The usable memory may be less than the installed memory on Windows 7-based computers

Symptoms

On a computer that is running Windows 7, the usable memory (RAM) may be less than the installed memory.

For example, a 32-bit version of Windows 7 may report that there is only 3.5 GB of usable system memory on a computer that has 4 GB of memory installed.

Or, 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. Usable memory is a calculated amount of the total physical memory minus "hardware reserved" memory.

To view the installed memory and the usable memory in Windows 7, follow these steps:

  1. Click Start windows icon, right-click Computer, and then click Properties.

  2. View the Installed memory (RAM) value under System. For example, if it displays 4.00 GB (3.5 GB usable), this means that you have 3.5 GB of usable memory out of 4 GB of installed memory.

Cause

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.

For more information about how to determine how memory is used on your computer, see the "Physical Memory Allocation in Windows 7" topic in the "More Information" section.

What To Try

There are several additional situations that could cause the usable RAM to be less than expected. These issues and possible solutions are listed here:

Check the system configuration settings

This problem may occur because the Maximum memory option is selected incorrectly. To fix this, follow these steps:

  1. Click Start windows icon, type msconfig in the Search programs and files box, and then click msconfig in the Programs list.

  2. In the System Configuration window, click Advanced options on the Boot tab.

  3. Click to clear the Maximum memory check box, and then click OK.

  4. Restart the computer.

Update the system BIOS

The problem may occur because the system BIOS is outdated. If you have an older computer, the system may be unable to access all the installed RAM. In this case, you have to update the system BIOS to the latest version.

To update the BIOS on your computer, visit the Web site of your computer manufacturer to download the BIOS update. Or, contact your computer manufacturer for help.

Check BIOS settings

The problem may occur because some BIOS settings are incorrect.

  • Enable the memory remapping feature

    Check the BIOS settings to see whether the memory remapping feature is enabled. Memory remapping gives Windows access to more memory. You can enable the memory remapping feature in the BIOS by booting to the system setup. See the User's Guide for your computer for instructions on how to boot to system setup on your computer. The name for the memory remapping feature may be different for different hardware vendors. This can be listed as memory remapping, memory extension, or something similar. Be aware that your computer may not support the memory remapping feature.

  • Change the AGP video aperture size in the BIOS settings

    Check the BIOS settings to see how much memory that you have allocated to AGP video aperture. This is the memory that the system is sharing with the video card that is used for texture mapping and rendering. This memory would not be used by the system, because it is locked by the video card. You can adjust the AGP video aperture size in the BIOS. Standard settings are "32MB,""64MB,""128MB,"and "Auto." After you change this setting in the BIOS, restart your computer, and then check the usable memory. You can test each setting to see which offers the best results.

Check possible issues with the physical RAM

The problem may occur because there are issues with the physical RAM installed.

  • Check whether you have bad memory modules

    To check whether you are experiencing this issue, turn off the computer, unplug the computer, and then swap the order of the memory.

  • Make sure that the memory arrangement is correct

    Refer to the User's Guide of the computer to determine in what order the memory modules should be inserted into the memory slots. The system may require you to use specific slots when you are not using all the available slots. For example, the computer has four slots available. But you may have to use slot 1 and slot 3 if you want to use only two memory modules.

  • Check whether memory standoff cards are used

    If you use a memory standoff card to hold multiple memory modules on the computer, the system may require specific configurations for this scenario. Therefore, the usable memory may be less than expected.

References

The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of these products.

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