"The CD contains two versions:  Paderborn and Reykjavik.  Reyjavik is the version that won the World Championship; Paderborn includes some ideas from my work at Illinois.  I myself do not know which one is better; you'll have to find that out for yourself.  The style of the program reflects my background as a computer engineer.  Rather than developing clever search tricks that may or may not work, I concentrated on getting the most out of modern hardware.  Zap!Chess contains one of the best parallel implementations in the world to run efficiently on multiple CPU systems, and it also uses 64-bit machines to their full potential.  The program contains large amounts of chess knowledge, and like most modern programs it is tuned fairly aggressively--it knows where the opponent's king lives.  This gives it an exciting style without being unsound.  While the program is optimized for long time controls and big hardware, don't despair if you own a smaller system.  Both versions come with an implementation of Singular Extensions, the famous Deep Blue search algorithm.  They are disabled by default, but they increase the tactical strength of the program at the cost of positional strength. Enjoy!"