View source for Berkeley Software Distribution

{{Short description|Unix operating system}}
{{Redirect|BSD|the family of free software licenses |BSD licenses|other uses}}
{{Use mdy dates|date=September 2018}}
{{Infobox OS
| name = BSD
| logo = BSD wordmark.svg
| logo_size = x64px
| screenshot = 
| caption = 
| developer = [[Computer Systems Research Group]]
| source_model = Originally [[source-available]], later [[open-source software|open-source]]
| kernel_type = [[Monolithic kernel|Monolithic]]
| userland = BSD
| influenced = [[386BSD]], [[NetBSD]], [[FreeBSD]], [[OpenBSD]], [[DragonFly BSD]], [[NeXTSTEP]], [[Darwin (operating system)|Darwin]]
| influenced_by = [[Unix]]
| supported_platforms = [[PDP-11]], [[VAX]], [[Intel 80386]]
| ui = [[Unix shell]]
| family = [[Unix]]
| released = {{Start date and age|1978|03|09}}
| latest_release_version = 4.4-Lite2
| latest_release_date = {{Start date and age|1995|06}}
| latest_test_version = 
| discontinued = yes
| latest_test_date = 
| marketing_target = 
| programmed_in = [[C (programming language)|C]]
| prog_language = 
| language = English
| updatemodel = 
| package_manager = 
| working_state = Discontinued
| license = [[BSD licenses|BSD]]
}}
The '''Berkeley Software Distribution'''{{efn|or '''Berkeley Standard Distribution'''<ref>{{Cite web|title=Why you should use a BSD style license for your Open Source Project|url=https://docs.freebsd.org/en/articles/bsdl-gpl/|access-date=2021-08-03|website=The FreeBSD Project|language=en|at=BSD (Berkeley Standard Distribution)}}</ref>}} ('''BSD'''), also known as '''Berkeley Unix''' or '''BSD Unix''', is a discontinued [[Unix]] [[operating system]] developed and distributed by the [[Computer Systems Research Group]] (CSRG) at the [[University of California, Berkeley]], beginning in 1978. It began as an improved derivative of [[AT&T]]'s original Unix that was developed at [[Bell Labs]], based on the [[source code]] but over time diverging into its own code. BSD would become a pioneer in the advancement of Unix and computing.<ref name=":0">{{Cite magazine |last=Levitt |first=Jason |last2=Schuman |first2=Evan |date=June 22, 1992 |title=For BSD Unix, It's Sayonara |url=https://www.tech-insider.org/unix/research/1992/0622.html |magazine=Open Systems Today}}</ref><ref name=":1">{{Cite magazine |last=Harding |first=Elizabeth U. |date=October 19, 1992 |title=Unix pioneer ends BSD research |url=https://www.tech-insider.org/unix/research/1992/10.html |magazine=Software Magazine}}</ref>

BSD's development was begun initially by [[Bill Joy]], who added [[virtual memory]] capability to Unix running on a [[VAX-11]] computer.<ref name=":1" /> In the 1980s, BSD was widely adopted by [[workstation]] vendors in the form of [[Proprietary software|proprietary]] Unix distributions such as [[Digital Equipment Corporation|DEC]] [[Ultrix]] and [[Sun Microsystems]] [[SunOS]] due to its [[permissive software license|permissive 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.<ref name=":0" /> BSD was sponsored by [[DARPA]] until 1988,<ref name=":1" /> which led to the implementation of [[ARPANET]] and later the [[TCP/IP]] stack to Unix by BSD,<ref name=":2">{{Cite web |title=A Brief History of Unix, BSD and FreeBSD |url=https://minnie.tuhs.org/Seminars/Questnet/node2.html |access-date=2024-12-05 |website=minnie.tuhs.org}}</ref> 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,<ref name=":2" /> and therefore NET/1 was released without an AT&T source license.<ref name=":1" />

The university ended its Unix research in 1992 following reduced funding as well as the [[UNIX System Laboratories, Inc. v. Berkeley Software Design, Inc.|Unix lawsuit]].<ref name=":1" /> Since the original BSD has become obsolete, the term "BSD" is now commonly used for its [[open-source]] descendants, including [[FreeBSD]], [[OpenBSD]], [[NetBSD]], and [[DragonFly BSD]]. BSD code have also served as the basis for [[Darwin (operating system)|Darwin]] and [[TrueOS]]; these, in turn, have been used by proprietary operating systems, including [[Apple Inc.|Apple]]'s [[macOS]] and [[iOS]],<ref>{{cite web|title=Apple Kernel Programming Guide: BSD Overview|url=https://developer.apple.com/library/archive/documentation/Darwin/Conceptual/KernelProgramming/BSD/BSD.html|access-date=March 27, 2021}}</ref> and [[Microsoft 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 the [[PlayStation 5]] and others.<ref>{{Cite web|url=https://playstationdev.wiki/ps5devwiki/index.php?title=Kernel|title=Kernel|website=PlayStation 5 Dev Wiki}}</ref>

