The SCSI Start/Stop Unit command is used to control the motor in a rotary device such as a SCSI disk-drive. It is also used to load or eject exchangeable media such as a tapes or CDs. It is a frequently-used command and is often the first one issued after initial communication has been established between the initiator and the target.

The CDB structure is:

bit→ ↓byte	7	6	5	4	3	2	1	0
0	Operation code = 1Bh
1	LUN			Reserved				Immed
2	Reserved
3	Reserved
4	Reserved						LoEj	Start
5	Control

The parameter fields in the CDB have the following meaning:

• Immed - immediate - if this is one then the target will not wait until the operation has completed before sending back the status code.
• LoEj (load/eject) and Start - these two bits are used together:
• 00 - Stop motor
• 01 - Start motor
• 10 - Eject media
• 11 - Load media