Chess Endgame - Longest Forced Win

Longest Forced Win

	a	b	c	d	e	f	g	h
8									8
7									7
6									6
5									5
4									4
3									3
2									2
1									1
	a	b	c	d	e	f	g	h

White to move has a forced win, starting with 1. Rg1+ (the only winning move). White wins a rook on move 290. Sixty-eight of the moves are the only moves that preserve the win.

	a	b	c	d	e	f	g	h
8									8
7									7
6									6
5									5
4									4
3									3
2									2
1									1
	a	b	c	d	e	f	g	h

Black to move, White converts to a simpler winning position in 330 moves.

	a	b	c	d	e	f	g	h
8									8
7									7
6									6
5									5
4									4
3									3
2									2
1									1
	a	b	c	d	e	f	g	h

With Black to move, White forces a win in 517 moves.

In October 2005, Marc Bourzutschky and Yakov Konoval announced that a position in the ending of a king, two rooks and a knight versus a king and two rooks requires 290 moves to convert to a simpler winning endgame. This type of ending is thought to be a draw in general. The old record was 243 moves from a position in a rook and knight versus two knights endgame, discovered by Lewis Stiller in 1991 (Endings of a rook and knight versus two knights are generally draws.) On March 10, 2006 Marc Bourzutschky and Yakov Konoval announced a new record for the longest endgame, requiring 330 moves to conversion to a simpler ending. In May 2006 a record-shattering 517-move endgame was announced. Marc Bourzutschky found it using a program written by Yakov Konoval. Black's first move is 1. ... Rd7+ and White wins the rook in 517 moves (see diagram).

It should be noted that such endgames do not necessarily represent strictly optimal play from both sides, as Black may delay checkmate by allowing an earlier conversion or White may accelerate it by delaying a conversion (or not making one at all). For example, for the earlier position found by Stiller, if Black plays to delay conversion as long as possible and White plays to convert as soon as possible, White captures a knight on the 243rd move and checkmates on the 246th move. However, if Black and White play, respectively, to maximize and minimize the distance to checkmate, White captures the first knight on the 242nd move, but only checkmates on move 262. Since space limitations make the computation of seven-man tablebases using the distance-to-mate metric impractical, the six-man position discovered by Stiller continues to be the longest forced checkmate discovered by computer (although longer forced checkmates have been constructed).

	a	b	c	d	e	f	g	h
8									8
7									7
6									6
5									5
4									4
3									3
2									2
1									1
	a	b	c	d	e	f	g	h

White to play and mate in 262. (Stiller)

	a	b	c	d	e	f	g	h
8									8
7									7
6									6
5									5
4									4
3									3
2									2
1									1
	a	b	c	d	e	f	g	h

The first point where distance-to-mate and distance-to-conversion diverge, given best play from the starting position in the previous diagram. 205...Nb6 maximizes DTC. 205...Nec7 maximizes DTM.

The fifty-move rule is ignored in the calculation of these results and lengths.