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DrChiper - as I understand version 3.0, it's 'merely' a new server and a browser based viewer

In this thread
Calibre 3.0 changes and bèta release date? you will find the following exchange between Kovid and me:
Quote:
Originally Posted by BetterRed
... Could I run the existing server from a 2.99 portable install [after v3.0 is released]? It does everything I want...
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Quote:
Originally Posted by kovidgoyal
... You can of course run the old server if you like. As long as there are no db structural changes (which is very rare) there should be no problems.
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That, and that fact that you can run the new server and viewer against existing libraries (in post #2 of that thread, Kovid tells us how to take a sneak peek from within the current release) says to me that there will be no database changes - I'm banking on it
BR