Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!sco!seanf
From: seanf@sco.COM (Sean Fagan)
Newsgroups: comp.arch
Subject: Re: True 46 Bit Addressing with 586?
Keywords: Intel 586
Message-ID: <8833@scolex.sco.COM>
Date: 19 Nov 90 01:18:15 GMT
References: <21691@well.sf.ca.us>
Sender: news@sco.COM
Distribution: comp
Organization: The Santa Cruz Operation, Inc.
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In article <21691@well.sf.ca.us> feustel@well.sf.ca.us (David Alan Feustel) writes:
>The 386 and 486 are advertised as having 46 bit addressing and 4
>gigabyte segment length capability.  This overstates their capabilities
>slightly, since the mapping of all segments into the single 32 bit virtual
>address space implemented in the 386 and 486 imposes the restriction
>that the sum of the length of the code, data and stack segments must be
>less than or equal to 4 gigabytes (ignoring the degenerate case of all 
>descriptors pointing to the same memory).

Uhm, no, it doesn't.  Take a look at how memory management is done on the
*86 again, and you'll see a couple of different ways you can do it.

Now, it's not *easy*, not by a long shot.  And you end up having to swap
lots of different things out, completely.  But you can do it.  It's just not
worth the bother (IMNSHO).

Also, I don't believe you can get 46-bit addressing completely.  The chip
can have a total of 46-bit virtual addresses, but some of those are going to
be for ring 0, some for ring 1, etc.

-- 
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