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Windows 2000 Artificially Throttles Intel’s New Xeon MPs

A major new feature of the Intel Xeon MP processors is artificially throttled because of the way that Microsoft's Windows 2000 Server operating systems interact with system BIOS, a Microsoft white paper confirms.

The Intel Xeon MP (for multiprocessing) chips that launched on Tuesday feature a technology called Hyper-Threading. Through Hyper-Threading, a single physical processor can act as two logical processors by executing multiple threads simultaneously.

A licensing issue arising from the way the Windows 2000 Servers interpret BIOS information means those servers can't fully exploit the Intel Xeon MP support for symmetric multithreading in some cases. In the best case, a server configured with half as many processors as the operating system supports can exploit the new technology. In another scenario, the Hyper-Threading technology is effectively disabled. In the worst case, the licensing SNAFU could cause a server with several physical processors to fail to recognize some of them. That would happen if the OS counted the virtual processors created by Hyper-Threading first and reached the licensed limit before counting all the physical processors. For more technical detail on the issue, click here for the sidebar.

Microsoft's current advice is for users to wait for the Windows .NET Servers, which correctly identify processors using Hyper-Threading. That support is built into the Beta 3 version of Windows .NET Servers, which are available now for select customers.

“The Windows .NET Server Family is engineered to take full advantage of the logical processors created by Hyper-Threading Technology,” according to the Microsoft whitepaper, which can be found here.

For Windows 2000, Microsoft assumes a pessimistic tone: “Microsoft expects to see positive performance gains with Windows .NET Server and Hyper-Threading Technology, while Windows 2000 performance gains are expected to be more modest.” The white paper discusses no engineering differences between the two generations of Windows servers other than the way each counts processors during system startup.

Since Microsoft produced the Hyper-Threading white paper in February, the company has pushed back the release target for the Windows .NET Server family into the late second half of 2002. The delay raises the possibility that there will not be a Windows operating system capable of fully exploiting the Hyper-Threading technology for nine months or more. Microsoft officials did not immediately return requests for comment on its plans for this problem.

Analyst Nathan Brookwood, of microprocessor consultancy Insight64, says the approach Microsoft uses to count Hyper-Threading-enabled processors in Windows 2000 isn't fair.

“Right now, Microsoft basically doesn’t distinguish between these virtual processors and real processors. You’re talking about, maybe, a 30 percent performance boost [with a logical processor] compared to what you get with a separate physical processor, which is close to 100 percent,” he says. “I think that Intel and Microsoft really are going to have to look at Microsoft’s licensing policy, at least with regard to multi-processor support as Hyper-Threading becomes more and more of a factor in the marketplace.”

Any performance boost from Hyper-Threading is less than the boost from the use of additional physical processors -– both logical processors still share the same execution resources of the processor core.

One user says he thinks Microsoft is blatantly using support for Hyper-Threading as a carrot to draw users to Windows .NET Server, but that it's probably not going to be a problem for his organization.

Andrew Baker is director of Internet operations with educational testing service Princeton Review Inc., which currently runs a number of Xeon servers in-house.

“We do have a lot of [Windows 2000] Servers, but we'll have flexibility to move to .NET Servers for applications, even if the domain controllers remain on Win2K,” Baker says. "I'd wager that [Microsoft has] no intention in providing this functionality in Win2K. While it would be nice, that's not how they typically operate.”

Analyst Al Gillen with market research firm IDC says it's too soon to determine whether or not Microsoft will issue a software update or service pack to allow Windows 2000 Server to take full advantage of Hyper-Threading technology.

“I have no indication of what the potential is for future updates to the OS,” he says. “My guess is that they wouldn’t do something at this point in time because Windows 2000 is about to be replaced by Windows .NET Server … by the end of the year.”

About the Author

Stephen Swoyer is a Nashville, TN-based freelance journalist who writes about technology.

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