Secrets of 'Space Invaders' -- and One Very Tiny Homegrown Cabinet

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IEEE Spectrum has republished an article from nearly 40 years ago remembering one of the long-forgotten secrets of the classic video game Space Invaders.

It's about that iconic descending musical notes accompanying the onslaught of the aliens...

The more aliens a player shot, the faster they approached; their drumbeat quickened, the tension mounted. Ironically, says Bill Adams, director of game development for Midway Manufacturing Co., of Chicago, Ill., which licensed Space Invaders for sale in the United States, these features of the game were accidental. "The speeding up of the space invaders was just a function of the way the machine worked," he explained. "The hardware had a limitation — it could only move 24 objects efficiently. Once some of the invaders got shot, the hardware did not have as many objects to move, and the remaining invaders sped up. And the designer happened to put out a sound whenever the invaders moved, so when they sped up, so did the tone."

Accident or not, the game worked. As of mid-1981, according to Steve Bloom, author of the book Video Invaders, more than 4 billion quarters had been dropped into Space Invaders games around the world — "which roughly adds up to one game per earthling."

But Space Invaders also enjoyed at least one special home-grown revival earlier this month. Hobbyist Nu Iotachi used an Arduino Pro Micro board to build their own Space Invaders arcade cabinet that's just 3.15 inches tall (80 millimeters).

Made from thin hand cut plywood with pinhead joysticks, "Its Microchip ATmega328 microcontroller contains a processor running at 16MHz," reports the project's site Hackster.io, "which is far faster than the processor in the original Space Invaders arcade cabinet."