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From: jru@etn-rad.UUCP (John Unekis)
Newsgroups: comp.sys.ibm.pc,comp.arch,comp.unix.wizards
Subject: Re: 386 demand paged virtual memory
Message-ID: <268@etn-rad.UUCP>
Date: Wed, 2-Sep-87 20:13:21 EDT
Article-I.D.: etn-rad.268
Posted: Wed Sep  2 20:13:21 1987
Date-Received: Sat, 5-Sep-87 08:22:20 EDT
References: <125@snark.UUCP> <299@nuchat.UUCP> <358@netxcom.UUCP>
Reply-To: jru@etn-rad.UUCP (0000-John Unekis)
Organization: Eaton Inc. IMSD, Westlake Village, CA
Lines: 33
Xref: mnetor comp.sys.ibm.pc:7420 comp.arch:2055 comp.unix.wizards:4043

In article <358@netxcom.UUCP> jallen@netxcom.UUCP (John Allen) writes:
>In article <299@nuchat.UUCP> steve@nuchat.UUCP (Steve Nuchia) writes:
>>	I saw an add that indicated that the V/386 product
>>	supported "demand paged virtual memory".  I this
>>	true, or have they come up with an obscure new
>>	meaning for those words?  I didn't think the 386
>>	had the hardware for real demand paging, am I wrong?
>
>The 386 processor has:
>
>64 terabytes of virtual address space,
>A page fault interrupt (14),
>and
>A restartable instruction set (two avoidable exceptions).
>
>What else would one need?

What else ?  How about an algorithm to timestamp the segments in the 
page list to determine the oldest ones for swapping to disk, to lock pages
in memory during I/O, to perform the disk I/O to a core image on a swap 
volume, to assign variable swapping priorities to pages to keep kernal
routines from swapping out and causing thrashing, etc., etc., etc.

When they say that the 80386 "supports demand paged virtual memory", what 
they mean is that since your operating system will have to manage tasks
as a group of segments in memory anyway, why not make the segments a small
fixed size and call them pages instead. Your operating system will still
be doing all the work, but using segments to represent virtual pages 
makes it look like intel had a reason for preserving segmentation beyond
continued compatibility with the 8086.

---------------------------------------------------------------
disclaimer: I was acting under orders from Ollie.