Format of ASPITAPE.SYS mtop parameter block:
Offset	Size	Description	)
 00h	WORD	operation code
		00h "MTWEOF" - write an end-of-file record
		01h "MTFSF" - forward space file
		02h "MTBSF" - backward space file
		03h "MTFSR" - forward space record
		04h "MTBSR" - backward space record
		05h "MTREW" - rewind
		06h "MTOFFL" - rewind and unload
		07h "MTNOP" - perform TEST UNIT READY
 02h	DWORD	repetition count