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Kill Screen

Overview

Kill screens are points found in games, most commonly arcade games, in which reaching a certain level or section in the game will cause progress to become virtually or literally impossible, bringing play to an abrupt end. Kill screens usually come in the form of a software crash and are usually the fault of a programming error or a design oversight that did not anticipate players being able to reach that point in the game. Reaching a kill screen is often seen as a mark of skill within retro game communities as it frequently requires a high degree of skill and endurance to achieve.

Kill screens were brought to widespread attention after the release of the documentary, The King Of Kong: A Fistful of Quarters, in which classic gamer Brian Kuh makes his way around the Fun Spot arcade to inform patrons that the kill screen in Donkey Kong is about to be reached. Donkey Kong provides an example of a game that does not crash upon reaching its skill screen, but instead becomes impossible due to gameplay constraints. On the 117th screen of the game the player is given only 7 seconds in which to complete the stage, a restraint that is literally impossible to overcome and so guarantees the end of play.

While the kill screen in Donkey Kong is one of the best known examples in video games, perhaps equally famous is the kill screen on the 256th level of Pac-Man where the game crashes and the right side of the screen fills with a glitching arrangement of game sprites. Both the Donkey Kong and Pac-Man kill screens are examples of kill screens that come about as a result of each game having to at some point rely on a value that is too large to be stored in the datatype that the game attempts to store it in. One of the most common forms of this and a very common cause of kill screens in early video games was the integer overflow error.

Integer Overflows

In mathematics an "integer" is any number that carries no decimal value. It might otherwise be known as a "whole number". In games integers may be used to store data such as the level the player is currently on or how much ammunition remains in their weapon. All data in computers is stored in bits, each consisting of a 1 value or 0 value, and while it's standard for modern video games to use 32 or more bits to store integers, many early games only used 8 bits (a single byte) to store integers. This reduced quantity of bits meant that these integers had a much lower maximum value they could store.

As bits can have two values we can calculate the maximum decimal number an integer can store by taking the number 2 and raising it to the power of how many bits are being used to represent the integer and then subtracting 1. Do note however that this equation assumes that the integer is "unsigned", i.e. it is not capable of representing a negative value. From this we can tell that an unsigned 8-bit integer can store a maximum value of 28 - 1 or 255. So for example, if a programmer was using an unsigned 8-bit integer to store the game's level value, as many did, as soon as the player hit level 256 a number would be generated that was too large for the relevant variable to store, resulting in a crash. This overflow of the level counter was perhaps the most common cause of kill screens.

Examples of Kill Screens

GameKill Screen Condition
Pac-ManStage 256
Donkey Kong22nd stage, 117th screen
Dig Dug256th round
Duck HuntLevel 100
GalagaInteger Overflow
FroggerInteger Overflow
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