Berkeley Software Distribution

Berkeley Software Distribution (BSD, sometimes called Berkeley Unix) is the UNIX operating system derivative developed and distributed by the Computer Systems Research Group (CSRG) of the University of California, Berkeley, from 1977 to 1995.

Historically, BSD has been considered a branch of UNIX — "BSD UNIX", because it shared the initial codebase and design with the original AT&T UNIX operating system. In the 1980s, BSD was widely adopted by vendors of workstation-class systems in the form of proprietary UNIX variants such as DEC ULTRIX and Sun Microsystems SunOS. This can be attributed to the ease with which it could be licensed, and the familiarity it found among the founders of many technology companies of this era.

Though these proprietary BSD derivatives were largely superseded by the UNIX System V Release 4 and OSF/1 systems in the 1990s (both of which incorporated BSD code), later BSD releases provided a basis for several open source development projects that continue to this day.

Today, the term of "BSD" is often non-specifically used to refer to any of these BSD descendants, e.g., FreeBSD, NetBSD, OpenBSD or DragonFly, which together form a branch of the family of Unix-like operating systems.

History

Evolution of Unix systems

PDP-11 beginnings

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 first Unix system at Berkeley was a PDP-11 installed in 1974, and the computer science department used it for extensive research thereafter.

Other universities became interested in the software at Berkeley, and so in 1977 Bill Joy, then a graduate student at Berkeley, assembled and sent out tapes of the first Berkeley Software Distribution (1BSD). 1BSD was an add-on to Sixth Edition Unix rather than a complete operating system in its own right; its main components were a Pascal compiler and Joy's ex line editor.

The Second Berkeley Software Distribution (2BSD), released in 1978, 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.

Later releases of 2BSD contained ports of changes to the VAX-based releases of BSD back to the PDP-11 architecture. 2.9BSD from 1983 included code from 4.1cBSD, and was the first release that was a full OS (a modified Version 7 Unix) rather than a set of applications and patches. The most recent release, 2.11BSD, was first released in 1992. As of 2008, maintenance updates from volunteers are still continuing, with patch 447 being released on December 31, 2008.^[1]

VAX versions

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 by Berkeley students to include a 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.

The success of 3BSD was a major factor in the Defense Advanced Research Projects Agency's (DARPA) decision to fund Berkeley's Computer Systems Research Group (CSRG), which would develop a standard Unix platform for future DARPA research in the VLSI Project. CSRG released 4BSD, containing numerous improvements to the 3BSD system, in October 1980.

4BSD (November 1980) offered a number of enhancements over 3BSD, notably job control in the previously released csh, delivermail (the antecedent of sendmail), "reliable" signals, and the Curses programming library.

4.1BSD (June 1981) was a response to criticisms of BSD's performance relative to the dominant VAX operating system, VMS. The 4.1BSD kernel was systematically tuned up by Bill Joy until it could perform as well as VMS on several benchmarks. (The release would have been called 5BSD, but after objections from AT&T the name was changed; AT&T feared confusion with AT&T's UNIX System V.^[2] One early, never-released test version was in fact called 4.5BSD.)

4.2BSD would take over two years to implement and contained several major overhauls. Before its official release came three intermediate versions: 4.1a incorporated a modified version of BBN's preliminary TCP/IP implementation; 4.1b included the new Berkeley Fast File System, implemented by Marshall Kirk McKusick; and 4.1c was an interim release during the last few months of 4.2BSD's development.

To guide the design of 4.2BSD Duane Adams of DARPA formed a "steering committee" consisting of Bob Fabry, Bill Joy and Sam Leffler from UCB, Alan Nemeth and Rob Gurwitz from BBN, Dennis Ritchie from Bell Labs, Keith Lantz from Stanford, Rick Rashid from Carnegie-Mellon, Bert Halstead from MIT, Dan Lynch from ISI, and Gerald J. Popek of UCLA. The committee met from April 1981 to June 1983.

The official 4.2BSD release came in August 1983. It was notable as the first version released after the 1982 departure of Bill Joy to co-found Sun Microsystems; Mike Karels and Marshall Kirk McKusick took on leadership roles within the project from that point forward. On a lighter note, it also marked the debut of BSD's daemon mascot in a drawing by John Lasseter that appeared on the cover of the printed manuals distributed by USENIX.

4.3BSD

4.3BSD was released in June 1986. Its main changes were to improve the performance of many of the new contributions of 4.2BSD that had not been as heavily tuned as the 4.1BSD code. Prior to the release, BSD's implementation of TCP/IP had diverged considerably from BBN's official implementation. After several months of testing, DARPA determined that the 4.2BSD version was superior and would remain in 4.3BSD. (See also History of the Internet.)

After 4.3BSD, 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.

Apart from 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.^[3]

Until then, all versions of BSD incorporated 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.

