RAID requires 2+ hard drives depending on what RAID level is used. (0, 1 = 2+, 3,4,5 = 3+) Either IDE or SATA. IDE supports only two devices per channel. SATA is one device per channel and uses different cables than IDE. The maximum number of devices in any given hardware RAID array depend on the controler. You can create arrays of arrays for greater numbers of devices, but this isn't common in the consumer arena.