History of IRIX

by Ryan Thoryk
email: ryan at thoryk.com

Updated October 7, 2020

A good portion of version numbers came from this Usenet thread

An emulation of an Indy running IRIX can be found here

IRIX 6.x
IRIX 5.x
IRIX 4.x
IRIX 3.x
IRIS 4D1 Unix 2.x and 1.x (IRIX 2.x and 1.x)
IRIS GL2 Unix (IRIX 0.x)

Information on the move from 68k to MIPS
IRIX name
Misc stuff (IRIS name, IP name and numbering, etc)

Version tables

6.5.30 - 08/16/06
6.5.29 - 02/08/06
6.5.28 - 08/03/05
6.5.27 - 02/02/05
6.5.26 - 11/03/04
6.5.25 - 08/04/04
6.5.24 - 05/05/04
6.5.23 - 02/04/04
6.5.22 - 11/05/03
6.5.21 - 08/06/03
6.5.20 - 05/07/03
6.5.19 - 02/05/03
6.5.18 - 11/08/02
6.5.17 - 08/07/02
6.5.16 - 05/08/02
6.5.15 - 02/06/02
6.5.14 - 11/07/01
6.5.13 - 08/08/01
6.5.12 - 05/09/01
6.5.11 - 02/07/01
6.5.10 - 11/08/00
6.5.9 - 08/09/00
6.5.8 - 05/09/00
6.5.7 - 02/10/00
6.5.6 - 11/03/99
6.5.5 - 08/06/99
6.5.4 - 05/11/99
6.5.3 - 02/09/99
6.5.2 - 11/17/98
6.5.1 - 08/24/98
6.5 - 06/98
6.4 - 11/96
6.3 - 09/96
6.2 - 03/96
6.1 - 07/95
6.0.1 XFS - 03/95
6.0.1 - 12/94
6.0 - 8/94

6.2 to current: X11R6, 4DWM window manager, Indigo Magic desktop (renamed to IRIS Interactive Desktop possibly in version 6.5)
6.0-6.1: X11R5 (source)
6.5 Screenshot

5.3 TIRIX - 06/95 (Trusted IRIX 5.3)
5.3 XFS - 12/94
5.3 - 11/94
5.2 - 03/94
5.1.1 - 09/93
5.1 - 9/93
5.0.1 - 06/93
5.0 - 3/93

GUI: X11R5, 4DWM window manager, Indigo Magic desktop environment
5.3 Screenshot

Versions are abbreviated with "4D1-" representing the 4D line of machines
4.0.5MM (Multimedia release)
4.0.5IOP - 04/93
4.0.5H A360 MCO
4.0.5H A360
4.0.5H - 03/93
4.0.5 EPL
4.0.5A (really revision B)
4.0.4T (second Trusted IRIX)
4.0.4 - 03/92
4.0.3 - 03/92
4.0.2 - 03/92
4.0.1T (first Trusted IRIX)
4.0.1 - 11/91
4.0 - 09/91 (first version that used X11)

GUI: X11R4, 4DWM window manager, and IRIS Workspace desktop environment
4.0.1 Screenshot

Announcement of IRIX 4:
"IRIS Indigo runs IRIX(tm) 4.0, Silicon Graphics' enhanced version of
the UNIX(R) operating system. IRIX is POSIX, X/Open(tm) XPG3 and FIPS
151-1 compliant. In IRIX 4.0, the X Window System(tm) (X11/R4) is
merged with the IRIS GL interface and Adobe's Display PostScript(r)
for flexible rendering."

Info on 4.0 shipping with the IRIS Indigo
"Irix 4.0 is based on Unix System V Release 3 with Berkeley enhancements" (the BSD enhancements were from BSD 4.3, like 3.x)

Versions are abbreviated with "4D1-" representing the 4D line of machines
3.3.2 - 12/13/90
3.3.1 - 09/04/90?
3.3 - 06/29/90?
3.2 - mid 1989
3.1G - 08/04/89
3.1F - 06/05/89
3.1D - 02/27/1989
3.1 - 04/07/89
3.0 (first regularly noted MIPS version) 10/6/88

GUI: Sun NeWS with SGI 4Sight
3.3 Screenshot

The Personal IRIS: A Technical Report (info on the first 4D workstations, 4Sight and IRIX 3.0

Excerpt from above link on IRIX 3:
"IRIS-4D Series Superworkstations include an enhanced version of the UNIX V.3 operating system called IRIX. IRIX incorporates many features of the Berkeley 4.3 BSD UNIX release, plus many local system enhancements to support real-time graphics. This extended software environment permits easier connectivity and improved system throughput. Other operating system enhancements include the Extent File System (EFS), a unique UNIX file structure handler that improves file handling performance two-fold over the standard System V file architecture. EFS is modified so it writes files in large extents to the disk. By writing disk files in this way, EFS improves disk seek times, which results in improved overall system performance."

