Origins of S-100 computers

Updated JUne 26 2011, adding info Apr 30 2021. This document copyright (c) Herbert R. Johnson 2021, with portions quoting materials which may have their own copyrights. Go to myS-100 home page for more information about the MITS Altair and other S-100 computers.


The term "S-100 bus" refers to the bus architecture of the MITS Altair 8800 computer of January 1975, and subsequent variations of bus-compatible computers of the 1970's, 80's and beyond. It often includes the IEEE-696 standard based on that bus. They all used variations of that 100-pin bus with its 5 X 11 inch circuit boards and 100-pin board connectors on a backplane. Originally known as the "Altair bus" by MITS, when several companies produced plug-compatible cards or systems, a collective decision in 1976 called the bus "S-100". In mid-1978, several manufacturers proposed an expanded version of the bus. They formed a committee of the IEEE to establish a standard called "IEEE-696", which was first published by the IEEE in July 1979. The standard was finalized in 1983; the IEEE ended support of the standard in June 1994.

By the 1980's, over 140 companies small and large had produced S-100 or IEEE-696 products , as listed on my home page of S-100 documents and resources. Many additional Web links are on that page. Contrary to popular belief, S-100 companies and their products did not crumble to dust the day after the IBM-PC was announced, or sold. Many S-100 products were developed and sold through the 1980's, especially for commercial, industrial, military and scientific customers. Information about major S-100 companies can be found by company name, via links on my S-100 home page. Interest in S-100 continues through the 21st century, as hobby groups and individuals restore old systems and design new cards.

Technical details of S-100 history are described and referenced on my technical Web page about the S-100 bus. This page provides more background and extensive references for the persons and companies which contributed to the Altair 8800 and the early S-100 and IEEE-696 busses. I'd appreciate any corrections. - Herb Johnson


Why fuss about the S-100 bus, or the Altair 8800?
Early work on the S-100 and IEEE-696 bus
Where did the name "Altair" come from?
So where did the term "S-100" come from?
Where did the MITS front panel design come from?
Ed Roberts of MITS and "S-100"
Death of Dr. Roberts in 2010
Background of this document

Why fuss about the S-100 bus, or the Altair 8800?

The original 100 pin computer bus was part of the design of the MITS Altair 8880, produced by MITS and designed by Ed Roberts, and announced to the world in the January 1975 issue of Popular Electronics. Documents for the Altair 8800 refer to the "100 pin bus" or the "Altair bus". The result of that publication and product announcement was a large interest - and lots of orders - for the Altair. That interest (among other considerations) inspired a number of other companies and individuals to produce additional computers or products for computers - many of them were compatible with the Altair's bus. By 1977, the name "S-100 bus" was established to describe that compatibility: a name not chosen or appreciated by MITS Inc., as noted in their publications of the time. Later, several S-100 manufacturers came together to establish an IEEE standard for an expanded-function S-100 bus known as IEEE-696. That standard was approved in final form late in 1982, but in preliminary form was discussed, published and produced as early as 1978.

Before discussing the details of the origins of the S-100 bus, it's useful to put that history in a larger context. The Altair was not the first microcomputer. The Altair followed personal computer kits like like the "Mark 8" kit of Jon Titus in the July 1974 issue of Radio-Electronics; and the Scelbi (SCientific, ELectronic and BIological) which appeared as an ad in the March, 1974, issue of QST magazine. Both were based on Intel's 8008 microprocessor. Meanwhile, industrial minicomputers like the PDP-8 from DEC; and the Intellec series of 4004, 4040, 8008 and 8080 based systems from Intel.

The idea of a "personal" computer was at the time a hope or a goal, or a marketing notion. Computers of 1975 were generally large and expensive, and not readily programmable. The Xerox "Alto" in retrospect was among the earliest and deliberate examples of what we call in the 21'st century "personal computing." Otherwise, small computers of the early 70's were generally special purpose, used for control or for business accounting. Software and even hardware for these systems was proprietary, expensive, and often only available from the original manufacturers. At best, only DEC and a few other minicomputer manufacturers offered any kind of "open marketplace" for products and designs at all.

