Spacewar! is one of the earliest digital computer video games. It is a two-player game, with each player taking control of a starship and attempting to destroy the other. A star in the center of the screen pulls on both ships and requires maneuvering to avoid falling into it. In 1971 it was unofficially ported into a coin-operated PDP-11 machine and renamed Galaxy Game. As an arcade machine it was installed at the Tresidder Union at Stanford University in September, 1971, two months before the official release of Computer Space, the first mass-produced video game. Only one unit was built initially, although the game later included several consoles allowing users to play against each other.