can't use available RAM

I am running Knoppix 5.1.1 on an AMD Athlon II X2 235e processor system with 6GB RAM, and would like to use all available RAM. For some reason, Knoppix only uses 3GB RAM, no matter what value I assign in the "mem=" command line cheat code.

Any ideas?

knetter136

[garaden]

My first instinct is that Knoppix is a 32-bit kernel and so is unable to address all of your memory except 4GB minus whatever the video card wants. However, I'm no memory expert, so I could be wrong.

[krishna.murphy]

My first instinct is that Knoppix is a 32-bit kernel and so is unable to address all of your memory except 4GB minus whatever the video card wants. However, I'm no memory expert, so I could be wrong.

Hmm-

I've read that Windows 32-bit kernels can't go beyond 3GB too; but that is no reason a Linux kernel can't do it. Maybe some lucky guru will spot this here and enlighten us all...

-Krishna

[garaden]

Ok, did a little more research and found out that a mechanism called Physical Address Extension is required to access extra memory using 32-bit OSs. Unfortunately, activating this mechanism results in kernel modules that won't work on processors that don't support it. Most (all?) modern processors support it, but Knoppix doesn't seem to be built that way for compatibility with old machines. Go here if you want a package that supports this capability (you can enable/disable PAE at will using various Grub entries included in the package). Unfortunately it's a few months out of date, but oh well.

Good luck!