ISIS, Intellec, PL/M and Intel

Most recent revision dated Nov 25 2012. (c)Copyright Herb Johnson 2012.

This document describes the earliest Intel 4-bit and 8-bit development systems and their software. There's also information about subsequent ownership of these products after Intel sold off the rights; and Web links to sites with more information and software.

  • Background
  • Before the 8080 and Multibus
  • ISIS II operating system
  • ISIS operating system
  • PL/M
  • ISIS and Multibus ownership
  • PL/M and ISIS Web links


    In the early 1970's, Intel offered a hardware development system which used the 4004 processor on a proprietary set of (non-Multibus) Intel cards to operate a paper-tape and PROM based system for software development, called the "Intellec 4"; for the 4004, and later the "Intellec 4/MOD 40" for the 4040. Details are described in a section below. There was also an 8008 version and an 8080 version, the "Intellec 8" and "Intellec 8 mod 80".

    At some point (probably 1976, see this reference), a floppy disk based OS from Intel called ISIS was available for the 8080, possibly on the Intellec 8/MOD 80 system. Versions of the ISIS OS called "ISIS-II" also ran on their subsequent Multibus-based, 8080-based "Intellec MDS" system, followed by their 8086 based systems. Intel's version of the programming language PL/M fist supported the 8008, then later the 8080 and subsequent Intel processors. It's also described in this and related Web pages. iRMX, not described here, was a later Intel real-time operating system which ran on Intel processors.

    Dr. Gary Kildall, who founded Digital Research in 1975 to promote CP/M, provided many of Intel's 8008 and 8080 software products including the PL/M compiler and cross-assemblers, which were written in FORTRAN. The earliest CP/M's were sold with an example BIOS for use with a Intel 8080 Multibus system. Intel turned down Gary Kildall's offer of what became CP/M. Further discussion of Gary Kildall and PL/M and CP/M is on my DRI Web pages and other pages linked from it.

    A copy of the Intel "Intellec 8/MOD 80 Operator's Manual",dated June 1974, refers to the "INTELLEC 8I to mean the Intellec 8 with 8080 CPU". It's likely Kildall got an 8080 upgrade to his Intellec 8 system not long after it became available; this suggests the upgrade was available by mid-1974. More information from this manual is described below.

    I have or had a substantial Multibus card and document collection. But I'd like more information on pre-Multibus Intel Intellec and MDS and other products and info, let me know if you have them.

    Before the 8080 and Multibus

    Intel's Multibus standards describes an 86-pin connector with specific signals and a secondary connector, all on a card of standard size. Multibus was designed as a general bus standard and product; it became an IEEE standard. But earlier Intel products for microprocessor development, were intended primarily to demonstrate designs, or for development only. However, they had an impact on the products developed with those tools (including CP/M); some were used to build actual products. Details about these development tools of the 1970's are difficult to find in the 21st century as they fell out of favor after the Multibus and the 8080 in the mid-1970's. Information here is from published accounts of the period, trade magazines and conference papers; and from surviving Intel manuals.

    Intel's first Intellec-branded products, introduced at least by August 1973, were cards using the 4004 or the the 8008 processor. These were followed by their 4040 and 8080 products, then the Multibus product line. By the mid-1970's, Intel was marketing only their Multibus-based systems and these older products fell into disuse.

    4004 and 4040

    The Intel MCS-4 User's Manual of Feb 1973, refers to a number of Intel 4004 development products. The SIM4-01 was a complete 4004 chip set with RAM and ROM, and a 72-pin edge connector. The SIM4-02 prototype board had similar features but more RAM and ROM, and two 86-pin connectors. The signals at these edge connectors are simply ROM, RAM and teletype signals, not a "bus". The MCS-4 PROM programming system product, uses a SIM4-01 or -02 and a programmer board (MP7-03) to program 1702 PROMs, as controlled by a Teletype and a ROMmed program. Other Intel products included the MBC4-10 and MBC4-20 interface and control modules. INtel ends the book with examples of how the 4004 or the SIM4 boards were part of non-Intel products such as point-of-sale terminals, data communications, control and business.

