CPU, which is oftentimes called just "processor", is an abbreviation for Central Processing Unit. This is the core of every computer or hosting server, as it runs all the calculations and logical input/output functions. Even though the performance of a site or an app relies on other things as well, such as the amount of physical memory or the connectivity of the hosting server, the rate at which a given processor works determines how fast an app will be executed. Later-generation processors have several cores which can seriously improve their overall power and efficiency, due to the fact that every core can handle a variety of processes separately or several cores can control 1 process that requires a substantial computing power. As each core runs at a certain speed, this architecture can be viewed as numerous independent processors cooperating.