INT 21 - DUBLDISK.SYS v2.6 - GET INFO
        AX = 4404h
        BL = drive number of DoubleDisk drive (00h = default, 01h = A:, etc.)
        CX = number of bytes (000Ah-0014h, call ignored otherwise)
        DS:DX -> data record (see below)
Return: CF clear if successful
            AX = number of bytes read
        CF set on error
            AX = error code (01h,05h,06h,0Dh) (see AH=59h)
Program: DUBLDISK.SYS is the device driver portion of DoubleDisk, a disk
          expander by Vertisoft Systems, Inc.
Note:   the installation check consists of scanning memory for the signature
          "FAT 2.6  byte:", which is immediately followed by a data table
SeeAlso: AX=440Dh
Index:  installation check;DUBLDISK.SYS

Format of data record:
Offset  Size    Description
 00h    WORD    (call) signature 4444h
 02h    BYTE    (call) function
                        00h ???
                        01h ???
---function 00h---
 02h    BYTE    (return) ???
 03h    BYTE    (return) ???
---function 01h---
 02h    WORD    (return) 4444h
 04h    WORD    allocation unit size???
 06h    WORD    ???
 08h    WORD    ???
 0Ah    BYTE    ???

Format of signature data table:
Offset  Size    Description
 00h  5 BYTEs   ???
 05h    BYTE    first drive number
 06h    BYTE    number of drives
 07h    ???

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