How long is the longest chess game ever?

Karjakin-Sergey, World Cup 2007 played Tuesday should have been a mate in 256 moves... but apparently Sergey didn't spend enough time learning how to win pawnless R+B vs N+N endgames... that and FIDE's enforcing some 'newfangled rule' allowing players to claim a draw if there are no captures or a pawn moves within 50 moves.

if you're a follower of the wiki
1989 featured the longest recorded game, according to Wikipedia. It's unlikely to be broken since all exceptions to the 50-move draw rule were eliminated in 1992.
how do you know this? is there a record of that game or is that just mathematically the longest possible match?

wat does that mean?
It means go to www.google.com and search for"longest chess game ever". Also, I believe an article was posted on this subject not quite too long ago, as a 259 move game that lasted over 20 hours.
How long is the longest chess game ever?