Wikipedia
The Berkeley Network, or Berknet, was an early local area network, developed at the University of California, Berkeley ca. 1979, primarily by Eric Schmidt as part of his master's thesis work. The network continuously connected about a dozen computers running Unix and provided email, file transfer, printing and remote command execution services to its users, and it connected the two other major networks in use at the time, the ARPANET and UUCPNET.
The network operated using what were then high-speed serial links; its software implementation shipped with the Berkeley Software Distribution from version 2.0 onwards. It consisted of a line discipline within the Unix kernel, a set of daemons that managed queues of commands to be sent across machines, and a set of user-level programs that enqueued the actual commands. The Berkeley Network introduced the file; Horton noted in 1984 that "Berknets are gone now", but support for Berknet's custom email addressing scheme was provided in the Sendmail program until 1993.