Kill screen
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A kill screen is a stage or level in a video game (often an arcade game) that stops the player's progress due to a programming error or design oversight. Rather than "ending" in a traditional sense, the game will crash, freeze, or behave so erratically that further play is impossible.
Video games, like any other computer software, can suffer from bugs. A bug in a video game is not automatically a kill screen; the bug must occur consistently in the same point in the game and must preclude any further play. While any type of bug could cause this sort of behavior, the most common cause is integer overflow of the level counter or simple oversight on the part of the game's programmers.
Kill screens were much more common during the Golden Age of Arcade Games. Games from this era were often written with the assumption that the player would stop playing long before the numerical limits of the game code were reached. Additionally, the limited hardware of these early machines often meant that programmers could not waste memory on logical checks of the state of the game.
Famous kill screens
While probably not the first game to suffer from a kill screen, Pac-Man's is possibly the most famous. Pac-Man's level counter was a single 8-bit byte, and could therefore store only 256 distinct values (0–255). Reaching the 256th board causes a counter that is used while drawing the fruit to overflow to zero, causing 256 fruit and seven blank spaces to be drawn. The final board is playable but cannot be completed, with the right half replaced by a series of garbled symbols and letters.
Donkey Kong also featured a kill screen in the 22nd stage, the 117th screen. This is an example of a kill screen that is not due to an integer overflow in a level counter, but a different oversight on the part of the designers. The amount of time allowed for any given screen is determined algorithmically during play, decreasing slowly as the player progresses. By the time the player reaches the 117th screen, the algorithm that determines the amount of time at the start of the level results in overflow, which causes the time to be set so low that there is simply not enough time for the screen to be completed.
Dig Dug, like Pac-Man, also experiences a kill screen on the 256th round, which is counted as round zero, and the resulting integer overflow results in an enemy starting on top of the player's character, instantly killing him.
Duck Hunt features a kill screen on level 100, causing the game to call it round zero, and glitch up the game. If the level is defeated with a certain cheat code, the game starts over at round one. This is almost certainly due to using a single byte level counter, like Pac-Man, but made worse by operating the 6500-series processor that ran the game in BCD mode.