Abstract

An expansible fixed disk drive data storage subsystem enables attachment of multiple bus-level interface fixed disk drives to a host computer at a single us-level interface fixed disk drive input/output logiical address location. The subsystem includes an interface for direct plug-in attachment to the input/output address, data and control buses of the host computer, and an expansible plurality of disk drive clusters operatively connectable to the interface, each cluster including plural disk drive cables wherein each cable provides an electrical connection to at least one bus-level interface fixed disk drive operatively associated with the cluster; a cluster and cable selection circuit for receiving and storing cluster and cable selection values sent by the host cmputer, gated data, address and control/status lines buffers for connecting a selected cable and its disk drive(s) to the input/output buses of the host computer in response to a particular cluster and cable selection value sent by the host computer, and a disk drive interrupt status register which when set by a said disk drive within the cluster and read by the host computer indicates to the host computer that the disk drive has performed some task or requires attention.