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The Dictionary of Chess Computing: FEN, PGN & Engine Terms
Modern chess is digital. To analyze your games or share them with friends, you need to speak the language of computers. This glossary defines the technical formats and terms used by engines, databases, and servers like ChessWorld.
1. The Language of Data (PGN & FEN)
PGN File
Portable Game Notation. The universal text format for saving entire chess games. It includes the move list, player names, event, and result.
1. e4 e5 2. Nf3 Nc6 ...
FEN String
Forsyth-Edwards Notation. A single line of text that describes a specific position on the board (not the whole game). It records piece placement, whose turn it is, and castling rights.
rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1
UCI Protocol
Universal Chess Interface. The language that allows a chess engine (like Stockfish) to talk to a graphical user interface (like ChessBase or a website).
2. Inside the Engine
Centipawn (cp) Measurement
The unit of advantage used by engines. 100 centipawns = 1 Pawn. A score of +0.50 means White is leading by half a pawn.
NNUE AI Tech
Efficiently Updatable Neural Network. A modern technology used by Stockfish that combines the speed of brute-force calculation with the "intuition" of a neural network.
Hash Table Memory
A portion of your computer's RAM set aside for the engine to remember positions it has already calculated, preventing it from doing the same work twice.
Horizon Effect Flaw
When an engine (calculating to a limited depth) misses a danger because the bad consequence happens just one move after it stopped calculating.
Depth / Ply Calculation
How many half-moves ahead the engine looks. "Depth 20" means the engine is looking 10 full moves ahead for both sides.
3. Databases & Accuracy
Tablebase Solved
A database of perfectly solved endgames (e.g., 7 pieces or fewer). The computer doesn't calculate; it just knows if the position is a Win, Loss, or Draw instantly. (e.g., Nalimov, Syzygy).
ACPL Statistic
Average Centipawn Loss. A measure of accuracy. It calculates how much value you lost per move compared to the perfect computer move. Lower is better (GMs are usually 15-20).
Opening Tree Database
A visual database showing all moves played in a specific position from historical games, along with their win/loss percentages.