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 BCD arithmetics 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.
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 integration 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, with one or more microprocessor as processing element in everything from the smallest embedded system and handled devices to the largest main frames and supercomputers.
Since the early 1970s, the increase in processing capacity of evolving microprocessors has been known to generally follow Moore's law. It suggests that the complexity of an integrated circuit, with respect to minimum component cost, doubles every 18 months. In the late 1990s, heat generation (TDP), due to current leakage and other factors, emerged as a leading developmental constraint.
Three projects arguably delivered a complete microprocessor at about the same time, namely intel's 4004, the Texas Instruments (TI) TMS 1000, and Garrett Airesearch's Central Air Data Computers (CADC).
In 1968, Garrett AiResearch, with designer and Steve Geller, were invited to produce a digital computer to compete with electromechanical systems then under development for the main flight control computer in the US navy's new F-14 tomcat fighter. The design was complete by 1970, and used a MOS-based chipset as the core CPU. The design was significantly (approximately 20 times) smaller and much more reliable than the mechanical systems it competed against, and was used in all of the early Tomcat models. This system contained a "a 20-bit, pipelined, parallel multi-microprocessor". However, the system was considered so advanced that the Navy refused to allow publication of the design until 1997. For this reason the CADC, and the MP944 chipset it used, are fairly unknown even today. developed the 4-bit TMS 1000, and stressed pre-programmed embedded applications, introducing a version called the TMS1802NC on September 17, 1971, which implemented a calculator on a chip. The Intel chip was the 4-bit 4004, released on November 15, 1971, developed by federico fraggin and marcian hoff, the manager of the designing team was leslie l.vadasz.
TI filed for the patent on the microprocessor. Gary Boone was awarded U.s.patent 3757306 for the single-chip microprocessor architecture on september 4 , 1973. It may never be known which company actually had the first working microprocessor running on the lab bench. In both 1971 and 1976, Intel and TI entered into broad patent cross-licensing agreements, with Intel paying royalties to TI for the microprocessor patent. A nice history of these events is contained in court documentation from a legal dispute between Cyrix and Intel, with TI as intervenor and owner of the microprocessor patent.
Interestingly, a third party (Gilbert Hyatt) was awarded a patent which might cover the "microprocessor". See a webpage claiming an invention pre-dating both TI and Intel, describing a "microcontroller". According to a rebuttal and a commentary, the patent was later invalidated, but not before substantial royalties were paid out.
A computer-on-a-chip is a variation of a microprocessor which combines the microprocessor core (CPU), some memory, and I/O lines, all on one chip. The computer-on-a-chip patent, called the "microcomputer patent" at the time, U.S.patent 4074351, was awarded to Gary Boone and Michael J. Cochran of TI. Aside from this patent, the standard meaning of microcomputer is a computer using one or more microprocessors as its CPU(s), while the concept defined in the patent is perhaps more akin to a microcontroller.
According to A History of Modern Computing, (MIT Press), pp. 220–21, Intel entered into a contract with Computer Terminals Corporation, later called datapoint, of San Antonio TX, for a chip for a terminal they were designing. Datapoint later decided to use the chip, and Intel marketed it as the 8008 in April, 1972. This was the world's first 8-bit microprocessor. It was the basis for the famous "mark-8" computer kit advertised in the magazine Radio-Electronics in 1974. The 8008 and its successor, the world-famous 8080, opened up the microprocessor component marketplace.
Notable 8-bit designs
The 4004 was later followed in 1972 by the 8008, the world's first 8-bit microprocessor. These processors are the precursors to the very successful intel 8080 (1974), zilog z-80 (1976), and derivative Intel 8-bit processors. The competing Motorola 6800 was released August 1974. Its architecture was cloned and improved in the MOS technology 654 in 1975, rivaling the Z80 in popularity during the 1980s.
Both the Z80 and 6502 concentrated on low overall cost, by combining small packaging, simple computer bus requirements, and including circuitry that normally must be provided in a separate chip (example: the Z80 included a memory controller). It was these features that allowed the "revolution" to accelerate sharply in the early 1980s, eventually delivering such inexpensive machines as the sinclair zx-81, which sold for US$99.
the western design centre,Inc. (WDC) introduced the CMOS 65co2 in 1982 and licensed the design to several firms. It became the core of the Apple IIc and IIe personal computers, medical implantable grade pacemakers and defibrilators, automotive, industrial and consumer devices. WDC pioneered the licensing of microprocessor technology which was later followed by ARM and other microprocessor Intellectual property (IP) providers in the 1990’s.
Motorola trumped the entire 8-bit market by introducing the Mc6809 in 1978, arguably one of the most powerful, orthogonal, and clean 8-bit microprocessor designs ever fielded – and also one of the most complex hard-wired logic designs that ever made it into production for any microprocessor. microcoding replaced hardwired logic at about this time for all designs more powerful than the MC6809 – because the design requirements were getting too complex for hardwired logic.
Another early 8-bit microprocessor was the signetics 2650, which enjoyed a brief surge of interest due to its innovative and powerful instruction set
A seminal microprocessor in the world of spaceflight was RCA's RCA 1802 (aka CDP1802, RCA COSMAC) (introduced in 1976) which was used in NASA's voyager and vikig spaceprobes of the 1970s, and onboard the Galileo probe to Jupiter (launched 1989, arrived 1995). RCA COSMAC was the first to implement C-MOS technology. The CDP1802 was used because it could be run at very low power, and because its production process (silicon on sapphire) ensured much better protection against cosmic radiation and electrostatic discharges than that of any other processor of the era. Thus, the 1802 is said to be the first radiation-hardened microprocessor.
The RCA-1802 had what is called a static design, meaning that the clockfrequency be made arbitrarily low, even to 0 Hz, a total stop condition. This let the voyeger,viking,galelio spacecraft use minimum electric power for long uneventful stretches of a voyage. Timers and/or sensors would awaken/speed up the processor in time for important tasks, such as navigation updates, attitude control, data acquisition, and radio communication.
