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Rybka is a UCI chess engine, not a standalone chess program, which means that you use it within almost any modern chess user interface such as Aquarium, Chess Assistant, Shredder, Fritz, Arena, Chessbase, ChessPartner, etc.
It uses one processor/core regardless of how many cores the hardware may have. With that limitation it also runs on all processors under the Windows operating system. If you want to take full advantage of multicore processor, use Deep Rybka 4 UCI.
System requirements: PC, 256 MB RAM, 4GB of free disk space, Windows 7/XP/Vista.