The Berkeley Software Distribution, known as BSD, was the version of Unix developed at the University of California, Berkeley. Marshall Kirk McKusick’s firsthand account “Twenty Years of Berkeley Unix” traces its beginnings to January 1974, when Unix was installed at Berkeley, and to the work of graduate students who began extending and redistributing it later in the decade.
Early Berkeley distributions bundled the local improvements that students and staff had written for Unix. Among them were tools built by Bill Joy, including the vi visual editor, the C shell (csh), and the Pascal system, packaged so that other sites could install them. These collections grew into the numbered BSD releases.
Under the Computer Systems Research Group and DARPA funding, BSD acquired the feature for which it is most remembered: an implementation of the TCP/IP networking protocols and the sockets programming interface, shipped in the 4.2BSD release. The sockets API became the standard way programmers write networked software, and it spread far beyond Berkeley.
McKusick records that Berkeley released “Networking Release 1” in June 1989 as the first freely redistributable Berkeley code under a permissive license, the ancestor of the modern BSD license. That work led to the free BSD operating systems that continue today, and BSD code also underpinned commercial systems such as those from Sun Microsystems.