The Najdorf Powerbook 2014 is based on a totally incredible number of games: 1.6 million! The lion’s share is provided by the engine room on playchess.com, with the addition of 87 000 games from human experts.
The Dragon Powerbook 2014 is based on over 93 000 games. Only the best games from classical tournaments (38 000) and correspondence chess (18 000) have been used. They are supplemented by over 36 000 games from the engine room on playchess.com.