You're confusing tops-10 and tops-20. Both were pdp-10 operating systems. tops-10 was a fairly ordinary timesharing system, built by DEC and probably with contributions from MIT in the early days. It started out as the operating system for the pdp-6. Each login session was one process (a `job'), there was no fork system call and the command interpreter was wired into the kernel.
tops-20 was DEC's evolution of BBN's Tenex, which was a much more interesting system, inspired by Multics. It had a fork system call and the command interpreter was an ordinary program, named `exec'. A fairly common host on the ARPAnet in the 1970s was a pdp-10 running Tenex or tops-20. It looks (to me at least) like Joy et al at Berkeley were familiar with Tenex and it influenced their thinking about how to do networking in 4.2BSD. David N. Cutler created RSX-11M by severely editing RSX-11D, thus creating the system that DEC's pdp-11 customers thought of as DEC's timesharing system, though it was nominally a multi-user real-time system (without typeahead) and DEC also offered RSTS, if you could live with BASIC as the only programming language. Cutler was the architect of VMS for the VAX, which looked to me like RSX on steroids. Indeed, the early VMS utilities were RSX pdp-11 binaries running in hardware and software compatibility modes. I don't see much tops-10 or tops-20 influence in VMS, though I didn't use VMS much. It sure didn't learn much from Unix. Process creation was a big deal, requiring an act of congress and sacrifice of goats. Cutler left DEC for Microsoft, and was the architect of Windows NT (WNT = VMS + 111). Process creation continued to require acts of congress and goats.