For more discussion about "first personal computer" and how the MITS Altair 8800 fits into that discussion, check this Web page which has a link to an excellent Web site's page specific to the "first".

Meanwhile, the digital chips of the early 1970's were only the "nuts and bolts" of any potential computer design, which would require hundreds or thousands of chips. The middle 1970's was a time when Intel provided the 8008 and later 8080 families of microprocessor and support chips. These chip sets and especially the 8080 provided an opportunity to produce not just a special purpose controller, but a general purpose computing system, one that could be designed without elaborate digital equipment and with only modest digital design experience. But a computer from Intel's chip set could be designed in any number of ways. To use Intel's Intellec or Multibus bus and boards would be expensive, both by license and by actual cost. And it was unclear how many people would WANT such computers, beyond the market already established and dominated by the minicomputer and mainframe companies: IBM, DEC, Data General, etc.

So when the MITS Altair 8800 was produced in 1975, it took advantage of the relatively simple 8080 design, avoided an expensive design license to use, and it was noteworthy on several other counts. It was relatively inexpensive and simple, yet potentially expandable and complex because of its 100 pin bus. It caught the interest of digital designers who were, in some sense, WAITING to use or produce some kind of digital computer, given the trends I've mentioned above. The physical design of the Altair was similar to minicomputers of the era, so it was "familiar" to those designers. Specifically, the front panel allowed it to be programmed without any additional (and expensive) equipment. After it was announced and as it became known there was a lot of interest in it. So the Altair set a target, if not a standard, for future products. Most certainly it established a market for those designers, for any boards that an Altair owner, potential or actual, might want.

By 1976 there was the introduction of the IMSAI 8080, with its "Altair compatible" bus. Meanwhile, other bus-compatible products were announced by companies (or individuals who started companies) such as NorthStar, Cromenco and others. They collectively established the Altair as the "first" of a series of hardware-compatible microcomputer systems.

This new marketplace expanded in other ways beyond Intel processors and S-100 buses. For instance, the SS-50 bus and systems by SWTP for Motorola 6800 and 6809 processors started a similar bus compatible systems market for those processors and chip families. There were parallel developments in operating systems and software, such as CP/M and BASIC. They were offered early in the developing S-100 world, and were portable across both S-100 and non-S-100 systems. As a kind of "software bus", these similar products also aided the expansion and stabilization of the microcomputer market of the 70's. The earliest "computer stores" of the 1970's started by selling these and other systems and software. Software companies began by offering programs by mail-order, with ads in the earliest electronic, amateur radio, and then computer-only magazines which also began in the era.

By the early 1980's, over 140 companies small and large had produced S-100 (or later, IEEE-696) products , as listed on my home page of S-100 documents and resources. By that time, microcomputers hardware at the chip level could be integrated onto single cards, not a "box" of cards. Computing uses became more standardized, chips became more complex and so fewer were needed, and the need for expansion and design flexibility gave way to reducing costs of production. Another kind of "standardization" occured in 1983, when IBM announced their "IBM Personal Computer" . The IBM name (and the relatively modest price, for an IBM product) established the business case for a "PC" for any company who previously hesitated to purchase microcomputers. Many of the S-100 companies produced single-board computers, and also IBM-compatible computers. When the "Tiawan clone PC's" were produced in high quantities at low prices, many American computer manufacturers were wiped out (even IBM was decimated).

But it's fair to say that MITS and the Altair were the "first" in the first wave of cross-compatible, inexpensive, owner-expandable AND license-free microcomputers. The open nature of hardware design, the kinds of software developed and used, and overall operation of these systems arguably led to most everything else that followed in 20th century personal computing. The now-iconic IBM PC product followed the "market rules" set by the Altair and its immediate successors - not IBM's proprietary "black box" rules. For these reasons, and in recognition of its popular and pivotal role in 1975, the Altair became generally known as the "first popular personal computer".

- first written by Herb Johnson in 2004, updated 2011.

