CPU, that is often called just "processor", is an abbreviation for Central Processing Unit. This is the core of each and every PC or server, as it executes all of the calculations and logical input/output procedures. Even though the performance of a site or an app is determined by other things also, such as the amount of physical memory or the connection of the server, the rate at which a given processor works determines how fast a program will be executed. Later-generation processors have a number of cores that can considerably increase their overall power and efficiency, because every single core can control several processes independently or a few cores can control a single process which requires a sizeable computing power. Since each core functions at a particular speed, this architecture can be looked at as a number of individual processors working together.