RAID names a concept of using several hard disks as if they were single. It's the abbreviation for Redundant Array of Independent Disks (I guess and wont verify this now). There are 7 or 8 different RAID configuration options, but the most common for desktop PCs are NRAID (JBOD), 0 and 1. This might be because most modern mainboards only support these three. Perhaps they only those 3 modes because that's most common for desktops... however.