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; to be one, the bug must occur consistently in the same point in the game and must preclude any further play. While almost any type of bug could cause this sort of behavior, the most common cause is simple oversights on the part of the game's programmers such as an integer overflow of the level counter.
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; most games from this period were intended to continue until the players lost all of their lives. Additionally, the limited hardware of these early machines often meant that programmers could not spend memory on logical checks of the state of the game.
Notable arcade kill screens
In the coin-operated version of Dig Dug the game ends on round 256 (round 0), since this board is essentially an unplayable kill screen. At the start of the level a Pooka is placed directly on top of where the player starts, with no way to kill it.
Template:Details Pac-Man has a famous kill screen, often referred to as the Pac-Man Bomb Screen. The game's level counter was a single 8-bit byte, and could therefore store only 256 distinct values (0–255). Reaching the 256th level causes a counter that is used while drawing the fruit to overflow to zero, causing 256 fruits and seven blank spaces to be drawn. It can, however, be fixed with a patch.
Donkey Kong also featured a kill screen in the 22nd stage, and the 117th screen (85th in the Japanese version). This is an example of a kill screen that is not due to an integer overflow in a level counter (since programmers prevented this), but a different oversight on the part of the designers. The amount of time allowed for any given screen is determined algorithmically during play by the level the player is on. The timer is calculated 100×(10×(level + 4)), and has a maximum value of 8000. When the level reaches 22, the game reads 100×(10×(22+4):) or 100×260. However, the 8-bit counter rolls over at 256, meaning the game calculates 100×4. This causes the timer to be set so low that there is barely seven seconds for the player to complete the level, simply not enough time for the screen to possibly be completed. Steve Wiebe, a competitor from Redmond, Washington, attained this screen when he attempted to beat Billy Mitchell's Donkey Kong high score (which was the world record) on G4TV at E3 2009. It was the first kill screen to be broadcast on live television.[Mr. Wiebe also reached a kill screen in the film The King of Kong: A Fistfull of Quarters about his attempts for the world record of Donkey Kong. ]
Notable home console kill screens
In the Nintendo Entertainment System game Duck Hunt, there is a kill screen that occurs in the 100th level. The level counter for Duck Hunt is stored in two numbers, that range from 01 to 99, but when level 99 is completed, the value rolls over to 0, creating a glitch. The 1st, 4th, and 6th through 10th ducks do not appear, and the other 3 appear in random places on the screen so quickly that it is nearly impossible to hit them. Even if they were hit, the level could not be completed with only 3 out of 10 ducks hit.
The kill screen level has been completed in a Tool-assisted speedrun.
Level 29 of Tetris is also a kill screen. On this level, blocks fall at twice the normal speed, making the level difficult to complete without using cheats, hacks or a tool-assisted speedrun. After level 29, level numbers are randomized and sometimes even contain letters.