Threaded? I'm guessing you mean that it did paging, did that need
threads in the current sense?
Read this:
https://en.wikipedia.org/wiki/Threaded_code
Yep, used to make heavy use of this back in my first post-college job writing database
handlers in Macro11. Each transaction was just a table of subroutine addresses.
This was about the last thing I had to do on a non-UNIX platform for years.