I recently started working on my girlfriends PC and I've ran across a very strange issue.  In windows, it's able to see the full allotment of ram, however states that only 50% of it is usable.

I've tried 4x2gb sticks, 2x2gb, 2x2g/2x1g no matter the amount of ram, half of it is always listed as reserved by hardware.

The PC is as follows:
I5 750
MSI P55-GD55 Motherboard
EVGA GTX280
G'Skil DDR3 (With Corsair from my PC mixed in for testing)
Corsair TX750 PSU

I'm stumped, the issue only occurs while running Windows 7, when I install something like Server 2008, it has no issues accessing the full amount of ram.

I've tried setting max memory under msconfig > Advanced > Boot.  I've tried patching, not patching, two bios updates, including a beta release bios from MSI.  I've also tried contacting MSI directly, however they say "This isn't an issue with the motherboard, it's either the OS or the Video card using RAM off the motherboard".

I'm stumped, I've never had this issue before, most of the people that have, have solved it using the above methods, or by adjusting "Memory Remapping" settings in the bios, which apparently doesn't exist on the MSI board.

Here is a screen shot of the Resource Monitor, System Properties, and Device Manager with the resource view up.  Let me know what you guys think..  And thanks in advance.

Screen shot shows 2GB RAM and 64-bit Windows Home Premium, so my best guess, and only a guess, is BIOS.
Seems might rule out RAM as you've tried various RAM types and configurations, and assume it is all P55 Core i5 compatible.
Links to memory?

I assume the screen shot is with the 2x1GB kit installed and nothing else. If that is correct I see nothing wrong.
If you had more installed when you took that screenie ^+1

There is a difference between "usable" and "in use" or "Used Physical Memory"

I see, do this.
Check the advanced boot options.
1. Go to Start, in the search bar type msconfig and press enter.
2. System Configuration window will open on the screen.
3. Click on tab named "boot".
4. Click on "Advanced Options" and uncheck the box for "Maximum Memory".
5. Click "Apply" followed by "OK"
6. Restart.

Tell me what you see as usable now?


edit: to place emphasis on uncheck

Re-seat, that is, Remove & Replace, the memory and CPU then and if that doesn't help You'll have to eliminate the hardware that causing your trouble. When you have the CPU removed use a magnifying glass and check for bent pins in the CPU socket.

Well, I think it was a RAM issue.  I was mostly using ram from my 790i setup to cut a few corners.  After using just ram from my x58 PC, it ran fine, removing all of the hardware reserved issues.  So I broke down an ordered some 1.5v Corsair DDR3 for it, works like a charm now..  I've had reallly poor luck with G'Skill as of late..  Gotta love Corsair though!

790i uses a much higher voltage ram than the p55 chipset, kind of odd though you would think that if it worked in one os it would work in another.

How can your statement of 32 bit that's the way it should be stand as correct? In a 32 bit configuration under vista this was not my observation (I had close to 3 GB available unreserved memory) but under win 7 I show 2 GB reserved memory.
 
I am running 2 9800 gx2 gpus in quad SLI on a 790i ultra mobo, p10 bios and qx9650 cpu.