Reading up on this, and specifically reading the Microsoft docs, it looks like it should be returning the number of PHYSICAL processors, and that you should use GetLogicalProcessorInformation to figure out how many LOGICAL processors you have.

Here's the doc I found on the SYSTEM_INFO structure: http://msdn.microsoft.com/en-us/library/ms724958(v=VS.85).aspx And here's the doc on GetLogicalProcessorInformation: (spaces added to get through spam filter) http:// msdn.microsoft.com/ en-us/ library/ ms683194.aspx

Reading up on it further though, in most of the discussions I've found on this topic, developers say to that GetSystemInfo (and the SYSTEM_INFO structure) report the number of LOGICAL processors.

When I search again, I find that MS did release some info on this (and a hot fix), here (spaces added to get through spam filter): http:// support. microsoft.com/ kb/936235

Reading that, it sounds like on Xp, pre-service Pack 3, GetSystemInfo reports the number of LOGICAL processors in the SYSTEM_INFO structure. It also reads to me that on Windows Vista and Windows 7, GetSystemInfo should be reporting the number of PHYSICAL processors (different to Windows XP pre-service Pack 3).

Does anyone know what it actually does? Does GetSystemInfo really report the number of physical processors (on the same computer) differently, depending on which OS it's running on?