CPU, that's often called just "processor", is an abbreviation for Central Processing Unit. This is the core of each computer or server, since it runs all the calculations and logical input/output functions. Even though the performance of an Internet site or an application relies on other things as well, including the amount of physical memory or the online connectivity of the web server, the speed at which a given processor runs determines how soon an application will be executed. Later-generation processors have multiple cores that can drastically increase their overall power and efficiency, as every core can take on a variety of processes separately or a number of cores can deal with a single process which needs a significant processing power. As every core runs at a particular speed, this architecture can be viewed as several individual processors working together.