Format of SRDISK device driver header:
Offset	Size	Description	)
 00h 10 BYTEs	same as standard device driver header
		  (see #01646 at INT 21/AH=52h)
 0Ah	BYTE	number of subunits (drives) supported by driver
 0Bh  3 BYTEs	signature "SRD"
 0Eh  4 BYTEs	memory type string ("XMS "/"EMS ")
 12h  4 BYTEs	ASCII driver version string "N.NN"
 16h	BYTE	00h
 17h	BYTE	configuration format version (currently 00h or 01h)
 18h	WORD	offset of drive configuration data
SeeAlso: #01646