The Spacewar! wiki last edited by bhtav on 12/21/15 01:38PM View full history


Spacewar! was one of the first graphical video games in existence. There were games before Spacewar!: two frequently cited examples are OXO, a Tic-Tac-Toe game developed by A.S. Douglas in 1952; and Tennis for Two, developed by William Higinbotham as an independent analog device (instead of a piece of software developed for an existing system).

The impact, though, of Spacewar! and its resultant dissemination among the small groups of computer users and programmers at the time arguably helped pave the way for the popularity of video games in the future.


PDP-1, note typewriter interface and round monitor
PDP-1, note typewriter interface and round monitor

The Massachusetts Institute of Technology had acquired an expensive computer called the PDP-1 from Digital Equipment Corporation, and had hired on several students attending the university to develop programs for the machine. Among these programmers were Steve "Slug" Russell and Martin "Shag" Graetz. Wayne Wiitanen contributed to the design and evolution of the game, but did not help in the actual writing of the code. In 1961, these three conceived of a complex program which would fully utilize the computer's vector based, circular cathode ray tube monitor, while fulfilling their ambition to see a game that reflected pulp science fiction sensibilities.

Using sine/cosine functions acquired by Alan Kotok from DEC, Steve Russell set about coding what would become Spacewar! in February of 1962. The reason, though, that the authorship of the game itself can not be put on one man was that the development of the game did not resemble the compartmentalized structuring that many programming firms use today. The basic game which Steve Russell wrote was later added to by other programmers, many working at what Russell had dubbed The Hingham Institute Space Warfare Study Group, a fancy way of saying Russell's house. As the game spread, the list of features and their designers grew.

Some of the influences on the game included E.E. Smith novels such as Skylark and the Lensman series, and Japanese sci-fi tokusatsu movies.


A modern play test through a working PDP-1
A modern play test through a working PDP-1

In the basic game, two players are pitted against each other in a duel. Each control a spaceship; one wedge shaped, one cigar shaped, which are destroyed if they run into any other object in the game.

Each ship has a limited number of torpedoes to fire at the other from the front of the craft, adding to the current speed of the craft, with a hit killing the target. These torpedoes have proximity fuses which would detonate if the torpedo gets too close to another object, including other torpedoes, eliminating the need for coding collision detection for them. The ships rotate about their center, and have thrusters, with limited fuel reserves, to propel forward. Initially, a random star field was added, because players needed to gauge their relative speed and position to try to be able to hit their opponent.

To help add variety to the battles, a hyperspace ability was added by Graetz, which allows ships to blink out of existence and reappear randomly elsewhere in the playing field; a mechanic used in later games such as Asteroids. Each time hyperspace is used, there is a chance that the ship will explode by coming too close to other objects. If hyperspace is used during a duel, the ship will automatically explode, to prevent player abuse of the feature. Finally, at the center of the playing area is a flickering star with gravitational influence upon the two ships, accelerating them slowly toward the center.

Rotate, thrust/hyperspace, fire
Rotate, thrust/hyperspace, fire

One notable addition is Peter Samson's star field (dubbed Expensive Planetarium, the term expensive being a joke referring to how much the machine itself had cost). This star field was is accurate representation of the night's sky, in contrast to the random star field coded by Russell. Samson's star field slowly rotates as the game progresses, giving players a full view of the actual position of stars over time. This did not add to game play as such, but it did show off the processing power of this machine to contemporaries.

Other options were added and features changed. These included toggle switches that altered gameplay: the central star's gravity could be switched on and off, the existence of angular momentum could be removed, the star field could be switched off, and a "winds of space" feature could be added which pushed spaceships in one direction, forcing players to use more thrust to go in certain directions and causing drift.

Players originally played the game using the debugging switches on the machine, but these quickly wore out, so controllers were built from scratch. These are the predecessors to modern video game joysticks.


A working PDP-1 at the Computer History Museum of Mountainview, CA. Note the streak effect behind the two ships, which helps opponents judge velocity.
A working PDP-1 at the Computer History Museum of Mountainview, CA. Note the streak effect behind the two ships, which helps opponents judge velocity.

As there was no video game market, and the machine that used Spacewar! was prohibitively expensive to all but the most wealthy institutions, it was decided that the game, as popular as it was with everyone who played it, would be distributed freely, and the source code was given to anyone who requested it. New PDP-1 machines were shipped with the game in their memory, both as a demonstration of its visual functions and its processing power. The game was also a valuable tool to debug the machine out of the box in case of irregularities.

Many early game programmers had their start with Spacewar! The game's influence helped energize the next generation of software designers, who would eventually create the first home video game consoles and arcade machines. Nolan Bushnell, who would later found Atari, created a conceptual clone of Spacewar! with single player capabilities. Others modified the design to include new features for the game, but because the memory of PDP machines could only hold so much code at one time, there were regional variations on the basic Spacewar! design. The ARPAnet, a pre-internet computer network, was used to disseminate different versions to others with similar systems.

Spacewar! was later remade in both arcade and home form. Features like gravity would later influence many games, and gravity, angular momentum, ammunition and fuel limits, and Samson's desire for a realistic star chart would hint at the coming desires for realistic physics and verisimilitude. Games that would borrow heavily from the formula of Spacewar! and its clones were Asteroids, now one of the famous games from the early era of popular video games, and Star Control, which even has a gravity well at the center of the play field while two ships with limited resources duel for supremacy.

While Spacewar! was incapable of entering every home on the expensive PDP, it helped show the appeal for such entertainment, and helped bring about the current age of video game entertainment.

Credited contributors


  • Steve "Slug" Russell
  • Martin "Shag" Graetz
  • Wayne Wiitanen

Initial Coding

  • Steve Russell

Contributing features

  • Dan Edwards
  • Peter Samson
  • Martin Graetz
  • Alan Kotok
  • Steve Piner
  • Robert A. Saunders

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