Berkeley Software Distribution

Simplified evolution of Unix systems. Not shown are Junos, PlayStation 3 system software and other proprietary forks.

The 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, 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 project.[6] Understanding BSD requires delving far back into the history of Unix, the operating system first released by AT&T Bell Labs in 1969. 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.

At first, BSD was not a clone of Unix, or even a substantially different version of it. It just included some extra utilities, 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 implementation for the system. Graduate students Chuck Haley and Bill Joy improved Thompson's Pascal and implemented an improved text editor, ex.[6] 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.[7] 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.[6]

The second Berkeley Software Distribution (2BSD), released in May 1979,[8] 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 (a visual version of ex) and the C shell. Some 75 copies of 2BSD were sent out by Bill Joy.[6]

The VAX-11/780, a typical minicomputer used for early BSD timesharing systems

A VAX computer was installed at Berkeley in 1978, but the port of Unix to the VAX architecture, UNIX/32V, did not take advantage of the VAX's virtual memory capabilities. The kernel of 32V was largely rewritten to include Berkeley graduate student Ozalp Babaoglu'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.

"4.3 BSD UNIX" from the 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 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 network protocol stack, improvements to the kernel virtual memory system and (with Van Jacobson of LBL) new TCP/IP algorithms to accommodate the growth of the Internet.[9]

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 freely redistributable under the terms of the BSD license. It was released in June 1989.

After Net/1, BSD developer 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 and the proprietary 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.[10]

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 license has allowed many other operating systems, both open-source and proprietary, to incorporate BSD source code. For example, Microsoft Windows used BSD code in its implementation of TCP/IP[11] and bundles recompiled versions of BSD's command-line networking tools since Windows 2000.[12] 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, also incorporate BSD code.

Several operating systems are based on BSD, including FreeBSD, OpenBSD, NetBSD, MidnightBSD, GhostBSD, 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 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's SunOS, Sequent's DYNIX, NeXT's NeXTSTEP, DEC's Ultrix and OSF/1 AXP (now Tru64 UNIX). NeXTSTEP later became the foundation for Apple Inc.'s macOS.

• BSD Daemon
• BSD licenses
• Comparison of BSD operating systems
• List of BSD operating systems
• Unix wars

• 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 S. Quarterman, The Design and Implementation of the 4.3BSD UNIX Operating System (Addison Wesley, November 1989; ISBN 978-0-201-06196-3)
• McKusick, Marshall Kirk (January 1999). "Twenty Years of Berkeley Unix – From AT&T-Owned to Freely Redistributable". In DiBona, Chris; Ockman, Sam; Stone, Mark (eds.). Open Sources: Voices from the Revolution (first ed.). O'Reilly. ISBN 978-1-56592-582-3.
• 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)

• Berkeley Software Distribution at Curlie
• A timeline of BSD and Research UNIX
• UNIX History – History of UNIX and BSD using diagrams
• The Design and Implementation of the 4.4BSD Operating System
• The Unix Tree: Source code and manuals for old versions of Unix
• EuroBSDCon, an annual event in Europe in September, October or November, founded in 2001
• BSDCan, a conference in Ottawa, Ontario, Canada, held annually in May since 2004, in June since 2015
• AsiaBSDCon, a conference in Tokyo, held annually in March of each year, since 2007
• mdoc.su – short manual page URLs for FreeBSD, OpenBSD, NetBSD and DragonFly BSD, a web-service written in nginx
• BXR.SU – Super User's BSD Cross Reference, a userland and kernel source code search engine based on OpenGrok and nginx