IRIX was first released in 1988 when UNIX 3.0 was released for the IRIS series of servers and work stations. Integrating IRIX provided the first real-time 3D X Windows by integrating Open Graphics Library with the X Window System environment. IRIX supports symmetric multiprocessing (SMP) as well as 64-bit and 32-bit environments. IRIX is the first UNIX-based operating system supporting SMP. It is designed for SGI computers.

The main versions of the IRIX OS are:

1. 4D1 3.0 (1988): This is the earliest version. It was based on UNIX System V Release 3 with 4.3BSD enhancements and also included the 4Sight windowing system (based on NeWS and IRIS GL).
2. 4D1 4.0 (1991): This was another major version. 4Sight was replaced with the X Window System (X11R4), using the 4Dwm window manager and providing a similar look and feel to 4Sight windowing system.
3. IRIX 5.0 (1993): This version incorporated certain features of UNIX System V Release 4, including ELF-format executables. The XFS journaling file system was introduced in IRIX 5, after the release of the OS.
4. IRIX 6.0 (1994): This supported a 64-bit OS.
5. IRIX 6.5: This was the last major release. IRIX 6.5.30 was introduced in August 2006, after which the OS was deprecated.