The Unix wars were the struggles between vendors of the Unix

Unix

Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...

 computer

Computer

A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...

 operating system

Operating system

An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...

 in the late 1980s and early 1990s to set the standard for Unix thenceforth.

Origins

In the mid-1980s, the two common versions of Unix were BSD, from the University of California, Berkeley

University of California, Berkeley

The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...

, and System V

UNIX System V

Unix System V, commonly abbreviated SysV , is one of the first commercial versions of the Unix operating system. It was originally developed by American Telephone & Telegraph and first released in 1983. Four major versions of System V were released, termed Releases 1, 2, 3 and 4...

, from AT&T

AT&T

AT&T Inc. is an American multinational telecommunications corporation headquartered in Whitacre Tower, Dallas, Texas, United States. It is the largest provider of mobile telephony and fixed telephony in the United States, and is also a provider of broadband and subscription television services...

. Both were derived from the earlier Version 7 Unix

Version 7 Unix

Seventh Edition Unix, also called Version 7 Unix, Version 7 or just V7, was an important early release of the Unix operating system. V7, released in 1979, was the last Bell Laboratories release to see widespread distribution before the commercialization of Unix by AT&T in the early 1980s...

, but had diverged considerably. Further, each vendor's version of Unix was different to some degree.

A group of vendors formed the X/Open

X/Open

X/Open Company, Ltd. was a consortium founded by several European UNIX systems manufacturers in 1984 to identify and promote open standards in the field of information technology. More specifically, the original aim was to define a single specification for operating systems derived from UNIX, to...

 standard

Open standard

An open standard is a standard that is publicly available and has various rights to use associated with it, and may also have various properties of how it was designed . There is no single definition and interpretations vary with usage....

s group in 1984, with the aim of forming compatible open system

Open system (computing)

Open systems are computer systems that provide some combination of interoperability, portability, and open software standards. The term was popularized in the early 1980s, mainly to describe systems based on Unix,...

s. 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

Sun Microsystems

Sun Microsystems, Inc. was a company that sold :computers, computer components, :computer software, and :information technology services. Sun was founded on February 24, 1982...

 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

Ballistic Research Laboratory

The Ballistic Research Laboratory at Aberdeen Proving Ground, Maryland was the center for the United States Army's research efforts in ballistics and vulnerability/lethality analysis....

'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

Open Software Foundation

The Open Software Foundation was a not-for-profit organization founded in 1988 under the U.S. National Cooperative Research Act of 1984 to create an open standard for an implementation of the UNIX operating system.-History:...

 (OSF) in 1988. The same year, AT&T and another group of licensees responded by forming UNIX International

Unix International

Unix International or UI was an association created in 1988 to promote open standards, especially the Unix operating system. Its most notable members were AT&T and Sun Microsystems, and in fact the commonly accepted reason for its existence was as a counterbalance to the Open Software Foundation ,...

. 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.

The move towards open source code

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

Novell

Novell, Inc. is a multinational software and services company. It is a wholly owned subsidiary of The Attachmate Group. It specializes in network operating systems, such as Novell NetWare; systems management solutions, such as Novell ZENworks; and collaboration solutions, such as Novell Groupwise...

, and in October Novell transferred the Unix brand to X/Open.

In 1996, X/Open and the new OSF merged to form the Open Group. COSE work such as the Single UNIX Specification

Single UNIX Specification

The Single UNIX Specification is the collective name of a family of standards for computer operating systems to qualify for the name "Unix"...

, 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

Hewlett-Packard

Hewlett-Packard Company or HP is an American multinational information technology corporation headquartered in Palo Alto, California, USA that provides products, technologies, softwares, solutions and services to consumers, small- and medium-sized businesses and large enterprises, including...

/SCO "3DA

3DA

3DA was an alliance formed between The Santa Cruz Operation and Hewlett Packard in September 1995. Its purpose was to unify SCO's OpenServer product, UnixWare , and HP-UX from HP; the resulting product would then become the de facto Unix standard for both existing x86 systems and the upcoming...

