UCI Options

Threads: number of threads Chiron will use while thinking. By default it is set 1.

Hash: search hash table size in MB. The maximum size is 2GB in the 32 bit version and 1TB in the 64 bit version. Don’t use more than the available physical memory otherwise also virtual memory (ie the hard disk) will be used and Chiron will run slower.

Clear Hash: when this button is pushed the hash table, the pawn hash table and the evaluation cache are cleared.

Log File: if checked Chiron will create a log file in the subfolder “logs”.

Tablebases: type of endgame tablebases to use. It can be Syzygy, Nalimov or Gaviota.. Set it to Disabled if you don’t want to use tablebases.

Tablebases Usage: it can be Never (tablebases never probed), Only At Root (tablebases probed only at the root when on the board there are 5 or less pieces) or Everywhere (tablebases probed also in the search).

Tablebases Probe Depth: minimum depth for probing the endgame tablebases. By default it’s set to 6. Lower it if you have a SSD.

NalimovPath: location of the Nalimov endgame tablebases.

NalimovCache: size of the Nalimov EGTB cache in MB. It contains the results of positions for which the Nalimov tablebases have been already probed.

GaviotaTbPath: location of the Gaviota endgame tablebases. Chiron will automatically detect the compression scheme.

GaviotaTbCache: size of the Gaviota EGTB cache in MB. It contains the results of positions for which the Gaviota tablebases have been already probed.

SyzygyPath: location of Syzygybases.

Syzygy50MoveRule: uncheck it if you want Chiron to ignore the 50 moves rule otherwise leave it checked.

Use Scorpio Egbb: it must be checked if you want Chiron to use Scorpio endgame bitbases.

Scorpio Egbb Path: location of Scorpio bitbases.

Scorpio Egbb Cache: size of the Scorpio bitbases cache in MB. It contains the results of positions for which the Scorpio bitbases have been already probed.

Scorpio Egbb Load Type: type of bitbases loading in RAM at program startup. It can be LOAD_NONE if you don’t want to load bitbases in RAM at all, LOAD_4MEN to load all the 4 pieces bitbases, SMART_LOAD to load the most used and LOAD_5MEN to load all the 5 pieces bitbases (about 225MB)

Ponder: it is checked if pondering (ie thinking during opponent’s time) is allowed. Chiron’s time management is different when pondering is allowed.

OwnBook: it must be checked if you want Chiron to use its own opening book. If it’s not, the GUI will handle the opening book.

Book File: path of the opening book. Chiron supports Polyglot and CTG opening books. It deduces the format of the book from the file extension.

Tournament Book: if checked Chiron will always play the best moves according to its opening book (ie the one with the highest weight).

Auto Limit Book: if checked Chiron will automatically limit its opening book knowledge (depth and width) according to the Elo set in UCI_Elo. UCI_LimitStrenght must be selected too. The purpose of this option is to avoid that Chiron plays too many moves from the opening book even at a low Elo, which would be unrealistic.

Book Depth: if you set a value different from 0, Chiron will limit the depth in full moves of its opening book to the value set. This option overrides the limit imposed by the Auto Limit Book option.

MultiPV: if you set a value different from 1, Chiron will show the variations for the n best moves but the search will be a bit slower. It is recommended to use MultiPV only for analysis and not for engine-engine playing.

Contempt: Chiron’s draw contempt in centipawns. If you want Chiron to avoid draws set a positive value otherwise negative. The default value is 0.

NUMA: it should be checked if Chiron runs on a NUMA system (typically one with multiple sockets) to improve speed.

Use Large Pages: if checked Chiron will try to allocate the memory for the hash table using large pages. Large pages can speedup memory access, increasing Chiron speed.

Blockage Detection: it can be Disabled, Analysis (to use the pawn blockage detection only in analysis mode) or Always.

UCI_ShowCurrLine: if checked Chiron will show the current line it is calculating.

UCI_LimitStrength: if checked Chiron will limit its playing strength.

UCI_Elo: Elo to which Chiron should limit its playing strength. UCI_LimitStrength must be checked.