Otherwise known as the "split-screen level" or a "kill screen", the Map 256 Glitch refers to the 256th level in the original Pac-Man. On this stage, the right side of the screen turns into a jumbled mess of numbers and letters, while the left side is normal. It is impossible to beat.
Unique glitches occur in the other main arcade Pac-Man titles. In Ms. Pac-Man, the screen goes blank with nothing except Ms. Pac-Man and the ghosts appearing. This screen has a chance of appearing on levels 134 to 138; if level 142 is reached, the game will automatically reset. Ms. Pac-Man does have a split-screen on map 256, but the unavoidable reset means it cannot be reached. The same glitch also happens in Jr. Pac-Man, except there are bits of the sprites of the houses and balloon from the cutscenes.
Why It Occurs
The level counter in the original Pac-Man is stored as an 8-bit integer, meaning the highest value it can hold is 255. The level counter starts with 0 internally, but for calculating the fruit counter it adds 1; however, because of overflow, adding 1 to 255 would result in 0, and the game tries to count fruits from 1, causing the game to attempt to draw 256 fruit to the screen until it overflows to 0. The result is the garbled mess on the right side of the maze, because the screen memory starts with the bottom, followed by the columns from the right side.
The game checks for 244 Pac-Dots eaten by Pac-Man for the level to end. The right half of the screen contains only 9 dots. 122 on the left half plus the mere 9 on the right half is 131, not nearly enough to progress. (The nine dots can be consumed again on each life, but you can't get enough lives to make it to 244.) This also explains why Ms. Pac-Man's kill screen doesn't automatically progress to the next level despite the lack of dots. If you do somehow manage to beat it, it will go straight back to level 1.
- On a 12-in-1 Plug 'N Play from Bandai, a "game" titled Pac-Man 256 appears (not to be confused with the unique 2015 game). This is a modified version of Pac-Man starting on level 255, allowing the player to easily access map 256.
- In the early 80s, the Map 256 Glitch (at least, in the small gaming circles it was known about in) was generally referred to as "The Schoolyard Fence". The glitch was defined as making "[...] half the machine break down at the 251st [sic] rack".
- "Oui" Magazine, April 1982 (18+ content, link excluded)