ChronoFive
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Setting the scene
By 1969, computers were large, expensive mainframes that couldn't communicate with each other. The U.S. Department of Defense's Advanced Research Projects Agency (ARPA) wanted to create a network that could survive nuclear attack by having no central hub—if one node was destroyed, traffic would reroute. Paul Baran at RAND had theorized packet switching—breaking data into packets that could travel different routes and reassemble. ARPA funded research at UCLA, Stanford, UC Santa Barbara, and the University of Utah to build the ARPANET.
What happened
On October 29, 1969, at 10:30 p.m., UCLA graduate student Charley Kline attempted to log in to a computer at Stanford Research Institute 350 miles away. He typed 'L'—the system crashed. He typed 'O'—crashed again. On the third try, he typed 'L-O-G' and the system crashed again. The first message on the ARPANET was 'LO'—as in 'lo and behold,' though they had intended to type 'LOGIN.' An hour later, the system was fixed and the full login worked. The network used Interface Message Processors (IMPs)—early routers built by BBN Technologies.
Why it still matters
The ARPANET grew to 4 nodes by December 1969, 23 by 1971, and eventually became the internet. The first email was sent in 1971, TCP/IP protocol was adopted in 1983, and the World Wide Web was invented in 1989. The ARPANET demonstrated packet switching worked and created the decentralized architecture that makes the internet resilient. The 'LO' message, though accidental, marked the beginning of networked computing. The ARPANET was decommissioned in 1990, but its protocols and principles underpin the modern internet used by 5 billion people. It was a military project that became the foundation of the information age.
Background
The message crashed after the first two letters: 'LO.'.