Windows 7 - Little bit confused about RAM

I am confused about this Ram thing.I have Asus N75SF laptop with two graphic cards.
One is Intel HD graphic card
the other is Nvida Ge Force GT 555M 2 gb with optimus techology.
I have 8gb of Ram,when i go in properties on My computer i cant see usebale memory
see on the screenshot.

so I open task manager to see how much useable memory i have and this is confusing me it says 8102 total
Cached 1561
Avaliable 6419 and
Free 5055
And this is confusing me is this normal? How much useable memory i have?I am running Windows ultimate 7 64 bit.

And i went to system infromation and here is a screen shot from there

Can someone help me why my laptop doesnt use the whole ram memory?Is it because of the graphic cards?
Thanks in advance

It's OK.
So, Avaliable 6419 + Used 1.6GB = 8GB Total.
You can use all 8GB of RAM memory. And yes, I think that graphic card is using some of your ram memory because it's integrated.

Ok thamks very much StalkeR.So i dont have to worry anymore.But i have one more queistion.Why when i go propereties i cant see how much useable memory i have.I only see the installed memory and that is 8 gb.I have that on the first screenshot.
Thanks

That is normal as system properties just shows what is installed, not how much is being used.

Ok thanks

The best way to look at your RAM is in Resource Monitor > Memory tab. On the colored graph, everything that is blue (light and dark) is available.

Example:

Usable memory is not listed there.
As whs said that is the best way to see....

So is this normal?Is it ok? Sorry for asking too much but i just want to be sure that everything is fine with my Laptop
Here is again screenshot

Yes...that's OK

Thanks a lot to all of you