[TUHS] Any Interdata war stories?

[Lawrence Stewart]

It isn’t Unix related, but it is a fun Interdata war story.

I hung out at the MIT Architecture Machine in the early 70’s (the Media Lab before it was the Media Lab.)
The lab used Interdata minis, with homegrown software.  My part was designing and building
various I/O devices, including parts of a network interconnecting the various minis.

There were Interdata model 3, model 5, model 75, and one blazing fast model 85 with semiconductor memory.  The rest were core.

I think the first 7/32 we got had two 32K core modules.  There was a microcode bug, such that in some case the microcode did not disable a non-maskable interrupt, so if the ISR was so foolish as to cause one, the machine got stuck in an interrupt loop.  You couldn’t clear it by reset or by power cycling the machine, because core!  The bad state was in the memory and was non-volatile.  It was possible to clear (sometimes) by swapping the two core modules with the power off, if the other one didn’t have the poison bits, but if they did, the only thing that worked was to unplug the memory module with the power on.  Luckily the OS guys figured out how to fix the ISR before we trashed anything permanently.

-L