    I have an Intel 4040 processor reference book from 1974, which discusses the Intellec 4/40. The 4/40 was used without a disk operating system for development of 4004 and 4040 products. Software was loaded and saved via front panel, punched paper tape, or by ROM; a PROM programmer was one of the peripherals or "modules" available. The 4040-based "Intellec" is described (page 13-8 following) as the "Intellec 4/MOD 40 Microcomputer Development System" and is photographed as a box badged with "Intellec 4/40". Several modules could be added, all connected via an unnamed "bus" not described at the signal level, but clearly not Multibus, possibly like the bus in the Intellec 8. The standard software was the "PROM resident system monitor, the RAM resident macro assembler". No disk-based products or hardware are described.

    I acquired at a hamfest in the 2000's, an Intel MCS Intellec 4/40 system; also an Intel Universal PROM Programmer or UPP.Here's a Web page about those systems.

    Photos of my Intel "Universal PROM Programmer", show the board set inside. There is a "2716 personality module" with chips from 1980, a UPP-833 or UPP-033 4040 CPU personality module, and a PROM Programmer control module. The boards have 100 pin edge connectors which look like those used with the Intellec 8 and 80 systems described below; and with intellec 4040 system boards.

    8008, 8080

    An Intel ad in August 1973 IEEE Computer "introduces two modular microcomputer development systems called Intellec 4 and Intellec 8", to design "MCS-4 and MCS-8 OEM systems", that being the names of Intel's chip sets for the 4004 and 8008 processors. "These microcomputer sets were first introduced by Intel in November, 1971". (By context "microcomputer" refers to the chip sets, not the Intellec systems.) The Intellec systems were ROM and paper tape based hardware platforms, using code developed on the minicomputers and mainframes of the time. "A standard software package is also included with each Intellec system and a new high level language has been introduced for the Intellec 8". Presumably that's Kildall's PL/M. The ad refers to a systems introduction "at the National Computer Conference and [they] will be available in October." Prices were between $2200 and $2400 per system.

    Intel offered a simple 8008 development system in 1972, using a 8008 processor and memory board called "SIM8-01" inserted into a motherboard (possibly called "MP7-02") with lights, switches and a power supply. A 4004 model was also available. I will write more about this system at a later time. My references include discussions of the development of the MCM-70 computer in 1971-72, using this development system, as described by the York University Computer Museum MCM-70 collection. A nice view of a SIM-08 card is at this link.

    A copy of the Intel "Intellec 8/MOD 80 Operator's Manual", 98003-A, dated June 1974, refers to the "INTELLEC 8I to mean the Intellec 8 with 8080 CPU". The Operator's Manual describes a paper-tape based assembly development environment, with text editor, assembler, and ROM-based monitor. Some of the I/O features of the monitor are similar to I/O features of CP/M's BIOS. There's a description of the 100 pins of the Intellec system card set - this is NOT named as "the Intellec bus", merely "a bus", "the bus", "CPU bus", etc.


    In Dr. Dobb's Journal #21, there was an article "ISIS: Anatomy of a Real-World Operating System", written by Perry Hutchison of Iowa State University. Recieved Dec 23 1977 by DDJ, his article discusses ISIS internals based on his analysis of ISIS "written entirely in PL/M" and as run on an Intel Intellec MDS system. He examined "object code of version 1.2 of 32K ISIS, received Aug 1976 [with] V1.1 of ASM80, V1.3 of EDIT, V1.1 of UPM, and 2.0 of ICE80." He mentions the "MDS-DOS Hardware Reference Manual", that the floppy controller uses ports 78H-7FH. He references an article in Kilobaud Dec 1977 about ISIS "but not by name" by David Yulke. (Thanks to Udo Munk for archiving this article with his collection of ISIS documents.)

    A typical document of the era for more information is: "Automatic design of multiprocessor microprocessor systems" by Hoo-min D. Doon of MIT; pages 6-14, Annual ACM IEEE Design Automation Conference, published 1977 in the "Proceedings of the Symposium on Design Automation and Microprocessors".

