Donald Davies

Donald Watts Davies, (7 June 1924 – 28 May 2000) was a Welsh computer scientist who was employed at the UK National Physical Laboratory (NPL).

It is said that Davies spotted mistakes in Turing's seminal 1936 paper On Computable Numbers, much to Turing's annoyance.

These were perhaps some of the first "programming" bugs in existence, even if they were for a theoretical computer, the universal Turing machine.

The ACE project was overambitious and floundered, leading to Turing's departure.

He received a BSc degree in physics (1943) at Imperial College London, and then joined the war effort working as an assistant to Klaus Fuchs on the nuclear weapons Tube Alloys project at Birmingham University.

He then returned to Imperial taking a first class degree in mathematics (1947); he was also awarded the Lubbock memorial Prize as the outstanding mathematician of his year.

From 1947, he worked at the National Physical Laboratory (NPL) where Alan Turing was designing the Automatic Computing Engine (ACE) computer.

Davies took over the project and concentrated on delivering the less ambitious Pilot ACE computer, which first worked in May 1950.

A commercial spin-off, DEUCE was manufactured by English Electric Computers and became one of the best-selling machines of the 1950s.

Davies also worked on applications of traffic simulation and machine translation.

In 1955, he married Diane Burton; they had a daughter and two sons.

Davies' work was independent of the work of Paul Baran in the United States who had a similar idea in the early 1960s, and who also provided input to the ARPANET project, after his work was highlighted by Davies' team.

Davies was born in Treorchy in the Rhondda Valley, Wales.

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.

He attended the Southern Grammar School for Boys.

In the early 1960s, he worked on government technology initiatives designed to stimulate the British computer industry.

In 1965 he conceived of packet switching, which is today the dominant basis for data communications in computer networks worldwide.

Davies proposed a commercial national data network in the United Kingdom and designed and built the local-area NPL network to demonstrate the technology.

In 1965, Davies developed the idea of packet switching, dividing computer messages into packets that are routed independently across a network, possibly via differing routes, and are reassembled at the destination.

Davies used the word "packets" after consulting with a linguist because it was capable of being translated into languages other than English without compromise.

Davies' key insight came in the realisation that computer network traffic was inherently "bursty" with periods of silence, compared with relatively constant telephone traffic.

He designed and proposed a commercial national data network based on packet switching in his 1966 Proposal for the Development of a National Communications Service for On-line Data Processing.

In 1966 he returned to the NPL at Teddington just outside London, where he headed and transformed its computing activity.

He became interested in data communications following a visit to the Massachusetts Institute of Technology, where he saw that a significant problem with the new time-sharing computer systems was the cost of keeping a phone connection open for each user when the data communication traffic was “bursty” in nature.

He applied the principle of time-sharing to the data communications line as well as the computer to create the concept of what he called "packet switching".

Davies was the first to describe the concept of an "interface computer", in 1966, today known as a router.

He and his team were the first to write protocols in a modern data-commutation context in 1967.

The NPL team also carried out simulation work on packet networks, studying datagrams and network congestion.

His work on packet switching, presented by his colleague Roger Scantlebury, initially caught the attention of the developers of ARPANET, a U.S. Department of Defense (DoD) network, at the Symposium on Operating Systems Principles in October 1967.

In Scantlebury's report following the conference, he noted "It would appear that the ideas in the NPL paper at the moment are more advanced than any proposed in the USA".

Larry Roberts, of the Advanced Research Projects Agency of the DoD, applied Davies' concepts of packet switching for the ARPANET, which went on to become a predecessor to the Internet.

Davies first presented his own ideas on packet switching at a conference in Edinburgh on 5 August 1968.

At NPL Davies directed the development of a local-area packet-switched network, the Mark I NPL network.

Many of the wide-area packet-switched networks built in the 1970s were similar "in nearly all respects" to his original 1965 design.

The ARPANET project credited Davies for his influence, which was key to the development of the Internet.

These early years of computer resource sharing were documented in the 1972 film Computer Networks: The Heralds of Resource Sharing.

Davies original ideas influenced other research around the world, including Louis Pouzin's CYCLADES project in France.

The NPL Network was replaced with the Mark II in 1973, and remained in operation until 1986.

Unbeknown to him, Paul Baran of the RAND Corporation in the United States was also working on a similar concept; when Baran became aware of Davies's work he acknowledged that they both had equally discovered the concept.

Baran was happy to acknowledge that Davies had come up with the same idea as him independently.