2.x and 1.x
This was an early and short-lived line for MIPS (possibly of beta quality), and was not referred to as "IRIX" until later, with the 3.0 release.
1.x might have been an internal-only testing release.
Originally SVR3 with BSD 4.2 and SGI Extensions
Versions are also abbreviated with "4D1-" representing the 4D line of machines, like 3.x
The Typewritten site has a copy of 2.0, and the master tape is labeled "4D1-2.0 Standard System Tape 1 11/18/87".
In some of the software, there are references to 1.x releases.
4D1-2.2 - mentioned here
4D1-2.0 - August 1987
4D1-1.0 - late 1986 or early 1987

GUI: MEX (the MEX article on Wikipedia says that MEX was dropped after the 4D1-2.3 release, for 3.0)

0.x / IRIS GL2 Unix

The series for the Motorola 68000 line of processors was an earlier version (the later MIPS line appears to be simply a port of this code, maintained separately) and was provided by UniSoft. Basically this was UniSoft UniPlus System V with SGI customizations. References to it refer to it as either IRIS UNIX or SGI UNIX. I've referred to it as IRIS GL2 Unix, but it can also be referred to as the IRIX 0.x series (since IRIX really just means IRIS Unix - the MIPS versions could just as well be referred to as IRIS 4D1 Unix). There was a separate versioning sceme reflecting a models/features mix. It was used on the SGI 1000, 2000 and 3000 lines of workstations and terminals. Some of the 1000's were diskless terminals and thus had no OS. These systems used the MEX (short for Multiple EXposure) windowing system for graphics. This PDF has some info and pics of a graphics app being used on MEX.
The 1.5 kernel was called (in the following documents) "Silicon Graphics System V". This is because many vendors simply adopted a standard Unix for their systems, but didn't offically give their adaptation/fork a name until later on. See below for more info on this (section on the Unix trademark).

Some info here (IRIS FAQ)

Versioning sceme is this:
(GL version)-(W/T)(2/3).(OS release number)

GL refers to the IRIS Graphics Library (both hardware and software) and was either GL1 or GL2. GL is the proprietary precursor to OpenGL.
T means Terminal (shown in this document) and W means Workstation.
The "2" refers to machines with 68010 processors (the 2000 series), while "3" refers to ones with 68020's (the 3000 series; more info below). It appears that these were both maintained as separate streams, for example 2.5 and 3.5 would've been released simultaneously.

Full name release history (known versions):
GL2-W3.7 (unreleased)
GL2-W3.6 - 1987
GL2-W3.5 - December 1986
GL2-W2.4 - March 1986

"W2" and "T2" (68010) run on the IRIS 1400, 1500, 2000, 2200, 2300, 2400, 2500 machines
"W3" and "T3" (68020) run on the IRIS 2300T, 2400T, 2500T, 3010, 3020, 3030, 3110, 3115, 3120, 3130 machines

The GL2-W3.4 software release notes says that the GL2-W3.x series is for "IRIS series 3000 workstations and IRIS series 2000 workstations with the Turbo Option upgrade."

If you cut off the "GL2-W3." off the top one (the W3.6), it would be "6", meaning IRIS Unix Release 6, or IRIX 0.6. System references refer to this version as "IRIS 3.6 release"

So the versions would be:
0.7 (seen on the Typewritten site)
0.6 - 1987
0.5 - December 1986
0.4 - March 1986
0.3.1 (earliest release seen mentioned so far online)
0.1.5 - mid 1984
0.1 - 1983

This workstation guide has early kernel version information:
Kernel number: System 5 UNIX #135 [Fri May 4 11:15:09 PST 1984]
Release: Beta-1.5
(C) Copyright 1983 - UniSoft Corporation
(C) Copyright 1983 - Silicon Graphics Inc.

