I'll continue on RAID. It was originated as server technology, like mt3rj said, raid systems are mirrored. for example, if you have 4 harddrives of the same stature (lets say 20gb), and you set them up in a raid array, you have either choice, to use data stripping, or data mirroring. Stripping basically takes a file that is being written to the hard drive, and splits it (in this case) into four parts, and places a part on each drive. Mirroring, on the other hand, places the file on all four drives. So basically a raid system turns multiple drives into a single drive "system". Oh yeah!, you can tell the difference between drives by: IDE=big ribbon cable, whereas SATA=Small thin cable with a black head (usually).