Dr. Torode, his floppy controller, and Digital Systems

Written by Herb Johnson, with materials from other writers as noted, last edit Aug 25 2019. While this document includes quotes from others, Herb Johnson is responsible for any errors or omissions and welcomes comments. An email link to me is at the end of this document.

Note Aug 2019: This material of introduction and history sections, was removed from a previous document. That Web page retains the technical information about Digital Systems' various floppy controller products. - Herb


This Web page discusses the history of Dr. John Torode's early floppy disk controller, first to be sold with CP/M, produced by Torode's "Digital Systems" for S-100 bus microcomputer systems of the mid-1970's. Floppy drives became the dominant mass storage and archive device for personal computers of the 1970's. Dr. Torode's company, Digital Systems (later Digital Microsystems), grew to offer a series of other products and was one of a number of companies he developed, merged with, or co-developed. The subsequent history of Digital (Micro)Systems is described on another Web page. The operating system for that controller was CP/M, developed by his colleague, Dr. Gary Kildall of Digital Research. Torode was first to license and sell CP/M from Kildall, and it became a standard for Intel/Zilog based microcomputers of the era.

Torode's controller for the "Altair bus" in 1975-76 ws the first floppy controller sold to run with CP/M, and first to run CP/M on the S-100 bus. It was an early product in what became the S-100 bus marketplace of over one hundred companies thru the mid-1980's. In my opinion, Torode's FDC-1 floppy controller product for the Altair bus, and his licencing and sales of CP/M with it, was a pivotal development of the era.

More pages: The "race" for microprocessor-supporting floppy controllers between Digital Systems, MITS, IMSAI, iCOM and others, is discussed on this Web page. I have a collection of Web pages about the activity and products around Digital Research and CP/M, IMSAI and MITS. These are all linked from my DRI home page. Additionally, I have document lists of manuals from over 100 S-100 companies which can be accessed from this S-100 home page. and, in 2013-2016, I've acquired some some Digital Systems floppy system hardware.

Acknowledgements: My thanks to Dr. John Torode, who provided discussion of and information about his early work in the late 2000's. Thanks to Dwight Elvey for his programs and his work to re-engineer, restore and program his FDC-1 controller; and his many discussions of that work with me. Also thanks to Stan Sieler, who provided FDC-1 schematics to Dwight. Jeff Shook, an early customer of Digital Systems, provided Dwight and I with manuals from his FDC-2 system, and provided notes about his purchase of it. Thanks to Jack Rubin, who provided what appears to be the earliest version of the FDC-1 product's documents. Thanks to Vern Potter who provided me with original FDC-3 documents, and who gave me my first technical view of Dr. Torode's Digital System products. Also, thanks to the various people who sold me Digital Systems hardware and software. - Herb

Dr. John Torode and his associates

The following are capsule descriptions of the persons around Torode and Kildall before and after the development of these early floppy controllers and of CP/M. These are far from complete biographies, as they emphasize the 1970's and all of these persons have outstanding achievements after, and even before, that period.

Dr. John Torode, was a graduate of MIT and the University of Washington; his PhD at the U of W in 1972 under Dr. Theodore Kehl was on microprogrammable controllers. He published papers with Kehl and Lawrence Dunkel; they also published works on digital design. Later he joined the faculty at UC Berkeley. Dr. Torode started or was a principal member of several technology companies, from Digital Systems which he started in 1967 as a graduate student; to IC Designs which became part of Cypress Semiconductor. The subsequent history of Digital (Micro)Systems is described on another Web page.

Torode eventually returned to the U of W area, and partnered with Kehl and many others in business, research and academia. Digital Systems Inc. became Digital Microsystems Inc. or DMS, and developed and sold microcomputers and Hinet networking products until the company was sold in 1986. Torode was honored as a UW Distinguished Alumnus in 1996. A biography of Dr. John Torode was available as of 2007 at the U of W. at this link.

