IRIX is a System V based UNIX operating system developed by Silicon Graphics, Inc. (SGI) to run natively on their MIPS workstations and servers. It takes the basis of System V, adds BSD and proprietary extensions. IRIX is the operating system on which many innovations were pioneered and later ported to other operating systems, including OpenGL, the XFS filesystem, and GLX extensions.

The last major version of IRIX was IRIX 6.5, released in May 1998. New minor versions of IRIX 6.5 were released every quarter until 2005; since then there have been four further minor releases. Through version 6.5.22, there were two branches of each release: a maintenance release (identified by an m suffix to the version number) that included only fixes to the original IRIX 6.5 code, and a feature release (with an f suffix) that included improvements and enhancements. An overlay upgrade for prior versions (6.5.1-21) was made available free of charge. 6.5.23 - 6.5.30 required an active support contract with SGI, which is no longer available due to Silicon Graphics International's acquisition by HP Enterprise. Security patches and hotfixes were available through December 2013 when the last SGI support contracts expired.


The IRIX name was first used around the time of release 3.0 of the operating system for SGI's IRIS 4D series of workstations and servers, in 1988. Previous releases were identified only by the release number prefixed by "4D1-", e.g. "4D1-2.2". The 4D1- prefix continued to be used in official documentation to prefix IRIX release numbers.

IRIX 3.x is based on UNIX System V Release 3 with 4.3BSD enhancements, and incorporated the 4Sight windowing system, based on NeWS and IRIS GL. SGI's own Extent File System (EFS) replaced the System V filesystem.

IRIX 4.0, released in 1991, replaces 4Sight with the X Window System (X11R4), the 4Dwm window manager providing a similar look and feel to 4Sight.

IRIX 5.0, released in 1993, incorporated certain features of UNIX System V Release 4, including Executable and Linkable Format executables.

In 1994, IRIX 6.0 added support for the 64-bit MIPS R8000 processor, but was otherwise similar to IRIX 5.2. Later 6.x releases supported other members of the MIPS processor family in 64-bit mode. IRIX 6.3 was released for the SGI O2 workstation only. IRIX development stabilized with IRIX 6.5, released in 1998. The last version of IRIX was 6.5.30, released in August 2006.

Since around 2001 SGI had been moving its efforts to Linux and Microsoft Windows but MIPS/IRIX customers had forced it to continue to support that platform through 2006. On September 6 of that year, an SGI press release heralded the end of the MIPS/IRIX product line. Production ended on December 29, 2006, with last deliveries in March 2007, except by special arrangement. Support for these products ended in December 2013 and they will receive no further updates.


IRIX 6.5.x is compliant with UNIX System V Release 4, UNIX 95 and POSIX (including 1e/2c draft 15 Access Control Lists and Capabilities).

IRIX has strong support for real-time disk and graphics I/O. IRIX was among the first widely available UNIX version to feature a graphical user interface for the main desktop environment. IRIX continues to serve niche roles in some media production houses and scientific modeling, long after other competitors have surpassed its capabilities.

IRIX was a leader in Symmetric Multiprocessing, scalable from 1 to greater than 1024 processors with a single system image made possible by its use of Cray/NUMALinking, acquired from SGI's purchase of Cray.

IRIX used the IRIX Interactive Desktop, which by default used the 4Dwm X window manager with a custom look based on the Motif Window Manager. Performance Co-Pilot is another product made famous by IRIX.

The Open64 compiler began life as the MIPSPro compiler, the primary compiler for SGI IRIX.

IRIX was the first operating system to implement system wide OpenGL for desktop applications, games, and rendering applications such as Alias Power Animator.