Format of Get_ExtDPB data buffer:
Offset	Size	Description	)
 00h	WORD	(call) length of following data (003Dh)
 02h 61 BYTEs	(ret) drive parameter block (DPB) (see #01787)
 
Format of Extended Drive Parameter Block:
Offset	Size	Description	)
 00h 24 BYTEs	standard DOS 4+ DPB
 18h	BYTE	"dpb_flags" (undocumented)
		FFh force media check
 19h	DWORD	pointer to next DPB (see note)
 1Dh	WORD	cluster at which to start search for free space when writing,
		usually the last cluster allocated
 1Fh	WORD	number of free clusters on drive, FFFFh = unknown
 21h	WORD	high word of free cluster count
 23h	WORD	active FAT/mirroring
		bit 7: do not mirror active FAT to inactive FATs
		bits 6-4: reserved (0)
		bits 3-0: the 0-based FAT number of the active FAT
		    (only meaningful if mirroring disabled)		
 25h	WORD	sector number of file system information sector, or
		  FFFFh for none (see also #01788)
 27h	WORD	sector number of backup boot sector, or FFFFh for none
 29h	DWORD	first sector number of the first cluster
 2Dh	DWORD	maximum cluster number
 31h	DWORD	number of sectors occupied by FAT
 35h	DWORD	cluster number of start of root directory
 39h	DWORD	cluster number at which to start searching for free space
Notes:	except for offset 18h, all of the first 33 bytes are identical to
	  the standard DOS 4-6 DPB
	unless the proper value is given in SI on entry to "Get_ExtDBP", the
	  next-DPB pointer and device driver address are set to 0000h:0000h
SeeAlso: #01786,#01395 at AH=32h,#01664