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To: linux-kernel@vger.kernel.org
From: Parag Warudkar <parag.warudkar@gmail.com>
Subject: Re: memory remapping, 4gb memory on 945gt
Date: Fri, 4 Jan 2008 23:02:56 +0000 (UTC)
Message-ID: <loom.20080104T225120-118@post.gmane.org>
References: <20080104154914.GA589@codeblau.de> <p73lk758sri.fsf@bingen.suse.de> <20080104181918.GA21797@gallifrey> <477EAD37.4070903@zytor.com>
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H. Peter Anvin <hpa <at> zytor.com> writes:

> 
> Supposedly WinXP-32 doesn't use memory over 4 GB even if it is available 
> (a market-segmentation decision of the part of Microsoft, to force 
> people to buy WinServer 2003; WinXP SP2 does PAE so there is no 
> technical reason.)  This probably has disincentivized hardware vendors 
> from providing support for remapping the memory from the aperture above 
> the 4 GB mark.  The logic isn't all that trivial, especially if the 
> aperture size is configurable, so I can understand why they would punt.
> 

The reason according to Microsoft is that enabling PAE induced driver
incompatibilities - to me it sounds quite plausible given the quality of drivers
for consumer versions of XP/Vista and the fact that 4GB RAM in consumer class
machine is a newer thing.

There is a KB document detailing the reasons for disabling >4Gb RAM in XP SP2
and later 32-bit OSes - http://support.microsoft.com/kb/888137 .

Parag


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