Format of SCSITAPE control block:
Offset	Size	Description	)
 00h	WORD	command type
		'F' Format (argument 1 = interleave, argument 2 = format type)
		'E' Erase
		'R' Rewind
		'L' Load
		'N' No Load
		'S' Space (argument 1 = count, argument 2 = type)
		'M' File Mark (argument 1 = count)
		'A' Reassign
 02h	WORD	argument 1
 04h	WORD	argument 2
 06h	WORD	segment of command buffer
 08h	WORD	offset of command buffer
 0Ah	WORD	length of command buffer