BrainStorm tries to preserve your work to enable you to recover from a system crash or accidental abandonment of a working file.
BrainStorm saves your work periodically, as long as Autosave is set. If you are working on a new file, and haven't yet named it, a special file with a .$$$ extension is stored in your /local settings/temp directory. As soon as you name the file through doing an explicit Save or Save as, then this filename is used. When you reload an existing file, as soon as you Save it or Autosave it, the original is renamed with a .bak extension and all saves during the current session are saved to the .brn filename.
In the event of a system crash, BrainStorm will recover any temporary (.$$$) files. All files (.brn and .$$$) are restored from the last autosave. We strongly recommend that you set autosave to a very short time. We set ours to a minute, (See Preferences. It's amazing how much you can lose when your creativity is in full flow.
Should you need to get back to the previous version of a model, open the .bak file. It opens as a read-only file and cannot be altered unless you explicitly save it first. If you have the warnings (in Preferences) set to 'popup' a message will appear to this effect, if set to 'beep' BrainStorm will beep at you and if set to 'none' then BrainStorm will stop you editing but issue no warning.