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Spacewar!
Developer	Steve Russell et al.
Released	1962
Genre	Space combat simulation, Shoot 'em up
Mode(s)	Two players, simultaneously (only)
Platform(s)	PDP-1

Spacewar! is one of the earliest known digital computer games.

Steve "Slug" Russell, Martin "Shag" Graetz and Wayne Wiitanen of the fictitious "Hingham Institute" conceived of the game in 1961, with the intent of implementing it on a DEC PDP-1 at the Massachusetts Institute of Technology. After Alan Kotok obtained some sine and cosine routines from DEC, Russell began coding, and by February 1962 had produced his first version. It took approximately 200 hours of work to create the initial version. Additional features were developed by Dan Edwards, Peter Samson, and Graetz.

Contents 1 Gameplay 2 Options and features 3 A PDP-11-based GT40 Implementation at DEC 4 Spacewar! today 5 Other games inspired by Spacewar! 6 Earlier computer and video games 7 See also 8 References 9 Notes 10 External links

The basic gameplay of Spacewar! involves two armed spaceships called "the needle" and "the wedge" attempting to shoot one another while maneuvering in the gravity well of a star. The ships fired missiles which were unaffected by gravity (due to a lack of processing time). Each ship had a limited number of missiles and a limited supply of fuel. Each player controls a ship, and must attempt to simultaneously shoot at the other ship and avoid colliding with the star. Player controls included clockwise and counterclockwise rotation, thrust, fire, and hyperspace, using either the front-panel test switches with four switches for each player or optional control boxes.

The hyperspace feature could be used as a last-ditch means to evade enemy missiles, but the reentry from hyperspace would occur at a random location and there was an increasing probability of the ship exploding with each use.

Early versions of the game contained a randomly generated background starfield. However, the inaccuracy and lack of verisimilitude annoyed Samson, so he wrote a program based on real star charts that scrolled slowly: at any one time, 45% of the night sky was visible, every star down to the fifth magnitude. The program was called "Expensive Planetarium" (referring to the price of the PDP-1 computer), and was quickly incorporated into the main code.

There were several optional features controlled by sense switches on the console:

• no star (and thus no gravity)
• enable angular momentum
• disable background starfield
• the "Winds of Space"- a warping factor on trajectories that required the pilot to make careful adjustments every time they moved

Spacewar! was a fairly good overall diagnostic of the PDP-1 computer and Type 30 Precision CRT Display, so DEC apparently used it for factory testing and shipped PDP-1 computers to customers with the Spacewar! program already loaded into the core memory; this enabled field testing as when the PDP was fully set up, the field representative could simultaneously relax and do a final test of the PDP.

When the PDP-11-based GT40 vector graphics system was developed, Spacewar! was re-implemented to run on this system. As with the original version, gameplay was controlled by the front-panel toggle switches with four switches for each player controlling ship rotation left, ship rotation right, thrust, and weapons fire. It was quite common to see the paint worn off of the PDP-11 control panel above the eight switches used for Spacewar!.

Because the missiles were launched with a velocity that was relative to the ship, a common ploy in this version of the game was to fire a missile while being whiplashed by a close approach to the sun. If the firing ship was pointing backwards along its orbital path, the fired missile had almost no absolute velocity and was simply left floating in space. If the opponent was not paying close attention, they would simply fly into such a lurking missile as they pursued and thereby be destroyed.

Vint Cerf playing Spacewar! on the Computer History Museum's PDP-1, ICANN meeting, 2007

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. 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. On May 15, 2006, the museum presented The Mouse That Roared: A PDP-1 Celebration Event. The PDP-1 was demonstrated running Spacewar! as well as other programs, and members of the public were able to play the game using makeshift controllers. Further PDP-1 demonstrations will be scheduled on a biweekly basis on Saturday afternoons. Most recently, Spacewar! code has been given out with Microsoft XNA Game Studio Express.[1]

Over the years, many computer games have been inspired by Spacewar!; some are known by the same name. Some are straightforward clones, but most have introduced additional variations to the game play, such as:

• various rates of acceleration
• various levels of gravity (even negative)
• missiles affected by gravity
• fuel (energy) regeneration over time
• shields

Arcade versions of Spacewar! were released as the Galaxy Game (1971), Computer Space by Nutting Associates (1971), and Space Wars by Cinematronics (1977), the last being the most commercially successful.

The first networked version of this genre was Orbitwar(1974) by Silas Warner on the PLATO network. It included all the features of the original Spacewar! with the addition of a Big Board where PLATO users would await challenges from each other to play.

Home versions have appeared for most computer and console systems, with some becoming quite elaborate, such as the Star Control series, introducing a wide variety of gameplay frameworks around the basic one-on-one combat system at its core. Senko no Ronde can be described as a modern interpretation of Spacewar!, with a design heavily inspired by versus fighters such as Street Fighter II. The Escape Velocity series also owes its 2D inertial combat and navigation to Spacewar!.

Non-space themed variants with similar play (ie two players control a vehicle using similar controls - ie rotate left / rotate right / move forward / fire - and try to score by hitting their opponent with a missile, include Tank by Kee Games and Combat by Atari.

Although some accounts mistakenly identify Spacewar! as a motivation for the development of Unix, the game involved in that case was Space Travel.^[2]

The first graphical computer game is believed to have been OXO (a Tic-tac-toe game), developed by A.S. Douglas in 1952. William Higinbotham built Tennis for Two in 1958 using discrete analog hardware rather than a program for a digital computer.

• PDP-1
• Expensive Planetarium
• Alan Kotok
• Marvin Minsky
• Star Control

• Spacewar! page at the Computer History Museum
• History of Spacewar!
• The original Spacewar! code running on PDP-1 emulator in Java
• Dmoz directory for Spacewar!
• 1up.com's article naming Spacewar! the most important video game ever made
• "Spacewar", a 1972 Rolling Stone article by Stewart Brand
• A 1972 Saga Magazine article about Spacewar!
• Computer and Video Game History describes Spacewar! and earlier video games such as A.S. Douglas' Tic-Tac-Toe and William Higinbotham's Tennis for Two