INT 21 - DOS 1+ - GET DRIVE PARAMETER BLOCK FOR DEFAULT DRIVE
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

Format of DOS 1.1 and MSDOS 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

See also: 2132

211F - DOS 1+ - GET DRIVE PARAMETER BLOCK FOR DEFAULT DRIVE