[p_l]

My beard is not grey enough to have actually participated in this, but this is what I gathered as hobbyist:

TENEX started out as modification of TOPS-10 code base, afaik due to expanding needs leading BBN to create both TENEX and custom pager addon to PDP-10. Some time later DEC acquired TENEX code, cut it down some, modified some, and released it with support for the official DEC pager included in later PDP-10 models

[pinewurst]

I don’t think any of it came from TOPS-10. Tenex was essentially a port of the Berkeley Project Genie SDS940 OS to the PDP-10+demand paging from a custom (non-DEC) MMU.

[p_l]

After refreshing my memory a bit, indeed it was not forked from TOPS-10, but instead had what was essentially a syscall emulation layer for TOPS-10 binaries, something that ended up also present in some other PDP-10 OSes I think

[ChuckMcM]

That is what I remember. Basically this allowed it to run binaries built for TOPS-10.

At USC we ran TOPS-10 on the student machines and TENEX, and then later, TOPS-20, in the engineering computer lab. The TOPS-20 migration allowed us to run some accounting package from the student side on the staff side. That helped mitigate some of the impact on response time on the student side which was really poor with a couple hundred students logged in at the same time.