4.00GB (3.25GB usable) in Windows 7 x64

"Look in your BIOS and see if there a setting for something like ""Memory Remap"" or ""Memory Hole""? If so it should be enabled.

What is going on (if this is the case) is that PCI devices need address space below 4GB. The setting will some of your RAM to address space above 4GB so it is still accessible."

"First, double check you're really running 64-bit right now. Bring up System Properties by either Right Clicking on ""Computer"" and clicking Properties, or by pressing the Windows Key + Pause/Break.

Make sure it says 64-bit Operating System:

Even though you have a 64-bit processor, you must also install the 64-bit version of the operating system.

Secondly, for your memory testing application, you need to make sure you are using the 64-bit version of the application. If you're running a 32-bit application, it may only be able to recognize up to 4 GB of RAM.

Considering you've already checked the Chipset to make sure it supports 8GB, it sounds like the problem here must be that you're actually running a 32-bit version of the OS. In a 32-bit OS, only 4GB total memory would be recognized, including memory used by the Chipset and Video controllers. The result is usually somewhere between 3.0 and 3.5GB RAM usable in Windows.

The last thing I can recommend is a BIOS upgrade and checking for any settings that could be limiting the amount of RAM in use."