==History==
{{Main|History of the Berkeley Software Distribution}}
[[File:Unix history-simple.svg|thumb|300px|alt=A simple flow chart showing the history and timeline of the development of Unix starting with one bubble at the top and 13 tributaries at the bottom of the flow |Simplified evolution of [[Unix]] systems. Not shown are [[Junos]], [[PlayStation 3 system software]] and other proprietary forks.]]

The [[Research Unix|earliest distributions]] of Unix from [[Bell Labs]] in the 1970s included the [[source 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 professor [[Bob Fabry]] who had been on the program committee for the [[Symposium on Operating Systems Principles]] where Unix was first presented. A [[PDP-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 used [[RSTS/E|RSTS]], so that Unix only ran on the machine eight hours per day (sometimes during the day, sometimes during the night). A larger [[PDP-11/70]] was installed at Berkeley the following year, using money from the [[Ingres (database)|Ingres]] database project.<ref name="penguin7">{{cite book |first=Peter H. |last=Salus |author-link=Peter H. Salus |title=The Daemon, the Gnu and the Penguin |chapter=Chapter 7. BSD and the CSRG |chapter-url=http://www.groklaw.net/article.php?story=20050505095249230 |publisher=[[Groklaw]] |year=2005 |access-date=September 6, 2017 |archive-date=June 14, 2020 |archive-url=https://web.archive.org/web/20200614183924/http://www.groklaw.net/article.php?story=20050505095249230 |url-status=live}}</ref>

BSD began life as a variant of Unix that programmers at the University of California at Berkeley, initially led by [[Bill 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 a [[sabbatical]] from Bell Labs and came to Berkeley as a visiting professor. He helped to install [[Version 6 Unix]] and started working on a [[Pascal (programming language)|Pascal]] implementation for the system. Graduate students Chuck Haley and Bill Joy improved Thompson's Pascal and implemented an improved text editor, [[ex (text editor)|ex]].{{r|penguin7}} 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.<ref>Salus (1994), p. 142</ref> 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.{{r|penguin7}}

The second Berkeley Software Distribution (2BSD), released in May 1979,<ref name="tuhs-2bsd">{{cite web|last=Toomey|first=Warren|title=Details of the PUPS archives|url=http://minnie.tuhs.org/PUPS/archive_details.html|work=tuhs.org|publisher=[[The Unix Heritage Society]]|access-date=October 6, 2010|archive-date=July 9, 2006|archive-url=https://web.archive.org/web/20060709053205/http://minnie.tuhs.org/PUPS/archive_details.html|url-status=live}}</ref> included updated versions of the 1BSD software as well as two new programs by Joy that persist on Unix systems to this day: the [[Vi (text editor)|vi]] text editor (a [[visual editor|visual]] version of [[ex (text editor)|ex]]) and the [[C shell]]. Some 75 copies of 2BSD were sent out by Bill Joy.{{r|penguin7}}

[[File:VAX 11-780 intero.jpg|thumb|The [[VAX|VAX-11/780]], a typical minicomputer used for early BSD timesharing systems]]

A [[VAX]] computer was installed at Berkeley in 1978, but the [[porting|port]] of Unix to the VAX architecture, [[UNIX/32V]], did not take advantage of the VAX's [[virtual memory]] capabilities. The [[kernel (operating system)|kernel]] of 32V was largely rewritten to include Berkeley graduate student [[Özalp 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 <code>/vmunix</code> until 4.4BSD.

[[File:4.3 BSD UWisc VAX Emulation Login.png|thumb|alt=Black and white 4.3 BSD UWisc VAX Emulation Login screenshot|"4.3 BSD UNIX" from the [[University of Wisconsin–Madison|University of Wisconsin]] {{Circa|1987}}. System startup and login.]]

