It's not a hardware issue. The OS has to have room in the ram to do its thing. And that's protected. You're not going to be able to use that.
Wallpaper (desktop background) will eat up some ram also. If you have one turn it off and check the ram again.
Anti virus that runs in real time will eat some more as will any software that is running in the background.
Like I said in my previous post, it's just how it is. You're not going to get to play with all of the installed ram.
I have 16gigs of ram in my rig. I only have 11gigs available.