Bigmem/SMP IN dell PE

Arjan van de Ven arjanv at redhat.com
Tue Oct 7 04:47:00 CDT 2003


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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