INT 21 - Stacker - GET STACVOL FILE SECTORS
        AX = 4404h
        BL = drive number (0 is current drive)
        CX = byte count (i.e., 200h = 1 sector)
        DS:DX -> buffer (see below)
Return: Data Buffer contains the number of sectors requested from the
          STACVOL physical file for the drive specified.

Format of stacker buffer:
Offset  Size    Description
 00h    WORD    01CDh
 02h    WORD    sector count
 04h    DWORD   number of starting sector
 08h    DWORD   far pointer to Data Buffer

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