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April 2013 Retro Gaming Article


May 20, 2013 Retro Gaming Blog Post:

Golden Age math & memory gave precision to the elusive arcade Kill Screen

It's not uncommon to hear someone say they beat, completed or finished a particular video game. They could be referring to a PC or console game. Modern games can have several different types of "endings". A player can successfully complete all the levels or perform all side-missions or find all the hidden artifacts. Developers present several scenarios toward completing a game to give the title replay value. After all, most games had NO ending in the early days!

25 cent arcade token As a kid playing Space Invaders, Donkey Kong or Asteroids at the arcade, I played until I ran out of quarters or energy. Like many games of that era of the early 1980s, games didn't have an ending - players persevered until they ran out of lives. The coin-op nature of arcade games were for-profit. Arcade owners wanted players to drop more quarters or tokens into these machines. Giving a player the idea that they had won or were finished might diminish their desire to drop more quarters. The concept of high scores was actually created as a tactic to increase a player's desire to beat the top score - more quarters.

High scores first became popularized on pinball machines, but later transfered to video games. Midway's Seawolf, originally released in 1976, was one of the first video games to use the term high score. Arbitrary scores were determined in the game and players strove to surpass this number in an allotted time frame. This was before games had the ability to save information, thus it was simply a mathematical calculation during game play. Taito's Space Invaders (1978) was the first game to save a player's score. This created a competitive aspect as players would return to beat or defend their high scores. Not long after, video games also allowed players to enter their initials which would aid in identifying them on the scoreboard.

Pac-Man arcade kill screen

The Kill Screen

The term kill screen is actually a generic term for any game in which a programming glitch causes the game to crash or become unplayable at a consistent point in the game. We've all become accustomed to computer bugs that happen randomly without giving the user any indication of what went wrong. These sort of software bugs also existed in video games, but their randomness is what differentiates them from being labeled Kill Screens. Kill Screens appear in a consistent manner often due to an oversight in development.

In this modern era, we're used to downloading patches that fix glitches and bugs as well as add more functionality to a game. This is due to consoles and computers being able to connect to the Internet as well as store game info to a writable device like a hard drive. Now, contrast that with an arcade PCB that is solid state and fairly permanent - bugs and all.

You may also be thinking that Quality Assurance testing would reveal most consistent glitches that cause kill screens. This is true to an extent, but think back to all the Y2K woes. What would existing computer systems do when date-based calculations suddenly saw the year decrease from '99 to '00. Many programmers of the 1960s and 70s never thought their programs would still be in use at the turn of the century, so many date fields were relegated to 2-digits assuming we would be in the 1900s. That's the sort of oversight that caused Kill Screens in the Golden Age of arcade games.

Much like programmers figured their applications would be extinct before the year 2000, game developers of the late 70's and 80's never imagined that gamers would be able to maintain game play long enough to cause memory errors as memory registers reached maximum values. A mathematical glitch began to appear as gamers stood playing for endless hours in fron of an arcade cabinet - integer (or arithmetic) overflow. Think of 1999 turning into the year 2000 or a car's odometer going from 999,999 to zero! These feats were not outlandish, but they are not always anticipated. People upgrade software yearly (if not more often) and people lease cars for 3 years at a time. So, who imagined a player lasting for 20+ hours playing an arcade game?

High score competitions often lead to insane hours of continuous game play. Integer overflow occurs when a calculation results in a number above the allotted memory space. Adding 1 to the largest possible value creates a mathematical anomaly that can't be resolved and the computer (or arcade game) crashes or freaks out making continued game play impossible. Such things happen to older arcade games in terms of maximum levels. When a player attempts to go pst the last mathematically feasible level, the game fails. The logic behind this comes from our cherished term, 8-Bit.

The register width of a processor dictates the allowed values that can be presented for calculations.
8 bits: the maximum value 28 - 1 = 255

Very often arcade games flip-out when a player completes the 255th level and the game can't calculate the next level - 256. The resulting on-screen behavior due to such mathematical oddities results in a variety of bizarre visuals as seen in the Pac-Man Kill Screen above. The resulting game behavior may seem random and peculiar, but the circumstance of it's occurrence is a mathematically predictable. this predicability is what defines the term Kill Screen and clearly defines player achievement when they reach this point in a game.

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