Many games of chess use time controls to speed the play or ensure a finish in a reasonable period. There are two main forms of time controls.
The first time control type is moves-per-time. In this type a player must complete a specified number of moves within a fixed period of time.
The second time control type is called “sudden death”. In this type there is a fixed amount of time to complete the game, regardless of the number of moves made.
Within the time control there can be a time delay to compensate for the time lost in physically making a move. In the “Bronstein delay” the clock does not start running at the beginning of the player's move until the delay time is over. If the move is completed before the delay time expires, no time is subtracted from the player's clock. In the “Fischer delay” the delay time is added to the player's remaining time before the move. If the move is made before the delay time expires, the remaining delay time is kept by the player and their clock time increases. Similarly, a fixed time can be added to the player's clock after a move is completed. When time is added to the clock, the time amount is referred to as the “time increment”.
Time controls vary widely depending upon the game, game type and any sponsor. Also during a game there may be several types of time controls joined together, with unused time added to the next time control. For all major World Chess Federation (FIDE) events the time control is 90 minutes for the first 40 moves followed by 30 minutes sudden death, with an additional 30 seconds per move beginning with the first move. The defaults on FICS (Free Internet Chess Server) are 2 minutes for the game (sudden death), plus 12 seconds time increment for each move. Many major events use 90 minutes sudden death for their time control. The US Chess Federation Blitz chess time control is 5 minutes for the game, with no time delays/increments.