Function  1Bh   Get Current Drive File Allocation Table Information 
      Returns information from the FAT on the current drive 
entry   AH      1Bh 
exit    AL      number of sectors per allocation unit (cluster) 
	DS:BX   address of the current drive's media descriptor byte 
	CX      number of bytes per sector 
	DX      number of allocation units (clusters) for default drive 
note 1) Save DS before calling this function. 
     2) This call returned a pointer to the FAT in DOS 1.x. Beginning with 
	DOS 2.00, it returns a pointer only to the table's ID byte. 
     3) IBM recommends programmers avoid this call and use int 25h instead.