TheBerkeley Software Distribution[a] (BSD), also known asBerkeley Unix orBSD Unix, is a discontinuedUnixoperating system developed and distributed by theComputer Systems Research Group (CSRG) at theUniversity of California, Berkeley, beginning in 1978. It began as an improved derivative ofAT&T's original Unix that was developed atBell Labs, based on thesource code but over time diverging into its own code. BSD would become a pioneer in the advancement of Unix and computing.[2][3]
BSD's development was begun initially byBill Joy, who addedvirtual memory capability to Unix running on aVAX-11 computer.[3] In the 1980s, BSD was widely adopted byworkstation vendors in the form ofproprietary Unix distributions such asDECUltrix andSun MicrosystemsSunOS due to itspermissive licensing and familiarity to many technology company founders and engineers. It also became the most popular Unix at universities, where it was used for the study of operating systems.[2] BSD was sponsored byDARPA until 1988,[3] which led to the implementation ofARPANET and later theTCP/IP stack to Unix by BSD,[4] which were released in BSD NET/1 in 1988. The codebase had been rewritten so much that as little as 5% of BSD contained original AT&T code,[4] and therefore NET/1 was released without an AT&T source license.[3]
The university ended its Unix research in 1992 following reduced funding as well as theUnix lawsuit.[3] Since the original BSD has become obsolete, the term "BSD" is now commonly used for itsopen-source descendants, includingFreeBSD,OpenBSD,NetBSD, andDragonFly BSD. BSD code have also served as the basis forDarwin andTrueOS; these, in turn, have been used by proprietary operating systems, includingApple'smacOS andiOS,[5] andMicrosoft Windows which used (at least) part of its TCP/IP code. Code from BSD's open descendants have themselves also been used to create modern operating systems, for example the system software for thePlayStation 5 and others.[6]
Theearliest distributions of Unix fromBell Labs in the 1970s included thesource code to the operating system, allowing researchers at universities to modify and extend Unix. The operating system arrived at Berkeley in 1974, at the request of computer science professorBob Fabry who had been on the program committee for theSymposium on Operating Systems Principles where Unix was first presented. APDP-11/45 was bought to run the system, but for budgetary reasons, this machine was shared with the mathematics and statistics groups at Berkeley, who usedRSTS, so that Unix only ran on the machine eight hours per day (sometimes during the day, sometimes during the night). A largerPDP-11/70 was installed at Berkeley the following year, using money from theIngres database project.[7]
BSD began life as a variant of Unix that programmers at the University of California at Berkeley, initially led byBill Joy, began developing in the late 1970s.It included extra features, which were intertwined with code owned by AT&T.
In 1975,Ken Thompson took asabbatical from Bell Labs and came to Berkeley as a visiting professor. He helped to installVersion 6 Unix and started working on aPascal implementation for the system. Graduate students Chuck Haley and Bill Joy improved Thompson's Pascal and implemented an improved text editor,ex.[7] Other universities became interested in the software at Berkeley, and so in 1977 Joy started compiling the first Berkeley Software Distribution (1BSD), which was released on March 9, 1978.[8] 1BSD was an add-on to Version 6 Unix rather than a complete operating system in its own right. Some thirty copies were sent out.[7]
The second Berkeley Software Distribution (2BSD), released in May 1979,[9] included updated versions of the 1BSD software as well as two new programs by Joy that persist on Unix systems to this day: thevi text editor (avisual version ofex) and theC shell. Some 75 copies of 2BSD were sent out by Bill Joy.[7]
TheVAX-11/780, a typical minicomputer used for early BSD timesharing systems
AVAX computer was installed at Berkeley in 1978, but theport of Unix to the VAX architecture,UNIX/32V, did not take advantage of the VAX'svirtual memory capabilities. Thekernel of 32V was largely rewritten to include Berkeley graduate studentÖzalp Babaoğlu's virtual memory implementation, and a complete operating system including the new kernel, ports of the 2BSD utilities to the VAX, and the utilities from 32V was released as 3BSD at the end of 1979. 3BSD was also alternatively called Virtual VAX/UNIX or VMUNIX (for Virtual Memory Unix), and BSD kernel images were normally called/vmunix until 4.4BSD.
After 4.3BSD was released in June 1986, it was determined that BSD would move away from the aging VAX platform. ThePower 6/32 platform (codenamed "Tahoe") developed byComputer Consoles Inc. seemed promising at the time, but was abandoned by its developers shortly thereafter. Nonetheless, the4.3BSD-Tahoe port (June 1988) proved valuable, as it led to a separation of machine-dependent and machine-independent code in BSD which would improve the system's future portability.
In addition to portability, the CSRG worked on an implementation of theOSI network protocol stack, improvements to the kernel virtual memory system and (withVan Jacobson ofLBL) new TCP/IP algorithms to accommodate the growth of the Internet.[10]
Until then, all versions of BSD used proprietary AT&T Unix code, and were therefore subject to an AT&T software license. Source code licenses had become very expensive and several outside parties had expressed interest in a separate release of the networking code, which had been developed entirely outside AT&T and would not be subject to the licensing requirement. This led toNetworking Release 1 (Net/1), which was made available to non-licensees of AT&T code and wasfreely redistributable under the terms of theBSD license. It was released in June 1989.
After Net/1, BSD developerKeith Bostic proposed that more non-AT&T sections of the BSD system be released under the same license as Net/1. To this end, he started a project to reimplement most of the standard Unix utilities without using the AT&T code. Within eighteen months, all of the AT&T utilities had been replaced, and it was determined that only a few AT&T files remained in the kernel. These files were removed, and the result was the June 1991 release of Networking Release 2 (Net/2), a nearly complete operating system that was freely distributable.
