Editing Computer chess (section)

==== Other optimizations ====
Many other optimizations can be used to make chess-playing programs stronger. For example, [[transposition table]]s are used to record positions that have been previously evaluated, to save recalculation of them. [[Refutation table]]s record key moves that "refute" what appears to be a good move; these are typically tried first in variant positions (since a move that refutes one position is likely to refute another).  The drawback is that transposition tables at deep ply depths can get quite large – tens to hundreds of millions of entries. IBM's Deep Blue transposition table in 1996, for example was 500&nbsp;million entries. Transposition tables that are too small can result in spending more time searching for non-existent entries due to threshing than the time saved by entries found. Many chess engines use [[pondering]], searching to deeper levels on the opponent's time, similar to human beings, to increase their playing strength.

Of course, faster hardware and additional memory can improve chess program playing strength.  Hyperthreaded architectures can improve performance modestly if the program is running on a single core or a small number of cores.  Most modern programs are designed to take advantage of multiple cores to do parallel search.  Other programs are designed to run on a general purpose computer and allocate move generation, parallel search, or evaluation to dedicated processors or specialized co-processors.