CPU, that's sometimes called just "processor", is an abbreviation for Central Processing Unit. That is the core of any laptop or computer or web server, since it performs each of the calculations and logical input/output functions. Despite the fact that that the performance of a site or an application depends on other things also, such as the amount of physical memory or the connection of the hosting server, the speed at which a specific processor runs determines how fast an application will be executed. Later-generation processors have several cores which can drastically boost their overall power and efficiency, due to the fact that each core can handle several processes individually or a number of cores can handle 1 process that needs a significant computing power. As each core works at a certain speed, this architecture can be seen as a few individual processors cooperating.