Skewer (chess)

In chess, a skewer is an attack upon two pieces in a line and is similar to a pin. A skewer is sometimes described as a "reverse pin"; the difference is that in a skewer, the more valuable piece is in front of the piece of lesser value. The opponent is compelled to move the more valuable piece to avoid its capture, thereby exposing the less valuable piece which can then be captured (see chess piece relative value). The long-range pieces (queen, rook, and bishop) can skewer.

Details

Skewers can be broken down into two types: absolute and relative. In an absolute skewer, the king is in check, therefore the check must be handled (under the rules of chess), whereas in a relative skewer, the pieces involved don't necessarily need to be addressed.

Relative skewer

In this diagram, with Black to move, the black queen is skewered by White's bishop. To avoid capture of the queen, Black must move the queen, and on the next move, White can capture the rook. This is a relative skewer; Black is likely to move the queen, which is more valuable than the rook—but the choice is still available.

Chess annotation symbols

When annotating chess games, commentators frequently use widely recognized annotation symbols. Question marks and exclamation points that denote a move as bad or good are ubiquitous in chess literature. Some publications intended for an international audience, such as the Chess Informant have a wide range of additional symbols that transcend language barriers.

The common symbols for evaluating the merits of a move are "??", "?", "?!", "!?", "!", and "!!". In these cases, the corresponding symbol is juxtaposed in the text immediately after the move (e.g. Re7? or Kh1!?, see algebraic chess notation).

Use of these annotation symbols is subjective, as different annotators use the same symbols differently. Moreover, an annotator's use of symbols is often influenced by the player's strength: a positional misjudgment that an annotator might give a "??" if played by a strong grandmaster might pass unremarked if played by a beginner.

Annotators' use of punctuation also may possibly be influenced by the result of the game (regardless of the actual quality of the move); one possible example came in the 11th game of the 1972 World Championship, when Spassky played an unexpected move, 14.Nb1, retreating the knight to its initial square. Spassky won the game, and several annotators gave the move two exclamation points. Edmar Mednis asserted that if Spassky had lost the game, the move would likely have been given two question marks instead.

Chess (Northwestern University)

Chess was a pioneering chess program from the 1970s, written by Larry Atkin and David Slate at Northwestern University. Chess ran on Control Data Corporation's line of supercomputers. Work on the program began in 1968. It dominated the first computer chess tournaments, such as the World Computer Chess Championship and ACM's North American Computer Chess Championship. Chess was the first published use of the bitboard data structure applied to the game of chess.

In 1976, Chess 4.5 won the Class B section of the Paul Masson American Chess Championship, the first time a computer was successful in a human tournament. The performance rating was 1950.

In February 1977 Chess 4.6, the only computer entry, surprised observers by winning the 84th Minnesota Open against competitors just under Master level. It achieved a USCF rating close to or at Expert, higher than previous programs' Class C or D, by winning five games and losing none. Stenberg (rated 1969) became the second Class A player to lose to a computer in a tournament game, the first being Jola.

Computer chess

Computer chess is computer architecture encompassing hardware and software capable of playing chess autonomously without human guidance. Computer chess acts as solo entertainment (allowing players to practice and to better themselves when no sufficiently strong human opponents are available), as aids to chess analysis, for computer chess competitions, and as research to provide insights into human cognition.

Current chess engines are able to defeat even the strongest human players under normal conditions. Whether computation could ever solve chess remains an open question.

Availability

Chess-playing computers are now accessible to the average consumer. From the mid-1970s to the present day, dedicated chess computers have been available for purchase. There are many chess engines such as Stockfish, Crafty, Fruit and GNU Chess that can be downloaded from the Internet for free. These engines are able to play a game that, when run on an up-to-date personal computer, can defeat most master players under tournament conditions. Top programs such as the proprietary Shredder or Fritz or the open source program Stockfish have surpassed even world champion caliber players at blitz and short time controls. In October 2008 Rybka was rated top in the CCRL,CEGT, CSS,SSDF, and WBEC rating lists and has won many recent official computer chess tournaments such as CCT 8 and 9, the 2006 Dutch Open Computer Championship, the 16th IPCCC, and the 15th World Computer Chess Championship. As of February 03, 2016, Stockfish is the top rated chess program on the IPON rating list.