CPU, that is sometimes called just "processor", is an abbreviation for Central Processing Unit. That is the core of every personal computer or web server, because it runs each of the calculations and logical input/output functions. Though the performance of a site or an app relies upon other things too, like the amount of physical memory or the connectivity of the web server, the speed at which a given processor operates determines how quickly a program shall be executed. Later-generation processors have numerous cores which can drastically increase their overall power and efficiency, as each and every core can take on numerous processes separately or a few cores can handle one process which requires a significant computing power. Because every single core works at a particular speed, this architecture can be looked at as a few individual processors working together.