P.S. I am aware of the history of the Apple Macintosh, first offered in 1984, and of Apple Computer from their early days of the Apple I and II. There's many other microcomputers which are not directly derived from the S-100 and SS-50 and other bus-based computers of the mid-1970's. I note above that IC and PC board developments in the 1980's, allowed for single-board non-bussed computers to be produced in quantity at low costs. However, the history of 1980's computing is already well-documented and written about. But all that history is AFTER the "microprocesor revolution" of the 1970's. The S-100 bus is of THAT time. Micro-computing in the 1970's is often forgotten, even disparaged, today. These Web pages are my attempt to preserve that legacy. - Herb Johnson

Early work on the S-100 and IEEE-696 bus

An account by David B. Gustavson, a researcher at SLAC, describes how he obtained an early Altair and influenced some of its design in 1974. He became involved with other notible S-100 developers, in the IEEE effort to standardize the S-100 bus, a design which became IEEE-696. He describes his activities and colleagues, as part of a paper he published in 1984. The paper itself, "Computer Buses - A Tutorial" was published in IEEE Micro in August 1984, and earlier by SLAC.

Where did the name "Altair" come from?

There are apparently two common statements of origin for the name "Altair" for the MITS Altair 8800 computer. A bit of Google searching on July 2004 yielded the material in this section.

An early "hit" from Google yielded the following informative and well-cited reference from --quote--

Why call it "Altair"? The story is, that Les Solomon, the (then) technical director of Popular Electronics magazine, asked his daughter about a name, and she suggested "Altair", because "that's where the Enterprise is going in this episode" - she was watching Star Trek, the science fiction TV series.

Actually, Altair is a real star (Altair VI - Alpha Aquilae), and was mentioned in only one Star Trek episode: "Amok Time", episode 34 - original airdate: 9/16/1967.

Alternately, Forrest M. Mimms III states in the November 1984 issue of Creative Computing that the Altair was originally going to be named the PE-8 (Popular Electronics 8-bit), but Les Solomon thought this name to be rather dull, so Les, Alexander Burawa (associate editor), and John McVeigh (technical editor) decided that "It's a stellar event, so let's name it after a star." Within minutes, John McVeigh said "Altair".

--end quote--

But an early mention of the origin is in MITS's own "Computer Notes" newsletter of April 1976. Quoting a Saturday (March 28 1976) speech given at the "World Altair Computer Convention" by Les Solomon, the author Annette Milford wrote: "The name for MITS' computer, for example, was inspired by his 12-year-old daughter. 'She said why don't you call it Altair--that's where the Enterprise is going tonight.'"

A Google search of "altair computer star trek" on July 2 2004 gave these results (among 2700+) for Altair as a name suggested by Les Solomon's daughter:
      - an on line encyclopedia
     - a click-in survey of 3421 members in 2002 selected among the following;
         a Star Trek episode 45%
         Stephen Altair, a science fiction author of the era - 33%
         a US satellite launched that year 16%
         the Alto personal computer 6%
      - daughter of "the man responsible for the name"
      - also notes Altair was the planet setting for the movie "Forbidden Planet"
        (actually it was the name of the daughter of the scientist on that planet)
     - daughter of "Pop. Electronics editor"
      Ed Robert's daughter, a star (actor or object) in Star Trek
      - lengthy quote of Stan Veit who refers to BOTH origins
      - 1996 interview of Ed Roberts by David A. Greelish

A Google search for "altair computer stellar" on July 2 2004 yielded 1540 hits, mostly about the star Altair, but among the first references were:
   - Creative Computing magazine, article by Forrest Mimms Nov 1984
   - references meeting of Les, Burawa, McVeigh

A Google search for "altair computer origin" on July 2 2004 yielded 2870 hits, but few links were to contents referring to the MITS product; most were astronomical references.

Other interesting links, via other searches:
      - article by Mary Bellis which also cites the Mark-8 and SCELBI products
        which preceeded the Altair
   - article by Les Solomon
   - the movie "Forbidden Planet" was released in 1956. It was very popular, 
     very "modern", and is considered a "great" film. Animations in the film were by a
     veteran of Disney. Many people who grew up in the period were 
     influenced by it. Gene Roddenberry says he was - he developed "Star Trek",
     first aired on TV in 1966. Other S-F film and TV directors of the 20th century
     can trace their work, themes, even their props, to this film.

