A multi-bay backplane module is a box the size of a couple optical drives stacked on top of one another that stores a handful of serial ATA hard drives in compact, individually hot swappable drive caddy's. When internal hard drive space in a computer case is full, or if quick access to hard drives is called for, this box will allow you to add up to three SATA hard drives in the space normally occupied by two 5.25" optical drives. IcyDock call this module the MB453SPF-B.



Link: PCStats