Topic Last Modified: 2005-11-18

The Microsoft® Exchange Server Analyzer Tool reads the following registry entry to determine whether the threshold for logging an event regarding virtual memory fragmentation has been manually overridden:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIS\ParametersSystem\ VM Info Update Interval

If the Exchange Server Analyzer finds the VM Info Update Interval registry value present but not equal to 3600, a non-default configuration message is displayed.

In 32-bit Microsoft Windows® systems, there are two kinds of memory: physical memory (the amount of actual memory installed in the system) and virtual memory address space (a virtualized 4 gigabyte memory space). Regardless of how much physical memory is installed on the system, the total size of the virtual address space is always the same: 4 GB. Although it is not the case for all 32-bit applications, for Exchange Server, virtual address space equals virtual memory; in other words, the terms are used interchangeably.

During the regular course of its operations, the Microsoft Exchange Information Store service will repeatedly allocate, use, and de-allocate virtual memory. When virtual memory is allocated, used, and de-allocated frequently, it can cause virtual memory fragmentation. Virtual memory fragmentation is similar to file system fragmentation that can occur over time. After a while, allocated segments of virtual memory are no longer contiguous, and performance begins to suffer. For the file system, you can run an application that performs defragmentation of the file system, and most of the time you can do this while the system is online and being accessed. For virtual memory fragmentation, there is no defragmentation tool; instead, to correct the problem you must stop and start the Microsoft Exchange Information Store service or restart the system.

By default, the Microsoft Exchange Information Store service checks for free virtual memory once an hour (for example, every 3,600 seconds). The VM Info Update Interval registry value represents a configuration opportunity that lets an administrator override the default 3,600 seconds interval. If you do override the default level, it is recommended that you do not set the value lower than 5 minutes (300 seconds).

This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore the registry if a problem occurs. For information about how to restore the registry, view the "Restore the Registry" Help topic in Regedit.exe or Regedt32.exe.

To revert to the default configuration

  1. Open a registry editor, such as Regedit.exe or Regedt32.exe.

  2. Navigate to: HKLM\System\CurrentControlSet\Services\MSExchangeIS\ParametersSystem

  3. In the right pane, delete the value for VM Info Update Interval.

  4. Close the registry editor and restart the Microsoft Exchange Information Store service for the change to take effect.

For more information about troubleshooting virtual memory fragmentation in Exchange Server 2003 and Exchange 2000 Server, see the Microsoft Knowledge Base article 325044, "HOW TO: Troubleshoot Virtual Memory Fragmentation in Exchange 2003 and Exchange 2000" (