After 4.3BSD was released in June 1986, it was determined that BSD would move away from the aging VAX platform. The [[Computer Consoles Inc.#Power 5 and Power 6 computers|Power 6/32]] platform (codenamed "Tahoe") developed by [[Computer Consoles Inc.]] seemed promising at the time, but was abandoned by its developers shortly thereafter. Nonetheless, the '''4.3BSD-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 the [[OSI model|OSI]] network protocol stack, improvements to the kernel virtual memory system and (with [[Van Jacobson]] of [[Lawrence Berkeley National Laboratory|LBL]]) new TCP/IP algorithms to accommodate the growth of the Internet.<ref name="beyond43">{{cite conference |url=https://docs-archive.freebsd.org/44doc/papers/beyond43.pdf |first1=M.K. |last1=McKusick |first2=M.J.|last2=Karels |first3=Keith |last3=Sklower |first4=Kevin |last4=Fall |first5=Marc |last5=Teitelbaum |first6=Keith |last6=Bostic |date=1989 |title=Current Research by The Computer Systems Research Group of Berkeley |book-title=Proceedings of the European Unix Users Group Spring Conference}}</ref>

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 to '''Networking Release 1''' ('''Net/1'''), which was made available to non-licensees of AT&T code and was [[free software|freely redistributable]] under the terms of the [[BSD licenses|BSD license]]. It was released in June 1989.

After Net/1, BSD developer [[Keith Bostic (software engineer)|Keith 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.

Net/2 was the basis for two separate ports of BSD to the [[Intel 80386]] architecture: the free [[386BSD]] by [[William Jolitz|William]] and [[Lynne Jolitz]], and the [[proprietary software|proprietary]] [[BSD/OS|BSD/386]] (later renamed BSD/OS) by [[Berkeley Software Design]] (BSDi). 386BSD itself was short-lived, but became the initial code base of the [[NetBSD]] and [[FreeBSD]] projects that were started shortly thereafter.

BSDi soon found itself in legal trouble with AT&T's [[Unix System Laboratories]] (USL) subsidiary, then the owners of the System V [[copyright]] and the Unix trademark. The ''[[USL v. BSDi]]'' lawsuit was filed in 1992 and led to an [[injunction]] 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 the [[Linux 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.<ref>{{cite web|url=http://www.catb.org/esr/writings/taoup/html/ch02s01.html|title=The Art of Unix Programming: Origins and History of Unix, 1969–1995|author=Eric S. Raymond|access-date=July 18, 2014|archive-date=October 5, 2014|archive-url=https://web.archive.org/web/20141005172623/http://www.catb.org/esr/writings/taoup/html/ch02s01.html|url-status=live}}</ref>

The final release from Berkeley was 1995's '''4.4BSD-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 as [[FreeBSD]], [[NetBSD]], [[OpenBSD]] and [[DragonFly BSD]]) have been maintained.

The permissive nature of the [[BSD licenses|BSD license]] has allowed many other operating systems, both [[open-source software|open-source]] and proprietary, to incorporate BSD source code. For example, [[Microsoft Windows]] used BSD code in its implementation of TCP/IP<ref>{{cite web|url=http://www.kuro5hin.org/?op=displaystory;sid=2001/6/19/05641/7357|date=June 19, 2001|first=Adam|last=Barr|title=Microsoft, TCP/IP, Open Source, and Licensing|archive-url=https://web.archive.org/web/20051114154320/http://www.kuro5hin.org/?op=displaystory%3Bsid%3D2001%2F6%2F19%2F05641%2F7357|archive-date=November 14, 2005|url-status=dead|access-date=June 7, 2019}}</ref> and bundles recompiled versions of BSD's [[Command-line interface|command-line]] networking tools since [[Windows 2000]].<ref name="windows">{{cite web|url=http://www.everything2.com/index.pl?node=BSD%20Code%20in%20Windows|title=BSD Code in Windows|date=March 20, 2001|work=everything2.com|access-date=January 20, 2009|archive-date=August 25, 2008|archive-url=https://web.archive.org/web/20080825084349/http://everything2.com/index.pl?node=BSD%20Code%20in%20Windows|url-status=live}}</ref> [[Darwin (operating system)|Darwin]], the basis for Apple's [[macOS]] and [[iOS]], is based on 4.4BSD-Lite2 and FreeBSD. Various commercial Unix operating systems, such as [[Solaris (operating system)|Solaris]], also incorporate BSD code.