So where did the term "S-100" come from?

MITS Altair 8800 designer Ed Roberts referred to that system's bus as the "Altair bus". As subsequent companies designed bus compatible cards and systems, the bus was referred to as "the Altair/IMSAI bus", "the Altair/IMSAI/PTC bus", and so on. Some saw this as either unwieldy or as advertizing for their competitors. When the name "S-100 bus" was proposed, sometime in 1976, it became accepted by most everyone but MITS. I've tracked the earliest use of "S-100" in magazine advertizing and computer club newsletters as below. I've also obtained some first-person accounts. These all suggest a date at or before the August 28-29 1976 "Personal Computing '76" show in Atlantic City NJ. The term S-100 grew into practice shortly after that event. SOme claim Roger Melen of Cromemco originated the term; it's not clear. - Herb Johnson

Appearances of S-100 bus vs "plug-in" bus

The earliest S-100 manufacturers after MITS included IMSAI, Processor Tech, Cromemco. Copies of early IMSAI ads in 1976 refer to the "Altair bus" or "Altair boards are 'plug-in' usable". Others refer to the "Altair/IMSAI bus". Only later do they use the phrase "S-100".

Robin Shirley, a member of the Computer Conservation Society in the UK, wrote in their spring 1993 publication as follows: "Roger Melen of the then-small company Cromemco, proposed the name 'Standard 100' bus, or S-100 for short, because it had 100 lines, and this was the name that stuck." Cromemco is often remembered for their early S-100 product, the "Dazzler", a two-card color video board. The story of Roger Mellen and "S-100" is also mentioned in "Interfacing to S-100/IEEE 696 Microcomputers" by Garetz and Libes, in a history section (p. 6, second ed.).

The name "S-100" clearly originated during 1976, based on magazine ads and articles of that year. Ed Roberts himself, commented in opposition to the term in his article in the November 1976 MITS "Computer Notes" (details below). The November 1976 BYTE magazine has a big yellow Cromenco ad for their joystick product on page 1 which says "The D + 7A plugs into the Standard 100 (S-100) bus of your Altair or IMSAI computer." [Thanks for Tor Artsen for this reference.]

Also in BYTE's Nov 1976 issue (pgs 72-74), as well as the Dec 1976 issue (pages 71-76) and the Jan 1977 BYTE issue (pages 5-10), there was a multi-page ad for Processor Tech's "Sol" computer which uses the phrase "S-100 (Altair 8800/IMSAI/PTC)". Incidently, the Dec 1976 and Jan 1977 ads also say the Sol has "[what] you want in your personal computer", an early use of that term.

Issues of the Homebrew Computer Club of the California Bay Area, first mention "S-100" in a December 1976 issue. There's a description of an "S-100 System Symposium" of Nov 20 1976 at Diablo Valley College, where "perspectives were given by Dr. Harry Garland [Cromemco], George Morrow [Morrow], and Lee Felsenstein [Processor Tech]". It was organized by Dr. W. J Schenker and R. J. Hendrickson. Garland, Morrow, and Felsenstein were early members of that club which had their first public meeting on March 15 1975.

Technical Design Labs also had a Jan 1977 BYTE ad (p. 69) for "S100" memory. More ads used the S-100 reference in and after 1977. BYTE magazine for Jan 1977 has a page 1 full-page ad for Cromemco which notes their Z-1 system (with an obvious IMSAI 8080 front panel) "uses the standard 'S-100' bus supported by over a dozen manufacturers".

I've not yet examined my S-100 documentation for first-use of "S-100".

Carl Galletti of TDL, and early S-100 activity

In April 2007 I was contacted by Carl Galletti, the founder of Technical Design Labs, an early S-100 manufacturer. With permission, here's his experience about the term "S-100". Notes or minor corrections by me are in []'s. Carl Galletti, now a top Internet marketer, currently lives in Sedona, Arizona. - Herb Johnson.

