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The Silicon Gate Design of the 4004: From Idea to Reality
“Now it’s a team effort. In 1970 Federico Faggin designed the 4004 microprocessor chip by himself at Intel in nine months; our 32-bit microprocessor took 100 man-years!”: Bob Noyce (co-founder of Intel) in the article “Silicon Valley” by Moira Johnston, pag. 466, National Geographic, October 1982.
“Now the wait was finally over and Federico Faggin, father, mother and midwife expectantly approached his newborn [the 4004 microprocessor]”: Thomas H. Lee (Professor of Electrical Engineering at Stanford University), in his article : “From Mechanism to Monolith”, “The path to the microprocessor”, page 69, IEEE Solid State Circuits magazine, Winter 2009, vol. 1, No. 1
"The Designer Behind the World's First Microprocessor," filmed at the Intel Museum in Santa Clara, California www.youtube.com/watch?v=CcOk3jMRoyA
“The silicon design is the essence of the first microprocessor” Federico Faggin. "The crucial role of silicon design in the invention of the microprocessor"
The silicon-gate-based design, entirely created by Federico Faggin, was the invention that made the first microprocessor a reality in 1970. This was not a routine design since such complexity had never been integrated into a single chip before. It was only because of his innovations in silicon gate technology (SGT) that Faggin could design the 4004 in one chip.
At that time, engineers knew how to architect small computers and create software programs. The idea of microprocessor, a central processing unit (CPU) in one chip, was in the air. It had been pursued in a few places and some CPU architectures had been realized in several chips. However, no one had yet been able to figure out how to fit nearly 2500 transistors of random logic -- the minimum number for a simple CPU -- into a single chip small enough to be manufacturable at low cost. This chip also required high speed to be useful, and low power dissipation to fit into existing packages. The real challenge was to create the design methodology and develop the circuits and the layout designs using the newly developed Silicon Gate Technology (SGT) which had not yet been used before for random logic.
In April 1970, Federico Faggin was hired by Intel, from Fairchild Semiconductor where in 1968 he had developed the Silicon Gate Technology (SGT) and had designed the 3708, the world’s first commercial integrated circuit (IC) using SGT. The SGT was the first commercial technology for the fabrication of MOS Integrated Circuits to use self-aligned gates made with poly-crystalline silicon. At Intel, he was put in charge of the design and implementation of the MCS-4 project, which included the 4004.
Faggin possessed the rare combination of knowledge and skills, indispensable to lead and to carry to successful production such a complex and technology-dependent project because he knew computer architecture and logic design, circuit design, layout and process technology. Before joining Intel Faggin had co-designed and built a small transistorized experimental computer, using magnetic core memory, at Olivetti (Italy) at the age of 19. AT SGS Fairchild (Italy) he had developed their first MOS process technology and designed two commercial MOS ICs.
In 1969, Ted Hoff, head of the Application Research Department at Intel, had formulated the MCS-4 architecture, reducing to 4 chips Busicom’s custom logic architecture which would have required 7 chips, 3 of which were dedicated to make a programmable CPU. Hoff was assisted by Stan Mazor and interacted with Busicom engineers, among them Masatoshi Shima. Hoff believed that the CPU could be done in one chip but then, neither he nor his assistant Stan Mazor, were chip designers, and Hoff’s architectural proposal had been idling for about 6 months. Masatoshi Shima, came back to Intel in April 1970 to check on the project which he found still at the idea stage. Alarmed by the delay he stayed on and was the only engineer who assisted Faggin during the first six months of the MCS-4 development. Shima was a software and logic design engineer with practically no knowledge of MOS process technology and chip design. He took directions and learned from Faggin while completing the tasks he was assigning to him. In his book "The Birth of the Microcomputer: My Recollections," Published in August 1987 by Iwanami Shoten, Tokyo, Shima remembers how Faggin taught him “the semiconductor process, circuitry design, layout design” and also “mask design” and “the methodology of LSI development” which led him to become an LSI engineer" (p.75).
In the book “Inventors at Work” by Kenneth A. Brown (1988 Microsoft Press, p. 285) Ted Hoff himself is explicit about his role in the microprocessor which he explains consisted pretty much in defining the architecture and its related concepts. But then, Hoff says that he turned his architecture over to the MOS Design Department for its conversion into actual chips.
Faggin’s silicon gate design methodology (SGDM), combined with the circuit and the layout designs that he created at Intel, incorporated many of his inventions and took advantage of the strengths of the SGT that he knew intimately. The SGDM was very successful, and was used not only for the 4004 but also for all the other early Intel and Zilog microprocessors.
A good example to show how necessary the SGDM was to designing Intel’s early microprocessors is the 8008, architected by Computer Terminal Corporation (CTC). The chip definition of the 8008 (originally called 1201) was already under way when Faggin joined Intel but the project, assigned to Hal Feeney, did not go very far because Intel at that time had no methodology and no library of circuits for random logic design. The 8008 was then suspended and was resumed in January 1971, under Faggin's direction, after he had successfully produced the 4004, and was completed using his SGDM and all the circuits he developed for the 4004.
The SGT that Federico Faggin developed at Fairchild Semiconductor for the fabrication of MOS integrated circuits was adopted by Intel and subsequently by the world semiconductor industry. Gordon Moore, Intel’s co-founder, acknowledges that a major component of Intel’s success was due to their adoption of the SGT.
The SGT allowed also the production of the first commercially successful dynamic random access memories (RAMs), charged coupled devices (CCD) image sensors, non-volatile memories, and the microprocessor, providing for the first time all the key components for the realization of general-purpose computers with large scale integration (LSI) ICs.
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