Chess engine

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A chess engine is a computer program that can play the game of chess.

Contents

[edit] Interface

Most chess engines do not have their own graphical user interface (GUI) but are rather console applications that communicate with a GUI such as XBoard (Linux) and WinBoard (Windows) via a standard protocol.

[edit] Protocols

The command line interface of GNU Chess became the initial de facto standard, called the Chess Engine Communication Protocol and first supported by XBoard. When XBoard was ported to the Windows operating system as WinBoard this protocol was popularly renamed to 'WinBoard Protocol'. The WinBoard Protocol was itself upgraded and the two versions of the protocols are referred to as: 'WinBoard Protocol 1' (original version) and 'WinBoard Protocol 2' (newer version). There is another protocol, the Universal Chess Interface. Some engines support both major protocols, and each protocol has its supporters. The Winboard Protocol is more popular but many chess engine developers feel that the Universal Chess Interface is easier to implement. Some interface programs, such as Arena, support both protocols whereas others, such as WinBoard, support only one and depend on subsidiary interpretors, such as Polyglot, to translate.

[edit] Increasing strength

Main article: Computer chess

Chess engines increase in playing strength each year. This is partly due to the increase in processing power that enables calculations to be made to ever greater depths in a given time. In addition, programming techniques have improved enabling the engines to be more selective in the lines that they analyse and to acquire a better positional understanding.

Some chess engines use endgame tablebases to increase their playing strength during the endgame. An endgame tablebase is a database of all possible endgame positions with small groups of material. Each position is conclusively determined as a win, loss, or draw for the player whose turn it is to move, and the number of moves to the end with best play by both sides. Endgame tablebases in all cases identify the absolute best move in all positions included (identifying the move that wins fastest against perfect defense, or the move that loses slowest against optimal opposition). Such tablebases are available for all positions containing three to six pieces (counting the kings) and for some seven-piece combinations. When the maneuvering in an ending to achieve an irreversible improvement takes more moves than the horizon of calculation of a chess engine, an engine is not guaranteed to find the best move without the use of an endgame tablebase, and in many cases can fall foul of the fifty-move rule as a result.

[edit] Comparison between engines

[edit] Tournaments

The results of computer tournaments give one view of the relative strengths of chess engines. However, tournaments do not play a statistically significant number of games for accurate strength determination. In fact, the number of games that need to be played between fairly evenly matched engines, in order to achieve significance, runs into the thousands and is , therefore, impractical within the framework of a tournament [1]. Most tournaments also allow any types of hardware, so only engine/hardware combinations are being compared.

Historically, commercial programs have been the strongest engines. The 2008 WCCC was won by Rybka. To some extent, this is a self-fulfilling prophecy; if an amateur engine wins a tournament or otherwise performs well (for example, Zappa in 2005), then it is quickly commercialized. Titles gained in these tournaments garner much prestige for the winning programs, and are thus used for marketing purposes.

[edit] Chess engine rating lists

Chess engine rating lists aim to provide statistically significant measures of relative engine strength. These lists play multiple games between engines on standard hardware platforms, so that processor differences are factored out. Some also standardize the opening books, in an attempt to measure the strength differences of the engines only. These lists not only provide a ranking, but also margins of error on the given ratings. Also rating lists typically play games continuously, publishing many updates per year, compared to tournaments which only take place annually.

There are a number of factors that vary among the chess engine rating lists:

  • Time control. Longer time controls, such as 40 moves in 120 minutes, are better suited for determining tournament play strength, but also make testing more time-consuming.
  • Hardware used. Faster hardware with more memory leads to stronger play.
  • 64-bit (vs. 32-bit) hardware and operating systems favor bitboard-based programs.
  • Multiprocessor vs. single processor hardware.
  • Ponder settings (speculative analysis while the opponent is thinking).
  • Transposition table sizes.
  • Opening book settings.

These differences affect the results, and make direct comparisons between rating lists difficult.

