Bigmem/SMP IN dell PE

Nitin Gizare nitin.gizare at wipro.com
Tue Oct 7 06:04:00 CDT 2003


HI

Thanks for the info.

Rgds
nitin

-----Original Message-----
From: Arjan van de Ven [mailto:arjanv at redhat.com] 
Sent: Tuesday, October 07, 2003 3:16 PM
To: jason andrade
Cc: Nitin Gizare; linux-poweredge at dell.com
Subject: RE: Bigmem/SMP IN dell PE


On Tue, 2003-10-07 at 09:29, jason andrade wrote:
> On Tue, 7 Oct 2003, Nitin Gizare wrote:
> 
> > Yes I have same amount of memory in both m/c 's ie.4GB
> 
> and both have multiple cpus ? if you have the same number
> of cpus and the same amount of ram in both it is indeed strange that 
> the installer has put different kernels onto each system.

no it's actually not strange....
The key is the following:
The installer will install the bigmem kernel *IF* there is physical ram
above the 4Gb barrier. You may think "but I have only 4Gb, so it should
never". 
Well, almost.
In reality, your machine has PCI, and PCI requires some address space
below the 4Gb mark (generally called the PCI gap). Now if you have 4Gb
or more ram, there's an overlap between ram and the PCI gap. Some
chipsets will just make the RAM disappear for the overlap (typically
256Mb to 384Mb). Other chipsets will remap the RAM to be elsewhere. If
you have EXACTLY 4Gb, such a remap means that the remapped ram will end
up ABOVE the 4Gb mark, so the installer will install the bigmem kernel.

I'm guessing the two machines have a different chipset (or bios setting,
I think on some chipsets this is a bios setting)

Greetings,
    Arjan van de Ven


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