" alliance in 1995, and Project Monterey

Project Monterey

Project Monterey was an attempt to build a single Unix operating system that ran across a variety of 32-bit and 64-bit platforms, as well as supporting multi-processing...

 in 1998, a teaming of IBM

IBM

International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...

, SCO, Sequent

Sequent Computer Systems

Sequent Computer Systems, or Sequent, was a computer company that designed and manufactured multiprocessing computer systems. They were among the pioneers in high-performance symmetric multiprocessing open systems, innovating in both hardware and software Sequent Computer Systems, or Sequent, was...

 and Intel

Intel Corporation

Intel Corporation is an American multinational semiconductor chip maker corporation headquartered in Santa Clara, California, United States and the world's largest semiconductor chip maker, based on revenue. It is the inventor of the x86 series of microprocessors, the processors found in most...

 which was followed by litigation (SCO v. IBM

SCO v. IBM

SCO v. IBM is a civil lawsuit in the United States District Court of Utah. The SCO Group asserted that there are legal uncertainties regarding the use of the Linux operating system due to alleged violations of IBM's Unix licenses in the development of Linux code at IBM.-Summary:On March 6, 2003,...

) between IBM and the new SCO, formerly Caldera.

The Berkeley Software Distribution

Berkeley Software Distribution

Berkeley Software Distribution is a Unix operating system derivative developed and distributed by the Computer Systems Research Group of the University of California, Berkeley, from 1977 to 1995...

 emerged as an independent Unix-like operating system, with the purging of code copyrighted by AT&T, in the period 1989-1994. During this time various open-source BSD derivatives took shape, starting with 386BSD

386BSD

386BSD, sometimes called "Jolix", was a free Unix-like operating system based on BSD, first released in 1992. It ran on PC compatible computer systems based on the Intel 80386 microprocessor...

, which was soon succeeded by FreeBSD

FreeBSD

FreeBSD is a free Unix-like operating system descended from AT&T UNIX via BSD UNIX. Although for legal reasons FreeBSD cannot be called “UNIX”, as the direct descendant of BSD UNIX , FreeBSD’s internals and system APIs are UNIX-compliant...

 and NetBSD

NetBSD

NetBSD is a freely available open source version of the Berkeley Software Distribution Unix operating system. It was the second open source BSD descendant to be formally released, after 386BSD, and continues to be actively developed. The NetBSD project is primarily focused on high quality design,...

. OpenBSD

OpenBSD

OpenBSD is a Unix-like computer operating system descended from Berkeley Software Distribution , a Unix derivative developed at the University of California, Berkeley. It was forked from NetBSD by project leader Theo de Raadt in late 1995...

 emerged in 1995 as a fork of NetBSD.

Rise of GNU and Linux

During BSD's period of legal turmoil, the nearly-complete GNU

GNU

GNU is a Unix-like computer operating system developed by the GNU project, ultimately aiming to be a "complete Unix-compatible software system"...

 operating system was made operational by the inclusion of the Linux

Linux

Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...

 kernel, and countless operating systems, lumped together under the label "GNU/Linux", emerged that were based on this combination. Linux derivatives are not compatible enough to qualify for the Unix trademark. On the other hand, BSD systems can at least claim direct ancestry to Version 7 Unix

Version 7 Unix

Seventh Edition Unix, also called Version 7 Unix, Version 7 or just V7, was an important early release of the Unix operating system. V7, released in 1979, was the last Bell Laboratories release to see widespread distribution before the commercialization of Unix by AT&T in the early 1980s...

. Or, according to Open Source advocate Eric Raymond, BSD systems can be considered "genetic Unix", if not "trademark Unix".
Mac OS X v10.5

Mac OS X v10.5

Mac OS X Leopard is the sixth major release of Mac OS X, Apple's desktop and server operating system for Macintosh computers. Leopard was released on 26 October 2007 as the successor of Tiger , and is available in two variants: a desktop version suitable for personal computers, and a...

is the first operating system with open source BSD code to be certified as fully Unix compliant.