First Release Date: 1988-1989
Final Release Date: August 16th, 2006
Released By: Silicon Graphics
Source Code: Never officially released, partially leaked
History:

SGI 4D1 was the followup to gl2, combining elements of that and MIPS Computer Systems risc/os. Early versions were based on System V Release 2 and 3, later versions, called IRIX, were based on Release 4.

4D1 was the official name between release 2.x and 3.x (2.x was the earliest public release). Starting with 4.x, IRIX (short for IRIS UNIX) was the official name.

IRIX was well known for its distinctive GUI using Xsgi (an X11 derivative) and its Motif-derived interface, IRIX Interactive Desktop (also called Indigo Magic Desktop).

IRIX was planned to be ported to the Merced Itanium architecture in 1997, but delays and concerns about Itanium's viability aborted the port. Ultimately, IRIX was canceled in 2006 after the release of 6.5.30

Works Cited

1. https://tech-pubs.net/wiki/index.php/4D1-3.x
2. https://tech-pubs.net/wiki/index.php/IRIX_5.3
3. https://tech-pubs.net/wiki/index.php/IRIX_6.5
4. http://sgistuff.net/software/irixhistory/index.html