Unix (officially trademarked as UNIX®) is a computer operating system originally developed in the 1960s and 1970s by a group of AT&T employees at Bell Labs including Ken Thompson, Dennis Ritchie and Douglas McIlroy. Today’s Unix systems are split into various branches, developed over time by AT&T as well as various commercial vendors and non-profit organizations.
The present owner of the trademark UNIX® is The Open Group, an industry standards consortium. Only systems fully compliant with and certified to the Single UNIX Specification qualify as “UNIX®” (others are called “Unix system-like” or “Unix-like”).
During the late 1970s and early 1980s, Unix’s influence in academic circles led to large-scale adoption of Unix (particularly of the BSD variant, originating from the University of California, Berkeley) by commercial startups, the most notable of which is Sun Microsystems. Today, in addition to certified Unix systems, Unix-like operating systems such as GNU/Linux, Mac OS X and BSD derivatives are commonly encountered.
HISTORY
Thompson thus re-wrote the game in assembly language for Digital Equipment Corporation’s PDP-7 with help from Dennis Ritchie. This experience, combined with his work on the Multics project, led Thompson to start a new operating system for the PDP-7. Thompson and Ritchie led a team of developers, including Rudd Canaday, at Bell Labs developing a file system as well as the new multi-tasking operating system itself. They included a command line interpreter and some small utility programs.
1970s
In 1970 the project was named Unics, and could – eventually – support two simultaneous users. Brian Kernighan invented this name as a contrast to Multics; the spelling was later changed to Unix.
Up until this point there had been no financial support from Bell Labs. When the Computer Science Research Group wanted to use Unix on a much larger machine than the PDP-7, Thompson and Ritchie managed to trade the promise of adding text processing capabilities to Unix for a PDP-11/20 machine. This led to some financial support from Bell. For the first time in 1970, the Unix operating system was officially named and ran on the PDP-11/20. It added a text formatting program called roff and a text editor. All three were written in PDP-11/20 assembly language. Bell Labs used this initial “text processing system”, made up of Unix, roff, and the editor, for text processing of patent applications. Roff soon evolved into troff, the first electronic publishing program with a full typesetting capability. The UNIX Programmer’s Manual was published on November 3, 1971.
In 1973, the decision was made to re-write Unix in the C programming language. The change meant that it was easier to modify Unix to work on other machines (thus becoming portable), and other developers could create variations. The code was now more concise and compact, leading to accelerated development of Unix. AT&T made Unix available to universities and commercial firms, as well as the United States government under licenses. The licenses included all source code including the machine-dependent parts of the kernel, which were written in PDP-11 assembly code. Copies of the annotated Unix kernel sources circulated widely in the late 1970s in the form of a much-copied book by John Lions of the University of New South Wales, the Lions’ Commentary on UNIX 6th Edition, with Source Code, which led to considerable use of Unix as an educational example.
Versions of the Unix system were determined by editions of its user manuals, so that (for example) “Fifth Edition UNIX” and “UNIX Version 5” have both been used to designate the same thing. Development expanded, with Versions 4, 5, and 6 being released by 1975. These versions added the concept of pipes, leading to the development of a more modular code-base, increasing development speed still further. Version 5 and especially Version 6 led to a plethora of different Unix versions both inside and outside Bell Labs, including PWB/UNIX, IS/1 (the first commercial Unix), and the University of Wollongong’s port to the Interdata 7/32 (the first non-PDP Unix).
In 1978, UNIX/32V, for the VAX system, was released. By this time, over 600 machines were running Unix in some form. Version 7 Unix, the last version of Research Unix to be released widely, was released in 1979. Versions 8, 9 and 10 were developed through the 1980s but were only released to a few universities, though they did generate papers describing the new work. This research led to the development of Plan 9 from Bell Labs, a new portable distributed system.
A late-80s style Unix desktop running the X Window System graphical user interface. Shown are a number of client applications common to the MIT X Consortium’s distribution, including Tom’s Window Manager, an X Terminal, Xbiff, xload, and a graphical manual page browser.
AT&T now licensed UNIX System III, based largely on Version 7, for commercial use, the first version launching in 1982. This also included support for the VAX. AT&T continued to issue licenses for older Unix versions. To end the confusion between all its differing internal versions, AT&T combined them into UNIX System V Release 1. This introduced a few features such as the vi editor and curses from the Berkeley Software Distribution of Unix developed at the University of California, Berkeley. This also included support for the Western Electric 3B series of machines.
