The iconic arcade machines of the 80s and 90s were not just entertainment hubs; they were revenue-generating businesses. Protecting that revenue from clever players was a constant battle, leading to the development of ingenious, hardware-focused cheat detection and prevention systems long before modern online anti-cheat software existed.

One of the primary methods was checksum verification. The game's code (stored on ROM chips) contained a pre-calculated checksum value—a digital fingerprint of the code itself. Upon boot-up, the main CPU would calculate a new checksum of the ROM data and compare it to the stored value. If a player attempted to modify the game ROMs (e.g., for infinite lives), the checksums would not match, and the machine would either halt entirely or display a checksum error message, effectively preventing the game from running.

For preventing other forms of tampering, developers employed watchdog timers. This was a hardware circuit on the printed circuit board (PCB) that required the game's software to send a regular "all clear" signal. If the game code crashed, froze, or was manipulated in a way that stopped this signal, the watchdog timer would expire and automatically trigger a full reset of the entire machine, clearing any attempted software-based hacks.

Physical security was equally important. Arcade cabinets were built like fortresses, using specialized locks on the coin doors and back panels to prevent unauthorized access to the internal DIP switches and wiring. These switches were used to set difficulty, the number of credits per coin, and other vital settings. Tamper-proof switches were also common; if the cabinet door was opened, a switch would trigger, and the game would write a "tamper" flag to its non-volatile memory (NVRAM). An operator could then check this log to see if a machine had been interfered with.

Furthermore, anti-cheat measures were designed directly into the game's code. This included routines to detect impossible scores, such as a score that increased too rapidly or exceeded a maximum possible value, which would often result in the score being reset to zero. Some games would also detect if a player was credits without inserting a coin by monitoring the coin counter circuit.

While not as complex as today's solutions, these methods formed a robust, multi-layered defense system. They effectively safeguarded the profitability of arcade cabinets by ensuring fair play and preventing both physical and digital manipulation, relying on the ingenious integration of hardware and software.