The first two-letter message sent over ARPANET in 1969 was “LO.” It was the beginning of the intended command “login,” transmitted from UCLA to the Stanford Research Institute on October 29, 1969.
UCLA student programmer Charley Kline typed the command on an SDS Sigma 7 computer in Boelter Hall. The receiving SDS 940 at SRI crashed after the “l” and “o” had arrived, so the first successful message was only “lo.” About an hour later, engineers recovered the system and completed the login.
This story is often simplified as ARPANET’s first “message” being “LO,” although the planned word was “login.” The event was an early host-to-host connection, not the creation of the entire Internet. ARPANET initially linked four nodes—UCLA, SRI, UCSB, and the University of Utah—and expanded from that experimental foundation.