Since the newer commercial UNIX licensing terms were not as favorable for academic use as the older versions of Unix, the Berkeley researchers continued to develop BSD Unix as an alternative to UNIX System III and V, originally on the PDP-11 architecture (the 2.xBSD releases, ending with 2.11BSD) and later for the VAX-11 (the 4.x BSD releases). Many contributions to Unix first appeared on BSD systems, notably the C shell with job control (modelled on ITS). Perhaps the most important aspect of the BSD development effort was the addition of TCP/IP network code to the mainstream Unix kernel. The BSD effort produced several significant releases that contained network code: 4.1cBSD, 4.2BSD, 4.3BSD, 4.3BSD-Tahoe (“Tahoe” being the nickname of the CCI Power 6/32 architecture that was the first non-DEC release of the BSD kernel), Net/1, 4.3BSD-Reno (to match the “Tahoe” naming, and that the release was something of a gamble), Net/2, 4.4BSD, and 4.4BSD-lite. The network code found in these releases is the ancestor of much TCP/IP network code in use today, including code that was later released in AT&T System V UNIX and early versions of Microsoft Windows. The accompanying Berkeley Sockets API is a de facto standard for networking APIs and has been copied on many platforms.
Other companies began to offer commercial versions of the UNIX System for their own mini-computers and workstations. Most of these new Unix flavors were developed from the System V base under a license from AT&T; however, others were based on BSD instead. One of the leading developers of BSD, Bill Joy, went on to co-found Sun Microsystems in 1982 and create SunOS (now Solaris) for their workstation computers. In 1980, Microsoft announced its first Unix for 16-bit microcomputers called Xenix, which the Santa Cruz Operation (SCO) ported to the Intel 8086 processor in 1983, and eventually branched Xenix into SCO UNIX in 1989.
For a few years during this period (before PC compatible computers with MS-DOS became dominant), industry observers expected that UNIX, with its portability and rich capabilities, was likely to become the industry standard operating system for microcomputers.[3] In 1984 several companies established the X/Open consortium with the goal of creating an open system specification based on UNIX. Despite early progress, the standardization effort collapsed into the “Unix wars,” with various companies forming rival standardization groups. The most successful Unix-related standard turned out to be the IEEE’s POSIX specification, designed as a compromise API readily implemented on both BSD and System V platforms, published in 1988 and soon mandated by the United States government for many of its own systems.
AT&T added various features into UNIX System V, such as file locking, system administration, streams, new forms of IPC, the Remote File System and TLI. AT&T cooperated with Sun Microsystems and between 1987 and 1989 merged features from Xenix, BSD, SunOS, and System V into System V Release 4 (SVR4), independently of X/Open. This new release consolidated all the previous features into one package, and heralded the end of competing versions. It also increased licensing fees.
1990s
In 1990, the Open Software Foundation released OSF/1, their standard Unix implementation, based on Mach and BSD. The Foundation was started in 1988 and was funded by several Unix-related companies that wished to counteract the collaboration of AT&T and Sun on SVR4. Subsequently, AT&T and another group of licensees formed the group “UNIX International” in order to counteract OSF. This escalation of conflict between competing vendors gave rise again to the phrase “Unix wars”.
In 1991, a group of BSD developers (Donn Seeley, Mike Karels, Bill Jolitz, and Trent Hein) left the University of California to found Berkeley Software Design, Inc (BSDI). BSDI produced a fully functional commercial version of BSD Unix for the inexpensive and ubiquitous Intel platform, which started a wave of interest in the use of inexpensive hardware for production computing. Shortly after it was founded, Bill Jolitz left BSDI to pursue distribution of 386BSD, the free software ancestor of FreeBSD, OpenBSD, and NetBSD.
By 1993 most commercial vendors had changed their variants of Unix to be based on System V with many BSD features added on top. The creation of the COSE initiative that year by the major players in Unix marked the end of the most notorious phase of the Unix wars, and was followed by the merger of UI and OSF in 1994. The new combined entity, which retained the OSF name, stopped work on OSF/1 that year. By that time the only vendor using it was Digital, which continued its own development, rebranding their product Digital UNIX in early 1995.
Shortly after UNIX System V Release 4 was produced, AT&T sold all its rights to UNIX® to Novell. (Dennis Ritchie likened this to the Biblical story of Esau selling his birthright for the proverbial “mess of pottage”.[4]) Novell developed its own version, UnixWare, merging its NetWare with UNIX System V Release 4. Novell tried to use this to battle against Windows NT, but their core markets suffered considerably.
In 1993, Novell decided to transfer the UNIX® trademark and certification rights to the X/Open Consortium.[5] In 1996, X/Open merged with OSF, creating the Open Group. Various standards by the Open Group now define what is and what is not a “UNIX” operating system, notably the post-1998 Single UNIX Specification.
