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Called
the “Needle” and the “Wedge”, the ships were piloted by
two players who faced off in a deadly arena, firing torpedoes at one
another as they dodged and spun, fighting the pull of inertia as well
as each other. Because it was difficult to judge the ships’
relative speed on the black screen, Russell created a random star
field to fill the background.
Once the basic game was in
place, the programmers began a series of hacks to modify and extend
its play. Through their ad-hoc efforts, Spacewar moved beyond
its origins as a demonstration program and became a fully realized
game.
Originally controlled from input switches on the PDP-1’s
frame, Spacewar was awkward to play, giving the person nearer
to the CRT an advantage. Tech Model Railroad members quickly pieced
together hand-held controllers out of spare switches, plywood, and
Bakelite.
Russell’s random dot background was discarded and
replaced by an accurate star field called “Expensive Planetarium”.
Programmed by Peter Samson, Expensive Planetarium used star chart
data to display a night sky that accurately showed the
constellations, including the individual stars’ varying magnitudes.
In J.M. Graetz’s article “The Origin of Spacewar!”
reprinted in Supercade by Van Burnham, Russell said, “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.”
Introducing a
strategic element to the game, Dan Edwards devised the “Heavy
Star”, a burning sun in the middle of the screen whose gravity
affected the motion of the ships. If ships did not maintain thrust
the Heavy Star would slowly draw them down into its fire, forcing
players to consider its mass when vectoring their attacks.
Finally,
Graetz created the Hyperspace jump. If things were getting dicey,
panicked players could hit a jump button and warp their ship out of
danger, leaving a delicate photonic stress signature in their wake.
However, resorting to hyperspace was a risky maneuver as players had
only three chances to use it and its results were unreliable. Ships
emerged from hyperspace at a random location on the screen, possibly
out of harm’s way or possibly right into the Heavy Star.
By
the spring of 1962, the game dreamed up under the influence of cheap
sci-fi was finished.
Computer Bums
Not long after
completing Spacewar, the hackers began to drift apart, drawn
by their own Heavy Stars. Wiitanen was the first to leave, called up
for military duty during the Berlin Wall crisis in the fall of ‘61.
Russell left for the West Coast and joined Stanford’s AI
Laboratory. Graetz and Kotok went to work for Digital while Samson
and Edwards moved on to MIT’s new Project MAC laboratory.
But
Spacewar had a life of its own, spreading across the computer
world like a benign virus. “It was the program that was run into
the PDP-1 before it was shipped. It was the last thing--it was used
as actually as a final test,” Graetz said. Because the PDP-1’s
memory was composed of magnetic cores, small ferrite rings whose
polarity indicated whether a bit was 1 or 0, the game stayed in
memory even after the power was turned off. “Core memory is
non-volatile and once Spacewar was working they just shut the
machine down and shipped it. So when the customer set it up and
turned it on the first thing they saw was Spacewar,” he
explained.
Students at university computer labs embraced the
game, drawn to its perfectly tuned combination of twitch and
technique. Over the next decade, they would play Spacewar
obsessively, holding impromptu late night tournaments. It was ported
to every succeeding machine over the years with new generations of
hackers adding variations and refinements to the game’s design.
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