Int 21 Fn 1B  - Dos 1+ - Get Allocation Information For Default Drive      [D]

   AH = 1Bh

Return: AL = sectors per cluster (allocation unit)
   CX = bytes per sector
   DX = total number of clusters
   DS:BX -> media ID byte (see #1044)

Notes: under DOS 1.x, DS:BX points at an actual copy of the FAT; later
     versions return a pointer to a copy of the FAT's ID byte
   this function may not be properly supported on CD-ROMs and other
     installable file systems (use AX=4402h"CD-ROM" for CD-ROMs
     instead)

See Also: AH=1Ch,AH=36h

(Table 1044)
Values for media ID byte:
 FFh   floppy, double-sided, 8 sectors per track (320K)
 FEh   floppy, single-sided, 8 sectors per track (160K)
 FDh   floppy, double-sided, 9 sectors per track (360K)
 FCh   floppy, single-sided, 9 sectors per track (180K)
 FAh   HP 200LX D: ROM disk, 16 sectors per track (995K)
   HP 200LX E: (Stacker host drive ???)
 F9h   floppy, double-sided, 15 sectors per track (1.2M)
   floppy, double-sided, 9 sectors per track (720K,3.5")
 F8h   hard disk
 F0h   other media
   (e.g. floppy, double-sized, 18 sectors per track -- 1.44M,3.5")