Donald Davies at his desk at the National Physical Laboratory, where he pioneered communication between computers

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Turing, Pilot Ace, Internet, Packet Switching

Scientist who enabled computers to talk to each other, and so made the Internet possible

After working with Alan Turing, the scientific genius who first conceptualised computer programming, Donald Davies went on to make one of the crucial breakthroughs that made possible modern computer communications. He pioneered packet-switching, which enables the exchange of information between computers, without which the Internet could not function.

When Davies was recommended for a Commonwealth Fund Fellowship in 1954, his senior officer described him as "outstanding not only in intellectual power but also in the range of his scientific, technical and general knowledge. He is equally unusual in his ability to apply this knowledge to mechanical and electrical design and even to the actual construction of complex equipment. He is, for example, one of the very small number of persons who could draw up a complete logical design of an electronic computer, realise this design in actual circuitry, assemble it himself (with a high probability that it would work as designed) and then program it and use it for the solution of computational problems." This breadth of interest and ability was a hallmark of his career.

Davies was author or joint author of four influential books in his areas of expertise, notably Computer Networks and their Protocols published in 1973. His contributions, in particular his work on packet-switching, were recognised by the British Computer Society, which conferred on him the John Player Award in 1974 and a Distinguished Fellowship in 1975; he became its technical vice-president in 1983. He was appointed CBE in 1983 and a Fellow of the Royal Society in 1987. He was a visiting professor at Royal Holloway and Bedford New College in 1987.

His versatility and his fascination with intellectual challenges and puzzles are evident in his private interests as well as in his formal computer work. Over the years these interests included the design and construction of noughts-and-crosses machines, which were considerable attractions at the annual NPL children's parties (the game was the subject of his first published paper, in 1950); historic cryptographic machines, particularly the German machines of the Second World War; and all puzzles and games capable of mathematical analysis.

His last project showed that his technical skills remained undiminished: he developed a simulator of the Pilot ACE for a modern personal computer, which was demonstrated earlier this month at a conference celebrating the machine's 50th anniversary, although sadly illness prevented Davies from attending.

Biography

Donald Watts Davies was born in Treorchy in the Rhondda Valley. His father, a clerk at a coalmine, died a few months later, and his mother took Donald and his twin sister back to her home town of Portsmouth, where he went to school.

At Imperial College, London, he gained BSc degrees in physics in 1943 and mathematics in 1947, both with first class honours; he was awarded the Lubbock Memorial Prize as the leading mathematician of his year at London University in 1947. In between the two degrees he worked at Birmingham University on atomic research as an assistant to Klaus Fuchs, and at ICI Billingham.

During his last year at university he attended a lecture by John Womersley, superintendent of the mathematics division of the National Physical Laboratory (NPL), about the ACE digital computer which was being developed there. Excited by the potential of the new technology, he immediately applied to join the group, and in September 1947 he joined the laboratory as a member of the small team, which was led by Alan Turing of Bletchley Park fame.

The group's work, based on Turing's design, eventually led to the Pilot ACE computer, which ran its first program on May 10, 1950; it was one of the first four or five electronic stored-program digital computers in the world, and certainly the first in London. Along with Ted Newman, Jim Wilkinson and others, Davies had played an important part in the detailed design and development of the machine, and its successor, the full-scale ACE.

As computer development moved from the laboratory to industry, Davies's interests widened to include the purposes for which computers could be used. For example, he developed a road traffic simulator, and in 1958 he initiated a project to use a computer to translate technical Russian into English.

In 1963 he was appointed technical manager of the advanced computer techniques project, responsible for government support for the British computer industry. His combination of managerial skills with technical ability led to rapid progress through the grades of the scientific Civil Service, and in 1966 he succeeded Albert Uttley as superintendent of NPL's autonomics division. He soon turned this into a division of computer science, giving it new and more practical objectives.

The key new project was the development of an idea he had originated in 1965: that to achieve communication between computers a fast message-switching communication service was needed, in which long messages were split into chunks sent separately so as to minimise the risk of congestion. The chunks he called packets, and the technique became known as packet-switching.

His network design was received enthusiastically by America's Advanced Research Project Agency (ARPA), and the Arpanet and the NPL local network became the first two computer networks in the world using the technique. Today's Internet can be traced back directly to this origin.

In 1979 Davies was able to relinquish his managerial post at NPL to concentrate on technical work. Realising that computer networks would be used widely only if malicious interference could be prevented, he started a group to work on data security, concentrating on the new method of public key cryptosystems. The group built a strong consultancy role round his expertise; all the major British clearing banks, for instance, used its services. He retired in 1984 and continued his work as a data security consultant.

Donald Davies married Diane Burton in 1955; she survives him, along with their daughter and two sons.

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