Mr. Walden eventually enrolled at San Francisco State College (now University) and received his bachelor’s degree in mathematics in 1964. His interest in computing grew from a course he took in numerical analysis that involved working on an IBM computer.
After college, he went to work for the Massachusetts Institute of Technology’s Lincoln Laboratories as a computer programmer in the Space Communications Division.
In 1965, he met Sara Elizabeth Cowles, an education administrator, and they married the next year. He was hired at Bolt Beranek and Newman in 1967. Soon after, the company won a contract to build the first I.M.P.
“It was a very small group working together all the time,” Mr. Walden said in a 1990 interview with the Charles Babbage Institute at the University of Minnesota, an archive and research center specializing in information technology.
“We were in and out of each other’s offices and helping each other debug,” he added.
Every discovery drew excitement. “We’d run in and say, ‘Look, I got this running!’” he said.
Mr. Walden left Bolt Beranek for a year in 1970 to work at Norsk Data, helping that company build a computer modeled after the I.M.P. He returned to Bolt Beranek in 1971 and stayed until 1995. He later became an expert in the field of management. An avid computer historian, he was an editor at the IEEE Annals of the History of Computing, published by what was originally the Institute of Electrical and Electronics Engineers.
Although he did not hold an advanced degree, Mr. Walden received an honorary doctorate from California State University in 2014 for his work on the Arpanet. “He remarked to me on more than one occasion that he never thought he would get that kind of honor,” Alex McKenzie, a former colleague of Mr. Walden’s, said in an interview.
In addition to his wife, Mr. Walden is survived by his son, Luke; his brother, Daniel; his sister, Velma Walden Hampson; and two grandchildren.