CONTROLLER PORT SWITCH ARRANGEMENT FOR SHARING STORED DATA AMONG DIFFERENT SYSTEMS

A digital data storage system having a switching arrangement permitting storage devices to be shared by two separate controllers, each of which in turn receives commands and transfers the stored data to a different data processing system. The arrangement involves a plurality of subchannels (01, 1, 2, 3) each of which comprises at least one addressable storage device (0;...N) and two addressable interlocked port switches (0, 0 min ) each of which functions to connect one side of the subchannel and the device to one of the controllers (10, 10 min ). The subchannel switching arrangement is characterised by each switch being addressable as if it were another device, which permits the port switches to be implemented with minimal changes to either the controller or the device.