Multi-processor  and multi-core threading not native to commercially available applications pre Vista (including many that were actually designed specifically to run on Vista)

Although multi - processor systems (and in certain cases more discrete forms of single processors with multiple processing cores) have been around long before Vista beta preview dumped on my computer, its only more recently that true multi-processor and multi-core process threading has become a little more common. However even on the brink of Windows 8 release true multi-core/multi-CPU process threading based  applications are only something that’s been implemented in the coding for high end industry related/and custom designed applications for the main part. Having said that Windows 7 does have a baked in means of allowing none native multi-core/multi-CPU process threading applications to access this feature to a certain degree but not in the truest pure technical sense, so there isn't necessarily a need to alter any setting for this in Windows 7 unless you want to assign particular individual processing threads to a particular processor or to a particular processing core.

 

XP's doesn't have the capability to natively harness multi-core threading despite the fact of having the ability to assign individual process threads to particular individual processors and cores of a multi processor and/or multi-core system.

Hint: The cores on a Multi-core CPU will be listed as an individual numbered CPU.