Int 21 Fn 1F  - DOS 1+ - Get Drive Parameter Block For Default Drive       [D]

   AH = 1Fh

Return: AL = status
       00h successful
       DS:BX -> Drive Parameter Block (DPB) (see below for DOS 1.x,
           AH=32h for DOS 2+)
       FFh invalid drive

Note:  this call was undocumented prior to the release of DOS 5.0; however,
     only the DOS 4+ version of the DPB has been documented

See Also: AH=32h

Format of DOS 1.1 and MS-DOS 1.25 drive parameter block:
Offset Size    Description
 00h   BYTE    sequential device ID
 01h   BYTE    logical drive number (0=A:)
 02h   WORD    bytes per sector
 04h   BYTE    highest sector number within a cluster
 05h   BYTE    shift count to convert clusters into sectors
 06h   WORD    starting sector number of first FAT
 08h   BYTE    number of copies of FAT
 09h   WORD    number of directory entries
 0Bh   WORD    number of first data sector
 0Dh   WORD    highest cluster number (number of data clusters + 1)
 0Fh   BYTE    sectors per FAT
 10h   WORD    starting sector of directory
 12h   WORD    address of allocation table

Note:  the DOS 1.0 table is the same except that the first and last fields
     are missing; see INT 21/AH=32h for the DOS 2+ version