As of April 2009, the top engines in the different lists are:

Rating list Time control
(moves/minutes)		 Year
started		 Last updated Engine/platform
entries		 Games
played		 Top three engines Rating
CCRL[1] 40/40[2] 2005 April 3, 2009 623 174,806 Rybka 3 64-bit 4CPU
Naum 4 64-bit 4CPU
Deep Fritz 11 4CPU		 3231
3155
3095
CEGT 40/20[3] 40/20[4] 2006 April 12, 2009 546 318,694 Rybka 3 x64 4CPU
Naum 4 x64 4CPU
Deep Fritz 11 4CPU		 3197
3098
3027
SSDF[5] 40/120 1984 April 10, 2009 311 119,166 Deep Rybka 3 64-bit 4CPU
Naum 4 64-bit 4CPU
Zappa Mexico II 64-bit 4CPU		 3224
3134
3073
WBEC[6] 40/40 2001 July 18, 2008 300+ 80,000+ Rybka 2.32a-x64
Zappa Mexico II-x64
Fruit 2.3.4n-x64		 3048
2984
2961
  • Note that the listings in the above table only count the best entry for a given engine.

These ratings, although calculated by using the Elo system (or similar rating methods), have no direct relation to FIDE Elo ratings or to other chess federation ratings of human players. Except for some man versus machine games which the SSDF had organized many years ago (which were far from today's level), there is no calibration between any of these rating lists and player pools. Hence, the results which matter are the ranks and the differences between the ratings, not the absolute level of the numbers. Nevertheless, in view of recent man versus machine matches, it is generally undisputed that the top computer chess ratings should be at least in the range of top human performances, if not even significantly higher.

[edit] Test suites

Engines can be tested by measuring their performance on specific positions. Typical is the use of test suites, where for each given position there is one best move to find. These positions can be geared towards positional, tactical or endgame play. The Nolot test suite, for instance, focuses on deep sacrifices. [7] Then there are the BT2450 and BT2630 test suites by Hubert Bednorz and Fred Toennissen. These suites measure the tactical capability of the engine[8] and have been used at least by REBEL.[9] There is also a general test suite called Brilliancy by Dana Turnmire. The suite has been compiled mostly from How to Reassess Your Chess Workbook.[10]

[edit] Engine categories

Ikarus and Ferret, both private engines, were past winners of the World Computer Speed Chess Championship.

[edit] Freely available chess engines

There are hundreds of freely available chess engines which conform to one of the above communication protocols. Many run on Windows or are open source. A few of the strongest are listed here. Others may be found by examining the rating lists or external links.

Elo ratings taken from CCRL 40/40, retrieved in November 2007.

  • Alaric (v707 Elo 2752) by Peter Fendrich (Sweden)
  • Aristarch (v4.50 Elo 2698) by Stefan Zipproth (Germany)
  • Baron (v1.8.1 Elo 2625) by Richard Pijl (The Netherlands)
  • Crafty (v21.5 Elo 2631 - 22.10 now available) by Bob Hyatt (US)
  • Delfi (v5.2 Elo 2756) by Fabio Cavicchio (Italy)
  • Fruit (v2.3.1 Elo 2863) by Fabien Letouzey (France)
  • Gambit Fruit (derived from Fruit) by Bryan Hofmann (US)
  • Glaurung (v1.2.1 Elo 2726) by Tord Romstad (Norway)
  • Ktulu (v4.2 Elo 2740) by Rahman Paidar (Iran)
  • List (v5.12 Elo 2720) by Fritz Reul (Germany)
  • Movei (v0.08.438 Elo 2748) by Uri Blass (Israel)
  • Naum (v1.91 Elo 2704) by Aleksandar Naumov (Serbia)
  • Pharaon (3.5.1 Elo 2708) by Franck Zibi (France)
  • ProDeo (v1.2 Elo 2689) by Ed Schröder (The Netherlands)
  • Ruffian (v1.0.5 Elo 2711) by Per-Ola Valfridsson (Sweden)
  • Rybka (v.2.2n2 - free version - Elo 3111, CCRL 40/40 list from November 14, 2008) by Vasik Rajlich (Czech Republic)
  • Scorpio (v1.9 Elo 2754) by Daniel Shawul (Ethiopia)
  • Sjeng (also the engine in Mac OS X Chess) by Gian-Carlo Pascutto (Belgium)
  • Slow Chess (vBlitz WV2.1 Elo 2740) by Jonathan Kreuzer (US)
  • Spike (v1.2 Turin Elo 2855) by Volker Böhm and Ralf Schäfer (Germany)
  • Strelka (v1.8 Elo 2867) by Yuri Osipov (Russia)
  • Toga II (v1.3.4 Elo 2868) (derived from Fruit) by Thomas Gaksch (Germany)
  • Wildcat (v7 Elo 2730) by Igor Korshunov (Belarus)
  • Zappa (v1.1 - free version - Elo 2687) by Anthony Cozzie (US)

