Microkernels are better
Posted Feb 26, 2013 10:46 UTC (Tue) by khim
In reply to: Microkernels are better
Parent article: MINIX 3.2.1 released
Didn't Intel use that to get round a small address bus? And wasn't it absolutely useless for security?
They are designed to be used for security and, e.g. OS/2 1.x used them for security. Sadly they broken the backward-compatibility on the way: you could use segments solely to extend memory or for security on 80286 — but not simultaneously. 80386 solved that problem but it introduced UNIX-like paging model and everyone forgot about segments.
iirc, assuming a 4K segment, addressing 4K+1 in segment 1 would get you the first byte of segment 2. On Primes, different segment meant different memory.
You can do that on 80386, too: it really depends on how your GDT/IDT/LDT are arganized. You can even change sizes of segments on the fly. Actually this architecture was pretty sophisticated and flexible, but it was pushed to the slow-path (and eventually eradicated in x86-64) when AMD and Intel found out that nobody uses it.
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