Memory 6GB total
2 x G.SKILL 2GB DDR2
2 x G.SKILL 1GB DDR2
When I turn on my computer, the motherboard is recognizing the 6gb of memory, but when I go into Ubuntu and look at my stats it says only 3.5GB. How can I get Ubuntu to recognize all 6GB? Is it possible?
Ensure that you have installed the 64bit version of Ubuntu. It sounds like you have the 32bit version installed. 32bit OSes can only address 4Gb or memory (this includes video memory), thus you getting only 3.5Gb.
If I'm not mistaken, you will need to enable PAE in both BIOS and OS. In my BIOS its called Allow > 4Gb Remapping, not sure what it's listed as in a Gigabyte BIOS. Your parts are 64bit compatible, and yes there are advantages for applications written in 64bit. They will handle memory intensive operations much faster.