In 1981 Dr. John L. Hennessy of Stanford University began design work on a RISC CPU. A group lead by Hennessy left Stanford in 1984 to found MIPS Computer Systems, Inc. (hereafter referred to as "MIPS"). MIPS' first workstation was the MIPS M/500.3 Introduced in October 1986,4 the MIPS M/500 featured MIPS' first RISC CPU the R20005 and ran a variant of UNIX named UMIPS (MIPS UNIX).6


UMIPS was "MIPS Computers' first operating system." UMIPS 1.0, the first release of UMIPS was "a port of Berkeley's BSD4.3 version of UNIX."7
4.3BSD was released in June of 19868 with MIPS receiving the source in July, and shipping the M/500 workstation with UMIPS 1.0 in October of the same year (1986).9
With the introduction of AT&T UNIX System V Release 3 in 198710 UMIPS became a dual-universe UNIX with the release of UMIPS 1.1 which supported universes (commands, directory trees, header files, libraries, man pages, etc.) for both BSD and System V.11
The name UMIPS was used by MIPS to refer to releases of their variant of UNIX from version 1.0 to 3.x. By the release of UMIPS 3.10, MIPS began to unofficially refer to UMIPS as RISC/os.12 This is similar to Silicon Graphics unofficially referring to its variant of UNIX as "IRIX" beginning with release 4D1-3.1D (IRIX System V Release 4D1-3.1D) in 1988, but not officially branding it IRIX until release 4D1-4.0 in 1990.


    UMIPS-BSD, also known as UMIPS/BSD refers to installs of UMIPS that are configured to provide users with a BSD environment.


    UMIPS-V, also known as UMIPS/V, UMIPS_V, or UMIPS (System V) refers to installs of UMIPS greater than UMIPS 1.0 that are configured to provide users with a System V Release 3 environment. this February 1989 Security Digest Archive thread where a user complains about poor performance from HP-UX 3.0 when compared to other Unices at his location, including "UMIPS 3.10." UMIPS 3.10C referred to as RISC/os [footnote]


RISC/os was "a derivative of UNIX System V Release 3," and "also one of the roots of IRIX"[footnote], with the other roots of IRIX presumably planted in IRIS Workstation Software Distribution, GL2-Wx.x.
"MIPS System VR3, RISC/os, and Irix" "are all ways of referring to the same basic operating system, a derivative of UNIX System V Release 3."[SeeMipsRunP452]

  • RISC/os 4.x

    RISC/os 4.x, also known as MIPS System VR3, MIPS System VR3, RISC/os, or RISC/os (UMIPS) was "a derivative of UNIX System V Release 3."
    RISC/os 4.x was distributed on one-to-two QIC-24 tapes[footnote]

  • RISC/os 5.x

    RISC/os 5.x, also known as RISC/os (UMIPS) was a derivative of AT&T UNIX System V Release 4.


  • UMIPS 1.x
    • UMIPS 1.0 (port of 4.3BSD)
    • UMIPS 1.1 (Dual universe: BSD or System V)
  • RISC/os 4.x (based on AT&T System V Release 3)
    • RISC/os 4.0
    • RISC/os 4.01
    • RISC/os 4.02
    • RISC/os 4.10
    • RISC/os 4.20
    • RISC/os 4.30
    • RISC/os 4.50 (June 1990)
    • RISC/os 4.50B
    • RISC/os 4.51 (August 1990)
    • RISC/os 4.52
    • RISC/os 4.52B
    • RISC/os 4.52B2[footnote]
    • RISC/os 4.52C
  • RISC/os 5.x based on AT&T System V Release 4
    • RISC/os 5.0 (October 28, 1991)
    • RISC/os 5.00B
    • RISC/os 5.01


EP/IX was "the CDC implementation of Unix for the Control Data 4000 series of computers."[footnote] and "an extension to/derivative of RISC/os."


ES/os was "a variant of RISC/os 4.52 with extra device drivers, a few bug fixes, etc." produced by Evans & Sutherland [footnote]


SEIUX, from Sumitomo Electric Industries was "mostly a clone of the RISC/os," "even binary compatible with RISC/os," and "should be very much like RISC/os 4." [footnote]


RISCwindows (Xmips) was the name of MIPS' implementation of the X Window System for its RISC/os. Initially RISCwindows used TWM (Tab/Tom's Window Manager)[21] Window Managers MWM (Motif Window Manager), RISCwindows 3.x including TWM (Tab/Tom's Window Manager)[21] Like RISC/os itself, RISCwindows 4.0 was distributed on a QIC tape[footnote]
  • RISCwindows 3.x
    • RISCwindows 3.00 (introduced 4th quarter of 1989 or 1st quarter or 1990)[20]
    • RISCwindows 3.10 (introduced 2nd quarter of 1990)
    • RISCwindows 3.11
    • RISCwindows 3.21[22]
  • RISCwindows 4.x
    • RISCwindows 4.00 (built with Motif 1.1.1)[footnote]
    • RISCwindows 4.10 (X11R4, built with Motif 1.1.1)[footnote]
    • RISCwindows 4.11


Beyond MIPS, several other hardware vendors produced or re-branded MIPS hardware to run RISC/os

  • Evans & Sutherland

  • MIPS Computer Systems[footnote]

    • MIPS M/500
    • MIPS M/800
    • MIPS M/1000
    • MIPS M/120 (Special thanks to Unknown)
    • MIPS M/120-3
    • MIPS M/120-5
    • MIPS M/2000
    • MIPS RS2030
    • MIPS RC2030
    • MIPS RC3240 (Special thanks to Miod Vallat)
    • MIPS RS3230
    • MIPS 'Magnum 3000' RC3230 (Special thanks to Miod Vallat)
    • MIPS RC3260
    • MIPS RC3330 (Special thanks to Walter Belgers)
    • MIPS RC3360
    • MIPS RC6260
    • MIPS RC6280
    • MIPS RC6380-100
    • MIPS RC6380-200
    • MIPS RC6380-400
    • MIPS RS4330
    • MIPS RS4340
    • MIPS RS4440
    • MIPS RC4370
    • MIPS RC4470


Since its founding in 1982 MIPS has changed ownership several times.

  • MIPS Computer Systems, Inc.

    MIPS Computer Systems, Inc. was acquired by SGI (Silicon Graphics, Inc) in 1992 and renamed MIPS Technologies, Inc.1
  • Silicon Graphics, Inc.

  • MIPS Technologies, Inc.

    On June 20, 2000 MIPS Technologies, Inc. was divested by SGI becoming its own company.
  • Imagination Technologies Group plc

    Imagination Technologies Group plc acquired MIPS Technologies, Inc. November 6, 20122
  • Tallwood MIPS, Inc.

    On September 22, 2017 Imagination Technologies Group plc was acquired by the private equity firm Canyon Bridge Capital Partners. "As part of the deal, Imagination will sell its U.S.-based embedded processor unit MIPS" to the California-based investment firm Tallwood Venture Capital to form Tallwood MIPS, Inc."1
    Later in 2017, control of MIPS was transferred to the venture capital firm Entropy Research Lab.
  • MIPS Technologies International Ltd.

    In 2018 Wave Computing, Inc. acquired MIPS from Entropy Research Lab for an undisclosed amount.


About Taygeta, Taygeta Scientific Inc.
Giga's Computer Museum
Mips RC 3230 (Magnum 3000)
NO-L.ORG: The risc/OS Repository
Richard Geiger: Resume
Toru Nishimura: MIPS and SGI relationship
XConsortium modifications for UMIPS