Space Invaders is an arcade video game designed by Tomohiro Nishikado in 1978. It was originally manufactured by Taito and licensed for production in the U.S. by the Midway division of Bally. Released initially in its native Japan in 1978, it ranks as one of the most influential video games ever created. Though simplistic by today's standards, it was one of the forerunners of modern video gaming.

Inspired by Taito's earlier electromechanical machine Space Monsters and Tomohiro's interpretation of alien descriptions in War of the Worlds, the game itself resembled an adaptation of the two. In this video game version of the game, the player controlled the motions of a movable laser cannon that moved back and forth across the bottom of the video screen. Rows and rows of video aliens marched back and forth across the screen, slowly advancing down from the top to the bottom of the screen. If any of the aliens successfully landed on the bottom of the screen, the game would end. Although the player's laser cannon had an unlimited supply of ammunition, it could only fire one shot at a time.

Meanwhile, the aliens would shoot back at the player, raining deadly rays and bombs that the player would have to dodge lest his or her cannon be destroyed. Players could also move the laser cannon under one of the shelter blocks, so that they could absorb the enemy shots until they are worn through. The player's cannon could be destroyed up to three times (the player had three lives), and the game would end after the player's last life was lost. Occasionally a bonus spaceship would fly across the top of the screen which the player could shoot for extra points.

As the player destroyed an increasing number of aliens, the aliens began marching faster and faster, with the lone remaining alien zooming rapidly across the screen. Shooting the last alien in the formation rewarded the player with a new screen of aliens, which began their march one row lower than the previous round.

Another important tactical element of the arcade game is that it is impossible for the players' spaceship to be harmed by an invader firing a missile from the lowest line on the screen before the invader lands.

One key feature of Space Invaders was the fact that as more and more of the aliens were shot, the remaining aliens would move faster and faster. The change in speed was minor at the beginning of a wave, but dramatic near the end. This action was originally an unintentional result of the way the game was written - as the program had to move fewer and fewer aliens, it could update the display faster - but the development team decided to retain this feature rather than implementing busy waiting when there were few invaders on the screen.

Space Invaders used an Intel 8080 as its processor, running at 2 MHz. Graphics were implemented through a 1 bpp frame buffer mapped from the main CPU address space. All sound effects were implemented individually with discrete electronics.

In the upright version the actual output of the game was displayed mirror-image on a black and white monitor which sat recessed in the game's cabinet. The image was reflected on a plastic panel which the player saw. Behind the reflective panel was a lunar landscape which gave the game an impressive background setting. It is interesting to note that there were two major uprights. There was the original Taito upright which utilized joystick control, but most people in America are familiar with the Midway licensed version which used directional buttons and arguably had inferior artwork on its bezel, side art, and moon backgrounds.

The Japanese version of the Space Invaders arcade cabinet. (Note Joystick)Since the actual video game console itself had a monochrome video image, Taito added color by coating the reflective screen with colored bands. It should be noted however, that the very first version of the game in Japan ("T.T.", or "Table Top" Space Invaders) was a cocktail table with purely black and white graphics (i.e., no color overlay). There was also a version of the game in which the graphics were converted to actual RGB color.

Space Invaders had no hardware for the generation of random numbers, so the seemingly random point values awarded by the UFO actually utilized a hash function based on the number of shots that the player had fired in the current invasion wave. It did not take long for experimenters to determine that the maximum 300-point value could be achieved every time if the player shot the wave's first UFO on the 23rd shot, and subsequent UFOs at 15-shot intervals thereafter.