    A paper I've not reviewed yet is: "Intel SIM8-01: A Proto-PC ", Zbigniew Stachniak York University, Canada; from the "IEEE Annals of the History of Computing", Volume 29, Issue 1 (January 2007), pages 34-48

    ISIS II operating system

    Most of the quotes below are from the "Intel Data Catalog 1977", and most of those quotes are from Ch 13, "Intellec Development Systems":

    (page 13-29 to 31, quoting) Title: Software - Intel Systems Implementation Supervisor (ISIS-II)

    The ISIS-II operating system resides on the system diskette and supports a broad range of user-oriented design aid software. Total file management and input editing features greatly reduce software development time. the ISIS-II Relocating Macro Assembler, Linker, Object Locator and Library Manager can be loaded from the diskette in seconds. All passes of the assembler can be executeed without the need for user intervention. Object code and listing may be directed to any output device, or stored as diskette files.

    Powerful system console commands are provided in an easy-to-use English context. Monitor mode can be entered by a special prefix to any system command or program call.

    A file is a user-defined collection of information of variable length. ISIS-II also treats each of the standard Intellec system peripherals as files through preassignment of unique file names to each device. In this manner data can be copied from one device to another (i.e. tape reader to tape punch) using the same command required to copy one diskette data file to another. ISIS-II provides automatic implementation of random access files. Each file is identified by a user-chosen name unique on its diskette. Up to 200 files may be stored on each 1/4 million byte diskette."

    ATTRIB	Assigns spedified attributes to a file such as write protect.
    COPY	creates copies of existing diskette files or transfers files from one device to another.
    DELETE	Removes a file from the diskette, thererby freeing space for allocation of other files.
    DIR	Listes name,s ize and attributes of files from a specified diskette directory
    RENAME	Allows diskette files to be crenamed.
    FORMAT	Initializes a diskette and allows creation of additional system or data diskettes.
    DEBUG	Loads a specified program from a diskette into memory and then transfers control
    	to the Intellec monitor for execution and/or debugging
    SUBMIT	Provides the capability to execute a series of ISIS-II commands which have
    	been previously written to a diskette file.

    The ATRIB, DELETE, and DIR commands have the additional capability of operating on several files at once via the wildcard file-naming convention. As an example, the command "DELETE *.OBJ" deletes all files in the diskette directory with the suffix ".obj"..

    --end quotes--

    Programs described in the "Intel Data Catalog 1977" include the 8080 Macro Assembler, Linker, Object locator, PL/M-80 "resident compiler", Text Editor, Library Manager. Also there's a reference to the ICE-80, an in-circuit emulator which includes hardware to plug into the 8080 processor socket of a target system.

    ISIS operating system

    Required hardware for ISIS-II is referenced as an "Intellec Microcomputer Development System, 32K bytes RAM memory, System console, Single Floppy Disk drive". Required hardware for ISIS-I (the only mention of this product in this manual) is an "Intellec Microcomputer Development System, 16K bytes RAM memory, System console, Single Floppy Disk drive." Media is the soft-sectored 8-inch SSSD diskette. The floppy controller hardware in the Intellec system was a two-card FDC channel board and FDC interface board, referred to collectively as the SBC 201 Diskette Controller; these are Multibus cards. A photo of the interface card shows it with a (c) 1975 copyright. (It's not clear that the Intel non-Multibus system had a floppy controller card set: I simply don't know for sure - Herb Johnson).

    The 8080-based "Intellec" is described as the "Intellec Microcomputer Development System" and is photographed as a box badged with "Intellec MDS", and contains Multibus cards. The "2K 8080 Intellec system monitor" provided means to load or save paper tape programs and files for assembly & text editing. The 8080 assembler is identified as "written in PL/M". Floppy disks, disk controllers and disk-based operations are not discussed in the text, but a diskette drive was described graphically as an "option".


    PL/M-80 is described in a subsequent section (pages 13-33) as an "Intellec Resident Compiler" which "has been substantially enhanced since its introduction in 1973". (That refers to the 8008 version noted in a 1973 Itel ad above.) Another section describes it as a FORTRAN-based cross complier running on minicomputers and mainframes. Intel's early product development tools ran either as cross-products or as paper-tape or ROM-based native products, until both the 8080 and a floppy disk subsystem were developed.

    In a 1975 article written by Kildall, "Microcomputer software design - a checklist" (National Computer Conference 1975, published in conference proceedings), Kildall describes "Intel's language, called PL/M, has been available since mid-1973 through a cross compiler, while National's product, called PL/M+, will be available in mid-1975 ...[and] is designed for the IMP-16 and PACE microcomputers." The article describes PL/M as producing code for the 8008 and 8080 processor. Kildall developed the Intel PL/M product; it's not clear if he developed the National product. A number of other companies provided PL/I-like cross-compilers. Later, Digital Research provided a PL/I subset G native compiler for CP/M-86.

