CPU, that's frequently called just "processor", is an abbreviation for Central Processing Unit. That's the core of each PC or hosting server, since it performs each of the calculations and logical input/output functions. Even though the performance of a site or an app depends on other things also, such as the amount of physical memory or the connectivity of the server, the pace at which a given processor operates determines how soon an app will be executed. Later-generation processors have several cores which can drastically boost their overall power and efficiency, since each and every core can manage numerous processes individually or a few cores can handle 1 process which needs a substantial processing power. As each and every core works at a specific speed, this architecture can be viewed as a number of separate processors working together.