Billy Mitchell was the first person ever to make a perfect score on Pac-Man with score 3.333.360 and game duration around 4 to 5 hours. Bill was awarded in the same year, as “Video Game Player of the Century” by Masaya Nakamura (Founder of Namco, the company behind Pac-Man).In order to achieve the perfect score he had to take advantage of some bugs in the game, like for example that one on 1:15 of the video below. The biggest bug the game actually was the last level, number 256.
What happens is that the right part of the screen stops responding normally because the game runs out of memory. The counter of the fruits is an 8-bit Integer, that makes it’s range 0-255. So when reaching 256 the game, memory overflows and causes the glitch below.
Finally because of the missing screen part, there are not enough dots to proceed to the next level. In order to proceed Mrs Pac-Mac has to eat 244 dots but there are in total 131 (122 in the left part of the screen and 9 more in the right part).