Initially conceived by Steve Russell, Martin Graetz and Wayne Wiitanen in 1961, Spacewar! is considered one of the earliest video games for a digital computer. The first version was written by Steve Russell in 1961. Significant improvements to the game were made in the spring of 1962 by Peter Samson, Dan Edwards and Martin Graetz. The game was rapidly copied and became a staple demonstration program for showing the sophisticated graphical capabilities of the PDP-1 system.

		It all began in the fall of 1961, when Digital Equipment Corporation's first production-model PDP-1 was installed in the "Kluge Room" next door to the TX-0. Its arrival had been anticipated for months; an early brochure announcing the machine had been circulating for some time. It was clear that the PDP-1 had TX-0 genes - the hackers would certainly feel right at home. The PDP-1 would be faster than the Tixo, more compact, and available. It was the first computer that did not require one to have an E.E. degree and the patience of Buddha to start it up in the morning. You could turn it on any time by flipping one switch, and when you were finished, you could turn it off. We had never seen anything like that before. Long before the PDP-1 was up and running Wayne, Slug, and I had formed a sort of ad-hoc committee on what to do with it, and in particular what to do with the Type 30 Precision CRT display that would arrive shortly after. It was clear from the start that while Bouncing Ball, the Mouse, and HAX were clever and amusing, they really weren't very good as demonstration programs. A good demonstration program ought to satisfy three important criteria:
THE STARTING POSITION: The ships are in the centers of diagonally opposite quadrants - you can see the stars of Orion at the left.

With the Fenachrone hot on our ion track, we dumped ideas on the table..."Look, you need action and you need some kind of skill level. You have be able to control things moving around on the scope." We warmed up the third-order projectors. "Spaceships are nice." "Doing what - a race? A contest?" We aimed our DeLameters at the zwilnik base, and fired simultaneously. "SPACEWAR!" we cried, as the last force screen flared into the violet and went down. (No, really, he did write like that.) The basic rules developed quickly. There would be at least two spaceships, each controlled by a set of console switches ("Gee, it would be nice to have a joystick or something like that..."). The ships would have a supply of rocket fuel and some sort of a weapon - a ray or beam, or possibly a missile. For really hopeless situations, we needed a panic button. Hmmm. . .aha! Hyperspace! And that, pretty much, was that.
		Spacewar "CBS Opening" from a eye-like shape.

		First Steps - By the end of 1961, all the elements were in place: a brand new, available computer, a cloud of eager hackers, tolerant (when not actively implicated) employers, and an exciting idea. Steve Russell was getting the heat from everyone to Do Something about Spacewar. Slug produced the first object-in-motion program in January 1962. This was nothing more than a dot that could accelerate and change direction under switch control. Even without a hardware multiply- divide capability - on the early PDP-ls, anything stiffer than integer addition and subtraction had to be done by subroutine - the computer was clearly not being pushed.
Spacewar photo from the PDP-1 CRT screen.

From dot to rocket ship was a surprisingly easy step, "I realized," Slug says, "that I didn't have to worry about the speed of the sine-cosine routine, because there were only two angles involved in each frame - one for each ship. Then the idea of rotating the grid came out." The ship outlines were represented as a series of direction codes starting from the nose of the ship - when the ship was vertical and tail-down, each code pointed to one of the five possible adjacent dots that could be displayed next. To display the ship at an angle, Russell added the appropriate sine and cosine to the original direction code constants, in effect rotating the entire grid. With this method, the two ships' angles had to be calculated only once in each display frame.

By February, the first game was operating. It was a bare-bones model: just the two ships, a supply of fuel, and a store of "torpedoes" - points of light fired from the nose of the ship. Once launched, a torpedo was a ballistic missile, zooming along until it either hit something - more precisely, until it got too close to a ship or another torpedo - or its "time fuse" caused it to self-destruct. The classic needle and wedge space ship outlines and the opposite-quadrant starting positions were established at this stage. Acceleration was realistic; it took time to get off the mark, and to slow down you had to reverse the ship and blast in the other direction. The rocket's exhaust was a flickering "fiery tail." At first, rotation was also realistically inertial, but the ships were so hard to control that Slug hid that feature under a console switch, and converted rotation into a simple start/stop effect - a sort of rotational Bergenholm, guess.
		1963 Screenshot of the Spacewar computer game.

It was apparent almost immediately that a feature less background was a liability as it was hard to gauge relative motion. When the ships were moving slowly you couldn't tell if they were drifting apart or together. What we needed, obviously, were some fixed stars. Russell created a random display of dots, and the quality of play improved. The only thing left, we thought, was Hyperspace, and that win the way. In fact, we'd only just begun.

		The Stars of the Heavens - One of the forces driving the dedicated hacker is the quest for elegance. It is not sufficient to write programs that work. They must also be "elegant," either in code or in function - both, if you can manage it. An elegant program does its job as fast as possible, or is as compact as possible, or is as clever as possible in taking advantage of the particular features of the machine in which it runs, and produces its results in an aesthetically pleasing form without compromising either the results or operation of the other programs associated with it. "Peter Samson," Russell remembers, "was offended by my random stars." In other words, while a background of miscellaneous points of light might be all very well for some run-down jerkwater space fleet, it just wouldn't do for the Galactic Patrol. So Samson sat down and wrote Expensive Planetarium.
1964 Crews playing Spacewar at the AFIPS Fall Joint Computer Conference.