This kernel would refer to IRIS Unix 1.5 (or IRIX 0.1.5).

From this page:
"Since its inception in 1982, SGI and its customers have relied on the power and stability of IRIX to conduct their critical businesses."

This quote isn't all that true, since the first machines were simply terminals with no OS.

IRIS Unix was based on UniSoft Uniplus System V Unix (UniSoft ported various versions of Unix to 68k for a number of companies), and later on included BSD 4.2 enhancements (don't know about pre-4.2 though). According to GL2-W3.5 Workstation release notes, the BSD 4.3 TCP/IP subsystem was merged into that release (release 5). For comparison, Sun Microsystems' SunOS originated from Uniplus Version 7, and that version is commonly referred to as SunOS 0.x.

Quote on the history of IRIX from a Usenet post:
"...with System Software 1.6 and 1.7(beta) installed. (ironically, in light of the name of this thread, this was way before anyone ever thought of rewriting/rebranding the OS as IRIX - the 'System Software' was still the original 'System V with BSD enhancements' UNIX as provided originally for SGI by UniSoft. IRIX came slightly after the transition to the MIPS architecture with the introduction of the 4D/60)."

This document, which is a GL2 to 4D1 porting guide, says this: "this port involved both moving from software release IRIS3.6 to 4D3.0, and moving from 2000/3000 graphics to 4D graphics."

Now why was it rebranded as IRIX? The reason's obvious, and is the same reason why suddenly there was a Unix rebranding going on in the whole industry: From here:
"On May 6, 1986, AT&T;'s UNIX trademark was placed on the Principal Register of the United States Patent and Trademark Office for computer programs, under Registration No. 1,392,203."

This was right during the MIPS transition. Before the Unix name was registered as a trademark, most companies that forked off their own Unix simply kept the name intact, since it was still Unix. But afterwards, the Unix name could no longer be used, and companies had to come up with their own names.

In the GL2-W2.4 release notes, it says that the GL2-W2.4 release introduced the Extent File System (EFS), which was later superceded by XFS.

In the GL2-W3.5 release notes (as noted earlier), it says that a BSD TCP/IP implementation was introduced in that release, replacing an earlier Excelan-based implementation from GL2-W2.4 and 3.4.

The MEX Wikipedia article says that the MEX window manager was introduced in GL2-W2.1.

The Pipeline Spring 1986 article says that the IRIS 3000 series was introduced in February 1986, and possibly came with the GL2-W3.3 software.


Information on moving from the Motorola 68k architecture to the MIPS platform from MIPS Computer Systems.

MIPS was a company founded by John L. Hennessy, the lead of the Stanford MIPS project, and was made to continue development of the architecture in the commercial area. Later they also manufactured their own computer systems with MIPS cpus (along with reference boards for development), although they (as an independent company) struggled financially due to a very vicious market at the time, but were fortunately bought by SGI in 1992. They had their own proprietary Unix for their systems known generally as RISC/os (no relation to Acorn RiscOS), which is sometimes referred to as MIPS OS, and the internal name is UMIPS (this shows up when using the uname command). I have a copy of RISC/os 4.52 (but no machine or emulator to run it on) and in many header files the OS itself is called UMIPS (which was possibly the original name of the OS, and probably meant Unix/MIPS). SGI's early MIPS systems were based on MIPS reference boards (see the end of this document for more info), and others have mentioned that IRIX was derived from some of the MIPS RISC/os code.

MIPS Computer Systems was purchased by SGI in 1992, became a wholly owned subsidiary of SGI known as MIPS Technologies (their subdomain was mti.sgi.com) and eventually was spun-off in 1998.


There's an article that says this:
"During 1Q86, we were bringing up UNIX on MIPS chips." (John Mashey of MIPS, referring to their own Unix)

It seems that the entire RISC/os was not actually merged with IRIX (this is because SGI didn't own MIPS until later on), but was probably used as code foundation in order to quickly port IRIX over to MIPS (and so I'm guessing that there should be fragments of RISC/os code in IRIX that MIPS provided). After the MIPS acquisition in 1992, SGI continued some support for RISC/os (since they now owned it), but phased it out; around this time they could have incorporated portions of that OS into IRIX.

This is interesting:
"The RISCos driver source was supplied with every system, and we did donate the source to Berkeley."

