Is it possible to have a Unix OS for 80286 machine (or any machine without paged memory mechanism but with segmented memory)?
80286 is a CPU without TLB, Page tables; only with segmented virtual memory and segmented protection of memory.
Is it possible to have a Linux on such machine?
UPD: the processor is very old, so I only ask about historic versions, not the ultra modern linux 2.6.42.11 or Solaris 13 or FreeBSD 10 or ...
User Zack says that Xenix (based on original UNIX) was capable of running on 80286:
There certainly were Unixes that ran on the 80286 -- Xenix comes to mind -- but I don't know if there's anything that implements what you would call a modern programming environment.
I'd checked, the Xenix FAQ http://www.uni-giessen.de/faq/archiv/sco-xenix/msg00000.html says
QA1 ... The PC/AT offered hardware memory protection, and SCO Xenix/286 took advantage of it.
So it was a PC/AT (80286) unix, which did used a memory protection using segmented memory (unlike modern unixes which use page based memory protection).
According to http://www.deinmeister.de/x86modes.htm 80286 have memory protection only in terms of segments, not a pages (pages was added in 80386).