A microprocessor is a computer's processor which incorporates the functions of a computer's central processing unit (CPU) on a single integrated circuit (IC), or at most a few integrated circuits. The microprocessor is a multipurpose, clock driven, register based, digital-integrated circuit which accepts binary data as input, processes it according to instructions stored in its memory, and provides results as output. Microprocessors contain both combinational logic and sequential digital logic. Microprocessors operate on numbers and symbols represented in the binary numeral system.
The integration of a whole CPU onto a single chip or on a few chips greatly reduced the cost of processing power, increasing efficiency. Integrated circuit processors are produced in large numbers by highly automated processes resulting in a low per unit cost. Single-chip processors increase reliability as there are many fewer electrical connections to fail. As microprocessor designs get better, the cost of manufacturing a chip (with smaller components built on a semiconductor chip the same size) generally stays the same.
Before microprocessors, small computers had been built using racks of circuit boards with many medium- and small-scale integrated circuits . Microprocessors combined this into one or a few large-scale ICs. Continued increases in microprocessor capacity have since rendered other forms of computers almost completely obsolete (see history of computing hardware), with one or more microprocessors used in everything from the smallest embedded systems and handheld devices to the largest mainframes and supercomputers.
The advent of low-cost computers on integrated circuits has transformed modern society. General-purpose microprocessors in personal computers are used for computation, text editing, multimedia display, and communication over the Internet. Many more microprocessors are part of embedded systems, providing digital control over myriad objects from appliances to automobiles to cellular phones and industrial process control.
During the 1960s, computer processors were constructed out of small and medium-scale ICs—each containing from tens of transistors to a few hundred. These were placed and soldered onto printed circuit boards, and often multiple boards were interconnected in a chassis. The large number of discrete logic gates used more electrical power—and therefore produced more heat—than a more integrated design with fewer ICs. The distance that signals had to travel between ICs on the boards limited a computer's operating speed.
In the late-1960s, designers were striving to integrate the central processing unit (CPU) functions of a computer onto a handful of MOS LSI chips, called microprocessor unit (MPU) chip sets. Building on earlier Busicom designs and concepts from 1968, Intel introduced the first commercial microprocessor, the 4-bit Intel 4004, in 1971, followed by its 8-bit microprocessor 8008 in 1972.
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-bit and 8-bit microprocessors, such as terminals, printers, various kinds of automation etc., followed soon after. Affordable 8-bit microprocessors with 16-bit addressing also led to the first general-purpose microcomputers in the 1970s.
Since the early 1970s, the increase in capacity of microprocessors has followed Moore's law; this originally suggested that the number of components that can be fitted onto a chip doubles every year. With present technology, it is actually every two years, and as such Moore later changed the period to two years.
Intel 4004 (1968-1971)
The Intel 4004 is generally regarded as the first commercially available microprocessor. The "Busicom Project" that produced the 4004 originated in 1968, when Busicom engineer Masatoshi Shima designed a special-purpose LSI chipset, along with his supervisor Tadashi Tanba, for use in the Busicom 141-PF high-performance desktop calculator. Busicom's original design called for a programmable chip set consisting of seven different chips. Three of the chips were to make a special-purpose CPU with its program stored in ROM and its data stored in shift register read-write memory. Shima's initial design included arithmetic units (adders), multiplier units, registers, read-only memory, and a macro-instruction set to control a decimal computer system. Sharp engineer Tadashi Sasaki was also involved with its development, and conceived of a single-chip CPU in 1968, when he discussed the concept at a brainstorming meeting that was held in Japan. Sasaki attributes the basic invention to break the calculator chipset into four parts with ROM (4001), RAM (4002), shift registers (4003) and CPU (4004) to an unnamed woman, a software engineering researcher from Nara Women's College, who was present at the meeting. Sasaki then had his first meeting with Intel in 1968, and discussed the woman's four-division chipset concept with Busicom and Intel.
The initial Busicom design, which consisted of seven chips, including a three-chip CPU, was eventually simplified down to four chips, including a single-chip CPU. This simplified approach was initially conceived by Sasaki, influenced by the unnamed Nara Women's College reseacher in 1968, and then designed by Intel's Ted Hoff in 1969. Hoff, the Intel engineer assigned to evaluate the project, believed the Busicom design could be simplified by using dynamic RAM storage for data, rather than shift register memory, and a more traditional general-purpose CPU architecture. Hoff's design consisted of a four-chip architectural proposal: a ROM chip for storing the programs, a dynamic RAM chip for storing data, a simple I/O device and a 4-bit central processing unit (CPU). Although not a chip designer, he felt the CPU could be integrated into a single chip, but as he lacked the technical know-how the idea remained just a wish for the time being.
The architecture and specifications of the MCS-4 came from the interaction of an Intel team led by Hoff and Stanley Mazor, a software engineer reporting to him, and a Busicom team led by Shima, in 1969. However, Mazor and Hoff moved on to other projects. In April 1970, Intel hired Italian-born engineer Federico Faggin as project leader, a move that ultimately made the single-chip CPU final design a reality. Shima meanwhile designed the Busicom calculator firmware and assisted Faggin during the first six months of the implementation. Faggin, who originally developed the silicon gate technology (SGT) in 1968 at Fairchild Semiconductor and designed the world’s first commercial integrated circuit using SGT, the Fairchild 3708, had the correct background to lead the project into what would become the first commercial general purpose microprocessor. Since SGT was his very own invention, Faggin also used it to create his new methodology for random logic design that made it possible to implement a single-chip CPU with the proper speed, power dissipation and cost. The manager of Intel's MOS Design Department was Leslie L. Vadász at the time of the MCS-4 development but Vadász's attention was completely focused on the mainstream business of semiconductor memories so he left the leadership and the management of the MCS-4 project to Faggin, who was ultimately responsible for leading the 4004 project to its realization. Production units of the 4004 were first delivered to Busicom in March 1971 and shipped to other customers in late 1971. The first known advertisement for the 4004 is dated November 15, 1971 and appeared in Electronic News.
NEC released the μPD707 and μPD708, a two-chip 4-bit CPU, began development in 1970 and was released in 1971. They were followed by NEC's first single-chip microprocessor, the μPD700, in April 1972. It was a prototype for the μCOM-4 (μPD751), released in April 1973, combining the μPD707 and μPD708 into a single microprocessor.
The Intel 4004 was followed in 1972 by the Intel 8008, the world's first 8-bit microprocessor. The 8008 was the precursor to the successful Intel 8080 (1974), which offered improved performance over the 8008 and required fewer support chips. It was designed by Masatoshi Shima and Federico Faggin.
In 1973, Toshiba developed the TLCS-12, the world's first 12-bit microprocessor. The project began in 1971, when Toshiba began developing a microprocessor for Ford Motor Company's Electronic Engine Control (EEC) project, which went on to utilize Toshiba's 12-bit microprocessor.
In 1975, Panafacom (a conglomeration of Fujitsu, Fuji Electric, and Matsushita) developed the first commercial 16-bit single-chip microprocessor CPU, the MN1610. According to Fujitsu, it was "the world's first 16-bit microcomputer on a single chip".
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