Berkeley software distribution (BSD) was a derivation of the Unix operating system. The pure BSD operating system was officially supported from 1977 to 1995. In that time, it went through four major forms and several revisions of each. Even though the original BSD operating system no longer exists, the basic BSD model continues in several variations. The later forms of BSD and any of the operating systems built upon it no longer follow the basic Unix guidelines—they are officially in a category called Unix-like operating systems.
The original BSD operating system came out in 1977, in Berkeley, California, as part of a project by a University of California student. The original versions were basic add-ons to the Unix operating system, rather than full software revisions. Between 1977 and 1980, BSD versions one through four were released.
Due to the open-source nature of BSD, multiple versions were maintained in parallel development. In 1983, an update to version two of BSD was the first true BSD operating system. Previous to this release, the versions were updates and add-ons to one of many Unix versions. Version two is still being updated, although not officially. Volunteers maintain the operating system with periodic patches and updates.
The main effort of the Berkeley team went into version three, then four. The release of version three was a major departure from version two, hence the parallel development. Version three didn’t last long because version four superseded it. Between the two revisions, the BSD operating system was picked as one of the main operating systems for the US Defense Advanced Research Projects Agency (DARPA).
Development continued on various projects through the 80s and early 90s. During this time, the BSD operating system officially separated itself from Unix. This allowed BSD to move in whatever direction it wanted, developmentally. This separation culminated in a lawsuit from American Telephone and Telegraph (AT&T) since they owned the Unix version on which BSD was based. This lawsuit ended in a major victory for BSD.
Even though official support ended in 1995, the BSD operating system lives on through several projects based upon it. FreeBSD, NetBSD and OpenBSD were originally the big three variations, but each of these versions has since spawned several other versions, giving the BSD operation system one of the largest coverage areas of any Unix or Unix-like system.
The various BSD operating systems work well as a standard operating system, but they also strip down very easily. Because of this, versions of BSD are commonly used as internal operating systems in embedded software and real-time computers. Considering these embedded systems along with the standard computer operating system, it makes BSD one of the most widely-used operating systems in the world.