Spacewar! (was Re: Laser display...)

From: Eric Smith <>
Date: Wed Feb 16 13:46:03 2005

Philip wrote:
> ISTR there was another game I wanted to play on one of my machines -
> there was a star in the middle of the screen, and two ships. The
> ships tended to move towards the star, and the objective was for one
> player to destroy the other player's ship by firing missiles.

der Mouse wrote:
> Spacewar, yes. One could argue it was the very first video game.

You don't have to argue. A court ruled that it was.

> Originally written for the..PDP-6, I think.


We *almost* got Spacewar running on the PDP-1 at the Computer History
Museum last night. The starfield and sun came up. (Both can be disabled
with sense switches.) The sun didn't look right. The ships appeared
directly above and below the sun, and did not look right. The ships
would only move on the vertical axis. Torpedos appeared from locations
with the same Y coordinate as the ship, but different X coordinates.
It appears that the game knows the correct X coordinates of the ship,
but is having trouble computing the points needed to actually display
it. Our current hypothesis is that either the CPU broke since we last
ran the instruction diagnostics, or there is a CPU fault not cuught
by the diags. At next week's meeting we will run the diags again.

We discovered that the reason that my test program to produce a
full-scale-deflection square with diagonals did not work correctly
last week is that the Type 30G Precision CRT Display has two
undocumented (and poorly labelled) switches that can be used to
set the X and Y origins to either the screen center (normal) or the
lower left corner. The program was written for the origin in the
center, but last week we had the switches in the wrong positions.
We ran the test program again, and it worked fine.

Apparently Spacewar was routinely used as a general PDP-1/Type 30
confidence test. It didn't require extended memory, or any
peripherals other than the Type 30, though if you wanted to play
it very much you'd want to wire up the interface to control boxes
rather than using the console toggle switches.

Received on Wed Feb 16 2005 - 13:46:03 GMT

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