If I'm not mistaken, most modern CPU architectures implement virtual memory in hardware for the obvious reason that checking every memory access with software would be very slow (essentially require running in a virtual machine) - this is not an area where the Burroughs architecture remained ahead of the times even in 1982 (at least w.r.t. Mainframes and minis). (The 68020 had a PMMU coprocessor which was included on chip in the 68030 and later. Similarly the 80386 iirc.)