The initial ARPANET consisted of four IMPs. They were installed at: * UCLA, where Leonard Kleinrock had established a Network Measurement Center (with an SDS Sigma 7 being the first computer attached to it).
* The Stanford Research Institute's Augmentation Research Center, where Douglas Engelbart had created the ground-breaking NLS system, a very important early hypertext system (with the SDS 940 that ran NLS, named 'Genie', being the first host attached).
* UC Santa Barbara (with the Culler-Fried Interactive Mathematics Centre's IBM 360/75, running OS/MVT being the machine attached).
* The University of Utah's Computer Science Department, where Ivan Sutherland had moved (for a DEC PDP-10 running TENEX).
The first message ever sent over the ARPANET (sent over the first host-to-host connection) occurred at 10:30 PM on October 29, 1969. It was sent by UCLA student programmer Charley Kline and supervised by UCLA Professor Leonard Kleinrock. The message was sent from the UCLA SDS Sigma 7 Host computer to the SRI SDS 940 Host computer. The message itself was simply the word "login." The "l" and the "o" transmitted without problem but then the system crashed. Hence, the first message on the ARPANET was "lo". They were able to do the full login about an hour later.
The first permanent ARPANET link was established on November 21, 1969, between the IMP at UCLA and the IMP at SRI. By December 5, 1969, the entire 4-node network was connected. When this happened, multiple thousands of connections were opened, beyond the amount of people at the time who could possibly connect. There is currently no official explanation for this anomaly.
The contents of the first e-mail transmission (sent in 1971) have long since been forgotten; in a FAQ on his website, the sender, Ray Tomlinson (who sent the message between two computers located side-by-side) claims that the contents were 'entirely forgettable, and I have, therefore, forgotten them', and speculates that the message was most likely 'QWERTYUIOP' or something similar¹