Hi Herb,

I was just visiting your site and noticed the story about the origin of the S-100 Bus.

I am the founder of Technical Design Labs (Later Xitan) and a split-off, Computer Design Labs. I was present when the term S-100 was propagated, so I have somewhat of a good idea of how it happened.

It was at a computer show, PC '76 (for "Personal Computing 1976", I believe) in Atlantic City, NJ. [In August 28-29.] John Dilks was the organizer. He's in NJ.

Someone went around to each booth that offered an Altair compatible bus to get the agreement to start calling it "S-100" so we wouldn't have to keep giving MITS Altair free advertising every time we referred to bus compatibility. I was at the booth and was the person who spoke with this "someone" and, in my company's name, agreed on the "S-100" designation.

Who that "someone" was is something which, although at the time I was certain I knew who it was, later became clouded. In later recollection, I thought it was Stan Veit, the editor of Computer Shopper at the time. However, years later when I was speaking with Stan I thanked him for the "S-100" effort and he claimed that it wasn't him.

That being the case, I'd have to say that it was perhaps Les Solomon, the editor of Popular Electronics. The reason I say this is two-fold. One, I was pretty sure it was an editor of some publication and that I was familiar with the name, even though, at the time I was not familiar with the "face", not having met either Stan or Les in person before PC'76.

I can tell you that it was definitely not Roger Melen of Cromemco because they were our closest competitors and I would have definitely remembered his name. Whoever it was going around the show getting a consensus on the "S-100" name, it was not Roger. It is possible that Roger was present when it was created...possibly even suggested the name but I never heard such a story and the closest I can personally verify is this "someone" who went around PC'76 getting the consensus.

One thing that seems certain to me now is that whoever came up with it, they came up with it at PC'76, probably at the show or during an evening get-together at a local hotel.

If Cromemco exhibited there, then Roger could have been involved in the session. Only the "someone" going around would know for sure. You can check with John Dilks and see if he knows if Cromemco was there or has a list of exhibitors. I don't recall them being there.

BTW, PC'76 predates the First West Coast Computer Show, which is where I think Cromemco appeared (at a show) for the first time.

Hope this helps. Looks like you're doing a great job keeping the docs alive...

My Very Best to You,
Carl Galletti

Where did the MITS front panel design come from?

In April 2021, I was asked by Jon Hales about the origins of the MITS Altair design, specifically the front panel. Jon provided some information with his question, which I was not able to confirm. Here's what I was able to confirm on the origin of the MITS Altair front-panel design. - Herb Johnson

Here's a link to a copy of, an Ed Roberts interview conducted and published apparently in 1995, by David Greelish who produced the "Historically Brewed" magazine issue #9 at the time. The WEb site virtualaltair has a copy of portions of the transcript or article, and a linked copy of the MP3 audio of the interview. My April 2021 copy of that Web page includes links I verified. The site of origin doesn't have that transcript or the references to the magazine. But it does have references to the interview in an Ed Roberts obituary, including a link to an MP3 on a Google drive. - Herb

In a transcript of a 1995 interview by David Greelish, Ed Roberts claims his design goals for the MITS Altair,were to produce a microcomputer that quote "in principal could do anything that a general purpose minicomputer of the time could do." end quote. That makes a case, that Roberts was following minicomputers designs known in the 1975 era. Here's the killer quote from the interview as to an exact origin:

Roberts: "We had a Nova 2 by Data General in the office that we sold time share on, and as a matter of fact that was how we got into building a little terminal. The front panel on an Altair essentially models every switch that was on the Nova 2." end quote.

Here's a Web link, to a DG Nova 2/10 owned by the RICM. Compare to this Altair 8800 image.

Roberts goes on to say, a front-panel computer today [1995], "would look just like an Altair, or Nova, PDP-10 or any of those front panel computers." And he's right to the extent he's defined a front-panel computer, essentially as of that same period. Thanks, Jon Hales for this question. - Herb

Ed Roberts of MITS and "S-100"

Ed Roberts responded to the use of "S-100" in an editorial column of MITS's own journal, "Computer Notes", in its November 1976 issue. A full quote is on this Web page. In summary, he calls it a "sham", "an attempt by a small group to steal the Altair bus", and to "not give recognition to MITS for its pioneering efforts".

