This part of ISO/IEC 14776 defines the command set extensions to facilitate operation of SCSI block devices. It specifies the functional requirements for the SCSI-Block Command set (SBC). SBC permits that SCSI block logical units, such as flexible disks, rigid disks, optical disks, etc. be attached to computers, and it provides the definition for their use. This standard defines a logical unit model for SCSI block logical units. Also defined are SCSI commands that apply to SCSI block logical units. The clause(s) of this standard pertaining to the SCSI block device class, implemented in conjunction with the applicable clauses of ISO/IEC 14776-311, fully specify the standard command set for SCSI block devices. The objectives of this standard are the following: a) permit an application client to communicate with a logical unit that declares itself to be a direct-access device, write-once device and optical memory device in the device type field of the INQUIRY command response data over an SCSI service delivery subsystem; b) define commands unique to the type of SCSI block devices; c) define commands to manage the operation of SCSI block devices; d) define the differences between types of SCSI block devices.