I was under the impression you needed 64bit to address > 4GB RAM.

Any of my VM’s ( or physicals for that matter ) that have 4GB of ram , only use 3 GB of this 4GB, due to the limitations of the 32-bit address space.

Mem: 3107660k total

However, you can actually address upto 64 GB after enabling PAE:

Mem: 8309576k total,

You can even do it on Windows 2003 :

http://support.microsoft.com/kb/283037

Centos Instructions:

yum install kernel-pae

reboot. hit any key before the kernel loads and in your boot menu choose the PAE kernel.

installing this kernel doesnt make it the default – assuming it works, goto /boot/grub/grub.conf and set the default value to equal the PAE kernel. In my case it was “Default=0″

perhaps this is old news to everyone else – but I thought it was damn cool.

my Zimbra box will get an upgrade to 8GB and hopefully startup in less than 6 minutes now.