HyperThreading is an Intel technology that takes advantage of unused CPU capabilities to simulate a second CPU. Why is this important? Intel promises speed gains of up to 30% for programs written for multiple CPUs, though 10-20% seems more likely for most applications.

As it turns out, Intel has always had HyperThreading technology in its Pentium 4 CPUs, but disabled it during production since Windows XP (released late 2001) was the first operating system to support it. Intel's high-end Xeon workstation and server CPUs have supported HyperThreading since earlier this year.

HyperThreading, or simultaneous multithreading as it is generically known, makes software think there are two CPUs. This allows your programs to multitask more smoothly, providing speed benefits. Think of your HyperThreading-compatible CPU as two parallel assembly lines rather than one really fast one, and you have the general idea.

One down side of this technology is that some experts believe there are circumstances where some programs will actually experience a performance decrease. Also, some multiprocessor-compatible applications license their product partly on the number of CPUs on the server, so they may have to rework their licensing. Microsoft is working with Intel to license Windows based on the number of physical processors instead of logical ones (Windows XP Pro, for instance, only supports up to two CPUs). Contrary to early reports from Microsoft, Windows XP Home will support HyperThreading even though it only supports one physical CPU.

Intel estimates that 25% of Intel-based business/consumer PCs in 2003 will support HyperThreading.

November 2002

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