Arcade machines, especially classic ones, rely on precise game state versioning to maintain backward compatibility across different ROM updates and hardware iterations. Here’s how they achieve it:

1. ROM Versioning: Arcade games often use ROM chips that store game data. Developers assign version numbers to ROMs, allowing the system to identify and adapt to different game states.

2. Checksum Verification: The machine checks the ROM’s checksum to ensure compatibility. If the checksum matches a known version, it loads the appropriate game state handlers.

3. State Flags and Variables: Games store state flags or variables in memory, which are preserved even after updates. This ensures that saved progress or settings remain functional.

4. Hardware Abstraction: Some arcade systems use abstraction layers to separate game logic from hardware, making it easier to adapt to new versions without breaking old saves.

5. Patch Systems: Modern arcade machines (or emulators) may apply patches to older ROMs, updating game states to work with newer hardware or software versions.

By combining these techniques, arcade machines maintain seamless backward compatibility, preserving the gaming experience across decades.