    Another paper is "Systems Languages: Management's Key to Controlled Software Evolution" by Gary Kildall. Proceedings of the 1974 Western Electronics Show and Convention (WESCON), September 1974 ("1974 WESCON Technical Papers", Volume 18, Session 19/2). In this paper, Kildall discusses how PL/M is an example of a high-level language for microprocessor development. He writes: "Several versions of Intel's PL/M compiler have been released since its first introduction in June of 1973" (Ver 1) for the 8008; another 8008 version (Ver 3) in Feb 1974, and the first 8080 version in March 1974. A text version of the article is at this Web link.

    I have much more to say about PL/M, and these and other references, in my Web page on the history of Gary Kildall and Digital Research..

    ISIS, iRMX and Multibus ownership

    This section describes the origins and history of ownership of Intel's Multibus line and software. In brief, Intel developed the Multibus, an 86-pin bus with a secondary bus connector, in the mid-1970's. In 1999 Intel sold its Multibus I rights to Radisys: see these SEC document extracts for some business details.

    Check my Digital Research Web page for some discussion of PL/M and ISIS. As of early 2009, I do not know who "owns" ISIS from Intel. But a document on the Hitex Ltd. Web site suggests that Intel "jettisoned" and "stop support" of MDS in 1993. Discussion of Multibus and iRMX is below.

    The subsequent owners of Intel Multibus rights and materials was InBus Engineering: as of 2005 the Inbus site said they are "the world's largest supplier of retired Intel Motherboards and systems". But by Dec 2005 US Technologies had this Web page statement, a letter from Radisys dated about 2002:

    "UST is the exclusive authorized and licensed source for Intel/RadiSys Multibus I and II printed circuit boards in the world. Only UST has the original Multibus I and II test software, test fixtures and engineering updates insuring you the highest quality OEM Multibus product. RadiSys has recently sold their entire Multibus business to UST. We are the world's #1 source for long-term support, including repair, upgrade, and refurbishment services for all Multibus products previously manufactured by Intel or RadiSys."

    Other companies also offer iRMX services or related products. Tenasys (described below) provides versions of iRMX. Links to these and other Multibus or iRMX vendors are listed below.

    In 2009 I contacted NorthWest Technical and got these comments on Intel property history; "We have been supporting the Intel Multibus platform since the 1980's and in 1989, Northwest Technical was formed. We sell and repair Multibus boards and systems. See our current website for details. Our new website will be going online very shortly. U.S. Technologies did purchase most of the assets and IP from Radisys Corp., who had previously purchased the same from Intel Corp. We consulted for UST before their purchase and still sell and repair boards for them. They mostly do small builds of Multibus I boards for existing customers who still need them." My NT contact says they continue to buy Multibus inventories, intellectual property (for example the Zendex Corporation).

    Profimatics GmbH is apparently a company in Germany which offers some iRMX support. Their site has some iRMX manuals in PDF format, as of Dec 2003.

    Tenasys is another company which offers iRMX type operating systems. They say they were founded by former Intel iRMX developers. As of at least 2008, they offer a version of iRMX 2.3, and an iRMX for Windows product, with support and current development. Check their site for details.

    Hitex Ltd. is/was a UK company which offers software development tools. They have a long history of 8080 based tools and provide some support for use of old Intel tools. On their Web site, I found this document (no longer available there) which discusses the history of use of ISIS, MDS systems and so forth particularly in military applications support. The document says: "Ultimately, the death nell for all the old Intel MDS was Intelís 1993 decision to jettison its tools arm and stop support for all the old systems." They add "Hitex was one of the leading pioneers of PC-hosted development tools for Intel microprocessors in the early 1980s. Unlike other independent tool manufacturers of the time, Hitex developed PC/MS-DOS interfaces to Intel MDSs and their operating systems. These are still available from Hitex to help in the maintenance of older projects." Hitex's support seems to be through emulators, simulators, and similar tools on MS-DOS based systems which can run the older products. (However, as of 2009 Hitex Ltd. appears to be part of Hitex.)

