Edit: this SO question be related to your issue, and there is another good explanation of the how memory-mapped IO reservations can reduce the usable RAM. With Gigabyte p55a ud3r and Kingston KHX1600C9D3K4/8GX.
Again, this may not be exactly the problem you are facing, but those blogs tell you how you can determine if it is. When you buy RAM, you get it in pairs, as it turned out each pair/memory stick can only work on memory channel 1 or memory channel 2.
Being that cache is an internal component, it can be accessed directly and, therefore, maintain the speed of the processor.
If you put a pair of memory that designed to work only on channel 1, on channel 2 (like I did unknowingly).
The BIOS only recognizes them, "BUT" not made available to use.
The output data can either be stored temporarily or permanently, meaning the computer must have a way to contain this data while processing is being performed. A computer stores data in memory, and retrieves the data it requires from either Read-Only Memory (ROM) or Random Access Memory (RAM).
ROM is permanent memory that retains data even when the system is turned off.
I added another 2 GB and windows reports that there is 6GB of physical RAM, but now 4GB is "hardware reserved". The video card is an n Vidia Quadro FX 580, so it shouldn't be using any shared memory at all.
Why is all my extra RAM marked as "hardware reserved" in Windows 7?
It is mainly provided by common input devices, such as a keyboard, mouse, scanner, or modem.
Once the computer analyzes the input, that data is then processed and converted into output.
The Central Processing Unit (CPU), or processor, is a component that acts as the brain of a computer system.
Instead of actually thinking, however, it moves data around the system in ways defined by computer programmers. It accepts input, processes data, and provides output.
I had this same issue and have fixed it on my particular machine. I went into the MB BIOS and under chipset configuration/ internal graphics/ I changed the setting for Frame Buffer Location from [Above 4G] to [Below 4G}... Windows sees all *G as usable I had a similar problem with a Samsung R519.