In 1995, the business of administering and supporting the existing UNIX licenses, plus rights to further develop the System V code base, were sold by Novell to the Santa Cruz Operation.[1] Whether Novell also sold the copyrights is currently the subject of litigation (see below).
2000 to present
In 2000, SCO sold its entire UNIX business and assets to Caldera Systems, which later on changed its name to The SCO Group. This new player then started legal action against various users and vendors of Linux. SCO have alleged that Linux contains copyrighted Unix code now owned by The SCO Group. Other allegations include trade-secret violations by IBM, or contract violations by former Santa Cruz customers who have since converted to Linux. However, Novell disputed the SCO group’s claim to hold copyright on the UNIX source base. According to Novell, SCO (and hence the SCO Group) are effectively franchise operators for Novell, which also retained the core copyrights, veto rights over future licensing activities of SCO, and 95% of the licensing revenue. The SCO Group disagreed with this, and the dispute had resulted in the SCO v. Novell lawsuit.
In 2005, Sun Microsystems released the bulk of its Solaris system code (based on UNIX System V Release 4) into an open source project called OpenSolaris. New Sun OS technologies such as the ZFS file system are now first released as open source code via the OpenSolaris project; as of 2006 it has spawned several non-Sun distributions such as SchilliX, Belenix, Nexenta and MartuX.
The Dot-com crash has led to significant consolidation of Unix users as well. Of the many commercial flavors of Unix that were born in the 1980s, only Solaris, HP-UX, and AIX are still doing relatively well in the market. Of these, Solaris has the most market share, and may be gaining popularity due to its feature set and also since it now has an Open Source version.
Free Unix-like operating systems
In 1983, Richard Stallman announced the GNU project, an ambitious effort to create a free software Unix-like system; “free” in that everyone who received a copy would be free to use, study, modify, and redistribute it. GNU’s goal was achieved in 1992. Its own kernel development project, GNU Hurd, had not produced a working kernel, but a compatible kernel called Linux was released as free software in 1992 under the GNU General Public License. The combination of the two is frequently referred to simply as “Linux”, although the Free Software Foundation and some Linux distributions, such as Debian GNU/Linux, use the combined term GNU/Linux. Work on GNU Hurd continues, although very slowly.
In addition to their use in the Linux operating system, many GNU packages — such as the GNU Compiler Collection (and the rest of the GNU toolchain), the GNU C library and the GNU core utilities — have gone on to play central roles in other free Unix systems as well.
Linux distributions, comprising Linux and large collections of compatible software have become popular both with hobbyists and in business. Popular distributions include Red Hat Enterprise Linux, SUSE Linux, Mandriva Linux, Fedora Core, Ubuntu, Debian GNU/Linux and Gentoo.
A free derivative of BSD Unix, 386BSD, was also released in 1992 and led to the NetBSD and FreeBSD projects. With the 1994 settlement of a lawsuit that UNIX Systems Laboratories brought against the University of California and Berkeley Software Design Inc. (USL v. BSDi), it was clarified that Berkeley had the right to distribute BSD Unix — for free, if it so desired. Since then, BSD Unix has been developed in several different directions, including the OpenBSD and DragonFly BSD variants.
Linux and the BSD kin are now rapidly occupying the market traditionally occupied by proprietary Unix operating systems, as well as expanding into new markets such as the consumer desktop and mobile and embedded devices. A measure of this success may be seen when Apple Computer sought out a new foundation for its Macintosh operating system: it chose NEXTSTEP, an operating system developed by NeXT with a freely redistributable core operating system, renamed Darwin after Apple acquired it. It was based on the BSD family and the Mach kernel. The deployment of Darwin BSD Unix in Mac OS X makes it, according to a statement made by an Apple employee at a USENIX conference, the most widely used Unix-based system in the desktop computer market. Due to the modularity of the Unix design, sharing bits and pieces is relatively common; consequently, most or all Unix and Unix-like systems include at least some BSD code, and modern BSDs also typically include some GNU utilities in their distribution, so Apple’s combination of parts from NeXT and FreeBSD with Mach and some GNU utilities has precedent.
In 2005, Sun Microsystems released the bulk of the source code to the Solaris operating system, a System V variant, under the name OpenSolaris, making it the first actively developed commercial Unix system to be open sourced (several years earlier, Caldera had released many of the older Unix systems under an educational and later BSD license). As a result, a great deal of formerly proprietary AT&T/USL code is now freely available.
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