Hi Steve.
It's hard to understand -- but not _that_ hard 🙂 . A book is not required. See if this short description helps.
Be careful (and specific) with your nomenclature -- it will keep you from getting mired in the bogs of confusion that rim our sun-lit plateau. Your camera creates files. You import files into Aperture. On import, Aperture puts that file somewhere, and thereafter refers to it as a Master. The Master is never altered. You control where Aperture puts it (and you can have Aperture move it at any time). What you see in Aperture is an Image. Every Image has a Version and a Master. The Version is a text file containing instructions on how to vary the Master to produce the Image. The Version of the first Image created by Aperture when it imports a file is essentially null (it contains no information). When you create a new Version, Aperture names it "Version 2". (The confusion here is that Aperture encourages the user to call Images "Versions". This is a bit of a devil's bargain: it helps the casual user, but confuses the careful user.) You can see the Master of any Image displayed in the Viewer at any time by typing "m" (it triggers the Image/Master toggle).
All you need to do is have Aperture move some or all of your Masters to your external drive. Note that you can easily, at any time, convert Masters from Managed to Referenced and vice versa. Note too that backing up your Library does not back up any Referenced Masters. You must back up Referenced Masters in addition to backing up your Library.
Message was edited by: Kirby Krieger -- minor clarification.