4.3BSD-Reno came in early 1990. It was an interim release during the early development of 4.4BSD, and its use was considered a "gamble", hence the naming after the gambling center of Reno, Nevada. This release was explicitly moving towards POSIX compliance,^[3] and, according to some, away from the BSD philosophy (as POSIX is very much based on System V, and Reno was quite bloated compared to previous releases). Among the new features was an NFS implementation from the University of Guelph.

In August 2006, Information Week magazine rated 4.3BSD as the "Greatest Software Ever Written".^[4] They commented: "BSD 4.3 represents the single biggest theoretical undergirder of the Internet."

Net/2 and legal troubles

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. For example, vi, which had been based on the original Unix version of ed, was rewritten as nvi (new vi). Within eighteen months, all 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. Although not released until 1992, development of 386BSD predated that of Linux. Linus Torvalds has said that if 386BSD had been available at the time, he probably would not have created Linux.^[5]

4.4BSD and descendants

The lawsuit was settled in January 1994, largely in Berkeley's favor. Of the 18,000 files in the Berkeley distribution, only 3 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.

In June 1994, 4.4BSD was released in two forms: the freely distributable 4.4BSD-Lite contained no AT&T source, whereas 4.4BSD-Encumbered was available, as earlier releases had been, only to AT&T licensees.

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.

In addition, the permissive nature of the BSD license has allowed many other operating systems, both free and proprietary, to incorporate BSD code. For example, Microsoft Windows has used BSD-derived code in its implementation of TCP/IP and bundles recompiled versions of BSD's command-line networking tools with its current releases.^[6] Also Darwin, the system on which Apple's Mac OS X is built, is a derivative of 4.4BSD-Lite2 and FreeBSD. Various commercial UNIX operating systems, such as Solaris, also contain varying amounts of BSD code.

Technology

Berkeley's Unix was the first Unix to include libraries supporting the Internet Protocol stacks: Berkeley sockets. By integrating sockets with the Unix operating system's file descriptors, it became almost as easy to read and write data across a 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 better architecture, but the wide distribution of the existing sockets library, together with the unfortunate omission of a function call for polling a set of open sockets equivalent to the select call in the Berkeley 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.

Today, BSD continues to be used as a testbed for technology by academic organizations, as well as finding uses in a lot of commercial and free products and, increasingly, in embedded devices. The general quality of its source code, as well as its documentation (especially reference manual pages, commonly referred to as man pages), make it well-suited for many purposes.

The permissive nature of the BSD license allows companies to distribute derived products as proprietary software without exposing source code and sometimes intellectual property to competitors. Searching for strings containing "University of California, Berkeley" in the documentation of products, in the static data sections of binaries and ROMs, or as part of other information about a software program, will often show BSD code has been used. This permissiveness also makes BSD code suitable for use in open source products, and the license is compatible with many other open source licenses. The permissive nature of the BSD license also allows derivative works of code released originally under the BSD license to become less permissive with time.

BSD operating systems can run much native software of several other operating systems on the same architecture, using a binary compatibility layer. Much simpler and faster than emulation, this allows, for instance, 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.

Current BSD operating system variants support many of the common IEEE, ANSI, ISO, and POSIX standards, while retaining most of the traditional BSD behavior. Like AT&T Unix, the BSD kernel is monolithic, meaning that device drivers in the kernel run in privileged mode, as part of the core of the operating system.

Significant BSD descendants

Bar chart showing the proportion of users of each BSD variant from a BSD usage survey in 2005.^[7] Each participant was permitted to indicate multiple BSD variants

See also: Category:BSD and Comparison of BSD operating systems

BSD has been the base of a large number of operating systems. Most notable among these today are perhaps the major open source BSDs: FreeBSD, NetBSD and OpenBSD, which are all derived from 386BSD and 4.4BSD-Lite by various routes. Both NetBSD and FreeBSD started life in 1993, initially derived from 386BSD, but in 1994 migrating to a 4.4BSD-Lite code base. OpenBSD was forked in 1995 from NetBSD. The three most notable descendants in current use — sometimes known as the BSDs — have themselves spawned a number of children, including DragonFly BSD, FreeSBIE, MirOS BSD, DesktopBSD, and PC-BSD. They are targeted at an array of systems for different purposes and are common in government facilities, universities and in commercial use. A number of commercial operating systems are also partly or wholly based on BSD or its descendants, including Sun's SunOS and Apple Inc.'s Mac OS X.

Most of the current BSD operating systems are open source and available for download, free of charge, under the BSD License, the most notable exception being Mac OS X. They also generally use a monolithic kernel architecture, apart from Mac OS X and DragonFly BSD which feature hybrid kernels. The various open source BSD projects generally develop the kernel and userland programs and libraries together, the source code being managed using a single central source repository.

