RAID = Redundant Array of Independant Disks
It has a variety of types including 0, 1, 2, 0+1, 5, 7 etc. Each mode uses standard hard disk drives and uses them in a array of disks to somehow benifit the user.
Common RAID Levels for Desktop PCs are RAID 0 and RAID 1...
RAID 0 - Data Striping = Distributes the data over two hard drives so that data is optimised for fast storage/retrieval. There is a slight performance gain but this is usually used in server setups and desktops with high data processing demands. Disadvantage of it is that if one hard drive fails, all the data in the "RAID Set" is useless and cannot be recovered, unlike having two separate disks and volumes/partitions.
RAID 1 - Data Mirroring = Basically makes a mirror image of a hard drive and copies it over to the 2nd hard drive exactly in complete synchronisation. This is used so that if one hard drive fails, the other one can take over without any risk of data loss due to hardware failure. THIS DOES NOT HELP IF DATA IS CORRUPTED HOWEVER! As the data corruption will also appear on the 2nd Hard Drive
RAID Controller = Controlls RAID Functions and RAID "Levels".
That should clear up everything about RAID
Dont get confused as there are different ways a RAID can be used