Berkeley Software Distribution (BSD, sometimes called Berkeley Unix) is a Unix operating system derivative developed and distributed by the Computer Systems Research Group (CSRG) of the University of California, Berkeley, from 1977 to 1995. Today the term “BSD” is often used non-specifically to refer to any of the BSD descendants which together form a branch of the family ofUnix-like operating systems. Operating systems derived from the original BSD code remain actively developed and widely used.
Historically, BSD has been considered a branch of UNIX—”BSD UNIX”, because it shared the initial codebase and design with the original AT&T UNIX operating system. In the 1980s, BSD was widely adopted by vendors of workstation-class systems in the form of proprietary UNIX variants such as DEC ULTRIX and Sun Microsystems SunOS. This can be attributed to the ease with which it could be licensed, and the familiarity the founders of many technology companies of the time had with it.
Although these proprietary BSD derivatives were largely superseded by the UNIX System V Release 4 and OSF/1 systems in the 1990s (both of which incorporated BSD code and are the basis of other modern Unix systems), later BSD releases provided a basis for several open sourcedevelopment projects, e.g. FreeBSD, NetBSD, OpenBSD or DragonFly BSD, that are ongoing. These, in turn, have been incorporated in whole or in part in modern proprietary operating systems, e.g. the TCP/IP (IPv4 only) networking code in Microsoft Windows and a part of the foundation ofApple‘s OS X.
Berkeley’s Unix was the first Unix to include libraries supporting the Internet Protocol stacks: Berkeley sockets. (A Unix implementation of IP’s predecessor, the ARPAnet’s NCP, with FTP and Telnet clients, had been produced at U. Illinois in 1975, and was available at Berkeley.However, the memory scarcity on the PDP-11 forced a complicated design and performance problems.)
By integrating sockets with the Unix operating system’s file descriptors, it became almost as easy to read and write data across a network as it was to access a disk. The AT&T laboratory eventually released their own STREAMS library, which incorporated much of the same functionality in a software stack with a different architecture, but the wide distribution of the existing sockets library reduced the impact of the new API. Early versions of BSD were used to form Sun Microsystems‘ SunOS, founding the first wave of popular Unix workstations.
Today, BSD continues to serve as a technological testbed for academic organizations. It can be found in use in numerous commercial and free products, and, increasingly, in embedded devices. The general quality of its source code, as well as its documentation (especially reference manual pages, commonly referred to as man pages), make it well-suited for many purposes.
BSD operating systems can run much native software of several other operating systems on the same architecture, using a binary compatibility layer. Much simpler and faster than emulation, this allows, for instance, applications intended for Linux to be run at effectively full speed. This makes BSDs not only suitable for server environments, but also for workstation ones, given the increasing availability of commercial or closed-source software for Linux only.
Most of the current BSD operating systems are open source and available for download, free of charge, under the BSD License, the most notable exception being Mac OS X. They also generally use a monolithic kernel architecture, apart from Mac OS X and DragonFly BSD which feature hybrid kernels.