Memory protection was not possible on the 8086 and quite half-baked on the 80286 (you could switch to protected mode but then you lost access to hardware BIOS f

Memory protection was not possible on the 8086 and quite half-baked on the 80286 (you could switch to protected mode but then you lost access to hardware BIOS facilities that relied on real mode, and switching back to real mode required hard-faulting the processor because there was no architectural support for it). The Intel 80386 was the first fully-featured x86 CPU wrt. running memory protected OS's.