Great! Thanks a lot. Apropos censorship, this same post of mine only survived a few minutes on Rybka forum. That's why I brought it here.

A mention of Houdini is like a red rag to a bull to Rybka team

Ok, thanks. That's probably it. Initially hashtable size was set to 320 MB in Fritz GUI, so I just matched it in Arena, but didn't notice it showed up as 256MB, so maybe RAM allocation was uneven - I'm really clueless about these things. Now I set each to 512MB and it seems to work fine.

I even triple-checked it. Number of threads, just as recommended by Houdini author, equals number of physical cores in both GUIs. Any other ideas?

Probably most engines are derivatives to some extent at least, including of course Rybka. Why reinvent the wheel when open source engines like Stockfish are readily available for reference? And unlike Rybka, Houdini is free, stronger and doesn't have a single processor version. Enjoy!

Hi. I use Houdini 1.5a with Arena (2.1 and 3.0) and Fritz 12 GUI and it's much slower in Arena and generally easily loses to its Fritz GUI self. Count of nodes per second is considerably lower. All engine specific settings are same. Any idea why is that? Thanks.