RISC/os seems to have been started around 1985, and the last line of it seems to have been 5.0x - sources here here here and here

Some roots of RISC/os:
"MIPS computers running RISC-OS can support four different personalities: default, BSD 4.3, System V.3, and System V.4 (older versions of RISC-OS don't support V.4)."

This page (section on MIPS) shows that MIPS developed systems until around mid 1992, due to financial troubles, and then after the merge with SGI they focused entirely on processor development.

Here is a very informative paper from November 1993 by a man who worked for MIPS during the buyout (which it says was July 1992, and describes the whole merger process)

Sidenote - I'm currently putting information together to make a history of RISC/os. This information is very scarce, but there should be great deals of information in old magazines at libraries. I found some pictures of a very old version of IRIX (either 3 or 4) in one, and once I find it again, I'll scan it - I think it was in a copy of Unix Magazine from the early 90's.

IRIX name

The name IRIX is a portmanteau of IRIS UNIX, or "IRIs uniX". So far it seems that the operating system was referred to as IRIX starting around version 3.0. I'm looking for earlier references. In the comp.sys.sgi.admin usenet archives, a person claims (on 1/7/89) their system is running
"IRIX System V Release 4D1-3.13809261636" - which is version 3.1
The earliest mention of IRIX in the ARL archives is dated 8/7/88 and says "Several people have asked for what I did to make ksh filename handling work under IRIX"

A quote I have above from a Usenet post states this:
"[The name] IRIX came slightly after the transition to the MIPS architecture with the introduction of the 4D/60)."

The IRIS acronym (used in the IRIS line of 68k machines, other machines, and software) stands for Integrated Raster Imaging System (reference).

From a Usenet message in 2002:
"Now, historically, IRIX derives from the first Silicon Graphics products, which contained their graphics engine, and which were called IRIS machines, for Integrated Raster Imaging System. "IRIX" is simply a portmanteau word combining IRIS and UNIX."

Misc stuff

A quote from Jim Clark in a Usenet message in 1999 on the meaning of "IRIS":
"IRIS was a name chosen at random when I was submitting the final copy of the Geometry Engine paper to SIGGRAPH in late 1981. The final draft contains an interesting "keyword", as you'll see by looking at the image file created by scanning it in (paper.rgb).
"Marcia Allen (who was the secretary shared by me, Forest [Baskett] and John Hennessey) had a picture of an Iris on her bulletin board. I was reviewing the draft when I discovered that SUN Microsystem's had been formed. SUN had alway's meant Stanford University Network, and "SUN Terminal" was sprinkled throughout my paper. I said I'd be damned if I was going to give the impression that the Geometry Engine was part of SUN Microsystems, so I had to quickly come up with a new name, since the paper had to be sent in that day. Whimsical "Apple" worked, so why wouldn't 'Iris'."

The "IP" name designation to systems means "Inhouse Processor". Reference and another one
The "PM" designation (before IP) possibly means "Processor Module"; this page says "PM1 - based on a design licensed from Andy Bechtolsheim, Stanford (before SUN)."

On IP numbering:

"IP1 never officially existed. If anything, it was a relabelling of the PM2 board as used in the IRIS 1400, 1500, 2000, 2200, 2300, 2400 and 2500. The first actually used IP series board was the IP2 as used in the 2300T, 2400T, 2500T and 3000 series machines. The main distinction between the PM and IP boards were that the PM were based on reference boards developed at Stanford University whereas the IP boards were (and still are, i hope ;) developed in house by SGI themselves (although often based on reference boards from MIPS - explicitly the case for the original IP4 boards used in the 4D/50; the first of the MIPS machines).
"Or perhaps the IP1 was a prototype of the "Turbo" 68020-based motherboard that eventually became the IP2.
"The antics of the IP numbering system are quite interesting, though - I've got a Personal Iris 4D/20 which is labelled up as a IP6.5 - and appears to be an IP12 complete with R3000@20MHz - but underclocked to 12MHz to render it functionally equivalent to a IP6. Dave Olson states in the past that at the end-of-life of the 4D/20 SGI ended up underclocking (possibly slightly defective) 4D/25s and selling them as 4D/20s - although makes no reference to changing the IP number on those boards. When I get a chance I intend to replace the crystal with a 20MHz one and see what happens."


Archive of comp.sys.sgi messages starting on April 11, 1989

Info-Iris messages from ARL start on July 15, 1986