the whole RAID array as one partition, but I wouldn't recommend this! With RAID 1, you don't get extra performance. Data is mirrored, so one drive is a copy of the other. This means if one fails, it doesn't matter, since you still have the data on the other drive. RAID 0+1 uses four drives, so each drive is mirrored and you also get striping. This is excellent, so you the extra speed, and it's also as reliable as an ordinary hard disk setup. On more expensive RAID cards you also have RAID 5, which is a combination of RAID 1 and 0. So it gives you a balance of extra speed (but not as quick as RAID 0 or 0+1) and reliability.

Before it was just servers and high-end workstations that employed RAID, now it's become cheaper and supports IDE, it's come to the masses. It's only a matter of time, before computer manufacturers fit it as standard to their more expensive machines.