BSD Definition

BSD (Berkeley Software Distribution) refers to a group of Unix-like operating systems that are descendants of the BSD UNIX that was developed at the University of California at Berkeley (UCB) in the 1970s and early 1980s.

The original BSD UNIX was written for the DEC VAX and PDP-11 computers by Bill Joy, then a graduate student at UCB, and others. (Joy is also well known for his development of the nearly universal vi text editor and as a co-founder of Sun Microsystems.) It was based on the first versions of UNIX that had been developed at Bell Labs by Ken Thompson beginning in 1969. The first version, called 1BSD, was released in 1977.

BSD UNIX 4.0, released in October 1980, included a number of innovative features such as virtual memory, which is the use of space on a hard disk drive to simulate additional main memory, and TCP/IP (transmission control protocol/Internet protocol),which is now the dominant networking protocol on the Internet and most other networks as well. These features, which became known as the Berkeley extensions, were then incorporated into the subsequent versions of UNIX that were developed by Bell Labs and they have become standard on all Unix-like operating systems.

BSD UNIX versions 4.1, 4.2, and 4.3, as well as the commercial versions derived from them, were the most advanced among the various versions of UNIX until AT&T standardized the operating system with its System V beginning in 1983.

Today there are four major BSD operating systems: FreeBSD, NetBSD, OpenBSD and Darwin. All are very similar but have slight differences in philosophy and emphasis. There are also several other operating systems that are derived from these BSDs, including DragonFly BSD.

All of the major BSDs are free software, which means that they are available to anybody at no monetary cost and to use for any desired purpose, including studying, modifying, extending, giving away and even selling for a profit. In contrast to Linux and most other free software, however, they are licensed under BSD-style licenses, which differ from the more commonly used GNU General Public License (GPL) in that they do not require that the source code for derivative works be made freely available. Source code is the version of an operating system or application programs as it is originally written by humans in a programming language; it is necessary to have the source code in order for others to be able to easily study and modify the software.

FreeBSD is the most popular of the BSD operating systems, accounting for approximately 80 percent of BSD installations (at least until Darwin came on to the scene). It was begun in early 1993 based on 4.3BSD UNIX, and the first version, 1.0, was released in December of that year.

NetBSD is likewise both a derivative of 4.3BSD and was launched in 1993. Its most distinctive feature is its extreme portability, possibly the most so of any operating system, with the ability to run on more than 50 processor types, ranging from the acorn26 to the x86.

OpenBSD was spun off from NetBSD in 1996 by Theo de Raadt in Calgary, Alberta because of a desire to place even more emphasis on security. OpenBSD has a goal of becoming the most secure operating system, and it claims to have had only one remote hole in the default installation in more than eight years.

Darwin, originally released in March 1999, serves as the core for the Macintosh OS X. A GNU version, which is called GNU-Darwin, is also available.

The BSDs have some advantages as compared with Linux. Primary among them are the fact that they are generally considered to be more stable and more secure. This is, at least in part, because they tend to wait to incorporate new features until they have been more thoroughly tested.

A disadvantage of the BSDs is that they have not been designed for novices, and thus they can be more difficult to install and configure than the more popular distributions (i.e., versions) of Linux. Another disadvantage is that a smaller number of application programs are available that have been specifically configured to run on them, mainly because of the much smaller user base.

The BSDs are relatively unknown by the general public, in contrast to the increasingly popular Linux. This is largely because their developers tend to have little interest in actively marketing them and instead prefer to focus their attention and limited financial resources on further refinement of their systems. It is also because the BSDs are intended for use by more advanced users rather than by the wide spectrum of users at which Linux is now aimed.

The question sometimes arises as to whether the BSD operating systems are, or should be considered, UNIX. They are widely regarded as being free implementations of UNIX, because of their direct lineage from BSD UNIX rather than being clones (i.e., contains all original source code) as is Linux. There is no controversy that BSD UNIX was indeed a UNIX, not only because of its official name but also because of new features and refinements developed at UCB for BSD UNIX that were incorporated back into the subsequent mainstream versions of UNIX developed by AT&T.

However, the UNIX trademark was subsequently acquired by The Open Group, an industry consortium, which attempts to restrict its usage to companies or other organizations that pay it a substantial amount of money. Thus, because of their small budgets and their desire to avoid costly legal battles, the non-commercial BSDs purposely avoid claiming directly that they are UNIX on their web sites and in other documentation.

Apple Computer, in sharp contrast, brazenly refers to its Mac OS X as being UNIX. Apple has vastly greater legal and financial resources than the non-commercial BSDs and most of the Linux distributions, and thus it is not afraid to call its operating system UNIX1.

1For example, on its web site Apple says: "Don't let its elegant and easy-to-use interface fool you. Beneath the surface of Mac OS X lies an industrial-strength UNIX foundation hard at work to ensure that your computing experience remains free of system crashes and compromised performance." As a result, the Open Group is suing Apple for alleged trademark violation. However, some industry observers expect that this case will be settled quietly out of court because neither side wants to risk a negative judgment.

Created July 11, 2006.
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