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)
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)
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DOS Fn 47H: Query Default Directory