I've installed 4GB ram on my system. It says that I've got 4GB installed and 3.19 usable!?...where is the rest???...I am running windows 7 64-bit...I've heard that the graphics card uses some of the ram, but if my graphics card uses it, why didnt it take some memory when I had 3GB installed??...I didnt get this kind of a message when I had 3GB...can someone help pls?