What is Fritz Powerbook 2015? Learning chess &amp; I thought Fritz Powerbook 2015 was THE chess-playing engine with GUI only to learn that it requires Fritz12, 13, 14 or 15 to use it. I had read that it had a lot of useful info on chess openings. I'm considering purchasing the new Fritz15 both to have it as well as make use of Powerbook 2015, but I'm wondering if anyone can clarify how and why one uses a "powerbook" in Fritz.
The powerbook contains 1.5 million games of grandmasters (including the most recent ones).  For the power book, these games have been processed so you can see their openings, and for each opening position you can see all the moves that have been played as well as the associated winning/drawing/losing rates.  So basically, it is an up-to-date overview of opening theory at the top level so far.