Re: 32-bit vs AMD64 on Opteron for LAMP server
On 07/07/07 04:45:57PM -0400, Roberto C. Sánchez wrote:
> On Sat, Jul 07, 2007 at 04:40:00PM -0400, Jim Crilly wrote:
> >
> > For 32-bit systems only if the kernel is compiled with CONFIG_HIGHMEM64G
> > enabled so you need one of the "bigmem" kernels. And the BIOS on the machine
> > has to support remapping the lost memory above the 4G mark, if it won't do
> > that for you there's nothing you can do to get access to that memory.
> >
> The stock Debian kernels are configured like this:
>
> CONFIG_HIGHMEM4G=y
> # CONFIG_HIGHMEM64G is not set
> CONFIG_HIGHMEM=y
>
> So, if you have a machine with 4-64 GB RAM, then a custom kernel is in
> order. Of course, as far as the BIOS goes, if the machine supports more
> than 4 GB RAM, then the BIOS should as well. After all, why would
> someone manufacture a machine that can handle more than 4 GB RAM and
> then put in a BIOS that cannot?
>
No, even with just 4G you need CONFIG_HIGHMEM64G because to access the
memory from ~3.5G-4G you need to remap it above the 4G mark since those
addresses were "stolen" by the various hardware components in your system
so you need a kernel able to address >4G.
> Regards,
>
> -Roberto
Jim.
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