Q: Sometimes when Houdini runs my computer appears to be frozen and goes very slow. What can I do to improve the responsiveness of my computer while the engine runs?

There are several ways to keep your computer more responsive while Houdini is thinking:

Run the engine at “Lower than normal” priority. Most chess GUI will provide this option, for example:

- Arena has a "Lower than normal process priority" checkbox in the Engine Management Options.

- Shredder GUI will automatically run engines at lower priority.

- Fritz/ChessBase has a "Priority Below Normal" checkbox in the dialog for creating the UCI engine.

If you want to use your computer for other purposes while analyzing chess positions, set the "Threads" configuration option to a value smaller than the the number of physical cores of your computer - for example, use 3 on a quad-core computer. This will leave one core available for other applications while the chess analysis runs in the background.


Q: What Hash Size do you recommend at various time controls?

For infinite analysis or long Time Control matches you should use the largest hash possible - typically about half of the total RAM memory of your computer. For example, on a system with 4 GB of memory you can use up to 2048 MB hash size, on a 12 GB RAM system you can use up to 8192 MB.

For shorter games, e.g. 3 to 5 minute games, it’s better to use 256 MB or 512 MB as this will provide the best performance. For 16 min games 1024 or 2048 MB hash size should be fine.


If you know the average move time T (in seconds) and the average node speed of your hardware S (in kN/s), you can compute the optimal hash size with the formula: (T x S / 100) MB.

For example if you use a Time Control of 10 minutes for 40 moves repeating, the average move time T = 15 seconds. On hardware that produces about 2,000 kN/s the optimal hash size would then be approximately (15 x 2,000 / 100) = 300 MB, in other words 256 MB or 512 MB would be the recommended values.


Q: I'm running Houdini on a quad-core Core i7 CPU with hyper-threading. Would you recommend to use hyper-threading with Houdini and run the engine with 8 threads?

The additional hyper-threads will yield about 25% to 30% extra node speed, but the inefficiency of the parallel alpha-beta search with the higher number of threads will partially offset this speed gain. Running with 8 instead of 4 threads will therefore produce only a small increase in Elo – probably at most 10 Elo.

If your CPU can be overclocked it may be wiser not to use hyper-threading. By not using the hyper-threading you will reduce the thermal load of the CPU which will allow you to reach a higher overclocking frequency.


To illustrate this, in a 12 vs 24 threads test match on a 12-core computer (Intel Xeon processor) the outcome after 1500 games was (+7 ±10 Elo) in favor of the 24-thread engine. In other words even with 1500 games played the measured Elo difference was still inside the error margin.


Q: The Fritz/ChessBase GUI often seems to freeze when I use Houdini. Furthermore the Fritz/ChessBase GUI doesn't memorize my Houdini settings, I select an option but next time I use the engine the value has been reverted. What is happening?

You’re not the only one struggling with the sometimes confusing Fritz/ChessBase interface.

First note that chess engines are very CPU-intensive - when configured to use all the cores of the computer they may prevent the graphical environment from interacting normally with the user. To avoid this, it is recommended to run Houdini at a lower process priority in Windows.


We can suggest the following.


1.In the “Create UCI Engine” dialog, pick the Houdini executable and check the Priority ”Below normal” box. This should make a big difference with respect to the ChessBase freezes.


2.The engine default properties are stored in a .uci file stored in your local Application Data folder. It’s a plain text file that you can easily modify with Notepad. Open a Windows Explorer window, type %appdata% in the address bar and press Enter. In the folder that appears, descend into the ChessBase\Engines.UCI folder in which you will find the .uci files of all the installed engines. You can simply add options to the .uci file with Notepad, here’s an example file:


Name=Houdini 6 x64-popc
Author=Robert Houdart
Filename=C:\Program Files\Houdini 6 Chess\Houdini 6.exe
Priority=below normal