Using ALL memory?

Not sure if this is really the best place to post this, but here goes. I've noticed lately that alot of the games I play are starting to have abysmal framerates. I've tweaked the in-game graphics every-which-way I can all to no effect.

Today, I noticed while looking at the performance tab under the task manager that my computer is using 5.3gb of memory out of an available 6gb, with nothing running. I looked down this list of open processes and did a quick tally of how much memory all the processes were using together, and it didn't even add up to 1gb. Now I know windows is going to be using some of the memory, but 5gb!? Help me?

I have a ASUS Notebook G72GX,
Intel Core 2 Duo CPU P8700 @ 2.53GHz
6.00gb installed RAM
Nvidia GeForce GTX 260M
Windows 7 Home Premium (x64) with Service Pack 1

Which games ? What are the game's recommended pc requirements ? How much ram does your pc have ? Do you have all the games fully patched/updated ? Is Windows fully updated ? Are your Nvidia video card driver's updated ?
You most likely need to install more ram. Also, alot of the newer games really need a quad-core cpu.
I recently installed Batman : Arkham City on my pc. It need's 8 GBs. of ram. I've got 16 GBs, so it runs fine on my pc.

To take is a step further from what brkkab has pointed out, have you noticed any ill affects during regular PC usage at all. Generally, as a good rule of thumb, when you have heavy RAM usage like that, that means you more than likely have some malware, spyware hanging about and well hidden in the system but not always. It could be hardware related as brkkab is pointing out. I would thoroughly check your system and do it in safe mode with networking. This way if you don't have a piece of software you can download and run it plus update any current malware software you have. Run full scans of the software.

After of course verifying you do NOT have a virus/malware, as has already been pointed out, if it is not that then ...

What anti-virus do you have installed? Sometimes the A/V itself can go screwy and take all your resources. Try uninstalling it, including downloading their uninstall tool and running that, and then see if the problem persists (As I said, only after you are sure it isn't in fact a virus.) If there is no change then reinstall. If it is the A/V then consider another one, maybe use free Microsoft Security Essentials for a while, but it is not safe to just go unprotected.

Note that your OS is designed to use all the RAM, it should be using any extra instead of paging your game out to the HD but if it is doing something unusual then that needs checked out.