A removable and transportable hard disk subsystem is provided for use with at least one computer and includes at least one hard disk module. The module contains a shock mounted, thin and compact micro-Winchester head and disk assembly which plugs into a base housing which is installable entirely within a well of the computer nominally allotted to receive a 51/4 inch half height disk drive. The base housing includes a head positioning and data module loading/unloading portion of the subsystem control electronics and an electromechanical mechanism for automatically loading and unloading the hard disk module. The base housing provides electrical connections for operating the head and disk assembly when loaded therein. The subsystem further includes an adapter board having a host interface portion of the subsystem control electronics and connected by a cable with the control electronics portion of the base housing, the adapter board for connecting the subsystem directly to address, data and control buses of said computer to enable storage and retrieval in the loaded module of host computer data blocks.