Matt Shaver wrote: > On Sat, 2009-01-03 at 21:38 -0800, Rafael Skodlar wrote: > >> No modern PC with water cooling, tons of LEDs, or shiny fans look as >> good as PDP-8 or PDP-11/44 front panels. You could tell what system was >> doing just by looking at LEDs. >> > > I know what you mean, I started my computer career in 1981 working on > these and I've always found PCs rather bland in comparison: > > http://users.monash.edu.au/~ralphk/burroughs.html > > Scroll down until you get to "The awesome backplane. Source of many > intermittent faults and surely the last word in heroic complexity." I > learned a lot working on these... > Really not that much more complex than a VAX 11/780 or KL10B backplane. I actually found an intermittent fault on our 780 where a wire had been caught on the point of a wire-wrap pin, and the pressure eventually pierced the insulation. We had it down to a single card slot as that board indicated bad, but two replacements didn't fix the trouble. So, while the DEC tech was looking in the front, I just started scanning all the wires on the backplane near that slot.
Yeah, after years of having blinky lights to look at, I was rather disappointed with the VAX. We got the complete print set, an 11 x 17 monster about 3" thick. I looked at them to see if one could build a useful set of lights from signals available on the backplane, but found that the most useful signals were buried within certain boards. Bringing out physical memory address and data was was possible, but nearly useless on a virtual-address OS. And, the virtual address and data, program counter, etc. were all buried and didn't flow across the backplane. Since the machine was microcoded, it might have been possible to decode writes to these registers and duplicate them outboard, thereby latching the desired values as they flew by. That would likely have required decoding the microinstructions, and having to reprogram the panel after every microcode update. Definitely more effort than I was willing to put in. Jon ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
