I have a machine with four CPUs, each with 8 cores, for a total of 32 cores. I have a multi-threaded application. How many cores will it be able to use? Which versions of Windows allows access to cores on all four processors? Thanks.

Windows isn't the governing factor here, it's the application. If the application was written to create an affinity with multiple processors then it could take advantage of as many as it likes. Windows doesn't come along and say, "I have 32 cores but you can only have access to 4". This is an in-depth Word document on a related topic, but it still has a wealth of information around the topic you're exploring. Cheers, Lain

Thank you, that article is informative. I am concerned that some versions of Windows will not allow access to all of the processors. For example, here http://answers.microsoft.com/en-us/windows/forum/windows_xp-hardware/multi-core-processor-and-multiprocessor-limit-for/abd0a0ce-4ac2-484b-88cb-fbf93beb54e0 there is discussion that Windows XP Home supports only one processor, while WIndows XP Professional supports up to two processors (each with multiple cores.) Windows Server 2003 allows more, as shown in the table at this link: http://support.microsoft.com/kb/888732 I am having trouble finding a similar charg for Windows Server 2008 from Microsoft, but the following chart gives information: http://www.directionsonmicrosoft.com/sample/DOMIS/update/2008/02feb/0208ws2plp_ch.htm

You're right about XP as that was a deliberate limitation with the HAL, but Vista/Server 2008 and Windows 7/Server 2008 R2 each increased the limit, so I guess it ultimately comes down to which operating system you're planning on using (or being forced to use). I hadn't assumed we were talking about XP/Server 2003 though given their age as these were designed for much older processor architectures where cores didn't exist and multiple CPUs were as expensive as billy-o. Cheers, Lain