How are edited photos stored in new Apple photos app? In Aperture I understood the process to be that changes made in post processing where stored as "instructions" (not sure of real term) to be applied to the original and in that way saved space for storage over iPhoto where it appeared to me that a duplicate copy of the photo was made. 

I'd like to understand what the new Photo does. I would bet the same as iPhoto?
For Photos.app, don't consider the edits necessarily edits. While looking through the file architecture one day, I found that what they're doing is storing the original and simply adding layers of "edits" which are much more like layers of removable filters. 

The original stays 100% in tact until you export it to a separate file where Photos will process those layers into an image. 

The only way you would lose originals and be stuck with the edited versions is if you specifically, in this order:


exported your edited version
deleted the photo from Photos.app
deleted your Photos.app Trash
put the exported version back (technically for the first time) into Photos.app.