===Relationship to Research Unix===
Starting with the 8th Edition, versions of [[Research 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 a [[Usenet]] posting from 2000, Dennis Ritchie described this relationship between BSD and Research Unix:<ref>{{cite web|url=http://yarchive.net/comp/bsd.html|title=alt.folklore.computers: BSD (Dennis Ritchie)|author=Dennis Ritchie|date=October 26, 2000|access-date=July 3, 2014|archive-date=July 14, 2014|archive-url=https://web.archive.org/web/20140714222327/http://yarchive.net/comp/bsd.html|url-status=live}}</ref>{{Better source needed|reason=This is a USENET post containing DMR guessing about v8 being based on "BSD 4.1c"; see Talk page.|date=December 2022}}

{{blockquote|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.}}

===Relationship to System V===
[[Eric S. Raymond]] summarizes the longstanding relationship between [[System V]] and BSD, stating, "The divide was roughly between longhairs and shorthairs; [[programmer]]s and technical people tended to line up with Berkeley and BSD, more business-oriented types with AT&T and System V."<ref>Raymond, Eric S. ''The Art of Unix Programming.'' 2003. p. 38</ref>

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:<ref>Curry, David. ''Using C on the UNIX System: A Guide to System Programming.'' 1989. pp. 2–3</ref>

{{blockquote|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 of [[programming language]]s.}}

==Technology==

===Berkeley sockets===
[[File:4.3 BSD UWisc VAX Emulation Lisp Manual.png|thumb|alt=Black and white 4.3 BSD UWisc VAX Emulation Lisp Manual screenshot|4.3 BSD from the [[University of Wisconsin]]. Displaying the [[man page]] for [[Franz Lisp]].]]
[[File:SunOS 4.1.1 P1270750.jpg|thumb|alt=SunOS 4.1.1 P1270750 1/4-inch tape|Tape for [[SunOS]] 4.1.1, a 4.3BSD derivative]]
[[File:sony news.jpg|thumb|[[Sony NEWS]] [[workstation]] running the BSD-based [[NEWS-OS]] operating system]]

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 [[Network Control Protocol (ARPANET)|NCP]], with [[File Transfer Protocol|FTP]] and [[Telnet]] clients, had been produced at the [[University of Illinois at Urbana–Champaign|University of Illinois]] in 1975, and was available at Berkeley.<ref>{{cite journal|first=G. L.|last=Chesson|date=1976|title=The network Unix system|journal=ACM SIGOPS Operating Systems Review|volume=9|issue=5|pages=60–66|doi=10.1145/1067629.806522|doi-access=free}}</ref><ref>{{IETF RFC|681}}</ref> However, the memory scarcity on the PDP-11 forced a complicated design and performance problems.<ref name="quarterman42bsd">{{cite journal |last1=Quarterman |first1=John S. | first2 = Abraham | last2 = Silberschatz | first3 = James L. | last3 = Peterson |title=4.2BSD and 4.3BSD as examples of the Unix system |journal=Computing Surveys |date=December 1985 |volume=17 |issue=4 |pages=379–418 |doi=10.1145/6041.6043 |citeseerx = 10.1.1.117.9743 |s2cid=5700897 }}</ref>

By integrating sockets with the Unix operating system's [[file descriptor]]s, it became almost as easy to read and write data across a [[computer network|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.

===Binary compatibility===
Some BSD operating systems can run native software of several other operating systems on the same [[computer architecture|architecture]], using a binary [[compatibility layer]]. This is much simpler and faster than [[emulator|emulation]]; for example, it allows 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. 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.

===Standards===
Current BSD operating system variants support many of the common [[Institute of Electrical and Electronics Engineers|IEEE]], [[American National Standards Institute|ANSI]], [[International Organization for Standardization|ISO]], and [[POSIX]] standards, while retaining most of the traditional BSD behavior. Like [[AT&T Unix]], the BSD kernel is [[monolithic kernel|monolithic]], meaning that device drivers in the kernel run in [[protection ring|privileged mode]], as part of the core of the operating system.

==BSD descendants==
{{See also|Comparison of BSD operating systems}}
Several operating systems are based on BSD, including [[FreeBSD]], [[OpenBSD]], [[NetBSD]], [[MidnightBSD]], [[MirOS BSD]], [[GhostBSD]], [[Darwin (operating system)|Darwin]] and [[DragonFly BSD]]. Both NetBSD and FreeBSD were created in 1993. They were initially derived from [[386BSD]] (also known as "Jolix"), and merged the 4.4BSD-Lite source code in 1994. OpenBSD was [[Fork (software development)|forked]] from NetBSD in 1995, and DragonFly BSD was forked from FreeBSD in 2003.

