# 1.9.3 Working Directory

- `xtrkcad.ckp` are the check-point files created periodically while running XTrackCAD. If your system XTrackCAD hangs or crashes you get the choice of loading the checkpoint file and so recover (most of) your work by saving it to your current layout file.

  The check-point frequency is set by the Check Point field found in the Preferences dialog (Options>Preferences).

- The `xtrkcad.cus` file contains parameter information. This is mostly information created by the Turnout Designer dialogs (Section 2.9.8) and Group (Section 2.9.3) command. You can use the Edit>Custom Management dialog to manipulate these parameters.

- The `xtrkcad.ini` (on MS-Windows) or the `xtrkcad.rc` (on Linux) file contains various parameter settings from each use of XTrackCAD. Most changes you make (such as scale, room size, window position) are saved in this file for the next time you use XTrackCAD.