Pac-Man has a bug in it that prevents it from being completely finished. This bug occurs at the 256th board, where it will cause an overflow in the 8-bit byte distinct values. As a result, the final board is almost unplayable, with the right half replaced by a series of scrambled symbols, garbage tiles, and letters.
How does this glitch occur?
It's extremely hard to do this glitch unless you have extreme patience and dedication. You have to play up to the 256th board, which can take up to 6 hours of non-stop playing. You can also use an emulator and skip to it.
Why does this exist?
256th board is treated as level 0 because of overflow. Since the logic to draw level indicator(icons at the bottom left of screen) is not intended to handle level 0, it draws tons of garbage level indicators, far exceeding the intended icon area.
If you want a full explanation watch this video: https://www.youtube.com/watch?v=NKKfW8X9uYk&t
How can I prevent this from happening in my arcade cabinet?
You can't with normal arcade machine versions. Some versions, however, have a board reset after completing the 255th board, meaning the player will start again at the first board with the score staying the same as before the reset. This allows the player to continue with the game without encountering the bug. Donhodges.com has a fix for the glitch. If the player somehow manages to beat level 256, they will return to level 1, as the game reads level 256 as level 0. Some tiles will act like walls.
So what does this mean for me?
- It means you can only get about 3,333,360 points (Current world record by Rick Fothergill). It means you can't play this game forever. As of 04/14/2018, Billy Michell's record was removed due to cheating.