When Donald Davies considered how computers might communicate, he noticed that their traffic did not behave like a telephone call. A user might send data in brief bursts, with long pauses in between; keeping a dedicated telephone line open throughout those silences was wasteful. Davies’s answer was packet switching: divide messages into small units that can travel independently across a network and be reassembled at their destination. Developed at the National Physical Laboratory in England, the idea became a foundation of modern data communications.
From Treorchy to the National Physical Laboratory
Donald Watts Davies was born in Treorchy, in the Rhondda Valley, on 7 June 1924. His father, a clerk at a coalmine, died when Davies was an infant. His mother took him and his twin sister to Portsmouth, where he attended the Southern Grammar School for Boys. The movement between a Welsh birthplace and an English education would be followed by a career spent working in Britain’s national scientific institutions.
Davies studied physics at Imperial College London, graduating in 1943. During the war he joined the Tube Alloys project at the University of Birmingham, assisting the physicist Klaus Fuchs. He returned to Imperial College and completed a first-class degree in mathematics in 1947, receiving the Lubbock Memorial Prize as the outstanding mathematician of his year. That same year he began work at the National Physical Laboratory (NPL) in Teddington.
At the NPL, Davies entered a computing project already associated with Alan Turing, who had been designing the Automatic Computing Engine. When that ambitious project faltered, Davies took it over and concentrated on a more attainable machine, the Pilot ACE. It first operated in May 1950. A commercial development, DEUCE, was manufactured by English Electric Computers and became one of the best-selling computers of the 1950s. Davies also worked on traffic simulation and machine translation, and in the early 1960s took part in government initiatives intended to stimulate the British computer industry.
A different way to send data
The idea that made Davies internationally significant grew from a practical problem. After attending an international computing congress in New York in 1965 and visiting the Massachusetts Institute of Technology, he began examining the cost of connecting users to time-sharing computers. A telephone line reserved for each user stayed occupied even when that user was not sending anything. Computer traffic, Davies recognised, came in bursts rather than the relatively continuous flow associated with a telephone conversation.
His solution was to share the communications line as well as the computer. Messages would be split into short, standardised packets, routed separately through a network and reassembled at the receiving end. Different packets belonging to one message could take different routes. Davies chose the word “packet” after consulting a linguist, in part because it could be translated into other languages without losing its meaning.
Davies developed his proposals at the NPL, where he became Superintendent of the Computer Science Division. His 1966 proposal for a national communications service set out a commercial data network and described high-speed switching nodes, the precursors of what are now called routers. He used queueing theory to address whether the system could deliver acceptable response times to users, and envisaged a future network carrying both speech and digital messages.
Davies’s work was independent of similar research by American engineer Paul Baran. Davies later acknowledged Baran’s parallel discovery, while Baran recognised that Davies had independently reached the idea and was the first to implement it. This distinction matters: packet switching was not a single isolated insight, but Davies’s design and the NPL team’s practical work made a major contribution to its development.
Building and connecting networks
Davies and his colleagues moved from proposals to construction. The NPL’s local-area network began operating in early 1969 and became fully operational as the Mark I in January 1970. It was the world’s first implementation of packet switching. The network was upgraded to Mark II in 1973, with a layered protocol architecture, and remained in operation until 1986. The team also used simulations to examine network congestion and the behaviour of packet networks over wider areas.
The NPL work reached beyond the laboratory. At a 1967 symposium, a paper on the network design, presented by Davies’s colleague Roger Scantlebury, caught the attention of the developers of ARPANET in the United States. The NPL research influenced ARPANET, an important predecessor of the internet, as well as France’s CYCLADES project. Davies’s contribution was not simply the invention of a useful term or a promising theory: it included a design, a working demonstration and research into how separate networks might communicate.
That further problem became a focus for Davies, his deputy Derek Barber and Scantlebury. They worked on protocols for internetworking and took part in the International Network Working Group from 1972. Their experiments connected the NPL network with the European Informatics Network and with the UK Post Office’s experimental packet-switched service. The work examined the advantages of using a common protocol rather than translating between different systems. Davies and Barber’s book Communication Networks for Computers appeared in 1973; Davies later published Computer Networks and Their Protocols in 1979.
Security, recognition and later work
In 1979, Davies gave up his management responsibilities to return to research. He became particularly interested in computer security and cryptography, and his research led to patents, including methods for secure communications involving smart cards. After retiring from the NPL in 1984, he worked as a data-security consultant to the banking industry. With David O. Clayden, he designed the Message Authenticator Algorithm, an early message-authentication method that gained wide acceptance and was adopted as an international standard in 1987. In 1987, Davies became a visiting professor at Royal Holloway and Bedford New College.
His recognition included appointment as a Distinguished Fellow of the British Computer Society in 1975, a CBE in 1983 and election as a Fellow of the Royal Society in 1987. In 2000, he shared the inaugural IEEE Internet Award. Further posthumous recognition followed with induction into the National Inventors Hall of Fame in 2007 and the Internet Hall of Fame in 2012. The NPL sponsors a gallery on packet switching, and a blue plaque commemorating Davies was unveiled in Treorchy in 2013.
Davies married Diane Burton in 1955. They had a daughter and two sons, and he was also survived by four grandchildren. He died in Esher, Surrey, on 28 May 2000, aged 75.
Why Donald Davies deserves a place in British Legacy
Donald Davies belongs in British Legacy because his work at the National Physical Laboratory helped transform a difficult communications problem into a practical system. Packet switching made it possible to send data in short bursts without reserving a continuous circuit for each user. Davies and his colleagues developed the design, built the first working implementation at the NPL and explored how networks could exchange information. Those contributions helped shape the technology and principles on which later computer networks, including the internet, were built.
His British significance is specific, not merely symbolic. Born in Wales and educated and employed in Britain, Davies carried out much of this influential work in a national laboratory whose research connected scientific ideas with working systems. His career also extended beyond packet switching: from the Pilot ACE and early commercial computing to network protocols and security for banking communications. The NPL network’s operation from 1969 into the 1980s shows how the work became an enduring testbed, while the later honours and Treorchy plaque mark both professional recognition and a continuing connection to his birthplace. Remembering Davies makes visible the collaborative, often institution-based engineering behind everyday digital communication.
Sources
Donald Davies — revision 1375701217 · Donald Davies
Adapted in part from Donald Davies by Wikipedia contributors, under CC BY-SA 4.0. Text has been edited and combined with the existing article; this adapted text is shared under the same licence. Contributor history.