CPUs (Central Processing Units), often known simply as processors, are systems of electronic circuits designed to execute the instructions of a computer program. Processors have evolved markedly since their initial invention, but while many elements--size and power, most notably--have undergone massive changes, the principals of operation remain roughly the same. Most CPUs contain two principal elements: an arithmetic logic unit (ALU), and a control unit (CU). Modern processors--those found in smartphones, for example--are technically microprocessors, but the older, larger variety are now so uncommon as to be largely excluded from the conversation.
Processing power is most often measured in terms of cycle speed, also known as Clock Rate. The frequency of cycles per second--measured, among contemporary devices, in megahertz or gigahertz--is the dominant means of indicating processor performance. That said, a variety of factors influence the perceived speed of a handset or computer, including the quality of the components and the efficiency of the design. A single cycle can accomplish more or less, depending on the processor’s design, for example.
Multi-core Processors: Increasingly common among smartphones and personal computers are processors with more than one ‘core’—meaning, simply, those that integrate multiple individual processors. Today’s smartphones often feature dual-core or quad-core processors, which allow for the simultaneous execution of multiple asynchronous computing tasks. Theoretically, an additional core should double the processing capability of a device; in virtually all cases, however, processing power is increases roughly 50% when the number of cores is doubled.