S-100 and the 8086

This page last updated Oct 13 2011. (c) Herb Johnson 2011


Intel introduced the 8086 in June 1978; the 8088 a year later (dates from Intel documents). S-100 systems, mostly 8080-compatible and in production since 1976, were among the first to use these processors. But Digital Research, providers of CP/M-80 since 1975, was slow to provide a CP/M-86. So, companies created their own 8086 operating systems; one of those became MS-DOS. This Web page is a PRELIMINARY introduction, to early 8086 and 8088 processors and their history on the S-100 bus. It's not a history of MS-DOS. This page was begun in July 2009. - Herb Johnson

For more information about S-100 systems, check my S-100 home page.<

CP/M and the 8086

I discuss and document development of CP/M for the 8080 by Digital Research and Gary Kildall, from this home Web page on that subject. CP/M was available for the 8080 processor in 1975; a number of versions followed as did more enhanced operating systems. My reference documents for the early history of CP/M-80 are on this Web page. Among those references are articles by Kildall which describe early CP/M development as well as his preferences for further CP/M development.

Kildall wrote a BYTE article in June 1981 titled, "CP/M: A Family of 8-and 16-Bit Operating Systems". A copy of the article is or was available at this DRI-supporting Web site. In that article, Kildall talks about developments at DRI of sets of tools - operating systems, programming languages, utilities. But as regards to what he called "new processor architectures", he considered the 16-bit processors - a clear reference to the 8088 and 8086 and subsequent versions, including remarks about segmented memory - as a "temporary phenomenon in the transition to 32-bit machines"; that "8-bit systems are here to stay...our best customer base". Digital Research, he says, has provided (by 1981) initial support for Intel's 16-bit 80186 and 80286, but "the future will be with 32-bit machines". Earlier remarks by Kildall in the late 1970's make similar suggestions.

These remarks are consistent with comments in the later 1970's by early CP/M-80 vendors who were producing 8086 systems. They could not convince Kildall to produce an 8086 version of CP/M-80 for them. They also remarked that Kildall was more interested in programming language development at the time.

Seattle Computer Products

Seattle Computer Products (SCP) was an S-100 company. They produced a number of memory cards, such as a series of 16Kbyte cards. Here's a 1978-designed SCP-16K card, produced in mid 1980. Here's a 1979-designed Apex model card by SCP, produced in 1980. Here's a 1980 Apex2 SCP card. My Web page on SCP and a list of available documents, is at this Web link.

Here's a photo of SCP's 1979-produced 8086 S-100 card, as built probably in mid-1981. SCP worked on this 8086 product, as did other companies, at the time when the 8086 became available. Those companies asked Digital Research - Gary Kildall - in various ways, to provide an 8086 version of his 8080-based CP/M. Kildall delayed or dismissed doing that; he thought more powerful, advanced 32-bit processors like the Motorola 68000 were the future (see the reference earlier in this document). So, as some did with CP/M-80, companies developed their own OS products.

Tim Paterson, then a programmer at SCP, has said on many occasions (including in legal deposition) that he essentially sat down with a CP/M manual, and developed his own operating system based on the programming interface and major features of CP/M-80. Additionally, he developed a different file system and made other changes. That operating system was provided by SCP as 86-DOS. An ad for "Seattle's" S-100 8086 "16 bit computer" with "86-DOS and BASIC-86", appears in November 1981 (kilobaud) Microcomputing, as sold by American Square Computers (p. 38). (I discuss this further on my Web page about CP/M history.

Accounts on Web sites and in books and articles, vary about how IBM approached Digital Research for an OS for their IBM PC. But the facts as reported are, that IBM did not initially obtain an agreement with DRI. The 86-DOS OS was obtained by Bill Gates, when Gates was approached by IBM for an operating system for what became the IBM PC. Gates bought rights to this OS, sold a license to IBM, and then "developed" it further into what IBM offered as "PC-DOS" and Gates' Microsoft offered as "MS-DOS". The IBM PC was announced by IBM in August 1981.

It's not my intention to provide a complete or iron-clad history of these events, for two reasons. One, it's been researched and published about many times - look up those resources. Two, there are still many people who are angry to this day about this turn of events, how DRI and Kildall missed (or was deprived of) an opportunity. I'm not going to fight that war.

We have a Web page of miscelaneous S-100 products by company at this link. We have a number of manuals available as part of our document services.

Techmar 8086

Techmar was an early third-party company to provide IBM-PC compatible products after the IBM-PC was introduced in 1981. But prior to that, they produced S-100 cards. For example I have a manual "Techmar TM AD212", an A to D converter/timer card, from 1980. Here's their 8086 S-100 CPU card.

We have a Web page of miscelaneous S-100 products by company at this link, including Techmar. We have a number of their manuals available as part of our document services.


Compupro was a major and early producer of S-100 cards; they strongly contributed to developing the IEEE-696 standard which expanded the S-100 bus architecture. We have a Web page about Compupro and their S-100 products at this link. We have a number of manuals available as part of our document services.

Here's Compupro's 8085/88 dual processor card; this one was produced in early 1984. A verson "B" document I have for this card, dates from August 1980. Note the CPU speed switch - 2MHz or 5MHz! The card would run either processor, and switch between them using a few bits of an I/O port.

Compupro provided a special CP/M, "CP/M-85" for this card. CP/M 86 was offered by Compupro in an ad in October 1981 (Kilobaud) Microcomputing (page 232). Later, Compupro offered Concurrent CP/M. Gifford Computer Systems provided an MS-DOS for the 8088 "side".

They also had an 8086 CPU card; an 80186 slave card with serial port; an 80286 CPU card. They produced these cards well into the 1980's. We'll have more to say about these in due course.

Contact information:

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

Copyright © 2011 Herb Johnson