Troubleshooter: Using Intel's Hyper-Threading Technology

Before launching into this column, I want to remind readers that Microsoft has an aggressive schedule in place for releasing new white papers and books covering Exchange Server 2003 migration, deployment, administration, and maintenance. If you haven't already visited Microsoft's Web site, drop by the Exchange technical library at and check out some of the resources. Microsoft is continually creating new documents, and each one is stamped with a date to tell you how long the contents are valid. Now, on with the questions!

Can Exchange Server take advantage of processors that implement Intel's Hyper-Threading Technology?

Exchange will happily use as many CPUs as the underlying Windows installation is licensed to use. How this number is determined, however, depends on which Windows version you're using. Pentium processors that can do hyperthreading appear to the OS to have two CPUs—for example, if you build a dual-processor server with two Xeon hyperthreading CPUs, Windows 2000 views this configuration as a four-CPU server. This miscalculation happens because the interfaces that Win2K uses to query the BIOS for processor information can't distinguish between real and virtual processors. Windows Server 2003 uses newer calls that let the OS tell the difference. Although a four-CPU Xeon server running Win2K will appear to have eight CPUs, the OS is only licensed to use four of them, thus negating hyperthreading's benefit. However, the same server running Windows 2003 can use all eight processors, which lets Exchange benefit from all eight CPUs when running on such a server.

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