Both Windows XP Home Edition and Windows XP Professional treat a Hyper-Threading enabled computer as a multiple processor computer. You can verify this by looking in Device Manager, under the Computer and Processors nodes:
In Computer, you can expect the computer to be described as a multiprocessor PC.
In Processors, you can expect multiple processors to appear installed.
If the Hyper-Threading feature is disabled in the computer's BIOS, Windows XP may describe the computer as a Uniprocessor PC and may show only a single processor installed in Device Manager.
When Hyper-Threading is enabled in the computer's BIOS, Windows XP automatically upgrades the hardware abstraction layer (HAL) if it must use a multi-processor HAL, and an additional processor or processors may be installed and listed under Processors in Device Manager. The system will prompt you to restart so that the new settings can take effect.
Hyper-Threading CPUs contain a second (virtual) CPU. With this feature, multi-threaded applications can run threads in parallel in each processor. As a result, you experience more efficient use of the processor resources and better performance with multi-threaded applications.
Windows XP Home
Note: Windows XP Home can use a maximum of one (1) physical processor. However, because Hyper-Threading is supported, the operating system takes advantage of the second (virtual) processor.