Why does my pc say only 3.25GB is useable

Windows 7 Pro.

it says:
Installed Memory (RAM): 4.00GB (3.25GB usable)

Why is onlyt 3.25GB useable.
i thought I could add at least 8GB of ram, using 64bit OS
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Gary CaseConnect With a Mentor RetiredCommented:
"... The usable ram is what is available after the  hardware takes their share ..."  ==>  NO !!    With a 32-bit OS that's limited to a 4GB address space, this would be true.   But not with a 64-bit OS.    The addresses hardware requirements (PCI bus addressing;  BIOS shadowing;  video aperture; etc.) are assigned FAR above the range where any installed memory is addressed.

What you're almost certainly seeing is that you have 4GB of RAM, but 750MB is in use for shared video RAM.    You can confirm this by opening Device Manager and selecting View - Resources by Type - Memory ... and studying the current memory allocation for addresses up through the 4GB point [FFFFFFFF]     Note that all the hardware addresses will be well beyond that address.
if you have an video card incorporated in the motherboard that might take some of your ram, check in your bios
PowerEdgeTechIT ConsultantCommented:
Also, if you system only supports a max of 4GB or RAM, it is possible you'll never see the full amount.  What system do you have?
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The usable ram is what is available after the  hardware takes their share.. there is nothing wrong with your machine
last time i checked onboard video is hardware.. but I could wrong :)
Gary CaseRetiredCommented:
The onboard video does not, however, use any of the address space -- it's simply assigned shared video by the OS.    In most cases, the amount of this shared video can be adjusted.    It's a completely different process than the assignment of hardware addresses with a 32-bit OS, where the video is actually assigned some of the address space.
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