Map 256 Glitch

A screenshot of Pac-Man's 256th round. The right side of the maze and game screen is corrupted with various sprite tiles and text.

In the original Pac-Man, an integer overflow caused by limitations of the original game's hardware causes the 256th round of the game to initiate a glitch where the right side of the game screen becomes corrupted, making the round impossible to complete under normal circumstances. This glitch has been dubbed as the Map 256 Glitch, split-screen level or kill screen by various sources.

Due to the glitch, the 256th round is normally considered to be the final round of Pac-Man, since progression is impossible without modifications to the original game. The glitch has notably become famous in relation to Pac-Man, and has been referenced in various media and Pac-Man games, such as Pac-Man 256.

Overview

Origin

The level counter in the original Pac-Man is stored as an 8-bit integer, in which the highest value it can hold is 255. The level counter starts with 0 internally, but for calculating the fruit counter it adds 1; 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 of attempting to draw 256 fruit on the screen results the garbled mess on the right side of the maze, as the screen memory starts with the bottom, followed by the columns from the right side.

History

Pac-Man

Screenshot of Pac-Man moving in the corrupted maze.

The integer overflow causes the right side of the maze to corrupt. This also causes the maze collision to corrupts, which can result in Pac-Man being able to wrap around to the other side of the maze by travelling past the corner of the screen like a Warp Tunnel, though it may also result in Pac-Man or the other ghosts becoming stuck within the corners. This is also the only round where vertical warps are possible since there are no walls between the top and bottom of the game screen.

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, in addition to 122 dots on the left half, resulting in a total of 131 Dots; only half of what is necessary in order to progress further (the 9 Dots present on the right half of the screen regenerate after Pac-Man loses a life, which can result in an extra 45 dots being eaten if the player has not lost any lives up until said moment, resulting up to a maximum of 176 Dots being able to have been eaten during the round of the 244 Dots needed to progress past the round. If gameplay modifications are made to progress past the round, the game will loop back to the first round, but will retain the ghost speed from the later rounds.

Ms. Pac-Man

A kill screen in Ms. Pac-Man also occurs like Pac-Man as they share the same hardware board, albeit it results in a blank screen instead due to programming differences to the original game. The blank screen has a chance of occurring in the 134th and 138th rounds; the game will crash when round 142 is reached, and will reset back to the attract screen. Because of the game crash, the 256th round cannot be accessed under normal circumstances. The glitched screen results in most of the layout from Pac-Man's glitched screen, albeit with sprites from Ms. Pac-Man.

Jr. Pac-Man

In Jr. Pac-Man, much of the scenario from Ms. Pac-Man is mirrored, though as with Ms. Pac-Man, much of the sprites in the glitched screen will also be based on Jr. Pac-Man's sprites.

Trivia

• The glitch has inspired several recurring elements in the Pac-Man series, such as the glitched display becoming a recurring aesthetic used in promotional material, characters such as Glitchy, The Glitch, the G-HOST Bug, and various references to the 256th round of Pac-Man.
• On the Pac-Man Connect & Play console from 2012, 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".

External links

• The Pac-Man Dossier
• Don Hodges's page regarding the bug