This Exchange front-end server has the /3GB startup switch 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 the Win32_OperatingSystem Microsoft Windows® Management Instrumentation (WMI) class to determine the amount of virtual address space allocated to user mode processes (MaxProcessMemorySize) on the Exchange Server computer. The Exchange Server Analyzer also examines the Exchange_Server WMI class in the root\MicrosoftExchangeV2 namespace to determine the value for the IsFrontEndServer key. A value of False indicates that the Exchange Server computer is not a front-end server. A value of True indicates that the Exchange Server computer is a front-end server.

If the Exchange Server Analyzer determines that the value for the MaxProcessMemorySize key is not equal to 2097024 and that the IsFrontEndServer key is set to True, a warning is displayed.

This warning indicates that the Exchange Server computer is not properly configured for optimal memory usage because the /3GB startup switch has been set in the Boot.ini file. This switch should only be used on Exchange Servers with 1 gigabyte (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.

When the /3GB parameter is included in the Boot.ini file of a server running Microsoft Windows 2000 Server or Windows Server 2003, Windows allocates 3 GB out of a maximum of 4 GB of virtual address space to the user process and 1 GB to the kernel. Normally (when the /3GB parameter is not used), Windows allocates 2 GB to the user process and 2 GB to the kernel. Therefore, with the /3GB switch, memory intensive applications have a larger virtual memory address space to operate in and performance is improved.

Using the /3GB switch primarily helps memory-intensive applications like the Store.exe process on an Exchange server that hosts user mailboxes. A front-end server does not host user mailboxes and, therefore, there is no benefit derived from using the /3GB switch on a front-end server.

To correct this warning

  1. In Windows Explorer, navigate to the system partition.

  2. If you are unable to see the Boot.ini file, it could be because the Folder Options are set to Hide protected operating system files. If this is the case, in the Windows Explorer window, click Tools, click Folder Options, and then click the View tab. Clear the Hide protected operating system files (Recommended) check box. When prompted with the warning box, click Yes.

  3. When the Boot.ini file is visible in Explorer, right-click the file, click Open With, and choose Notepad to open the file.

  4. In the [Operating Systems] section, delete the following switches from all startup lines: /3GB

  5. Save the changes and close Notepad.

  6. Restart the computer for the change to take effect.

For further details regarding the use of the /3GB startup switch, see the following Microsoft Knowledge Base articles: