As you probably know, AutoTRAX is a self-contained file format, in that all data is contained in a single file and there are no external dependencies on other files. This ensures integrity and avoids any devastating errors where you have missing files and therefore cannot reconstitute your project, resulting in a complete disaster. This feature also allows you to pass a design onto others as a single self-contained file.
In addition, AutoTRAX's history features where absolutely every change you do while creating your PCB are part are recorded in a special directory with the same name as the project and an extension of ‘.history’. One of the great features of this history directory is that undos can be done even after you have exited a design session. Undos can go back to changes that occurred in previous sessions. It also has the feature that if you failed to save your design, when you restart AutoTRAX you can use redo to reinstate all the changes that you made to your design before you failed to save it, how cool is that?
I have received requests to store some parts of the design in external files such as imported 3-D models. I have looked into this and done some experiments and I found that it could reduce the size of each history file by 0-90%. But the problem with this is that the project file is no longer self-contained and produces a great risk of you losing your 3-D models. Also, the current practice of storing the 3-D models in each of the history files makes each history file self-contained and capable of being used as a stand-alone project file. This redundancy, I believe, is well worth the extra space it consumes on your disk drive. It makes your design experience more comfortable in certain with a greatly reduced risk of losing your work.
My experiments involved using a compressed zip file as a virtual file system that can hold not only the project file but also the 3-D model file and the complete set of history files. But this makes your work even more susceptible to file corruption. If the compressed zip file became corrupt, then that’s all your work gone. So, using a compressed zip file is not a feasible alternative.