Dell 690 only seeing 3 GB RAM (was: slow last 128MB...)

[Chris]

On 4/19/07, Michael ODonnell <michael.odonnell at comcast.net> wrote:
>
>
> > RHEL 3 is pretty old.  I think it might be old enough that you need
> > to install a separate, special kernel package for systems which
> > "large memories".
>
> I'm building a kernel with the MTRR support disabled and,
> just for fun, I've also turned on PAE even tho I should
> theoretically not need it for just 4Gb of RAM.
>
> I've just learned that a cow-orker is running Vista on one of
> these 690 boxes equipped with 8Gb, and he says Vista sees it all.
>
> And on one machine w/these same symptoms I've installed Debian
> running a 2.6.16 kernel.  No joy - `still sees just 3Gb...
>
>         [...]
>
> > If you're running Linux on Dell, I highly recommend
> > the linux-poweredge mailing list hosted by Dell.  See
> > <http://linux.dell.com>.  It's nominally about PowerEdge servers,
> > but a lot of the discussion is either generic and also applies to,
> > or is even explicitly about, the Precision line.  There are some
> > real smart cookies on that list, including Dell's senior Linux
> > engineers (the guys actually writing the drivers).
>
> Good info - thanks.
>
>   --M
>
> UPDATE: just as I was about to send that msg my build completed
>         so I tested that kernel and ta-daaaa!  we can now see
>         all 4Gb.  I'm betting it was disabling the MTRR that
>         did it, not the PAE stuff...
>
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>

I have a feeling it was the PAE stuff.  Without PAE, the CPU can only
see the 4Gb. and the BIOS and PCI devices (especially ones that are
only 32-bit aware) are all in the memory between 3-4Gb.   With PAE
(Physical Address extension) the Kernel can use memory above the 4Gb
address range to map the previously unused 1Gb of memory.

Chris



-- 
IBA #15631