linux-kernel - Re: 4GB Physical. Less than 3GB in Linux.

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Date:	Mon, 16 Apr 2007 22:52:43 +0800
From:	"Jeff Chua" <jeff.chua.linux@...il.com>
To:	"Robert Hancock" <hancockr@...w.ca>
Cc:	lkml <linux-kernel@...r.kernel.org>
Subject: Re: 4GB Physical. Less than 3GB in Linux.

On 4/16/07, Robert Hancock <hancockr@...w.ca> wrote:
> Jeff Chua wrote:
> > I've noticed that with 4GB physical ram, I'm only see 3098000 MB on
> > the Dell 745, and 3107056MB on the IBM X60s.
> >
> > I've tested with CONFIG_HIGHMEM4G=y, CONFIG_HIGHMEM64G=y,
> > CONFIG_X86_PAE=y, but nothing makes any difference.
>
> Chipset limitation. It uses up most of the MMIO region above 3GB
> preventing RAM from being mapped there, and doesn't support remapping
> the covered RAM to above 4GB. Nothing the kernel can do about it.

Well, I guess I learned the hard way. So it's better not to buy 4GB
... it turns out to be the same as buying one with just 3GB RAM.

Thanks,
Jeff.
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