Tandem memo (why do computers stop)

On 30 Oct 2007 at 9:17, Chris Kennedy wrote: Yes, but as I said "it's nothing that simple"--to say that it was would be completely discounting the enormous investment in software that Tandem made to produce their NonStop systems. Heck, back around then, a friend and I prototyped a system with three PC/XT's and a proprietary expansion card that did three-way voting and also performed hot replacement of failed processors. Basically a garage operation and nearly sold to a then-cash-rich Everex. Maybe good enough for process control, but too weak for anything more involved than that. Our selling point was that it was off-the-shelf and cheap. I think I still have the OrCAD files for our board somewhere on a 5.25" 360K floppy. We did nothing about what software ran on the system--and that was the giant weakness. Without software, it was just another interesting piece of iron. Simple redundancy doesn't always identify which of the two systems is producing the error--only that there was an error--and that's where Tandem's genius comes in. Tandem was a whole world apart--not only did they have hardware redundancy (which would have been no great shucks back then), but their software was constructed along a modular transaction-based model, so that transactions were never lost. (Hence the popularity of these in the banking sector). Cheers, Chuck