$D.                      Device Checking                         Default: $D+

 {$D.}

    Checks text files opened by Reset, Rewrite, or Append, to see if they
    are devices. If a text file is a device, then buffering is disabled
    for the file. This directive is usually used in combination with the
    $P and $G directives.

             $D+    Performs device check. if device, no buffering is
                    used.

             $D-    Does not check for device. All I/O is buffered.

          Range:    Entire program.