Format of Set_DPBforFormat structure:
Offset	Size	Description	)
 00h	WORD	(call) size
 02h	WORD	(call) structure version???  (0000h)
		(ret) ???
 04h	DWORD	(call) function number
		00h invalidate DPB counts
		01h rebuild DPB from BPB
		02h force media change (next access to drive rebuild DPB)
		03h get/set active FAT number and mirroring
		04h get/set root directory cluster number
---function 00h---
 08h	DWORD	new DPB free count (00000000h=no change, FFFFFFFFh=unknown)
 0Ch	DWORD	new DPB next-free (00000000h=no change, FFFFFFFFh=unknown)
 10h	DWORD	unused
 14h	DWORD	unused
---function 01h---
 08h	DWORD	unused???
 0Ch	DWORD	(call) -> BIOS Parameter Block from which to rebuild DPB
 10h	DWORD	unused
 14h	DWORD	unused
---function 02h---
 08h	DWORD	unused
 0Ch	DWORD	unused
 10h	DWORD	unused
 14h	DWORD	unused
---function 03h---
 08h	DWORD	(call) new active FAT/mirroring state, or FFFFFFFFh to get
		bits 3-0: the 0-based FAT number of the active FAT
		bits 6-4: reserved (0)
		bit 7: do not mirror active FAT to inactive FATs
 0Ch	DWORD	(ret) previous active FAT/mirroring state (as above)
 10h	DWORD	unused
 14h	DWORD	unused
---function 04h---
 08h	DWORD	(call) new root directory cluster number
		    FFFFFFFFh to get current
 0Ch	DWORD	(ret) previous root directory cluster number
 10h	DWORD	unused
 14h	DWORD	unused