Packet switching is the foundational technique of modern computer networks: rather than holding open a dedicated circuit between two parties for the whole of a conversation, a message is broken into small, discrete units that each carry addressing information and are routed independently across the network, then reassembled at the destination. Because each packet finds its own way and links are shared among many conversations, the approach makes far better use of communication capacity and tolerates the loss of individual nodes or lines.
The idea was conceived independently on two continents. At the RAND Corporation in the United States, Paul Baran described a “distributed adaptive message block network” in his 1964 series of reports, “On Distributed Communications,” the first volume of which (RAND research memorandum RM-3420) introduced the use of redundant routing and message blocks to build a communications system that could survive heavy damage, such as a nuclear attack. Baran’s motivation was survivability: a distributed mesh with many redundant paths had no single point whose loss would sever communication.
In Britain, Donald Davies at the National Physical Laboratory arrived at the same core mechanism from a different motivation: making interactive, time-shared computing efficient over data links. As the Internet Hall of Fame records, in 1965 Davies developed the concept of dividing lengthy messages into smaller units transmitted separately to reduce congestion, and it was Davies who “coined the term ‘packet’” for those units. His June 1966 “Proposal for a Digital Communication Network” contained the first use of the word, chosen, he later said, because it translated cleanly into other languages.
The two strands converged through the ARPANET. When ARPA program manager Lawrence Roberts encountered Davies’s group at a 1967 symposium, he adopted both the term “packet switching” and the design ideas, and drew on Baran’s earlier work as well. The result was that the survivable mesh imagined at RAND and the efficient data network imagined at NPL became the same technology, and packet switching went on to underpin the ARPANET, the wider Internet, and essentially every digital network in use today.