Space Invaders

Nishikado kept a hardware bug that made aliens speed up as they died. Tomohiro Nishikado built the board himself with microprocessors imported from the US, and they could not draw the whole alien army at the speed he wanted. Each dead alien left one fewer sprite to draw, so the rest moved faster, and instead of fixing the bug he built it into the final game.

The aliens first creep across the field, and with a few left they rush the player quickly and aggressively. The result, in Mark Brown's words: "the better you did, the harder the game got."

Starting each stage one row lower turned a single ramp into a wave. Each Space Invaders stage begins with the aliens one row closer to the bottom, so difficulty climbs within a level, drops when the next one starts, then climbs again from a higher baseline. Rising challenge meets growing skill, and the easier restart gives tension, then relief and time to learn.

Nishikado admired how Atari's 1976 Breakout got harder as you played, with the ball speeding up at intervals, but Breakout has only two identical levels, so its escalation stops there. Nearly every traditional video game now uses some version of this wavy curve.

Music that sped up with the aliens built a mood of impending doom. Space Invaders was the first game with a soundtrack that played throughout the gameplay: a simple heartbeat thud, or perhaps a jackboot march. Because it speeds up as the aliens do, it works as a prototypical adaptive soundtrack.

Enemies that shoot back force players to dodge as well as attack. Space Invaders was one of the first shooters where enemies fired at the player, who hops in and out from behind destructible shields. That second task, moving out of the way, gives a very simple setup room for strategy.

Clearing the outer columns slows the formation's descent. Shooting aliens on the far side of the formation means the remaining ones travel further each step before dropping down, which buys the player time. Players can manipulate the play space to their advantage.

A UFO worth random points adds an optional risk and reward target. A UFO floats across the top of the screen and gives a random number of points when shot. It sits apart from the main threat, so the player chooses whether to spend shots and attention on it.

Recording a high score turned solo play into local competition. Space Invaders was the first arcade game to record a high score, so nearby players competed to see who held out longest. Star Fire let players enter their initials the following year.

Rising difficulty plus a score to beat made the game addictive. The difficulty curve and high score together made Space Invaders perhaps the first video game phenomenon: it earned billions in its first few years, Japanese arcades were sometimes called "Invader Houses", and news stories ran about Space Invaders addicts.

The story that it caused a 100 yen coin shortage in Japan is almost certainly false.

The hit drew Nintendo into games and doubled Atari 2600 sales. Shigeru Miyamoto said Nintendo decided to go into the video game business after Space Invaders became a huge hit. A 1980 port doubled Atari 2600 sales to more than two million units and made the console popular with developers and gamers.

Nintendo's own first attempt at cashing in was Radar Scope.

Copycats grew into the shoot 'em up genre. Galaxian (Namco), Defender (Williams), Asteroids (Atari), Gorf (Midway), Astro Fighter, Astro Invader and Ozma Wars followed it, and Galaga, Ikaruga, Star Fox and DoDonPachi all trace back to it. High scores, destructible cover, adaptive soundtracks and the difficulty curve all came from the game.

Taito still extends the series with Space Invaders Extreme, a score-chasing reboot, and Space Invaders Infinity Gene.