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INT 21 - DOS internal - GET DEFAULT DRIVE PARAMETER BLOCK
        AH = 1Fh
Return: AL = 00h No Error
             FFh Error
        DS:BX -> drive parameter block (see below for DOS 1.x, AH=32h others)
Note:   for DOS 2+, this just invokes function 32h with DL = 00h
SeeAlso: AH=32h

Format of Eagle MSDOS 1.25 drive parameter block:
Offset  Size    Description
 00h    BYTE    entry number
 01h    BYTE    physical drive number
 02h    WORD    bytes per sector
 04h    BYTE    number of sectors per cluster - 1
 05h    BYTE    ???
 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    number of clusters on disk
 0Fh    BYTE    sectors per FAT
 10h    WORD    starting sector of directory
 12h    WORD    address of allocation table