This standard defines the command set extensions to facilitate operation of SCSI direct access block devices. The clauses in this standard@ implemented in conjunction with the applicable clauses of SPC-4@ specify the standard command set for SCSI direct access block devices. The objectives of this standard are to: a) permit an application client to communicate over a SCSI service delivery subsystem (see SAM-5) with a logical unit that declares itself to be a direct access block device in the PERIPHERAL DEVICE TYPE field of the standard INQUIRY data (see SPC-4); and b) define commands and parameters unique to the direct access block device type.