INT 2fH 4a11H BX=0007H: Get Dblspace Disk Size / Free Space

                                                         Compatibility: 6.0+ 
 Expects: AX    4a11H (mux number)
          BX    0007H (DoubleSpace fn code)
          DL    compressed drive to query
 Returns: AX    DoubleSpace API Error Code (0000H = success)
          DS:SI address of DsSpaceInfoRec (see below)
    Info: This obtains the true total space and free space available in the
          specified volume.

          Note: the newer (6.2) DS IOCTL 'S' function is the preferred
          method of obtaining this information.

    DS:SI on return, DS:SI points to the following data structure:

            Offset Size Contents
            ▀▀▀▀▀▀ ▀▀▀▀ ▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀
             +0      4  lTotSects   total data sectors in the disk
             +4      4  lFreeSects  available sectors in the disk
                     8              size of a DsSpaceInfoRec (undocumented)

   Notes: ■ This changes DS, pointing it into DBLSPACE.BIN local data area.
            So take notice (and change it back to point to your local data
            area after this call).

          ■ The return values in lTotSects and lFreeSects are expressed in
            512-byte sectors.

          ■ The maximum physical size of a DoubleSpace compressed volume
            is 512 MB.  Thus, the largest value you can expect returned in
            lTotSects is 1,048,576 (0010 0000H) sectors.

          ■ Use DOS fn 36H to obtain the estimated storage for the drive.

          ■ The documented API does not provide an estimated compression
            ratio, but you can derive it by comparing lTotSects to the
            value obtained from DOS fn 36H.

See Also: DoubleSpace Overview
          DS IOCTL 'S' (Get DriveSpace Pointers)
          DoubleSpace API
          INT 2fH: Multiplex Interrupt
          DOS Functions