The PDP-1, developed by Digital Equipment Corporation and donated to MIT, marked a significant moment in computing history by enabling the creation of the first computer game, Spacewar, in the early 1960s. Alan Kotok and Steve Russell, among others, adapted and enhanced the computer's capabilities, leading to innovative features such as collision detection and the use of gravity in gameplay. Spacewar became a collaborative project within the hacker community, with open-source code allowing for continuous modifications and leading to the invention of the first computer joysticks.

1. Spacewar
In the annals of hacking history, there are many great computing machines however; none
would change the history of computing as much as the (Programmed Data Processor-1) PDP-
1. Designed by Digital Equipment Corporation (DEC), it was donated to the MIT labs. The
PDP-1 replaced the TX-0. The TX-0 was the world’s first personal computer. Costing $3
million in the late fifties, it would trigger the formation of a dedicated community of hackers
around it.
The PDP-1 however would go on to make history. First produced in 1960, it would be on this
computer that music would first be created via a computer program and the first computer
game would be created.
When the PDP-1 was delivered to MIT, it came with a simple collection of systems software,
which the TX-0 hackers considered completely inadequate. The TX-0 hackers had become
accustomed to the most advanced interactive software anywhere, a dazzling set of systems
programs, written by hackers themselves and implicitly tailored to their relentless demands
for control of the machine.
Alan Kotok already an accomplished TX-0 hacker designed a debugger for the PDP-1 called
the DDT. It was him and a dedicated team of hackers that would write their own assembler
over a weekend. They accomplished this feat by reworking code from the TX-0 and not
sleeping!
During the summer of 1961, a plan for the most elaborate hack yet was devised. Steve
Russell and his friends came up with a plan to create an elaborate display hack on the PDP-1

2. using the CRT screen. They collectively agreed that the most effective demonstration of the
computer’s magic would be a visually striking game. Given their collective background in
science fiction, the team decided to build a game that would feature space warfare.
Steve Russell delayed starting work on the project for several months. When pressure
mounted from other hackers, he muttered that he had not started the project because he had
not figured out how to write the elaborate sine-cosine routines necessary to plot the
spaceships. Given the spirit of hackerdom, a library was found for the trigonometric functions
and work could start.
At that point, Steve Russell had no excuse. So he spent his off-hours writing this fantasy
PDP-1 game, the likes of which no one had seen before. He began in December 1961 and
when the calendar wrapped around to 1962, he was still hacking. By that time, Russell could
produce a dot on the screen that you could manipulate: by flicking some of the tiny toggle
switches on the control panel, you could make the dots accelerate and change direction.
He then set about making the shapes of the two rocket ships: both were classic cartoon
rockets, pointed at the top and blessed with a set of fins at the bottom. To distinguish them
from each other, he made one chubby and cigar-shaped with a bulge in the middle, while the
second he shaped like a thin tube. Russell used the sine and cosine routines to figure out how
to move those shapes in different directions. Then he wrote a subroutine to shoot a “torpedo”
(a dot) from the rocket nose with a switch on the computer. The computer would scan the
position of the torpedo and the enemy ship; if both occupied the same area, the program
would call up a subroutine that replaced the unhappy ship with a random splatter of dots
representing an explosion. (That process was called “collision detection.”)
In the later stages of programming, Bob Saunders helped Steve Russell out, and they hacked
a few intense six-to-eight-hour sessions. Sometime in February, Russell unveiled the basic
game. There were the two ships, each with thirty-one torpedoes. There were a few random
dots on the screen representing stars in this celestial battlefield. You could manoeuvre the
ships by flicking four switches on the console of the PDP-1, representing clockwise turn,
counter clockwise turn, accelerate, and fire torpedo.
Once a rough version of the game once shown to the community of hackers, there was no
going back! Since the code was open-source, modifications beyond the original design were
made to it.
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.

3. Another programmer, named Dan Edwards was dissatisfied with the unanchored movement
of the two duelling ships. He felt 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.
The variations made to the game where endless. Spacewar was played a lot of times. So much
so that Russell eventually wrote a subroutine that would keep scores (High Scores Screen). In
the course of playing Spacewar, the tedium involved in working the switches on the console
of the PDP-1 led to the invention of the first computer joysticks! The first computer joysticks
had their control boxes made of wood with Masonite tops. They had switches for rotation and
thrust as well as a button for hyperspace.
Like the hackers’ assemblers and other programs, Spacewar was never sold. It was placed in
the drawer for anyone to access, look at, and rewrite as they saw fit. Gradually the popularity
of the program would spread and DEC engineers would use it as a final diagnostic program
on PDP-1s before they rolled them out the door.
Sources
Hackers Heroes of the Computer Revolution by Steven Levy
Wikipedia en.wikipedia.org