do I need to do something special to use more than 4 Gigs under Feisty?
Gavin McCullagh
gmccullagh at gmail.com
Wed May 30 17:05:25 BST 2007
Hi,
On Wed, 30 May 2007, john wrote:
> I just installed Edubuntu 7.04 on Server running a dual opteron, dual
> core setup.
That's a 64-Bit machine right? Are you running 64-Bit Edubuntu?
> The mobo is a Tyan S3992G3NR. The kernel is setup as SMP and all cores
> are recognized. My problem is that only 3 Gigs of memory is recognized.
> That seems odd to me, as I would expect problems (if they occurred) to
> start at 4G.
The 4GB limit is due to the amount of memory which can be addressed in 32
bits.
2^32 = 4294967296
So you'd imagine you could address 4GB RAM in that much space. However,
each PCI device gets mapped into the top end of the 32-Bit address space
and takes up some chunk of it. This means that there's a limited amount of
address space (< 4GB) left for memory. As a result, some amount of RAM x,
roughly
3GB < x < 4GB
is left addressable. It _may_ be possible to squeeze a little more out of
it by disabling or removing PCI devices that you don't need.
> Does anyone know if there is something special one has to do to enable
> large memory support for Ubuntu Feisty?
It can be done in 32-Bit Linux, but (as I understand it) this comes at a
cost. However, I would have thought that if you are running 64-Bit Ubuntu
Linux this shouldn't be an issue at all. Are you? I use "may" and
"should" because I've yet to use a 64-bit a machine with >4GB ram.
Gavin
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