BSD was also used as the basis for several proprietary versions of Unix, such as [[Sun Microsystems|Sun]]'s [[SunOS]], [[Sequent Computer Systems|Sequent]]'s [[DYNIX]], [[NeXT]]'s [[NeXTSTEP]], [[Digital Equipment Corporation|DEC]]'s [[Ultrix]] and OSF/1 AXP (now [[Tru64 UNIX]]). NeXTSTEP later became the foundation for [[Apple Inc.]]'s [[macOS]].

==See also==
* [[BSD Daemon]]
* [[BSD licenses]]
* [[Comparison of BSD operating systems]]
* [[List of BSD operating systems]]
* [[Lumina (desktop environment)]]
* [[Unix wars]]

==Notes==
{{notelist}}

==References==
{{reflist|30em}}

==Bibliography==
* Marshall K. McKusick, Keith Bostic, Michael J. Karels, John S. Quartermain, ''The Design and Implementation of the 4.4BSD Operating System'' (Addison Wesley, 1996; {{ISBN|978-0-201-54979-9}})
* Marshall K. McKusick, George V. Neville-Neil, ''The Design and Implementation of the FreeBSD Operating System'' (Addison Wesley, August 2, 2004; {{ISBN|978-0-201-70245-3}})
* Samuel J. Leffler, Marshall K. McKusick, Michael J. Karels, [[John Quarterman|John S. Quarterman]], ''The Design and Implementation of the 4.3BSD UNIX Operating System'' (Addison Wesley, November 1989; {{ISBN|978-0-201-06196-3}})
* {{cite book |editor1-first=Chris |editor1-last=DiBona |editor2-first=Sam |editor2-last=Ockman |editor3-first=Mark |editor3-last=Stone |title=Open Sources: Voices from the Revolution |url=https://www.oreilly.com/openbook/opensources/book/ |publisher=O'Reilly |edition=first |date=January 1999 |isbn=978-1-56592-582-3 |first=Marshall Kirk |last=McKusick |author-link=Marshall Kirk McKusick |chapter-url=http://www.oreilly.com/catalog/opensources/book/kirkmck.html |chapter=Twenty Years of Berkeley Unix – From AT&T-Owned to Freely Redistributable}}
* [[Peter H. Salus]], ''The Daemon, the GNU & The Penguin'' (Reed Media Services, September 1, 2008; {{ISBN|978-0-9790342-3-7}})
* [[Peter H. Salus]], ''A Quarter Century of UNIX'' (Addison Wesley, June 1, 1994; {{ISBN|978-0-201-54777-1}})
* [[Peter H. Salus]], ''Casting the Net'' (Addison-Wesley, March 1995; {{ISBN|978-0-201-87674-1}})

==External links==
{{Wikiquote}}

* [https://cgit.freebsd.org/src/plain/share/misc/bsd-family-tree A timeline of BSD and Research UNIX]
* [http://www.levenez.com/unix/ UNIX History]&nbsp;– History of UNIX and BSD using diagrams
* [http://www.freebsd.org/doc/en_US.ISO8859-1/books/design-44bsd/ The Design and Implementation of the 4.4BSD Operating System]
* [http://minnie.tuhs.org/cgi-bin/utree.pl The Unix Tree:  Source code and manuals for old versions of Unix]
* [http://EuroBSDCon.org/ EuroBSDCon], an annual event in Europe in September, October or November, [http://www.ukuug.org/events/eurobsdcon2009/history/ founded] {{Webarchive|url=https://web.archive.org/web/20200620125743/http://www.ukuug.org/events/eurobsdcon2009/history/ |date=June 20, 2020 }} in 2001 <!-- 2003 did not happen, so, this one has not been "held annually", as per http://www.ukuug.org/events/eurobsdcon2009/history/ -->
* [http://BSDCan.org/ BSDCan], a conference in [[Ottawa|Ottawa, Ontario]], Canada, held annually in May since 2004, in June since 2015
* [http://AsiaBSDCon.org/ AsiaBSDCon], a conference in Tokyo, held annually in March of each year, since 2007
* [http://mdoc.su/ mdoc.su&nbsp;– short manual page URLs for FreeBSD, OpenBSD, NetBSD and DragonFly BSD], a web-service [http://nginx.conf.mdoc.su/mdoc.su.nginx.conf written] in [[nginx]]
* [http://BXR.SU/ BXR.SU&nbsp;– Super User's BSD Cross Reference], a userland and kernel source code search engine based on [[OpenGrok]] and [[nginx]]

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