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ARPANET
October 29, 1969· Invention or discovery· Communication & computing
Well documentedSolid records, physical evidence or scientific consensus.
A Pentagon-funded computer network that linked US universities from 1969 and proved the idea of packet switching.
See it on the Technology & Medicine map →How it works
ARPA, the Pentagon's research agency, funded it so researchers could share scarce, expensive computers. Data was split into small 'packets,' each routed separately through refrigerator-sized relay computers built by the firm BBN, then reassembled: an idea developed by Paul Baran in the US and Donald Davies in Britain. On October 29, 1969, a UCLA student sent the first message to SRI near Stanford: 'LO,' before the system crashed typing 'LOGIN.' Email arrived in 1971.
Why it mattered
It proved packet networks worked, created online habits like email and openly shared technical standards, and became the backbone of the early Internet.
Think of it like
Like shipping a big order as numbered boxes on whatever trucks are free, then reassembling it at the destination, instead of reserving one truck end to end.
How we know
The UCLA log book entry for October 29, 1969, BBN's reports, the Request for Comments (RFC) memos begun that year, and oral histories from Leonard Kleinrock, Larry Roberts and others.
Still unknown or debated
It is often said to have been built to survive nuclear war; that was Baran's motive, but ARPANET's builders say its purpose was sharing computers.
Connections (2)
▸ARPANET grew into The Internet (TCP/IP)Well documented
The connection
ARPANET was a single network. As other packet networks appeared, using radio and satellites, Cerf and Kahn designed TCP/IP so different networks could interconnect. On January 1, 1983, ARPANET switched to TCP/IP and became the first backbone of the Internet; the military split off its own network that year, and ARPANET was retired in 1990.
When and how
Cerf at Stanford and Kahn at ARPA, 1973–74; the switch-over on January 1, 1983, called 'flag day'; the National Science Foundation's network then took over as backbone.
How we know
The RFC memos, especially Jon Postel's 1981 transition plan (RFC 801), and ARPA records chart the change step by step.
Debates and open questions
Whether TCP/IP won on merit is debated: an international standard, OSI, competed into the early 1990s, and TCP/IP may have won simply because it was already running and free.
▸Sputnik 1 prompted the agency that built ARPANETWell documented
The connection
Sputnik shocked Washington into creating the Advanced Research Projects Agency (ARPA) in February 1958, so the US would not be surprised by technology again. Space work soon moved to NASA, and ARPA turned to other fields, including computing; its computer office, set up in 1962 under J. C. R. Licklider, funded the network that became ARPANET.
When and how
ARPA founded in Washington in February 1958 under President Eisenhower; Licklider's office from 1962; Bob Taylor won ARPANET funding in 1966.
How we know
ARPA's founding papers cite the post-Sputnik need; Taylor and Larry Roberts described the office's role in oral histories, and official ARPA histories agree.
Debates and open questions
How much credit Sputnik deserves is a matter of emphasis: ARPA's computing office also grew from military command-and-control needs and Licklider's own vision of interactive computing.