Topic Last Modified: 2005-11-18

The Microsoft® Exchange Server Analyzer Tool queries the Win32_ComputerSystem Microsoft Windows® Management Instrumentation (WMI) class to determine the current value for NumberOfProcessors. If the Exchange Server Analyzer finds that the value for NumberOfProcessors is larger than 8, a warning is displayed. However, if this server is configured to use Intel Hyper-Threading Technology, this warning can be safely ignored. Hyper-Threading Technology enables multi-threaded software applications to run threads in parallel. Hyper-Threading Technology requires a computer system with an Intel Pentium 4 processor supporting Hyper-Threading Technology and an HT Technology-enabled chipset, BIOS, and operating system.

Exchange 2000 Server and Exchange Server 2003 can effectively use only eight processors on a computer. Specifically, the Microsoft Exchange Information Store service is optimized for a maximum on eight processors.

On computers that have more than eight processors, it is recommended that you use hardware partitioning to partition the computer into multiple eight-processor computers or into multiple four-processor computers. Alternatively, you can configure CPU affinity for the Microsoft Exchange Information Store process (Store.exe) to only eight processors.

As soon as the Microsoft Exchange Information Store process has been limited to eight processors either through CPU affinity or through hardware partitioning, it is recommended that you upgrade to the latest available service pack and Exchange update rollups. This is especially important if you are running Exchange Server 2003.

Previously, Exchange server performance has shown marginal improvements when the number of processors in back-end servers increases to more than four. With more than eight processors, the performance increase is marginal at best, and sometimes performance can decrease. The falloff in performance gain with additional processors has become more pronounced with the types of processors used on more recent computers. With Exchange Server 2003 Service Pack 1, scalability with additional processors is much improved. When hyper-threading is enabled, eight-processor servers now provide a 50 percent increase in performance over four-processor servers. Using eight-processor computers for back-end servers is now appropriate in many scenarios. Dual-processor servers are still recommended for front-end servers.

As stated, if this Exchange Server computer is using Hyper-Threading Technology, this warning can be safely ignored.

To correct this warning on systems that do not use Hyper-Threading Technology

  1. Apply the latest service pack and update rollups for Exchange, which you can download from the Downloads for Exchange Server 2003 Web site (

  2. Set the CPU affinity for the Microsoft Exchange Information Store service (Store.exe) to eight CPUs, or use hardware partitioning to create an eight-processor Exchange server. Contact your hardware manufacturer for details about how to do this.

For more information about Exchange Server resource scalability, see the Microsoft Knowledge Base article 827281, "CPU and Memory Scalability for Exchange 2000 and Exchange 2003" (

For more information, see also the Knowledge Base article 271088, "XGEN: Optimizing Windows 2000 Active Directory Servers with Six or Eight Processors to Run with Exchange 2000" (

For more information about Hyper-Threading Technology, see the Intel Web site (

Web addresses can change, so you might be unable to connect to the Web site or sites mentioned here.