286 and for that matter even 386 has the segment-based memory protection mechanism that is somewhat reminiscent of Burroughs mainframes, GECOS and maybe AS/400.

286 and for that matter even 386 has the segment-based memory protection mechanism that is somewhat reminiscent of Burroughs mainframes, GECOS and maybe AS/400. There are two giant issues with the idea: it does not work that well on 16b word system and it is totally incompatible with what most of existing code written in C expects. So with 386 Intel had combined that mechanism with traditional MMU and somewhat hack-ish method to turn all that of (reportedly because Microsoft wanted that for Windows/386)