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TheUnix wars were struggles between vendors to set a standard for theUnixoperating system in the late 1980s and early 1990s.
BothAT&T Corporation andUniversity of California, Berkeley are important in the earlyhistory of Unix. Although AT&T'sBell Labs createdUnix, by the 1980s, Berkeley'sComputer Systems Research Group was the leading non-commercial Unix developer.[1] In the mid-1980s, the three common versions of Unix were AT&T'sSystem III, the basis ofMicrosoft'sXenix and the IBM-endorsedPC/IX, among others; AT&T'sSystem V, which it sought to establish as the new Unix standard;[2] and theBerkeley Software Distribution (BSD). All were derived from AT&T'sResearch Unix but had diverged considerably. Further, each vendor's version of Unix was different to some degree.
For example, at a mid-1980sUsenix conference, many AT&T staff had buttons that read "System V: Consider it Standard" and a number of major vendors were promoting products based on System V. On the other hand, System V did not yet have TCP/IP networking built-in, while BSD 4.2 did; vendors of engineering workstations were nearly all using BSD, and posters reading "4.2 > V" were available.
Several vendors formed theX/Openstandards group in 1984 to promote compatibleopen systems, and they chose to base their system on Unix. X/Open caught AT&T's attention. To increase the uniformity of Unix, AT&T and leading BSD Unix vendorSun Microsystems started work in 1987 on a unified system. (The feasibility of this had been demonstrated a few years earlier by theUS ArmyBallistic Research Laboratory's System V environment for BSD Unix.) This was released in 1988 asSystem V Release 4 (SVR4) which still lives to this day through its derivativeOpenIndiana.[3]
While this decision was applauded by customers and the trade press, certain other Unix licensees feared Sun would be unduly advantaged. They formed theOpen Software Foundation (OSF) in 1988. The same year, AT&T and another group of licensees responded by formingUnix International (UI). Technical issues soon took a back seat to vicious and public commercial competition between the two "open" versions of Unix, with X/Open holding the middle ground.
A 1990 study of various Unix versions' reliability found that in each version, between a quarter and a third of operating system utilities could be made tocrash byfuzzing; the researchers attributed this, in part, to the "race for features, power, and performance" resulting from BSD–System V rivalry, which left developers little time to worry about reliability.[4]
The 1988POSIX standard initially concentrated on systemC library functions beyond what was included in the forthcoming C standard; later it expanded to specify other aspects of the system environment. POSIX specified a "lowest common denominator" that could be met by both System V and BSD-based variants, as well as some non-Unix systems, with a reasonable amount of effort.
In March 1993, the major participants in UI and OSF formed theCommon Open Software Environment (COSE) alliance, effectively marking the end of the most significant era of the Unix wars. In June, AT&T sold its Unix assets toNovell, and in October Novell transferred the Unix brand to X/Open.
In 1996, X/Open and the new OSF merged to form theOpen Group. COSE work such as theSingle UNIX Specification, the current standard for branded Unix, is now the responsibility of the Open Group, which also controls the current POSIX standards.
Since then, occasional bursts of Unix factionalism have broken out, such as theHP/SCO "3DA" alliance in 1995, andProject Monterey in 1998, a teaming ofIBM,SCO,Sequent, andIntel which was followed by litigation (SCO v. IBM) between IBM and thenew SCO, formerly Caldera.
BSD worked to purge copyrighted AT&T code from their version between 1989 and 1994. During this time, various open-source BSD x86 derivatives took shape, starting with386BSD, which was soon succeeded byFreeBSD andNetBSD.OpenBSD emerged in 1995 as a fork of NetBSD, andDragonFly BSD as a fork from FreeBSD in 2003.Mac OS X v10.5 is the first operating system with open source BSD code to be certified as fully Unix compliant.[5] BSD systems can claim direct ancestry fromVersion 7 Unix. According to Open Source advocateEric Raymond, BSD systems can be considered "genetic Unix", if not "trademark Unix".[6]
During BSD'speriod of legal turmoil (1992–94),[7] the nearly-completeGNU operating system was made operational by the inclusion of theLinux kernel and lumped together under the label "Linux". GNU had been written from scratch to avoid copyright issues. Linux systems broadly aim for compatibility withPOSIX.