[plug] maximum RAM linux can cope with

[Patrick Coleman]

On 5/7/07, David Buddrige <dbuddrige at bigpond.com> wrote:
>
>  Hi all,
>
>  I am currently helping a friend spec out a computer which is to be used for
> creating video productions.  The plan is to run a Linux based system
> utilising the various Free/OSS tools available for this task.  Given the
> task at hand, we are spec-ing it out with as much RAM, the best CPU,
> video-card and sound-card we can afford.  A question came up as to how much
> RAM is Linux capable of using [also whether it is capable of fully utilising
> quad-core CPU's.  We could for example stick 6 GB of RAM into this machine
> [the motherboard we're looking at has slots to allow for this] but I am not
> able to say at the moment [for certain] whether Linux is capable of using
> this much RAM - particularly using a bog-standard distro.  If we were to
> load it up with the latest fedora, would [fedora] be capable of making use
> of 6GB RAM?

Hi David,

I'm not familar with Fedora, but linux < 2.6.12 has a CONFIG_NOHIGHMEM
option (where you choose between having <1GB, 1-4GB or 4-64GB of
memory). I imagine fedora won't ship with this set to 'enormous', so
you may have to install a separate kernel package (probably named
along the lines of kernel-x.x.xx-highmem). Apparently the worst that
will happen if you get it wrong is that you will only see, say, 4GB of
the 6GB of memory.

linux >= 2.6.12 apparently (I don't have sources handy to check) deals
with this automatically; you don't have to set the CONFIG_HIGHMEM
option in the kernel. If Fedora therefore ships with a linux kernel >
2.6.12 (which it should do) there should be no issues with the memory.

> Also, if we put in a CORE 2 Quad Q 6600 [as per
> http://www.ple.com.au/?p=extremeint ] would it be able to
> use all 4 cores

Yep, should just work. If it doesn't automatically you may have to
install the fedora SMP (ie. multiprocessor, named along the lines of
kernel-x.x.xx-smp) kernel.

> [I'm not up-to-speed with whether a quad core system
> actually comprises 4 cpu's or a single cpu with 4 internal processing units
> or something].

A quad core CPU contains four actual CPUs wacked onto one chip. I'm
not completely sure if they share the same cache or not - I don't
think so (wasn't that why 'hyperthreading' sucked?), but I could be
wrong.

>  I've done a bit of a google on this but while it seems there are at least
> configurations out there that can utilise as much as 64GB of RAM, I don't
> know if you have to do some special configuration to allow linux to utilise
> this kind of hardware, or whether a bog-standard distro will recognise and
> use it?

It should do by itself if > 2.6.12 and is an SMP kernel; at worst if
it doesn't and there isn't a preconfigured fedora package you will
have to recompile a custom kernel.

Cheers,

Patrick


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