Your kernel is 32bit with no doubt.
My suggestion is: If you have too much ram next time buy less.
It's just pointless to load random thing in ram to use it. The os already do it when it's needed you are filling the RAM of random garbage instead of zeroes, still wasted.
A better use would be having an infiniband controller and sharing the ram with other machines.

Just built a 64-bit kernel and configure it appropriately. Duh.

If you bought more RAM than your motherboard (e.g. pre-boot diagnostic screens) says it can support, sell the extra on eBay.

ok guys, relax it was a humorous thread at the beginning... there's no reason to feel frustrated.
Kernel is 64, no doubt, it wouldn't be able to use all the ram otherwise. But it is (a quick look at top shows that)

@johnsfine:

yes I am loading the right kernel ahah - very funny
(I used and programmed on Linux for the last 12 years BTW)

Concerning ramfs, if I load 4G of directories in the ram, that means there is 12G left.
But what would happen if I had only 12G on my MB? would that be so terrible for the performance of my system? ...

Loading system directories in the ram (about 1.5G for me) + directories such as reasonably sized DocumentRoot is obviously better than waiting for a Linux cache.
Why?
Because the Linux cache will always wait for a first use.
So let's say a particular file is not used for some time, the first visitor will have a slower response time.
If the things are in ramfs, there is no question about that, and after all, you still have 12G to run your system... should be enough!

I still use tmpfs for everything that is not so important, and of course everything that can become too big.

Anyways, the server receives about 12,000 hits per hour and all websites are perl cgi with many sql requests,
These 12,000 are not full of pictures because I usually include all images elements in a single picture.
The is a dns lookup at each first request.
Despite of this, the average load time of a page is about 100ms and it's hard to find more than 200.

So I'm satisfied of my configuration, after all, the important is the results, not the words.
BTW, the HD is a bit slow, it's better not to overload it anyway (it would kill it faster also)

Again, your kernel reports itself as i686, which means it is in fact 32 bit. And yes, you are able to use all your RAM if you have PAE enabled in your Kernel. A Linux 32 bit kernel is able to use up to 64GB of RAM with PAE enabled. Not that it would make such sense to run such a configuration.

The lifetime of a harddisk is not affected by its speed.

TobiSGD: you are absolutely right, I'm sorry.

sundialsvcs: of course, sorry for mistaking.

Celyr: thank you for the advice, I'll let you know.

johnsfine: thanks again for the tips!

Don't be like that, i'm pretty sure your kernel is 32 bit with PAE. Try this:

About cache all my studies on operating systems tells that it's better to use the OS one anyway and that the first miss will be ininfluent after a very little time But maybe practice is different from theory