ARPANET carries its first message
A crashed login attempt between UCLA and Stanford becomes the internet's first words
Quick facts
- Sender
- Charley Kline, under Leonard Kleinrock, UCLA
- Receiver
- Bill Duvall, Stanford Research Institute
- Date/time
- 29 October 1969, 22:30
- Underlying technology
- Packet switching
What happened
UCLA professor Leonard Kleinrock and his student programmer Charley Kline set up a message transmission from the UCLA SDS Sigma 7 computer to a Stanford Research Institute computer 350 miles away, operated by programmer Bill Duvall. The plan was to remotely log in by typing 'login.' Kline transmitted the letters L and O; the system crashed before the G. The connection was fixed roughly an hour later and the full login completed. Kleinrock had spent years developing packet switching, a method of breaking information into small, independently routed pieces that get reassembled at their destination, and ARPANET (the Advanced Research Projects Agency Network) was the first network built to test the idea at scale, initially linking four university and research computers.
Why it matters
The accidental 'LO' is remembered as the internet's first words, but the more consequential achievement was proving packet switching worked over real distance between real computers. Every network built afterward, including the modern internet, routes data the same fragmented, reassembled way rather than by holding a dedicated circuit open the way a telephone call does.
How we know
UCLA's own historical record, maintained by Kleinrock's lab, documents the event from the IMP log kept at UCLA at the time, naming the participants, the computers involved, and the exact sequence of the crash.
Sources
- UCLA Samueli School of Engineering (Leonard Kleinrock's lab). Day the Infant Internet Uttered its First Words · Reputable sourcelk.cs.ucla.edu · The domain "lk.cs.ucla.edu" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
- UCLA Samueli School of Engineering. Internet50/Press · Reputable sourcesamueli.ucla.edu · The domain "samueli.ucla.edu" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
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