Space Invaders

Space Invaders is a fixed-screen shooter in which Earth is threatened by a formation of descending aliens. The player controls a laser cannon that moves horizontally along the bottom of the screen and must destroy the invaders before they reach the ground.

The aliens march from side to side, descending one row whenever the formation reaches the edge of the screen. Several visually distinct types occupy the formation, with those in the higher rows awarding more points. The invaders periodically fire missiles downward, and both their movement and accompanying marching sounds accelerate as their numbers decrease, making the final few enemies increasingly difficult to hit. A mystery ship occasionally crosses the top of the screen and awards bonus points when destroyed.

Several destructible barriers stand between the laser cannon and the invaders. These provide temporary protection from enemy fire but are gradually damaged by both alien missiles and the player’s own shots. They may also be destroyed when the descending formation reaches them. In the original arcade game and many conversions, only one player shot may be on screen at a time, making accuracy and timing important.

Clearing the entire formation advances the player to another wave, which may begin closer to the ground and becomes progressively more dangerous. The game ends when all available laser cannons are lost or the invaders descend to the bottom of the screen.

The numerous home conversions vary in their formation sizes, number of barriers, graphics, scoring, game variations, and multiplayer options. Where two-player play is supported, the players generally compete for the highest score by taking alternating turns.