A microprocessor incorporates most or all of the functions of a central processing unit (CPU) on a single integrated circuit (IC). The first microprocessors emerged in the early 1970s and were used for electronic calculators, using binary-coded decimal (BCD) arithmetic on 4-bit words. Other embedded uses of 4- and 8-bit microprocessors, such as terminals, printers, various kinds of automation etc, followed rather quickly. Affordable 8-bit microprocessors with 16-bit addressing also led to the first general purpose microcomputers in the mid-1970s.
Computer processors were for a long period constructed out of small and medium-scale ICs containing the equivalent of a few to a few hundred transistors. The integration of the whole CPU onto a single VLSI chip therefore greatly reduced the cost of processing capacity. From their humble beginnings, continued increases in microprocessor capacity have rendered other forms of computers almost completely obsolete (see history of computing hardware), with one or more microprocessor as processing element in everything from the smallest embedded systems and handheld devices to the largest mainframes and supercomputers.
Since the early 1970s, the increase in capacity of microprocessors has been known to generally follow Moore's Law, which suggests that the complexity of an integrated circuit, with respect to minimum component cost, doubles every two years. In the late 1990s, and in the high-performance microprocessor segment, heat generation (TDP), due to switching losses, static current leakage, and other factors, emerged as a leading developmental constraint.
