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This Exchange mailbox server has 1 GB or more of memory but does not have /3GB set in the Boot.ini file

[This topic is intended to address a specific issue called out by the Exchange Server Analyzer Tool. You should apply it only to systems that have had the Exchange Server Analyzer Tool run against them and are experiencing that specific issue. The Exchange Server Analyzer Tool, available as a free download, remotely collects configuration data from each server in the topology and automatically analyzes the data. The resulting report details important configuration issues, potential problems, and nondefault product settings. By following these recommendations, you can achieve better performance, scalability, reliability, and uptime. For more information about the tool or to download the latest versions, see "Microsoft Exchange Analyzers" at]  

Topic Last Modified: 2005-11-18

The Microsoft® Exchange Server Analyzer Tool queries two Microsoft Windows® Management Instrumentation (WMI) classes to determine the amount of physical memory in the Exchange server, and the amount of virtual address space allocated to user mode processes. The following table describes the classes and keys being evaluated by the Exchange Server Analyzer.

Class queried Keys queried Description



Maximum number of kilobytes of memory that can be allocated to a process.



Installed and licensed system product additions to the operating system.



Number of bytes of random access memory (RAM) installed in the computer.

If the Exchange Server Analyzer determines that the Exchange Server computer is not running Windows 2000 Server and has 1 gigabyte (GB) or more of physical memory installed, and the value for the MaxProcessMemorySize is more than 2097024 but less than 3104640, a warning is displayed.

This warning indicates that the Exchange server does not comply with the requirements set forth in the Microsoft Knowledge Base article 266096, "Exchange 2000 requires /3GB switch with more than 1 gigabyte of physical RAM" ( This is not a recommended production configuration.

Microsoft Windows Server™ 2003 includes support for two startup switches—/3GB and /USERVA—that let you tune the allocation of use of memory and memory address space. Regardless of the amount of physical memory in your system, Windows uses a virtual address space of 4 GB, with 2 GB allocated to user-mode processes (for example, applications) and 2 GB allocated to kernel-mode processes (for example, the operating system and kernel-mode drivers). On systems that have 1 GB or more of physical memory, these two startup switches can be used to allocate more memory to applications (3 GB) and less memory to the operating system (1 GB). This additional virtual address space helps reduce the amount of memory fragmentation in the virtual address space of the Exchange information store process.

The /3GB switch is used to effect this allocation change. The switch is entered in the system’s Boot.ini file and takes effect after a restart. This switch should only be used on Exchange servers with 1 GB or more of memory that are running any of the following operating systems:

  • Microsoft Windows Server 2003 Standard Edition

  • Microsoft Windows Server 2003 Enterprise Edition

  • Microsoft Windows Server 2003 Datacenter Edition

  • Microsoft Windows 2000 Advanced Server

  • Microsoft Windows 2000 Datacenter Server


The /3GB switch should not be used on Windows 2000 Server because it is unsupported and can cause application or operating system crashes. Furthermore, the /3GB switch is only supported on the operating systems listed previously when 1 GB or more of physical memory is installed.

The /USERVA switch is new to Windows Server 2003. Its purpose is to provide a finer level of control over the division of virtual address space between user-mode processes and kernel-mode processes. This switch should only be used for applications that support it, such as Exchange 2000 Server and Exchange Server 2003, and with the specific values supported by those applications.


Microsoft Product Support Services does not support arbitrary /USERVA settings. Customers should add this setting to the Boot.ini file based only on a manufacturer's recommendation.

When used on Exchange Server 2003 systems, the only supported value for /USERVA is 3030 (for example, /USERVA=3030). This value causes an additional 40 megabytes (MB) to be allocated to the operating system, and enables you to add more users without consuming all available system resources.

To correct this warning

  1. Right-click My Computer and select Properties. The System Properties dialog box will appear.

  2. Click the Advanced tab.

  3. In the Startup and Recovery area, click Settings. The Startup and Recovery dialog box will appear.

  4. In the System startup area, click Edit. This will open the Windows Boot.ini file in Notepad.

  5. In the [Operating Systems] section, add the following switches to the end of the startup line that includes the /fastdetect switch: /3GB /USERVA=3030

  6. Save the changes and close Notepad.

  7. Click OK two times to close the open dialog boxes, and then restart the Exchange Server computer for the change to take effect.

For more information about optimizing Exchange Server memory usage and performance, see the following Microsoft Knowledge Base articles: