Robert Melancton “Bob” Metcalfe is an American electrical engineer and entrepreneur best known as the principal inventor of Ethernet. He earned bachelor’s degrees from MIT in 1969 and, at Harvard, a master’s in applied mathematics and a 1973 PhD whose dissertation on packet communication drew on his work with the ARPANET at MIT’s Project MAC and with the ALOHAnet radio network at the University of Hawaii. That radio network’s randomized-retransmission scheme directly shaped his later thinking about sharing a single channel among many stations.
In 1972 Metcalfe joined the Xerox Palo Alto Research Center, working in the Computer Science Laboratory alongside Butler Lampson and Charles Thacker as they built the Alto personal computer. He has recalled that Ethernet was “born” on 22 May 1973, the day he circulated a memo proposing a broadcast network to connect the Altos within a building. With David Boggs he turned the idea into working hardware, and the two published the design in the July 1976 Communications of the ACM paper “Ethernet: Distributed Packet Switching for Local Computer Networks.”
In 1979 Metcalfe left Xerox and founded 3Com, a company that built Ethernet adapters and helped make the technology a mass-market product as personal computers proliferated. He was also instrumental in the standardization effort, helping bring Xerox, Digital Equipment Corporation, and Intel together behind a common specification that the IEEE later adopted as 802.3. He often argued that Ethernet’s openness, as much as its engineering, was the reason it won.
Metcalfe is also the namesake of Metcalfe’s Law, the rule of thumb that a network’s value grows roughly with the square of the number of connected users. He first presented the idea in sales slides in the 1980s to argue that networks become useful only past a critical mass of nodes, and decades later he revisited and defended it quantitatively in a 2013 IEEE Computer article.
In 2023 the ACM named Metcalfe the recipient of the 2022 A.M. Turing Award, often called the Nobel Prize of computing, with the citation “for the invention, standardization, and commercialization of Ethernet.” The Computer History Museum recorded a multi-part oral history with him in 2006 and 2007, preserving a firsthand account of the PARC years and the origins of the technology that still carries most of the world’s local network traffic.