I'm using a laptop with 32-bit Ubuntu 10.04. I used to have only 2 GB of RAM. Today, our IT-support upgraded my laptop to a total of 6 GB of RAM. They told me "Though you do now have 6 GB, when you use your current Ubuntu, you'll only have 3 GB available. You have to install the latest version of 64-bit Ubuntu to enable all of the 6 GB." He was in a hurry to leave without explaining more. I turned on my laptop, used gnome-system-monitor to check, and as he said, it shows I only have 3 GB of RAM. Could someone explain me why? Why do I have just 3 GB available, and why installing a 64-bit version makes all of the 6 GB available?