Sidetracking just a little bit, but I can't resist :
Dave Kreskowiak wrote:The bug was fixed starting with the 1976 production.
At CERN, the same thing happened with two completely independent computer families: First, CERN had bought the VAX 780, the very first VAX. When DEC announced the smaller VAX 750, they proudly announced that the 780 bug that made one instruction give rather unexpected results (sorry, I don't remember which instruction), CERN immediately stood up in protest: No! We have written our software to specifically compensate for that bug! If you change it in the 750, so that it gives a different, 'correct' result, we must update our software for that, and we have to maintain different program versions for the 780 and the 750. That is out of the question, and we will not buy any VAX 750.
The bug was not fixed in the VAX 750.
And the story repeats: CERN had used NORD-10 computers for process control (much due to extremely good interrupt handling: The first instruction of the handler was running 900 ns after the arrival of the interrupt signal, which was super-fast in the mid-1970s). Then comes a complete reimplementation of the architecture, labeled ND-100, with a similar happy message: Finally, we have fixed the bug that has been with the NORD-10 since its introduction ... CERN reacted in the same way: If you fix that bug, we can no longer run our software on your new machines; we have adapted to that bug! We will not buy any ND-100!
So the bug from NORD-10 was retained in the ND-100 - just like with the VAX.