At the Higham Institute sessions some months back, he and his friends had discussed the criteria for the ultimate display hack. Since they had been fans of trashy science fiction, particularly the space opera novels of E. E. “Doc” Smith, they somehow decided that the PDP-1 would be a perfect machine to make a combination grade-B movie and $120,000 [about $950,000 today —Editor] toy. A game in which two people could face each other in an outer-space showdown. …
Peter Samson, for instance, loved the idea of Spacewar, but could not abide the randomly generated dots that passed themselves off as the sky. Real space had stars in specific places. “We'll have the real thing,” Samson vowed. He obtained a thick atlas of the universe, and set about entering data into a routine he wrote that would generate the actual constellations visible to someone standing on the equator on a clear night. All stars down to the fifth magnitude were represented; Samson duplicated their relative brightness by controlling how often the computer lit the dot on the screen which represented the star. He also rigged the program so that, as the game progressed, the sky would majestically scroll at any one time the screen exposed 45 percent of the sky. Besides adding verisimilitude, this “Expensive Planetarium” program also gave rocket fighters a mappable background from which to gauge position. The game could truly be called, as Samson said, Shootout-at-El-Cassiopeia.
Another programmer named Dan Edwards was dissatisfied with the unanchored movement of the two dueling ships. It made the game merely a test of motor skills. He figured that adding a gravity factor would give the game a strategic component. So he programmed a central star a sun in the middle of the screen; you could use the sun's gravitational pull to give you speed as you circled it, but if you weren't careful and got too close, you'd be drawn into the sun. Which was certain death.
Before all the strategic implications of this variation could be employed, Shag Garetz, one of the Higham Institute trio, contributed a wild-card type of feature. He had read in Doc Smith's novels how space hot-rodders could suck themselves out of one galaxy and into another by virtue of a “hyper-spatial tube,” which would throw you into “that highly enigmatic Nth space.” So he added a “hyperspace” capability to the game, allowing a player to avoid a dire situation by pushing a panic button that would zip him to this hyperspace. You were allowed to go into hyperspace three times in the course of a game; the drawback was that you never knew where you might come out. Sometimes you'd reappear right next to the sun, just in time to see your ship hopelessly pulled to an untimely demise on the sun's surface. In tribute to Marvin Minsky's original hack, Garetz programmed the hyperspace feature so that a ship entering hyperspace would leave a “warp-induced photonic stress emission signature” a leftover smear of light in a shape that often formed in the aftermath of a Minskytron display.
The variations were endless. By switching a few parameters you could turn the game into “hydraulic Spacewar,” in which torpedoes flow out in ejaculatory streams instead of one by one. Or, as the night grew later and people became locked into interstellar mode, someone might shout, “Let's turn on the Winds of Space!” and someone would hack up a warping factor which would force players to make adjustments every time they moved. Though any improvement a hacker wished to make would be welcome, it was extremely bad form to make some weird change in the game unannounced. The effective social pressures which enforced the Hacker Ethic which urged hands-on for improvement, not damage prevented any instance of that kind of mischief. Anyway, the hackers were already engaged in a mind-boggling tweak of the system they were using an expensive computer to play the world's most glorified game!
Whenever I read Hackers, I was always wanted to play the version of Spacewar described and see the code. Sure, I had played the arcade version multiple times, and I even had a version of Spacewar for the IBM PC that I ran through a disassembler, printed the results and spent a summer going over the code (okay, this was back when I had the time to do such things, in high school) to see how it worked, but neither version sounded quite like the description in Hackers.
Now, thirty years later, computers are now fast enough that an emulator of the original Spacewar can be written in a scripting language and run on a web browser! Even better (well, for various values of “better”) is the extensive writeup about how Spacewar works, along with the actual source code (along with explanations of how one programs the PDP-1, a 5MHz 18-bit 1's complement machine with 4,096 18-bit words of memory.
My, how far we've come in 50 years.