Below is a portion of a 1996 interview of Ed Roberts by "Historically Brewed" (now "Classic Computing") editor David A. Greelish.

(Greelish asked Roberts about MITS Altair products):

Ed: .... We had another machine and I'm not sure what Pertec did with it after I left, but it was a self-contained computer that came with either a 40 digit or 64 digit display. It was sort of an "Apple" before the Apple II came out. As a matter of fact, it was somewhat like what Processor Technology came out with later. With the [PT] Sol computer, they used the "Altair Bus" and incorporated a keyboard and the display control in one box. It was still an Altair bus compatible machine. That's a bit of a sore point that everyone changed the name of the bus.

"HB": Yeah, I've read a lot about that.

Ed: Nobody wanted to steal the name, they did that because they hated to give us credit every time they talked about their own product. A bunch of vendors got together and decided to call the bus "S-100". We should have copyrighted the name or patented the bus, but we never did that. Anyway, the Sol was an Altair based bus machine and really was an "Apple" before the Apple ][. It was a good machine and they were good competitors.... - end of quote.

Death of Dr. Roberts in 2010

According to various news sources, Dr. Henry Edward Roberts, described by CBS News as "a developer of an early personal computer that inspired Bill Gates to found Microsoft", died April 1st 2010 in Georgia. He was 68. We have a tribute Web page about Ed Robert's at this link. It's factual to say that the Altair's announcement in 1975 caused Bill Gates and Paul Allen to found "Micro-soft" as they wrote a BASIC for the machine, and later sold to Robert's MITS. A CBS/AP statement on Dr. Roberts notes: "Though Roberts' name is less well known than some other computing pioneers, the Altair is widely credited as the first personal computer and for helping inspire the modern computer industry, reports CNET's Ina Fried." (I discuss the debate about the "first personal computer" on this Web page.)

references: for April 1st from Atlanta GA USA, story titled "Early Computer Developer Roberts Dies" - a tribute to Ed Roberts and the 40th anniversary of the Altair

Background of this document

In June-July of 2004 there was a thread of discussion in the Usenet newsgroup "comp.os.cpm", about the origins of the name "Altair" for the MITS Altair 8800. It was predicated by a brief outburst of email about a confused posting on some Web page reference, which suggested the IMSAI 8080 was produced or designed BEFORE the Altair 8800 - a patently incorrect statement. One correspondent suggested that another item of confusion was the origin of the name "Altair" for the MITS product. They posted a recent "revealing" quote from Ed Roberts that it was named by Les Solomon's daughter: again, a historic point that was well known although debated occasionally. There was also some mention of the oft-told comment that Ed Roberts was unhappy about the term "S-100 bus" for the bus that was subsequently developed from his original design of the MITS/Altair 100 pin bus.

I think it is useful and interesting to look further at these two events; namely the origins of the names "Altair" and "S-100 bus". I've searched the Web, and I have a number of primary documents relating to S-100 equipment and publications. Here are some results. I invite comments and corrections, but PLEASE refer to original documents or references that I can also check (at least in principle) when offering corrections. I have had no direct contact with any of the principles of the era in creating this document.

In 2010-11, I revisited this WEb page and adjusted some references, and of course added the obituary of Ed Roberts in 2010.

By 2021, I was drawn to this document, to answer a question about the design origins of the MITS Altair 8800 front panel; and by replication the IMSAI front panel. I found Ed Robert's interview where he states he modeled the Data General NOVA 2 in his office at MITS. And, as I cited above, a first-person quote was different from a unattributed reference. The 2021 Web has far more information on these matters, than the Web of 2012, or 2004. But living memory of these events of the 70's is becoming lost. And casual memory is overriding documented history. Thus this page, which depends on the latter, is more important than previous.

Herb Johnson

To go to the S-100 home page click here.

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

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