CPU, that is often called just "processor", is an abbreviation for Central Processing Unit. That is the core of each PC or web server, because it runs all of the calculations and logical input/output operations. Even though the performance of a site or an application relies upon other things too, such as the amount of physical memory or the connectivity of the web server, the speed at which a specific processor operates determines how fast an application will be executed. Later-generation processors have several cores which can significantly improve their overall power and efficiency, due to the fact that every single core can control a variety of processes independently or several cores can deal with 1 process which needs a substantial processing power. As every core works at a particular speed, this architecture can be viewed as a number of independent processors working together.