On 2012-06-30, Peter Humphrey <pe...@humphrey.ukfsn.org> wrote: > On Friday 29 June 2012 21:46:20 Grant Edwards wrote: > >> Things have been going steadily downhill since the days of V7 on a >> PDP-11 with 256K words of RAM, a 20MB hard drive and uucp via dial-up >> modems for "networking". Real programmers didn't _need_ more that >> 64k of text and 64k data to get the job done. > > Sorry, but that's just bloat. When I joined the software development > effort on the national grid control system in 1980 (I was the third of > three) we had two Ferranti Argus 500 computers, one on-line and one > standby, each with 32KB RAM (twice as much as the same machines had at > the newly commissioning AGR power stations)
Touche! > The displays were graphic stroke writers, as used in submarines and > other warships - none of that nasty raster technology. I think the > display drivers were more complex than the CPUs - all that D-A > conversion of multiple values at once. Can you imagine X and Y > amplifiers to drive a spot in a circle - and meet up? That's actually pretty trivial: Feed a sine wave into X and cosine into Y. AC amplitude controls size, DC offsets control position. Hint: cosine is just sine phase shifted by 90 degrees, so you can do that with a single resistor and capacitor. > Then a display full of them. Been there, done that. :) It was one of the standard junior-level homework lab assignements when I was in College back around 1980: design, build, and demonstrate a circuit that would display the contents of a 2716 EPROM (in binary) on an X-Y vector display (e.g. oscilloscope). It's not as hard as you might think. All it takes is a a counter, a half-dozen gates, and about three op-amps. It fit on one of these proto-boards: http://www.busboard.us/photos/BPS-IMG-BB830.jpg IIRC, it displayed one byte per line (eight '1' or '0' characters), eight bytes per "page". It used a dip-switch to select what "page" from the EPROM to display. Expanding the 8x8 display to something like 128x64 would just require slightly longer counters. -- Grant
