In turn-based games, permanent brain (also called pondering) is the act of thinking

Thought

"Thought" generally refers to any mental or intellectual activity involving an individual's subjective consciousness. It can refer either to the act of thinking or the resulting ideas or arrangements of ideas. Similar concepts include cognition, sentience, consciousness, and imagination...

 during the opponent's turn.

Turn-based games such as chess

Chess

Chess is a two-player board game played on a chessboard, a square-checkered board with 64 squares arranged in an eight-by-eight grid. It is one of the world's most popular games, played by millions of people worldwide at home, in clubs, online, by correspondence, and in tournaments.Each player...

 have a weakness: one of the players can spend too much time thinking. Time control

Time control

A time control is a mechanism in the tournament play of almost all two-player board games so that each round of the match can finish in a timely way and the tournament can proceed. Time controls are typically enforced by means of a game clock...

 solves this problem: each player receives certain amount of time for thinking. If a player spends more than the allotted time, he loses.

When a player thinks on his move, the opponent can relax. However, some players try to use the opponent's time for thinking too. Some players use this time for long-term planning (strategy). Other players try to predict the opponent's move and think about the next move. Players who are in time trouble

Time trouble

In chess played with a time control, time trouble, time pressure, or its German translation Zeitnot, is the situation where a player has little time to complete the required moves. When forced to play quickly, the probability of making blunders is increased, so handling the clock is an important...

 use pondering particularly frequently.

Use with chess programs

The strength of chess programs depends very much on the amount of time allocated for thinking. Many chess programs use pondering to improve their strength. Current programs cannot create strategic plans, so a program simply tries to predict the opponent's move and begins to think about its response. If the opponent's move has been guessed correctly, then the program continues to think. If the prediction fails, the program begins a new computation.

Pondering is less effective than normal thinking. For example, if the program guesses 25% of the opponent's moves correctly, the use of pondering is on average equivalent to increasing the normal thinking time by a factor of 1.25.

In chess games between two computers, pondering makes sense only if the competing chess engines use different processors

Central processing unit

The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...

 or cores. If they share the same core, the pondering program steals half of the time from the program thinking in the normal way and uses the stolen time less effectively. For this reason, chess GUIs (like Arena

Arena (chess)

Arena is a freeware GUI for chess engines by Martin Blume and runs on Windows.It supports the protocols UCI and Chess Engine Communication Protocol to communicate with the chess engines that provide the computer enemies. Arena therefore supports a vast amount of chess engines, e.g...

) have an option to turn the permanent brain off.