IRIX is a computer operating system developed by Silicon Graphics, Inc. (SGI) to run natively on their 32- and 64-bit MIPS architecture workstations and servers. It is based on UNIX System V with BSD extensions. IRIX is the origin of the XFS file system.
The current major version of IRIX is IRIX 6.5 which was 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 from 6.5.x to the 6.5.22 maintenance release is available as a free download, whereas versions 6.5.23 and higher require an active Silicon Graphics support contract, despite only running on Silicon Graphics hardware.
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 was 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, replaced 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 ELF-format executables. IRIX 5.3 introduced the XFS journaling file system.
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 6.4 improved multiprocessor scalability for the Octane, Origin 2000, and Onyx2 systems. The Origin 2000 and Onyx2 IRIX 6.4 was marketed as "Cellular IRIX", although it only incorporated some features from the original Cellular IRIX distributed operating system project. IRIX development stabilized with IRIX 6.5, released in 1998. The current version of IRIX is 6.5.30, released in August 2006.
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