Using data from the American Ephemeris and Nautical Almanac for stars brighter than fifth magnitude, Samson encoded the entire night sky between 22.5°N and 22.5°S, thereby including most of the familiar constellations. The display could remain fixed or move gradually from right to left, ultimately displaying the entire 45°-wide firmament. The elegance does not stop there. On the MIT machine, each dot was either on or off - essentially a 1-bit pixel. But you could make it brighter by intensifying the point repeatedly before the phosphor could decay. By firing each point the appropriate number of times, Samson produced a display that showed the stars at something close to their actual relative brightness. An attractive demonstration program in its own right, Expensive Planetarium was duly admired and "inhaled" into Spacewar!

The Heavy Star - Up to this point, Spacewar! was heavily biased toward motor skills and fast reflexes, strategy counting for very little. Games tended to become nothing more than wild shoot-outs, which was exciting, but ultimately unrewarding. Some sort of equalizer was called for. Steve Russell recalls, "Dan Edwards was offended by the plain spaceships, and felt that gravity should be introduced. I pleaded innocence of numerical analysis and other things, so Dan did the gravity calculations." The Heavy Star blazed forth from the center of the screen, its flashing rays a clear warning that it was not to be trifled with. Its gravity well encompassed all space - no matter where you were, if you did not move you would be slowly drawn into the sun and destroyed. (As a gesture of good will toward beginners and less skillful players, a switch option turned annihilation into a sort of hyperspatial translation to the "anti-point' that is, the four corners of the display.)
		1983 Alan Kotok, Steve Russell, Martin "Shag" Graetz play Spacewar! at the Computer Museum.

		After Spacewar - In May, 1962, the first meeting of DECUS (Digital Equipment Computer Users' Society) was held in Bedford, Massachusetts. At the meeting, I delivered the first paper on the subject, pretentiously entitled "Spacewar! Real-Time Capability of the PDP-1". Over the summer, the original Spacewar! hackers began to drift away. Alan Kotok and I went to work for Digital. Steve Russell followed John McCarthy to the SAIL. Peter Samson and Bob Saunders stayed in Cambridge for a while, but, eventually, they too went west. Dan Edwards remained with the Al group for a few years, then moved to Project MAC - along with Jack Dennis and the PDP-1 - which soon evolved into MIT's Laboratory for Computer Science.
A PDP-1 Emulator running SpaceWar.

Others took up the maintenance and development of Spacewar! as program tapes began showing up all over the country. The game migrated not only to almost every PDP built by DEC, but also to just about any research computer that had a program mable CRT. Eventually it even showed up in video arcades in the form of Cinematronics' hulking Space Wars and inspired the Atari classic Asteroids. Most attempts to port Spacewar! successfully to the PC or Macintosh did not succeed. Spacewar! on a PDP-1 was reviewed for the opening of the Computer Museum in Boston, in 1984, with joysticks substituting for the long-lost control boxes. The PDP-1 has since been retired to California, and the Computer Museum itself is history, having been merged into Boston's Museum of Science in 1998.

Previous efforts in bringing the experience of Spacewar! to a mass market were centered on the minicomputer paradigm of the college campuses where it originated - that of a central computer distributing software to various remote terminals. Computer Space was innovative for establishing the basic form of all arcade games to come - that of a dedicated computing device built to play only that one game. Computer Space was released in November 1971 by Nutting Associates. Created by Nolan Bushnell and Ted Dabney, who would both later found Atari. Computer Space was the first widely available video and arcade game, although it was not a success. For many, the gameplay was too complicated to grasp quickly.
		The 1971 Computer Space arcade cabinet.

While it fared well on college campuses, it was not very popular in bars and other venues. Bushnell later recruited Al Alcorn and created a sensation with the much easier to grasp Pong arcade game modeled on Ralph Baer's Magnavox Odyssey home system's Tennis game.

		Space War was one of the eleven Atari 2600 titles that were part of the second wave of games released in 1978. It is loosely based on Spacewar. Two players compete against each other by piloting a space craft equipped with photon torpedoes. The winner is the player who destroys the opponent more times. The first mode stays true to the traditional essence of Spacewar!; players pilot warring space craft in an effort to earn the most points by destroying the opponent. Various options are offered, such as invisible barriers around the edge of the screen, or the ability to warp across the screen, and the presence of a gravity producing sun.
1978 Atari 2600 game Space War (cover).

In the early days of video games, teaching players how to understand momentum and inertia was a challenge. The game attempts to model idealized Newtonian physics, so once a ship is floating through space, nothing is going to slow it down unless the player applies some thrust in the opposite direction. The speed of each player's missiles is also affected the speed of the ship firing them. It was released as Space Combat under the Sears Telegames label.

As of May 2006, there is only one working PDP-1 known to be in existence, at the Computer History Museum in Mountain View, California. The computer and display were completely restored after two years of work, and Spacewar! is operational. On selected days at the Museum, visitors on the PDP-1 tour get a chance to play Spacewar! first hand. A second PDP-1 belonging to the Computer History Museum is currently on tour as part of the Game On exhibition, previously shown at the Barbican in London. However, this PDP-1 is not operational.