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Article ID: 255600 - Last Review: September 12, 2007 - Revision: 4.4

This article was previously published under Q255600

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SYMPTOMS

Your computer has more than 4 gigabytes (GB) of random access memory (RAM), but when you view the amount of memory in System Properties or in a tool such as Microsoft System Diagnostics (WinMSD), the total physical memory is reported incorrectly as 4 GB.

CAUSE

This behavior is by design. The maximum amount of physical memory that is addressable by a 32-bit operating system is 4 GB, or 0 to 4 GB of addressing space.

All processors that are based on the IA-32 architecture,starting with the Intel Pentium Pro, support a new 36-bit physical addressing mode named Physical Address Extension (PAE). PAE allows for up to 64 GB of physical memory. PAE maps up to 64 GB of memory into a 32-bit (4 GB) virtual address space. Also, each operating system may hard-code an address limit less than 64 GB. Ffor example, there is an 8 GB hard-coded address limit in Microsoft Windows 2000 Advanced Server. The PAE mode kernel requires an Intel Architecture processor Pentium Pro or later versions, more that 4 GB of RAM, and either Windows 2000 Advanced Server,Windows 2000 Datacenter Server, Microsoft Windows Server 2003 Enterprise Edition, or Windows Server 2003 Datacenter Edition.

RESOLUTION

To allow for access to memory greater than the 4 GB address space (4 GB to 32 GB), you must manually change the Boot.ini file in the root folder of the system drive to add the /PAE switch to the appropriate operating system line:
  1. Click Start, click Run, type cmd in the Open box, and then click OK.
  2. Type attrib c:\boot.ini -r, and then press ENTER.
  3. Type exit, and then press ENTER.
  4. Click Start, click Run, type notepad c:\boot.ini in the Open box, and then click OK.

    A window opens to display the Boot.ini file..
  5. The line that starts with "default" is the location from which Windows 2000 Advanced Server will load on startup without user intervention. For example, the line may appear as:
    default=multi(0)disk(0)rdisk(0)partition(1)\WINNT
  6. Locate the line for Windows 2000 Advanced Server that corresponds to the information on the default line. It should look similar to the following:
    multi(0)disk(0)rdisk(0)partition(1)\WINNT="Windows 2000 Advanced Server" /fastdetect
  7. Add a space and /PAE to the end of the line. The line should now look similar to the following:
    multi(0)disk(0)rdisk(0)partition(1)\WINNT="Windows 2000 Advanced Server" /fastdetect /PAE
  8. Click the Close box to close the Notepad window, and then click Yes when you are prompted to save changes.
  9. Restart the system, and then verify that the correct amount of system memory is now available.
The following is an example of a Boot.ini file for a system that contains the /PAE switch:
[boot loader]
timeout=0
default=multi(0)disk(0)rdisk(0)partition(1)\WINNT
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINNT="Windows 2000 Advanced Server" /fastdetect /PAE

MORE INFORMATION

For additional information, see the user guides that came with your operating system. For more information about PAE and support for RAM greater than 4 GB, click the following article numbers to view the articles in the Microsoft Knowledge Base:
283037  (http://support.microsoft.com/kb/283037/ ) Large memory support is available in Windows Server 2003 and in Windows 2000
247904  (http://support.microsoft.com/kb/247904/ ) How to configure the Paged Address Pool and System Page Table Entry memory areas
274598  (http://support.microsoft.com/kb/274598/ ) Complete memory dumps not available on computers with 2 or more gigabytes of RAM


For additional information about PAE server design, visit the following Microsoft Web sites:
http://www.microsoft.com/whdc/system/platform/server/PAE/default.mspx (http://www.microsoft.com/whdc/system/platform/server/PAE/default.mspx)
http://msdn2.microsoft.com/en-us/library/Aa366796.aspx (http://msdn2.microsoft.com/en-us/library/Aa366796.aspx)
If you add more memory to the system, it is possible that the BIOS will recognize the full amount of physical RAM that is installed in the server but that Windows will recognize only a part of the RAM. If the server has a redundant memory feature or a memory mirroring feature that is enabled, the full complement of memory may not be visible 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. Both features are enabled or disabled in the BIOS and cannot be accessed through Windows. To modify the settings for these features, you may have to refer to the system user manual or the OEM Web site. Alternatively, you may have to contact the hardware vendor.

For example, if you are running a system that has 4 GB of RAM installed and you then add 4 GB of additional RAM, Windows may recognize only 4 GB of physical memory or possibly 6 GB 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 are similar to the symptoms that occur when you do not add the /PAE switch to the Boot.ini file.

APPLIES TO
  • Microsoft Windows Server 2003, Enterprise Edition (32-bit x86)
  • Microsoft Windows Server 2003, Datacenter Edition (32-bit x86)
  • Microsoft Windows 2000 Advanced Server
  • Microsoft Windows 2000 Datacenter Server
Keywords: 
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