[Bioclusters] Opterons and Linux

Farul M. Ghazali bioclusters@bioinformatics.org
Mon, 19 Jul 2004 22:08:05 +0800 (MYT)

On Mon, 19 Jul 2004, Jeremy Mann wrote:

> First, do you know if the opteron kernel will allow larger memory for user
> space in 64bit mode that just 4 GB?  We have two dual Xeon's with 4gb of
> memory which we could never get more than 3.5 GB recognized by the 2.4
> kernel.

If your user-space app is compiled as a 64-bit binary, it will see >4GB of
RAM (or whatever your RAM + swap is). If your app is a 32-bit binary, it
will see al the 4GB of RAM it can actually address, but nothing more.
However, the 32-bit binaries don't have to share the 4GB address space wih
other processes unlike what you're seeing with a 32-bit kernel/machine
now. Note that this is assuming you're running a 64-bit kernel of course.
Cmpiling 64-bit apps was a bit confusing at first (mixing 32-bit and
64-bit libs during linking, etc.) but we got the hang of it after a while.

Someone else will have to answer the power question, I only have a measly
half dozen Opterons (a mix of IBM x325 and home-made ones) at the moment.