500 GB hard diskReplacement hard disk for a 5AC801.HDDI-04 / 5AC901.CHDD-01 hard disk or a 5ACPCI.RAIC-06 RAID controllerAccessory for the APC510 (optional hard disk for I/O board)Specified for 24-hour operationS.M.A.R.T. supportThis 500 GB hard disk can be used as a replacement part or accessory.