"By the time SAGE was completely operational, the Soviet bomber threat had been replaced by the Soviet missile threat, for which SAGE was entirely inadequate."
They have a nice exhibit on this at the Computer History Museum in Mountain View, complete with actual old consoles and all. I highly recommend checking it out, had never heard of it before seeing it last year.
I don't know how the light gun worked, but the vector display used was pretty unusual. The 'Typotron' (a.k.a. 'Charactron') could display 25,000 characters per second. It didn't draw them in the usual fashion of a vector display. Instead it displayed them by deflecting the electron beam at the right location in a stencil, then deflecting it again to the right spot on the screen!
The Typotron was like a Charactron, but could store data, too. Apparantly the light gun was used only to click on light points, not on dark bits of the tube, so it was 'trivial' to determine what was clicked on (the second page of the PDF talks about how the light gun was basically invented and prototyped in one day somewhere in '48 or '49).
It probably wasn't that complicated. The light gun was used as a quicker means of selecting an object being drawn on the display. It doesn't seem to have ever been used to select or draw things in blank space.
Since a vector display always knows what object it is drawing a particular time, the presence of light at the tip of the gun is all you need to identify the object.
It did to Hollywood. Many decommissioned AN/FSQ-7 control panels were used in various movies and TV shows. Or maybe it was just the same one used over and over...
I'm sure there was some restoration, but I thought leaving the yellowed note on the phone with the General's number was a nice touch.
Those machines were pretty darned expensive. They were all taken very good care of. Except for the paper-handling equipment, almost anything that involved opening the cabinet would probably have been done by IBM personnel.
The military was also known for keeping just their ordinary stuff clean. It surely went double for the air defense computers. Top brass from the Pentagon were likely dropping by for a tour on a regular basis.
In the years following WWII as one of the only large industrial nations that had not been bombed to smithereens, the amount of capital the US had to spend on this kind of thing just boggles the imagination.
Wikipedia http://en.wikipedia.org/wiki/AN/FSQ-7 : The AN/FSQ-7 computer contained 55,000 vacuum tubes, occupied 0.5 acres (2,000 m2) of of floor space, weighed 275 tons, and used up to three megawatts of power. The fifty-two AN/FSQ-7s remain the physically largest computers ever built, and will likely hold that record in the future.
I don't have the citation to-hand, but part of SAGE's development cycle was a emulator/simulator on which tests were run. It was reported as being a reasonably effective debugging mechanism.
