Microsoft KB Archive/929580

= Windows Vista or Windows Server 2003 may report less memory than you expect =

Article ID: 929580

Article Last Modified on 11/2/2007

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APPLIES TO


 * Windows Vista Business
 * Windows Vista Enterprise
 * Windows Vista Home Basic
 * Windows Vista Home Premium
 * Windows Vista Starter
 * Windows Vista Ultimate
 * Microsoft Windows Server 2003, Datacenter Edition (32-bit x86)
 * Microsoft Windows Server 2003, Enterprise Edition (32-bit x86)
 * Microsoft Windows Server 2003, Standard Edition (32-bit x86)

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SYMPTOMS
On a computer that has 4 gigabytes (GB) of random access memory (RAM), the System Properties dialog box and the System Information dialog box may report less memory than you expect.

This problem occurs in Windows Vista and in Windows Server 2003.



CAUSE
This problem occurs because the address space is limited to 4 GB in a 32-bit hardware environment. Memory may be relocated to make room for addresses that the basic input/output system (BIOS) reserves for hardware. However, because of this limitation, Windows Server 2003 and Windows Vista cannot access memory that is relocated above the 4 GB boundary.



STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the &quot;Applies to&quot; section.



MORE INFORMATION
A 32-bit operating system can address memory that is relocated above the 4 GB boundary if the following conditions are true:
 * The computer is in Physical Address Extension (PAE) mode.
 * The computer has 4 GB of RAM.

In this case, the operating system correctly reports how much memory is installed.

Additionally, some x64-based operating systems can address up to 2 terabytes (TB) of RAM. For more information, visit the following Microsoft Web page:

http://technet.microsoft.com/en-us/windowsserver/bb294403.aspx

To enable PAE mode, you have to add PAE to the boot entry in the BCD file. Open an elevated command prompt. Type BCDEDIT /SET PAE ForceEnable.

Note There is no Boot.ini file in Windows Vista. The Boot.ini file is used for legacy Windows versions when dual-booting only

For more information, click the following article numbers to view the articles in the Microsoft Knowledge Base:

268230 Scaling out versus scaling up with Intel Physical Addressing Extensions (PAE)

283037 Large memory support is available in Windows 2000 and Windows Server 2003

If you add more memory to the system, the BIOS might recognize all the physical RAM even though Windows recognizes only a part of the RAM. If the computer uses a redundant memory feature or a memory mirroring feature, the full complement of memory may be invisible to Windows. Redundant memory provides the system with a failover memory bank when a memory bank fails. Memory mirroring splits the memory banks into a mirrored set. You can enable or disable these features by using the BIOS. You cannot enable or disable these features by using Windows. To modify the settings for these features, refer to the computer's user manual or to the BIOS manufacturer's Web site. Or, contact the manufacturer.

For example, if the computer has 4 GB of RAM installed, and you add 4 GB of additional RAM, Windows may recognize only 4 or 6 GB of RAM instead of the full 8 GB. The redundant memory feature or the memory mirroring feature may be enabled on the new memory banks without your knowledge. These symptoms resemble the symptoms that occur when you do not add the /PAE switch to the Boot.ini file.

Memory limits
For more information about the memory limits for Windows operating systems, visit the following Microsoft Web site:

http://msdn2.microsoft.com/en-us/library/aa366778.aspx

For more information about Physical Address Extensions (PAE), visit the following Microsoft Web site:

http://msdn2.microsoft.com/en-us/library/aa366796.aspx

For more information about memory addressing, see the following Microsoft Web log (blog):

http://blogs.msdn.com/oldnewthing/archive/2006/08/14/699521.aspx

Additional query words: msinfo msinfo32

Keywords: kbtshoot kbprb kbexpertiseinter KB929580

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