Man, this is not a criticism or anything, but all your questions are always beyond what I can think of and beyond me. In fact, they seem to short-circuit my brain on the first reading. And when I see people actually answering you, there's a "kaboom" within my skull. There's so much I don't know. Sorry, just had to let this out. 😁

I sometimes like questions like this because they are a good test of attention span and most people are easily lost early on. Also multy subject questions and statements that change quickly often lose people because of their lack of focus 😉 On the other end some people make complication of out very simple things to the point they become confusing. As for your question I thought that DEC was more or less almost dead/out of market by the mid 90s when they are bought out by Compaq. I don't know much in detail about DEC.

Ultrix was for mips/pdp11/vax equipment, osf/1 was for alphas [and became Tru64].