BSDi soon found itself in legal trouble with AT&T'sUnix System Laboratories (USL) subsidiary, then the owners of the System Vcopyright and the Unix trademark. TheUSL v. BSDi lawsuit was filed in 1992 and led to aninjunction on the distribution of Net/2 until the validity of USL's copyright claims on the source could be determined. The lawsuit slowed development of the free-software descendants of BSD for nearly two years while their legal status was in question, and as a result systems based on theLinux kernel, which did not have such legal ambiguity, gained greater support. The lawsuit was settled in January 1994, largely in Berkeley's favor. Of the 18,000 files in the Berkeley distribution, only three had to be removed and 70 modified to show USL copyright notices. A further condition of the settlement was that USL would not file further lawsuits against users and distributors of the Berkeley-owned code in the upcoming 4.4BSD release.[11]
The final release from Berkeley was 1995's4.4BSD-Lite Release 2, after which the CSRG was dissolved and development of BSD at Berkeley ceased. Since then, several variants based directly or indirectly on 4.4BSD-Lite (such asFreeBSD,NetBSD,OpenBSD andDragonFly BSD) have been maintained.
The permissive nature of theBSD license has allowed many other operating systems, bothopen-source and proprietary, to incorporate BSD source code. For example,Microsoft Windows used BSD code in its implementation of TCP/IP[12] and bundles recompiled versions of BSD'scommand-line networking tools sinceWindows 2000.[13]Darwin, the basis for Apple'smacOS andiOS, is based on 4.4BSD-Lite2 and FreeBSD. Various commercial Unix operating systems, such asSolaris, also incorporate BSD code.
Starting with the 8th Edition, versions ofResearch Unix at Bell Labs had a close relationship to BSD. This began when 4.1cBSD for the VAX was used as the basis for Research Unix 8th Edition. This continued in subsequent versions, such as the 9th Edition, which incorporated source code and improvements from 4.3BSD. The result was that these later versions of Research Unix were closer to BSD than they were to System V. In aUsenet posting from 2000, Dennis Ritchie described this relationship between BSD and Research Unix:[14][better source needed]
Research Unix 8th Edition started from (I think) BSD 4.1c, but with enormous amounts scooped out and replaced by our own stuff. This continued with 9th and 10th. The ordinary user command-set was, I guess, a bit more BSD-flavored than SysVish, but it was pretty eclectic.
Eric S. Raymond summarizes the longstanding relationship betweenSystem V and BSD, stating, "The divide was roughly between longhairs and shorthairs;programmers and technical people tended to line up with Berkeley and BSD, more business-oriented types with AT&T and System V."[15]
In 1989, David A. Curry wrote about the differences between BSD and System V. He characterized System V as being often regarded as the "standard Unix." However, he described BSD as more popular among university and government computer centers, due to its advanced features and performance:[16]
Most university and government computer centers that use UNIX use Berkeley UNIX, rather than System V. There are several reasons for this, but perhaps the two most significant are that Berkeley UNIX provides networking capabilities that until recently (Release 3.0) were completely unavailable in System V, and that Berkeley UNIX is much more suited to a research environment, which requires a faster file system, better virtual memory handling, and a larger variety ofprogramming languages.
Berkeley's Unix was the first Unix to include libraries supporting theInternet Protocol stacks:Berkeley sockets. A Unix implementation of IP's predecessor, the ARPAnet'sNCP, withFTP andTelnet clients, had been produced at theUniversity of Illinois in 1975, and was available at Berkeley.[17][18] However, the memory scarcity on the PDP-11 forced a complicated design and performance problems.[19]
By integrating sockets with the Unix operating system'sfile descriptors, it became almost as easy to read and write data across anetwork as it was to access a disk. The AT&T laboratory eventually released their ownSTREAMS 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 newAPI. Early versions of BSD were used to formSun Microsystems'SunOS, founding the first wave of popular Unix workstations.
Some BSD operating systems can run native software of several other operating systems on the samearchitecture, using a binarycompatibility layer. This is much simpler and faster thanemulation; for example, it allows applications intended forLinux 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. This also allows administrators to migrate legacy commercial applications, which may have only supported commercial Unix variants, to a more modern operating system, retaining the functionality of such applications until they can be replaced by a better alternative.
Current BSD operating system variants support many of the commonIEEE,ANSI,ISO, andPOSIX standards, while retaining most of the traditional BSD behavior. LikeAT&T Unix, the BSD kernel ismonolithic, meaning that device drivers in the kernel run inprivileged mode, as part of the core of the operating system.
Several operating systems are based on BSD, includingFreeBSD,OpenBSD,NetBSD,MidnightBSD,MirOS BSD,GhostBSD,Darwin andDragonFly BSD. Both NetBSD and FreeBSD were created in 1993. They were initially derived from386BSD (also known as "Jolix"), and merged the 4.4BSD-Lite source code in 1994. OpenBSD wasforked from NetBSD in 1995, and DragonFly BSD was forked from FreeBSD in 2003.
Marshall K. McKusick, Keith Bostic, Michael J. Karels, John S. Quartermain,The Design and Implementation of the 4.4BSD Operating System (Addison Wesley, 1996;ISBN978-0-201-54979-9)
Marshall K. McKusick, George V. Neville-Neil,The Design and Implementation of the FreeBSD Operating System (Addison Wesley, August 2, 2004;ISBN978-0-201-70245-3)
Samuel J. Leffler, Marshall K. McKusick, Michael J. Karels,John S. Quarterman,The Design and Implementation of the 4.3BSD UNIX Operating System (Addison Wesley, November 1989;ISBN978-0-201-06196-3)