Dr. Theodore Kehl was a 1961 Ph.D from the University of Madison, WI and was a professor of physiology and biophysics at the U of Wash. He may have been a founding member of the U of Wash. Computer Science Department in the mid-1960's. Among other work, Dr. Kehl developed digital designing methods for modular designs and semi-automated construction. In 1974 Kehl was a Computer Science associate professor at the University of Washington with Dr. Torode., and was Torode's Ph.D. thesis advisor. Dr. Kehl has several US and European patents in his name (some with David N. Cutler), assigned to DEC and Microsoft, dating from the 1990's and with a 2005 date.

Lawrence Dunkel was a member of the Physiology and Biophysics Dept. in 1974. Kehl and Dunkel partnered as digital designers and programmers and co-authors of publications.

Dr. Gary Kildall got his Ph. D. in Computer Science in 1972 at the University of Washington. He formed a company named MAA to do consulting and development work; and he became a faculty member of the Naval Postgraduate School. In 1973 Dr. Kildall provided to Intel a cross assembler, a simulator, and a PL/M cross compiler for the 8008, written in Fortran. In 1974, Kildall migrated these products to the 8080. Kildall then wrote a floppy disk operating system in PL/M for the 8080 and built a floppy controller which was made operational in 1974-75 by Dr. Torode, as described below. Kildall started Digital Research in 1975, did development with IMSAI, and offered CP/M 1.4 to the public. Digital Research Inc. (DRI) became a major operating system and programming language provider for microcomputers from that time through the mid-1980's and beyond; products from that company are in use today. See my Web site's history of Gary Kildall, his colleagues, and of CP/M development.

The history of the 1970's work of Torode, Kehl, Kildall, and of companies including IMSAI and MITS, is reviewed in outline form on my 30 years of CP/M Web page.

Technical context

During 1973-74, Kildall wrote a floppy disk operating system in PL/M for the 8080 and tried to build a floppy controller for his Intel development system. In late 1974 Dr. Torode worked with Dr. Kildall for the first successful run of CP/M. Torode's "Digital Systems Inc." in 1975 was first to license CP/M from Kildall, sold it to other clients and companies, and sold it with Torode's floppy disk controller for IMSAIs and Altairs. He later founded Digital Microsystems Inc. from that company in 1979. Torode's subsequent work is noted above, as is Dr. Kildall's early and later work.

The MITS' "Altair 8800" and IMS Associates Inc. "IMSAI 8080" systems of 1976 used a common bus of 100 pins. That bus became known as the "S-100 bus" after several manufacturers of compatible products agreed on that name. Over the next decade and more, over 100 companies produced S-100 products and systems. The bus was redesigned in the late 1970's as the "IEEE-696 bus" to support advanced products into the 1980's. In the 21st century, people collect, rebuild and operate these systems. A large part of my Web site provides lists of documents and descriptions of these companies. The home page for my S-100 activities has links to many S-100 companies' pages, technical descriptions, and related hardware and software.

IBM invented the floppy disk drive, as a loader of microcode or a bootstrap device for its mainframes. One of IBM's engineers, Al Shugart, started the premier floppy drive company, Shugart Associates. A number of companies offered floppy drive systems for minicomputers and the early microprocessors during the early 1970's, as 8-inch floppy drives moved from the mainframe world. iCOM, a diskette drive manufacturer, had a floppy drive system with a microprocessor-base OS as early as 1973! Information on that product, the "frugal floppy", is on this Web page.

Torode and Kehl's "Logic Machine"

Torode's Ph.D. thesis, under Dr. Kehl at the University of Washington in 1973, was titled "A Microprogrammable Logic Machine". In November 4 1973, The journal "IEEE Transactions on Computers" received an article from John Torode and Theodore Kehl titled "The Logic Machine: A Modular Computer Design System". It was revised early in 1974 and published in the November issue of that journal. (A search of IEEE on-line absracts will find these as copyrighted articles available to IEEE members or for fees. We'll provide a copy of this article if possible, methods to be determined, depending on copyright issues.) In 2011-12, Kehl's former student Charlie Garthwaite contacted me, about Kehl's lab and the logic machines, as described in this Web document.

Torode and Kehl advocated use of a "microprogrammed control processor", built from a set of TTL logic, "which is used unmodified in all devices." Specific computational needs are added as "functional units", designed as needed, and controlled through the program in the microcontroller. "A logic machine refers to the ensemble of control processor, single data bus, several functional units, and a microprogram all arranged so that a specific digital system is constructed".

