INT 21 U - DOS 4.0 internal - ???
        AH = 6Bh
        AL = subfunction
            00h ???
                DS:SI -> Current Directory Structure???
                CL = drive (1=A:)
            01h ???
                DS:SI -> ???
                CL = file handle???
            02h ???
                DS:SI -> Current Directory Structure???
                DI = ???
                CX = drive (1=A:)
Return: CF set on error
            AX = error code (see INT 21/AH=59h)
        CF clear if successful
Note:   passed through to INT 2F/AX=112Fh with AX on top of stack
SeeAlso: INT 2F/AX=112Fh