<P> Lee Boysel published influential articles, including a 1967 "manifesto", which described how to build the equivalent of a 32 - bit mainframe computer from a relatively small number of large - scale integration circuits (LSI). At the time, the only way to build LSI chips, which are chips with a hundred or more gates, was to build them using a MOS process (i.e., PMOS logic, NMOS logic, or CMOS logic). However, some companies continued to build processors out of bipolar chips because bipolar junction transistors were so much faster than MOS chips; for example, Datapoint built processors out of transistor--transistor logic (TTL) chips until the early 1980s . At the time, MOS ICs were so slow that they were considered useful only in a few niche applications that required low power . </P> <P> As the microelectronic technology advanced, an increasing number of transistors were placed on ICs, decreasing the number of individual ICs needed for a complete CPU . MSI and LSI ICs increased transistor counts to hundreds, and then thousands . By 1968, the number of ICs required to build a complete CPU had been reduced to 24 ICs of eight different types, with each IC containing roughly 1000 MOSFETs . In stark contrast with its SSI and MSI predecessors, the first LSI implementation of the PDP - 11 contained a CPU composed of only four LSI integrated circuits . </P> <P> Since the introduction of the first commercially available microprocessor, the Intel 4004 in 1970, and the first widely used microprocessor, the Intel 8080 in 1974, this class of CPUs has almost completely overtaken all other central processing unit implementation methods . Mainframe and minicomputer manufacturers of the time launched proprietary IC development programs to upgrade their older computer architectures, and eventually produced instruction set compatible microprocessors that were backward - compatible with their older hardware and software . Combined with the advent and eventual success of the ubiquitous personal computer, the term CPU is now applied almost exclusively to microprocessors . Several CPUs (denoted cores) can be combined in a single processing chip . </P> <P> 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, the ability to construct exceedingly small transistors on an IC has increased the complexity and number of transistors in a single CPU 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 . </P>

The central processing unit cpu is a type of