reverse engineering How we made the The 4004 is renowned as the world’s frst commercial microprocessor. Project leader and designer of the 4004, Federico Faggin, retraces the steps leading to its invention. Federico Faggin

omputers were, at first, a decidedly The emergence of these unintegrated technology. They were was undoubtedly a turning point for the Ccomposed of vacuum tubes, resistors, electronics industry. They fitted an entire capacitors, inductors and mercury delay lines, system into a small and low-cost and as a result were huge, expensive and printed circuit board by adding variable power hungry. The situation improved with amounts of read only memory (ROM) and developments in microelectronics based on RAM, plus application-specific input–output solid-state germanium transistors and diodes, electronics. With their development, the which began replacing vacuum tubes in radios same hardware could now be programmed and phonographs, and eventually led to the to perform a variety of applications that first commercial transistor-based previously required specialized custom in 1959. That same year, the development of hardware for each application. This was, the planar process at of course, the key advantage of computers, allowed tens of silicon transistors to be but meant that custom hardware had to fabricated at the same time on the surface of be replaced with software, and this turned a single-crystal silicon wafer (ten years later out to be a difficult transition — many it would be possible to fabricate thousands industries that could not adapt were swept of transistors). This invention was quickly away, including electromechanical calculator followed by the commercialization of the manufacturers such as Marchant, Facit first bipolar digital integrated circuits (ICs) and Comptometer. in 1962, and from that point on, progress Microprocessors quickly appeared in in semiconductor ICs became exponential, applications such as traffic light controllers, with the maximum number of components automatic blood analysers, point-of-sale integrated in a silicon chip doubling every Fig. 1 | Die shot of the . The chip registers, electric toothbrushes, electric year, at least initially. But what allowed all the measures 3 mm by 4 mm and contains about motor controllers and electronic games — functions of a general-purpose computer to be 2,300 MOS transistors. It is signed in the lower- applications where computers would have integrated together was a monolithic central right corner with the initials (F.F.) of Federico been considered incongruous only a few processing unit (CPU) — a microprocessor — Faggin, designer and project leader. Credit: image years earlier, given that mainframes and and the first commercial microprocessor was provided courtesy of Intel Corp. minicomputers were then much bigger than born nine years later in 1971 (Fig. 1). the products they were supposed to fit inside. Working at Fairchild Semiconductor in I moved to Intel in 1970. At that time, With microprocessors, it became feasible 1968, I was the project leader and architect many engineers knew how to create the to add a degree of intelligence to many of the metal–oxide–semiconductor (MOS) logic design of a small CPU. However, no existing products, providing significant silicon gate technology (SGT), a key one had achieved the circuit density needed improvements in their performance and ease breakthrough in the development of the first for a cost-effective general-purpose CPU of use. Today, a smartphone houses dozens microprocessor. With SGT, new device types that had sufficient speed to handle a wide of powerful embedded computers to manage could be fabricated such as dynamic random range of applications. At Intel, I used the a range of specialized communication, access memory (RAM), non-volatile memories perfected SGT process for random-logic sensing and control functions. It also and charged-coupled device imagers, design with the ‘buried contact’ and the contains powerful user-programmable increasing the range of IC functions possible silicon-gate bootstrap load that had been microprocessors that offer higher speeds with solid-state electronics. The SGT was the developed at Fairchild, which provided the and more memory than most mainframe first commercial self-aligned gate MOS process high speed and circuit density required computers of the late 1970s. Looking that was capable of building reliable, dense and for a single-chip CPU for the first time. back now, it is clear that the microprocessor fast MOS ICs. Compared with the incumbent The first microprocessor we made was a was one of the technologies that helped aluminium-gate MOS technology, the SGT 4-bit CPU, which was christened the ‘4004’. change what a computer could be and was five times faster, reduced the leakage It was custom designed for a Japanese could do, and also the way that they current by more than a factor of 100, and could manufacturer in order to build a family influence our lives. ❐ host twice as many random-logic transistors of electronic calculators. The first sales for the same power dissipation and chip area. for the 4004 were in March 1971 and it Federico Faggin The first commercial chip to use SGT was the was introduced to the general market in e-mail: [email protected] Fairchild 3708, an 8-bit analogue multiplexer November 1971. It was quickly followed by with decoding logic that I had designed. It was the first 8-bit microprocessor — the Intel Published online: 8 January 2018 introduced to the market at the end of 1968. 8008 — in April 1972. https://doi.org/10.1038/s41928-017-0014-8

88 Nature Electronics | VOL 1 | JANUARY 2018 | 88 | www.nature.com/natureelectronics © 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. © 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.