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:
This is expected behavior on computers that are running Windows 7. The reduction in available system memory depends on the configuration of the following:
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.
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There are several additional situations that could cause the usable RAM to be less than expected. These issues and possible solutions are listed here:
This problem may occur because the Maximum memory option is selected incorrectly. To fix this, follow these steps:
The problem may occur because the system BIOS is outdated.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.
The problem may occur because some BIOS settings are incorrect.
The problem may occur because there are issues with the physical RAM installed.
The following sections offer additional information about memory allocation as reported in the Resource Monitor, describe the terminology used, and offer additional information on Memory reporting and memory limitations in Windows 7.
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The following table shows how the Resource Monitor categorizes the memory currently installed on a Windows 7-based computer. Collapse this table Expand this table
|Hardware Reserved||Memory that is reserved for use by the BIOS and some drivers for other peripherals|
|In Use||Memory that is used by process, drivers, or the operating system|
|Modified||Memory whose contents must go to disk before it can be used for another purpose|
|Standby||Memory that contains cached data and code that is not actively in use|
|Free||Memory that does not contain any valuable data and that will be used first when processes, drivers, or the operating system need more memory|
Note To view how the installed memory is allocated in Windows 7, follow these steps:
The following table defines the Resource Monitors current reported status of the installed memory on a Windows 7-based computer. Collapse this table Expand this table
|Available||Amount of memory (including standby and free memory) that is immediately available for use by processes, drivers, and the operating system|
|Cached||Amount of memory (including standby and modified memory) that contains cached data and code for rapid access by processes, drivers, and the operating system|
|Total||Amount of physical memory that is available to the operating system, device drivers, and processes|
|Installed||Amount of physical memory installed in the computer|
Windows 7 reports how much physical memory is currently installed on your computer. Windows NT-based operating systems before Windows Vista Service P1 report how much memory is available to the operating system. The available memory reported in these earlier versions of Windows does not include hardware reserved memory. This is a reporting change only.
You will see this reporting change in Windows Vista SP1 and later versions of Windows in the following locations:
Additionally, the System Information tool (Msinfo32.exe) displays the following entries on the System Summary page:
The reporting in the following diagnostic tool has not changed:
When the physical RAM that is installed on a computer equals the address space that is supported by the chipset, the total system memory that is available to the operating system is always less than the physical RAM that is installed.
For example, consider a computer that has an Intel 975X chipset that supports 8 GB of address space. If you install 8 GB of RAM, the system memory that is available to the operating system will be reduced by the PCI configuration requirements. In this example, PCI configuration requirements reduce the memory that is available to the operating system by an amount that is between approximately 200 MB and approximately 1 GB. The reduction depends on the configuration.
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The following table specifies the limits on physical memory for the different versions of Windows 7. Collapse this table Expand this table
|Version||Limit in 32-bit Windows||Limit in 64-bit Windows|
|Windows 7 Ultimate||4 GB||192 GB|
|Windows 7 Enterprise||4 GB||192 GB|
|Windows 7 Professional||4 GB||192 GB|
|Windows 7 Home Premium||4 GB||16 GB|
|Windows 7 Home Basic||4 GB||8 GB|
|Windows 7 Starter||2 GB||2 GB|
For more information about memory limits for Windows releases, click the following link to view the article on the Microsoft Web site: Memory Limits for Windows Releases (http://msdn.microsoft.com/en-us/library/aa366778(VS.85).aspx)
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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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May 4, 2010 - Revision: 3.0