In the past, BSD was also used as a 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). Of these, only the last is still currently supported in its original form. Parts of NeXT's software became the foundation for Mac OS X, among the most commercially successful BSD variants in the general market.

A selection of significant Unix versions and Unix-like operating systems that descend from BSD includes:

• FreeBSD, a major open source effort focusing on performance and the x86 platform.
  • DragonFly BSD, a fork of FreeBSD to follow an alternative design, particularly related to SMP.
  • PC-BSD and DesktopBSD, distributions of FreeBSD with emphasis on ease of use and user friendly interfaces for the desktop/laptop PC user.
  • Nokia IPSO (IPSO SB variant), the FreeBSD-based OS used in Nokia Firewall Appliances.
  • Juniper Networks JunOS, the operating system for Juniper routers, a customized version of FreeBSD, and a variety of other embedded operating systems
  • Apple Inc.'s Darwin, the core of Mac OS X; built on the XNU kernel (part Mach, part FreeBSD, part Apple-derived code) and a userland much of which comes from FreeBSD
  • NetApp's ONTAP GX, the operating system for NetApp filers, is a customized version of FreeBSD with the ONTAP GX architecture built on top.
• NetBSD, an open source BSD with an emphasis on portability and clean design.
  • OpenBSD, a 1995 fork of NetBSD, focuses on portability, standardization, correctness, proactive security and integrated cryptography.
• F5 Networks, All F5 BIGIP Appliances use Free BSD as the underlying OS.
• DEC's Ultrix, the official version of Unix for its PDP-11, VAX, and DECstation systems
• OSF/1, a microkernel-based UNIX developed by the Open Software Foundation, incorporating the Mach kernel and parts of 4BSD
  • Tru64 UNIX (formerly DEC OSF/1 AXP or Digital UNIX), the port of OSF/1 for DEC Alpha-based systems from DEC, Compaq and HP.
• Early versions of Sun Microsystems SunOS (up to SunOS 4.1.4), an enhanced version of 4BSD for the Sun Motorola 68k-based Sun-2 and Sun-3 systems, SPARC-based systems, and x86-based Sun386i systems.
• NeXT NEXTSTEP and OPENSTEP, based on the Mach kernel and 4BSD; the ancestor of Mac OS X
• 386BSD, the first open source BSD-based operating system and the ancestor of most current BSD systems
• DEMOS, a Soviet BSD clone
• BSD/OS, a (now defunct) proprietary BSD for PCs

See also

• Comparison of BSD operating systems
• List of BSD operating systems
• BSD licenses
• BSD Daemon
• Bill Joy
• Marshall Kirk McKusick
• Keith Bostic
• Özalp Babaoğlu

References

1. ↑ Mueller, Walter (2009-01-04). "2.11BSD Patch 446+447; fixes for ulrem,umount,tar,tcsh,ps,vmstat,apropos,pstat,rk". www.classiccmp.org. http://www.classiccmp.org/pipermail/cctech/2009-January/101166.html. Retrieved 2009-01-20. 
2. ↑ M.K. McKusick in Open Sources, O'Reilly.
3. ↑ ^{3.0 3.1} M.K. McKusick, M.J. Karels, Keith Sklower, Kevin Fall, Marc Teitelbaum and Keith Bostic (1989). Current Research by The Computer Systems Research Group of Berkeley. Proc. European Unix Users Group.
4. ↑ Babcock, Charles (2006-08-14). "What's The Greatest Software Ever Written?". InformationWeek. http://www.informationweek.com/shared/printableArticle.jhtml?articleID=191901844. Retrieved 2009-01-20. 
5. ↑ Linksvayer, Mike (1993). "The Choice of a GNU Generation - An Interview With Linus Torvalds". Meta magazine. http://gondwanaland.com/meta/history/interview.html. Retrieved 2009-01-20. 
6. ↑ "BSD Code in Windows". everything2.com. 2001-03-20. http://www.everything2.com/index.pl?node=BSD%20Code%20in%20Windows. Retrieved 2009-01-20. 
7. ↑ "BSD Usage Survey". BSD Certification Group. 2005-10-31. http://www.bsdcertification.org/downloads/pr_20051031_usage_survey_en_en.pdf. Retrieved 2009-01-20. 

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 S. Quarterman, The Design and Implementation of the 4.3BSD UNIX Operating System (Addison Wesley, November, 1989; ISBN 978-0-201-06196-3)
• Chris DiBona, Mark Stone, Sam Ockman, Open Source (Organization), Brian Behlendorf and J. Scott Bradner, Open Sources: Voices from the Open Source Revolution. O'Reilly & Associates, 1999. Trade paperback, 272 pages. ISBN 978-1-565-92582-3. Online version; Marshall Kirk McKusick, chapter on BSD, "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 978-0-979-03423-7)
• 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

• 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 Slab Allocator: an object-caching kernel memory allocator Bonwick, 1994.

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