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From: johnl@ima.ima.isc.com (John R. Levine)
Newsgroups: comp.unix.xenix,comp.unix.microport
Subject: Re: Programs larger than real memory on an 80286 ???
Message-ID: <2631@ima.ima.isc.com>
Date: 15 Sep 88 16:52:54 GMT
References: <235@extro.ucc.su.oz> <466@uport.UUCP> <183@fsc2086.UUCP> <9391@ico.ISC.COM>
Reply-To: johnl@ima.UUCP (John R. Levine)
Organization: Not much
Lines: 20

In article <9391@ico.ISC.COM> rcd@ico.ISC.COM (Dick Dunn) writes:
>     - It's not practical to have mixed sizes of demand-pageable memory
>       chunks:  It immensely complicates swap-space allocation and page-
>       scheduling algorithms.  It's likely to cause serious fragmentation
>       of physical memory.  There isn't even any significant body of know-
>       ledge about how it would work-- ...

Sure there is, the B5000 series had an addressing architecture somewhat like
the 286 with lots of segments of various sizes, and they got its virtual
memory to work around 1960.

Then again, given that a 286 segment can and usually will consume an
appreciable part of physical memory, that some 286 chips don't take page
faults reliably, and that the cost difference between a 286 system and a 386
system is rapidly vanishing, I won't argue that it's a waste of time to try to
make a virtual memory 286 Unix.
-- 
John R. Levine, IECC, PO Box 349, Cambridge MA 02238-0349, +1 617 492 3869
{ bbn | think | decvax | harvard | yale }!ima!johnl, Levine@YALE.something
Rome fell, Babylon fell, Scarsdale will have its turn.  -G. B. Shaw