Format of DRFAT32 control block:
Offset	Size	Description	)
 00h	BYTE	data being requested
		00h device driver header address
		09h media change status
		48h address of DRFAT32 geometry table
		else error
---function 00h---
 01h	DWORD	device driver header address (see also AH=52h,#01646)
---function 09h---
 01h	BYTE	media change status
		00h don't know
		01h media unchanged
		FFh media has been changed
---DRFAT32 function 48h---
 01h	DWORD	address of DRFAT32 geometry table (see #04109)