How much RAM do you actually have?

Hey folks. I have a GNex, and it works perfectly with almost no lag in my daily work. However, the phone is supposed to have 1GB of RAM, but I find only a little over 200MB to be free, with close to 500MB being 'used'. Where's the rest? And damn, why is it saying 500MB used when I'm running zero apps in the background?

Any ideas?