TheLastColdBeer
you need to turn on the second core for windows to see it or have the correct OS
Versions of Windows
Knowing that, the limit of the number of processors is determined by your version of Windows XP. If you're not sure which version you're running, check the sticker on your computer. It will say the version there beside your license key; you may right-click "My Computer" and click "Properties." The window that pops up will tell you which version of XP you're running.
XP Home
The Home edition of Windows XP---the edition that came with most machines home users bought from the likes of Dell and HP, before Windows Vista---supports only one processor. This means if you want to install more than one processor and you run Windows XP Home, you may need to switch to Professional, or upgrade Windows to a newer version with support for multiple processors.
XP Professional
If you want to use two processors, Windows XP Professional is the way to go. While this advanced program cannot run more than two processors, this is an improvement over Home. Note that, because dual-core processors count as a single processor, you could theoretically have four cores with this license or even eight, if you are willing to buy two quad-core processors.