[edit] Pedagogical engines

These open source chess programs were expressly written to teach the craft of chess programming.

There are also copyrighted programs with available source:

[edit] Commercial programs

These chess programs are sold commercially. Most of these also include their own user interface.

[edit] Dedicated hardware

These chess playing systems include custom hardware or run on supercomputers. All but Hydra are also historical; chess supercomputers have not competed in computer tournaments since the dismantling of Deep Blue in the mid-nineties.

[edit] Commercial dedicated computers

In the 1980s and early 1990s, there was a competitive market for strong dedicated chess computers. Many form-factors were sold, from handheld peg-board computers to wooden auto-sensory boards with state-of-the-art processors. This market changed in the mid-90s when the economical embedded processors in dedicated chess computers could no longer compete with the fast processors in personal computers. Nowadays, most dedicated units sold are of beginner and intermediate strength.

  • Chess Challenger, a line of chess computers sold by Fidelity Electronics from 1977[2] to 1992. These models won the first four World Microcomputer Chess Championships.
  • ChessMachine, an ARM-based dedicated computer, which could run two engines:
  • Mephisto, a line of chess computers sold by Hegener & Glaser. The units programmed by Richard Lang won six consecutive World Microcomputer Chess Championships. They bought out Fidelity in 1989.
  • Novag sells a line of tactically strong computers, including the Constellation, Sapphire, and Star Diamond brands.
  • Saitek sells mid-range units of intermediate strength. They bought out Hegener & Glaser and its Mephisto brand in 1994.
  • Excalibur sells a line of intermediate strength units. Excalibur was started in 1992 by the son of the founder of Fidelity Electronics.
  • Phoenix Chess Systems makes limited edition units based around StrongARM and XScale processors running modern engines

[edit] Historical programs

These chess programs run on obsolete hardware.

[edit] See also

[edit] Notes and references

 This article needs additional citations for verification.
Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (January 2009)
  1. ^ "CCRL 40/40 - Complete list". April 3, 2009. http://www.computerchess.org.uk/ccrl/4040/rating_list_all.html. Retrieved on 2009-04-20. 
  2. ^ Also available: 40 moves in 4 minutes
  3. ^ "CEGT 40/20". Chess Engines Grand Tournament. April 12, 2009. http://www.husvankempen.de/nunn/rating.htm. Retrieved on 2009-04-20. 
  4. ^ Also available: 40 moves in 4 minutes, 40 moves in 120 minutes
  5. ^ "The SSDF Rating List". Swedish Chess Computer Association. April 10, 2009. http://ssdf.bosjo.net/list.htm. Retrieved on 2009-04-20. 
  6. ^ "BayesianElo Ratinglist of WBEC Ridderkerk". http://wbec-ridderkerk.nl/html/BayesianElo_ed15.htm. Retrieved on 2008-07-20. 
  7. ^ Nolot test suite
  8. ^ BT2450 test suite
  9. ^ Rebel
  10. ^ Brilliancy suite TalkChess forum

[edit] External links

Retrieved from "http://en.wikipedia.org/wiki/Chess_engine"
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