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I just upgraded my computer's RAM, adding another 4 GB to the computer.

Windows 7 acknowledges that 8 GB is installed, but says only 7.5 GB is accessible.

Any idea why? I thought since I had the 64-bit Professional version this wouldn't be an issue.

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up vote 13 down vote accepted

This is probably the same reason that you never see a full 4GB on a 32-bit build - namely, that some system device has reserved some of that memory for its own use at boot. It's hard to say without knowing your exact build, but most typically this happens with onboard video chipsets that don't have any dedicated RAM of their own.

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ditto. can you be more detailed on what devices/hardware are in the system? – Xantec Dec 1 '10 at 15:51
ahh that could be it. I have an onboard graphics card aswell. It's feasible that it's claiming that 500MB of memory. Thanks – Kurru Dec 1 '10 at 15:54

See this article : The usable memory may be less than the installed memory on Windows 7-based computers :

A 64-bit version of Windows 7 may report that there is only 7.1 GB of usable system memory on a computer that has 8 GB of memory installed. Note: The amount of usable memory in the examples are not exact amounts.

This is expected behavior on computers that are running Windows 7. The reduction in available system memory depends on the configuration of the following:

  • The devices that are installed in the computer and the memory that is reserved by those devices
  • The ability of the motherboard to handle memory
  • The System BIOS version and settings
  • The version of Windows 7 that is installed (For example, Windows 7 Starter Edition only supports 2 GB of installed memory.)
  • Other system settings

For example, if you have a video card that has 256 MB of on-board memory, that memory must be mapped within the first 4 GB of address space. If 4 GB of system memory is already installed, part of that address space must be reserved by the graphics memory mapping. Graphics memory mapping overwrites a part of the system memory. These conditions reduce the total amount of system memory that is available to the operating system.

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Check if your BIOS is capable of doing memory remapping; it should if it can take 8 GiB of memory. There is also an issue of driver support for this, but if you are running 64-bit version, it ought to support it also. (That is, try and see if it crashes!)

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