In one of the most gloriously inaccurate predictions ever made, IBM’s Thomas Watson once said that worldwide demand for computers would not exceed five. Donald Davies was one of the people who made that forecast look as ridiculous as it does today.

Born at Treorchy in the Rhondda, Davies attended Imperial College London, where he was the leading mathematician in his year. After graduation he joined a small team led by Alan Turing – famous for his part in cracking German wartime codes- that was developing early computers.

According to contemporaries, his skills were remarkable in their range. He was not only master of the theoretical aspects of computer science but could do the engineering too. Davies would come up with the idea for a machine and then design and built it himself. Among his projects were a traffic simulator and a computer that translated Russian into English.

In 1965, while working at the National Physical Laboratory, he produced his most important work. Realising that computers would be more useful if they could

“talk” to each other, he developed a system that allowed the machines to send

parcels of information backwards and forwards over public telecommunications networks.

His design was snapped up by the Advanced Research Project Agency in the United States and incorporated into its ARPNET network. “Packet Switching”, as it became known, remains the basis of the Internet.

In later work he refined his ideas as large companies and public institutions developed their own networks. He produced encryption technology used by the major banks. By the time he died, Davies had seen the Internet move from the fringes of theoretical science into everyday life.

His part in bringing about a world-changing technological development has only recently been appreciated in the land of his birth.