Function  1Ch   Get File Allocation Table Information for Specific Device  
      Returns information on specified drive 
entry   AH      1Ch 
	DL      drive number (1=A, 2=B, 3=C, etc) 
return  AL      number of sectors per allocation unit (cluster) 
	DS:BX   address of media descriptor byte for drive in DL 
	CX      sector size in bytes 
	DX      number of allocation units (clusters) 
note 1) DL = 0 for default. 
     2) Save DS before calling this function. 
     3) Format of media-descriptor byte: 
	bits:   0       0   (clear)   not double sided 
			1   (set)     double sided 
		1       0   (clear)   not 8 sector 
			1   (set)     8 sector 
		2       0   (clear)   nonremovable device 
			1   (set)     removable device 
		3-7     always set (1) 
     4) 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. 
     5) IBM recommends programmers avoid this call and use int 25h instead.