Abstract: A digital data storage unit, such as tape library, has a multiplicity of storage media slots, each storage media slot for receiving a storage media, such as a tape, one or more of data transfer drives, such as tape drives, for writing data to and reading data from the storage media, a robotic device to transport the storage media between the slots or between the drives and the slots, at least one interface bridge which is connected to one or more host computers to one or more tape drives and to the robotic device, the interface bridge is performing bridging and switching operations for commands sent by the host on the basis of sub addresses, such as LUN, to send robotic mover commands to the robotic device, wherein the tape drives are addressed by main address, such as SCSI ID.