DOS Fn 47H: Query Default Directory

                                                         Compatibility: 2.0+ 
 Expects: AH    47H
          DL    drive number (0=default, 1=A, etc.)
          DS:SI address of a local buffer to hold a pathname (64 bytes)
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 Returns: AX    error code if CF is set to CY
          ──────────────────────────────────────────────────────────────────
    Info: The buffer starting at DS:SI is filled with an ASCIIZ▲ pathname
          of the current default directory for the drive specified by DL.

          The pathname is returned in the form...
             d:\path\filename.ext◄0►

          There is no leading drive letter or leading or trailing
          backslash; for instance, if the current default directory is the
          root, all you'll get is a null string (DS:[SI] = 0).

          After calling this function, you can be certain that the media in
          drive DL is known to the system.  Use this to ensure that the
          device driver's BPB is correct before making a INT 25H/26H call.

See Also: Fn 19H (query default drive)
          Fn 3BH (set default directory)
          Directory and File Functions
          DOS Functions
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