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Unix genealogy tree

The Unix wars were the struggles between vendors of the Unix computer operating system in the late 1980s and early 1990s to set the standard for Unix thenceforth. These battles are commonly said to have harmed the market acceptance of Unix and created a market gap that allowed the rise of Windows NT.

In the mid-1980s, the two common versions of Unix were BSD, from the University of California, Berkeley, and System V, from AT&T. Both were derived from the earlier Version 7 Unix, but had diverged considerably (this conflict was also sometimes known as the "UNIX wars"). Further, each vendor's version of Unix was different to some degree.

A group of vendors formed the X/Open standards group in 1984, with the aim of forming compatible open systems. 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 vendor Sun Microsystems started work in 1987 on a unified system. (The feasibility of this had been demonstrated a few years earlier by the US Army Ballistic Research Laboratory's System V environment for BSD Unix.) This was eventually released as System V Release 4 (SVR4).

While this decision was applauded by customers and the trade press, certain other Unix licensees feared Sun would be unduly advantaged. They formed the Open Software Foundation (OSF) in 1988. The same year, AT&T and another group of licensees responded by forming UNIX International. 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.

In March 1993 the major participants in UI and OSF formed the Common 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 to Novell, and in October Novell transferred the Unix brand to X/Open. The following year, UI and OSF merged, and the combined entity retained the OSF name.

In 1996, X/Open and the new OSF merged to form the Open Group. COSE work such as the Single UNIX Specification, the current standard for branded Unix, is now the responsibility of the Open Group. However, the damage to Unix's market reputation had been done.

Since then, occasional bursts of Unix factionalism have broken out, such as the HP/SCO "3DA" alliance in 1995, and Project Monterey in 1998, a teaming of IBM, SCO, Sequent and Intel which was followed by litigation (SCO v. IBM) between IBM and the new SCO, formerly Caldera.

• Editor war

• Unix Wars (Living Internet)
• The UNIX Wars (Bell Labs)
• The UNIX System — History and Timeline (The Open Group)
• Unix Standards (Eric S. Raymond, The Art of Unix Programming)
• Chapter 11. OSF and UNIX International (Peter H. Salus, The Daemon, the GNU and the Penguin)