The Mac Pro had room for four internal 3.5" SATA-300 hard drives in four internal "bays". The hard drives were mounted on individual trays (also known as "sleds") by captive screws. A set of four drive trays was supplied with each machine. Adding hard drives to the system did not require cables to be attached as the drive was connected to the system simply by being inserted into the corresponding drive slot. A case lock on the back of the system locked the disks trays into their positions.