How do I check how much physical RAM I am using in GB or MB format?

How do I check my whether my Ubuntu is 32-bit or 64-bit and whether or not it is using full RAM? I'm concerned that because my system is 32-bit it isn't using the maximum OS-supported RAM. It says my PC has 8GB RAM, but how do I verify it is using or detecting this as 8GB RAM?

Regarding Sotanaht's answer: the System Tab shows Release 11.04 (natty), Kernel linux 2.6.38-11-generic-pae, Gnome 2.32.1 .

Follow up:

After finding my answer. Because I have 8GB hardware RAM, I don't want to be restricted to 4GB RAM, therefore removing my 32-bit Ubuntu 11.04, and downloading 64-bit Ubuntu 11.04 (so that my applications can utilize full hardware RAM too, specially for 3D animation rendering, image processing, video editing)

Solution 1:

In a terminal type free -to.

Quick and easy.

Solution 2:

PAE means your kernel is 32-bit but it's configured to use Physical Address Extension so the whole OS can use all your physical memory. The limitation of PAE, however, is that no application alone can use more than 4Gb of memory.

See the wikipedia article for more technical details

Solution 3:

If you open System Monitor (System > Administration > System Monitor) and go to the "System" tab, the number after "Memory" should correctly display your computer's ram in GB

Solution 4:

Sergey is right that PAE means you're running a 32-bit version. Another very easy way to see what version you have is to open a terminal window and type:

uname -a

In my case it returns:

~$ uname -a
Linux hotdog 2.6.38-11-generic #48-Ubuntu SMP Fri Jul 29 19:02:55 UTC 2011 x86_64 x86_64 x86_64 GNU/Linux

So the kernel is 2.6.38-11-generic, and the version of Ubuntu is x86_64 (or 64-bit).

However, a great way to get all sorts of information is to install System Profiler and Benchmark. It's in the Ubuntu Software Center and will likely become one of your favorite ways to get information about you system. Just install it, open it, and you'll know how to use it; it's obvious and intuitive so you won't need instruction.