INT 25 - Stacker - GET DEVICE DRIVER ADDRESS
        AX = CDCDh
        DS:BX -> buffer for address (see below)
        CX = 0001h
        DX = 0000h
Return: AX = CDCDh if Stacker installed
            DS:BX buffer filled

Format of driver address buffer:
Offset  Size    Description
 00h    WORD    signature CDCDh
 02h    WORD    ??? 0001h
 04h    DWORD   pointer to start of Stacker device driver

Format of device driver:
Offset  Size    Description
 00h    WORD    signature A55Ah
 02h    WORD    Stacker version * 64h
 04h    WORD    offset of volume-specific information offset table
                (list of WORDs, one per drive, containing offsets to various
                information)
 06h 56 BYTEs   n/a
 3Eh    BYTE    volume number, set after INT 21/AX=4404h
                (use to index into volume-specific info offset table)
 3Fh 19 BYTEs   n/a
 52h  4 BYTEs   ASCII string "SWAP"
 56h 26 BYTEs   drive mapping table (one byte for each drive A: through Z:)

Format of Stacker boot record:
Offset  Size    Description
1F0h  8 BYTEs   Stacker signature (first byte is CDh)
1F8h    DWORD   pointer to start of Stacker device driver
1FCh    WORD    Stacker volume number
1FEh    WORD    ???

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