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a chess program developed and written by [[Rudolf Huber]] in [[C]]. In its early times in the mid 90s, SOS running on various platforms and operating systems had an own futuristic [[GUI|graphical user interface]]. SOS supported the [[Chess Engine Communication Protocol]] <ref>[http://www.open-aurec.com/wbforum/viewtopic.php?f=18&t=30441 New Winboard engine, SOS by Rudolf Huber, Germany !] by [[Frank Quisinsky]], [[Computer Chess Forums|Winboard Forum]], 27 October 1999</ref> , was available as [[ChessBase#YoungTalents|Young Talent]] by [[ChessBase]] running under the [[Fritz#FritzGUI|Fritz6 GUI]], and since Rudolf is co-designer of the protocol, it finally changed to [[UCI]] <ref>[https://www.stmintz.com/ccc/index.php?id=208295 The new UCI / WB GUI Arena is available with UCI Arena SOS ..] by [[Frank Quisinsky]], [[CCC]], January 18, 2002</ref> , and is a ''Partner Chess Engine'' of [[Arena]] <ref>[https://web.archive.org/web/20120103164848/http://www.playwitharena.com/?Partner_Chess_Engines Arena Chess GUI 3.0 - Partner Chess Engines]([https://en.wikipedia.org/wiki/Wayback_Machine Wayback Machine])</ref> <ref>[https://web.archive.org/web/20120106001947/http://www.playwitharena.com/?Partner_Chess_Engines:SOS%26nbsp%3B Arena Chess GUI 3.0 - SOS]([https://en.wikipedia.org/wiki/Wayback_Machine Wayback Machine])</ref> . SOS evolved from [[Principal Variation Search|PVS]] to [[MTD(f)]] and further as [[ParSOS]] to [[Parallel Search|parallel]] MTD(f).

SOS is a conventional chess program. It uses [[Depth-First|depth first]] [[Minimax|minimax tree search]] with [[Quiescence Search|quiescence search]], [[Alpha-Beta|alpha-beta]] enhancement, [[Principal Variation Search|minimal window search]] and [[Null Move Pruning|null-move pruning]]. To improve the search efficiency, the [[History Heuristic|history heuristic]] and a [[Transposition Table|transpositional table]] is used. The search is [[Extensions|extended]] to deeper plies on those move sequences which have a high probability of being part of the [[Principal Variation|principal variation]]. For SOS, those sequences are [[Recapture Extensions|recaptures]] and [[Check Extensions|check evasions]]. Leaf node [[Evaluation|evaluation]] considers only [[Material|material]], [[Piece-Square Tables|piece placement]] and [[Pawn Structure|pawn structure]] and only about 10% of the CPU time is spent on this (not including the quiescence search which is capture only, but extends on "losing" captures which are checks and on checking sequences). The evaluation parameters are dynamic and [[Incremental Updates|continuously updated]] during tree search. SOS's weakest part is probably [[Endgame|endgame]] knowledge. SOS actively plays a wide range of [[Opening|openings]], but most of those lines are not very deep. With autoplay games against itself, the [[Opening Book|opening book]] is tuned to favour favor those lines which harmonize with SOS's style of play.

* [https://web.archive.org/web/20120106001947/http://www.playwitharena.com/?Partner_Chess_Engines:SOS%26nbsp%3B Arena Chess GUI 3.0 - SOS]([https://en.wikipedia.org/wiki/Wayback_Machine Wayback Machine])* [https://web.archive.org/web/20120106031235/http://www.playwitharena.com/?Newsticker:Archive_9 Interview with SOS programmer Rudolf Huber in German language!] by [[Frank Quisinsky]], [[Arena|Arena Chess GUI 3.0]] - Archive 9, 132, May 10, 2005([https://en.wikipedia.org/wiki/Wayback_Machine Wayback Machine])

* [https[://en.wikipedia.org/wiki/Wes_Montgomery Category:Wes Montgomery|Wes Montgomery]] - S.O.S. (take 3), [https://en.wikipedia.org/wiki/Full_House_(Wes_Montgomery_album) Full House], recorded at [https://en.wikipedia.org/wiki/The_Jabberwock_(club) Tsubo], [https://en.wikipedia.org/wiki/Berkeley,_California Berkeley, California], June 25, 1962, [https://en.wikipedia.org/wiki/YouTube YouTube] Video

[[Category:MusicWes Montgomery]]