Function  53h   "Used Internally by DOS" - Translate BPB 
 *              Translates BPB (BIOS Parameter Block, see below) into a DOS Disk 
		Block (see function call 32h).   
entry   AH      53h 
	DS:SI   pointer to BPB  
	ES:BP   pointer to area for DOS Disk Block. 
		Layout of Disk Block: 
		bytes   value 
		00h-01h bytes per sector, get from DDB bytes 02h-03h. 
		02h     sectors per cluster, get from (DDB byte 4) + 1 
		03h-04h reserved sectors, get from DDB bytes 06h-07h 
		05h     number of FATs, get from DDB byte 08h 
		06h-07h number of root dir entries, get from DDB bytes 09h-0Ah 
		08h-09h total number of sectors, get from:  
			((DDB bytes 0Dh-0Eh) - 1) * (sectors per cluster (BPB  
			byte 2)) + (DDB bytes 0Bh-0Ch) 
		0Ah     media descriptor byte, get from DDB byte 16h 
		0Bh-0Ch number of sectors per FAT, get from DDB byte 0Fh 
return  unknown