The Apple Drive Module (ADM) is a hot-pluggable Ultra ATA hard drive in a special drive carrier module designed for easy server and RAID upgradeability and maintenance. Apple Drive Modules are available in 250GB and 400GB sizes and operates at 7200 rpm and are equipped with 8MB disk cache. Using four 400GB ADMs, the Xserve (slot-load) can be configured with 1.6 terabytes of internal storage.