This figure shows the essential microcontroller from the 1974 paper. The "control store" are the ROMs which contain the microcode, the program which drives the controller. Blocks labeled "74161" are TTL counter chips which are the program counter (PC). The data outputs of the control store are captured by the 7475 TTL latches, and the logic gates and 75154's (1 of 16 decoder) to the right of those chips decode the instructions, to provide logic signals for control. Gates below the 74154's capture special instructions which test logical conditions for "jump on condition" instructions. If the conditions match the instruction, the jump address is loaded in the program counter chips.

As suggested, the microcontroller performs logical actions to outputs, and test and jumps on inputs. Note that one 74154 decoder is labeled "inst. 00 to 0F" and its outputs go to the "DOJUMP" logic gates. another 74154 decoder is labeled "inst. 80 to 8F", another "inst. 10 to 1F". These indicate Torode and Kehl used each set of 16 (or 10 hexadecimal) microcode instructions for those specific purposes.

Torode and Kildall

As published by Dr. Gary Kildall in 1980, through 1973 and into 1974 Kildall developed the core of CP/M and related tools, as part of his efforts with PL/M and with related products he developed for Intel. But he could not get his own design of a floppy controller working to test it. Dr. Torode worked with him on Kildall's controller late in 1974. But Dr. Torode states in private correspondence they first ran CP/M on Kildall's Intel system with a controller of Torode's design. Torode's Digital Systems was first to sell a floppy controller which ran CP/M, under license from Kildall. Through Digital Systems, Torode and Kildall initially sold CP/M to Lawrence Livermore Labs and to Omron (a terminal manufacturer). Subsequently, Kildall formed Digital Research to offer CP/M; license #3 went to IMSAI after Kildall developed CP/M 1.3 for their first floppy controller. For more on those events, read my DRI Web pages, starting with this more detailed account.

Digital Systems floppy controllers

In 1975, John Torode's Digital Systems began to provide his floppy disk controller card product and CP/M. The controller was to be operated from a microprocessor system, through a parallel DMA interface as another digital card. Torode designed, and later produced, a card for the then-new MITS Altair 8800 system and its "Altair bus". That bus eventually was called the S-100 bus. The Digital Systems FDC-1 is one of the first S-100 floppy disk controller products, and the first to run with CP/M.

Torode and Digital Systems, and CP/M, Kildall and Digital Research, were announced indirectly through 1976 in editor's comments in "Dr. Dobb's Journal". The first Digital Systems sales ad appeared in Jan 1977 in BYTE magazine, p 128: "Digital Systems" small ad. The ad reads: "Floppy disk system, completely assembled unit, $1595.00...Shugart drives and DIGITAL SYSTEMS FDC-1 controller...interface to the Altair/IMSAI bus...The powerful CP/M Disk Operating System, written by the originator of Intel's PL/M compiler, is available for only $70. Systems have been operating in the field for over two years.- Digital Systems, Livermore CA". The "two years" reference is consistent with Kildall's reference to late 1974 for his first runs of CP/M with Torode. Detailed references to the events above are on this Web page of Digital Research and Gary Kildall history.

For more dates and events and products, on another Web page, I discuss the "race" for floppy controller products on Altair and IMSAI-compatible systems, between Torode's FDC-1, MITS's 88-DCDD, and iCOM's "Frugal Floppy" or FD360.

Digital Systems built three versions of their floppy controller. The FDC-1 was a controller with a pair of 86-pin interface connectors to an 8080 system. The FDC-2 version had a 50 pin connnector to their Altair bus interface card. Those controllers were single density only. The FDC-3 controller with a similar Altair card supported double density. The FDC-3 was later incorporated into Digital Systems DSC-2, a Z80-single-board computer inside a DS drive cabinet as used to contain drives and the FDC-3 floppy controller.

For information and details, documents and software, on the FDC products, find them on this linked Web page.

More information about Digital Systems

The subsequent history of Digital (Micro)Systems is described on another Web page.

Documentation and discussion of Digital Systems earliest floppy based controller and CP/M system products, are on this linked Web page.

Contact information:

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

Copyright © 2019 Herb Johnson