I have 4GB or more of RAM but can't see it in Ubuntu. How can I enable support for more than 3GB ? Do I need a 64 bit edition of Ubuntu ?

Created by Fabián Rodríguez on on 2009-08-25
Keywords:
nvidia,pae,kernel,4GB,RAM,3GB,64bit,64
Last updated by:
Fabián Rodríguez on on 2010-07-09

There are two choices to enable support for more than 3GB of RAM in Ubuntu.

One of them is installing a 64-bit version of Ubuntu.

The other one, if you want to keep using a 32-bit version, is installing a Physical Address Extension (PAE) -enabled kernel. The server kernel provides such functionality. Installing the "linux-server" package will install such kernel and make it part of your choices at boot in the GRUB menu. if you want to easily manage that on a desktop install, you can also install the startupmanager package, then go to System > Administration > StartUp-Manager to change your default boot options and more.

To read more about PAE, see: http://en.wikipedia.org/wiki/Physical_Address_Extension

PAE is not enabled by default in 32-bit Ubuntu kernels. Starting with Ubuntu 9.10 (Karmic) a PAE-enabled kernel is available, see:
https://wiki.ubuntu.com/KernelTeam/Specs/KarmicKernelFlavours

*IMPORTANT* If you're using any binary drivers for display (Nvidia, ATI) disable them before installing the linux-generic-pae package.

After rebooting and logging into a PAE-enabled kernel Ubuntu version you may be able to re-enable your binary display drivers if so needed/wanted.

For further discussion and explanations on why PAE is not enabled by default on 32-bit kernels in Ubuntu, see:
http://brainstorm.ubuntu.com/idea/10892/
http://lkml.org/lkml/2000/8/3/41