All interactive video games are temporal simulations, meaning that the vir- tual game world model is dynamic-the state of the game world changes over time as the game’s events and story unfold. A video game must also respond to unpredictable inputs from its human player(s)-thus interactive temporal simulations. Finally, most video games present their stories and respond to player input in real time, making them interactive real-time simulations.
One notable exception is in the category of turn-based games like computerized chess or non-real-time strategy games. But even these types of games usually provide the user with some form of real-time graphical user interface. The term “game engine” arose in the mid-1990s in reference to first-person shooter (FPS) games like the insanely popular Doom by id Software.
Doom was architected with a reasonably well-defined separation between its core software components (such as the three-dimensional graphics rendering system, the collision detection system or the audio system) and the art assets, game worlds and rules of play that comprised the player’s gaming experience. The value of this separation became evident as developers began licensing games and retooling them into new products by creating new art, world layouts, weapons, characters, vehicles and game rules with only minimal changes to the “engine” software.