Format of SFS data packet:
Offset	Size	Description	)
 00h  4 BYTEs	signature string "SFS1"
 04h	WORD	SFS unit number (0-based)
 06h	WORD	drive on which the SFS volume is mounted
 08h	DWORD	sector offset of logical volume from start of physical volume
		0 if logical volume = physical volume
 0Ch	WORD	flag: 00h = no disk mounted, 01h = disk mounted
 0Eh	WORD	flag: 00h read/write, 01h read-only
 10h	WORD	quick-unmount hotkey
		(high byte = shift state, low = scan code) (see #00006)
 12h	WORD	auto-unmount time in minutes, or 0000h if already expired, or
		FFFFh if not set
 14h	WORD	time in minutes remaining before auto-unmount
 16h	WORD	internal driver check code
		0000h no error
		0001h driver consistency check failed
		0002h unit consistency check failed
 18h	WORD	disk access mode
		0000h BIOS
		0001h IDE direct access
		0002h SCSI direct access