Page "Central processing unit" Paragraph 16

Previous generations of CPUs were implemented as discrete components and numerous small integrated circuits ( ICs ) on one or more circuit boards.

Microprocessors, on the other hand, are CPUs manufactured on a very small number of ICs ; usually just one.

The overall smaller CPU size as a result of being implemented on a single die means faster switching time because of physical factors like decreased gate parasitic capacitance.

This has allowed synchronous microprocessors to have clock rates ranging from tens of megahertz to several gigahertz.

Additionally, as the ability to construct exceedingly small transistors on an IC has increased, the complexity and number of transistors in a single CPU has increased many fold.

This widely observed trend is described by Moore's law, which has proven to be a fairly accurate predictor of the growth of CPU ( and other IC ) complexity.