    Web links

    ...on this Web site

    Check my Digital Research Web page for some discussion of PL/M and ISIS.

    Here on my Web site we have some Intel and Multibus information, docs and boards. Also I have some Intel-related links in my Web page of S-100 and CP/M Web links. Parts of this document were moved from those pages in 2006-2007.

    At one time I had a substantial number of Intel ISIS diskettes. These were sold in 2006, and in 2010 the diskettes were "imaged" and put on a Web archive. See notes below for specifics. Some discussion of that collection, and how the diskettes were imaged, is on this Web page about diskette recording methods. Another discussion about the collection itself, may be on this Web page of my site.

    I have a a Web page about my restoration of an Intel System 320 running Xenix.

    Another fellow, Bill Beech, found that page and discussed with mehis Intel and ISIS work in 2009 and following years. There are links to his site's resources on that page.

    ...on other Web sites

    The "" archive Web site has a section for Intel MDS disk images. also has documents for the MCS-8, and some MCS-4 docs. There are mirror sites for that archive site, the home page will list them.

    ISIS has been discussed among the CP/M supporters of Usenet newsgroup comp.os.cpm. Here's the text of a 2009 discussion which helped to update this Web page.

    There is a Yahoo group for iRMX called "irmxstuff" which is active as of 2009. They have a number of members who offer assistance for both legacy iRMX systems, and those migrating from them; and current users of iRMX and INtime products. There seems to be a mix of commercial and personal-use members.

    An odd source of iRMX manuals (as of Oct 2006) is from Stanford University's support site for SLAC. They have an online list of PDF's to support their use of an iRMX system. A PL/M 386 manual is among them.

    The Classic Cmp Web site in Oct 2006 has a page by Joe Rigdon from about 2000 to 2003 which describes one Intel MDS product and lists some manuals. Unfortunately it's hard to navigate this site to see the other MDS systems he describes; search his home page for "intel" to find other MDS sections.

    The Unofficial CP/M Web site has some PL/M compiler sources in Fortran. Look around the page and site, for example the ISIS emulator at under the "PLM compiler" as "".

    In 2006-07, Udo Munk announced his updates to his Z80pack CP/M emulator for UNIX systems. This includes a number of collected CP/M OS sources, and also an MS-DOS version of an ISIS emulator to run the Intel PL/M native compiler. See my S-100 Web pointers page for more discussion of Udo Munk's work.

    Jan 2011, as announced in comp.os.cpm: I've now written an emulator which emulates enough of ISIS to run [PL/M ISIS] tools under Unix. I've also made an updated with Unix-y build scripts rather than DOS batch files, which may find its way to in due time." - John Elliott

    There's also a note on comp.os.cpm for Jan 2011, referencing a Web page about original CP/M based ISIS emulator called ISX, on the "Sourceforge" source code site for the P112 computer. The Web page by "Hector Peraza?", describes the disassembled ISX emulator, and discussion about how to run it under CP/M 3.0 (?). The page was last updated in 2007. The P112 is a Z180 computer offered in the 1990's and again over a decade later.

    Matthiew Benoit has a page on the Intel iPDS and ISIS and PL/M, with documents and files and links.

    Hitex, an embedded tools developer has a page which discusses old 8086 development tools including Intel's.

    The 2006 Wikipedia entry for PL/M has some interesting information and Web links. It will change of course over time.

    An old INFO-CPM thread, "Wanted: PL/M-80 compiler" from 1989 included a post from a Mark Alexander, possibly at Apple at the time. Says he wrote an ISIS emulator for MS-DOS and he offered sources. Reference was also made to an emulator by "RTCS Corp". The thread includes unhappy comments about some PL/M products at that time.

    On the Web site in 2009, there's a Web page on Intel MDS systems from "joe" in 2000: probably a copy from another Web site.

    Not referenced here is an article by Stan Mazor, co-creator of early Intel CPU's. "The History of the Microcomputer - Invention and Evolution", by Stanley Mazor, in the "PROCEEDINGS OF THE IEEE" VOL. 83, NO. 12, PP. 1600-1608, DECEMBER 1995. A copy of the article is here, with illustrations.

    Contact information:

    Herb Johnson
    New Jersey, USA
    To email @ me, see see my ordering Web page.

    Copyright © 2012 Herb Johnson