Modular unitary disk file subsystem

A modular unitary disk file subsystem (10) is disclosed for use directly with a host computer. The subsystem includes a common unitary mounting substrate (6) for signal connections to the host and for supplying signals back via data, address and control buses the host computer through a direct plug-in connection (365) without any cabling between the subsystem and the host. The substrate carries (6) and interconnects a unitary disk store head and disk assembly (10), a disk store control, a disk file controller, and a data and control interface with the computer. The modular unitary plug-in form factor, a single supervisory microcomputer controller and a memory containing basic input/output driver routines directly executable by the host computer are aspects of the present invention.