[eluser]WanWizard[/eluser]
Can be anything, although often it's the database engine that uses the CPU. Which shouldn't be a problem as long as this 100% means 'available capacity well used' and not 'system overloaded'.
For comparison, my dev server is a Core i7. Originally just running LAMP, MySQL had no problem getting the CPU graphs to 100% even with light loads. Now this same machine runs Hyper-V with 7 VM's. That same LAMP environment still bursts to 100% CPU, but the performance difference is hardly measurable. Only when performing stress-tests I see that the VM can handle less concurrent connections (which for development is not an issue

).