alt Hacker NewsXenix 2.1 could run on the IBM PC XT with Intel 8088 in late 1983, IIRC, and even before that on the Altos 586 which had MMU as an external chip.
Xenix 2.1 could run on the IBM PC XT with Intel 8088 in late 1983, IIRC, and even before that on the Altos 586 which had MMU as an external chip.
For that matter, the "second" version of UNIX ran on a PDP-11/20 with no memory protection or MMU, and there were a few versions after intended to run on similar hardware (LSX, MINI-UNIX).
The PDP-11's MMU option was closer to the 8088's segmentation model I think, but I've never coded either, so dunno really. It does seem like it was possible to port "PDP-11 UNIX" to a lot more platforms than would get "VMUNIX".