Arcade machines from the golden age of gaming employed sophisticated techniques to create the illusion of dynamic NPC behavior despite severe hardware limitations. The primary method was through Finite State Machines (FSM), where NPCs operated in predefined states like "patrol," "attack," or "flee." Player actions would trigger transitions between these states, creating responsive gameplay. For instance, in games like Pac-Man, ghosts switched between chase and scatter modes based on timer cycles and player position, while in shooters like Galaga, enemy formations would break and attack patterns would intensify as players destroyed more targets.

Memory constraints meant most behaviors were pre-programmed rather than truly adaptive. Developers used pattern-based systems where NPCs would select from multiple pre-scripted behaviors. Some advanced cabinets incorporated simple memory systems - if a player repeatedly used certain tactics, NPCs might temporarily counter those strategies before resetting. The hardware's real-time processing capabilities allowed for immediate reaction to player inputs through interrupt routines, giving the impression of smart adversaries.

These techniques created compelling gameplay through carefully designed behavior trees rather than true artificial intelligence. The limited ROM space meant every possible NPC reaction had to be anticipated and programmed in advance, yet through clever design, arcade machines delivered surprisingly nuanced NPC interactions that responded meaningfully to player decisions within their technical constraints.