IMSAI-based computers and docs list

This page last updated May 15 2024.

The IMSAI 8080 was [likely] the second "S-100" computer made, offered late in 1975 by "IMS Associates Inc.", known shortly afterward as "IMSAI". The first S-100 computer was the MITS Altair 8800 in January 1975.

IMSAI-related products have appeared by the "IMSAI" or "IMS Associates Inc." name; or as new products by "Fischer/Freitas"; or as a mix of old products and new designs from Fulcrum or W.W. Component Supply. Details are below. Do not confuse IMSAI products with those from "Industrial Micro Systems" or "IMS" or "IMS International". As of 2005 "IMSAI" was a trademark held by Todd Fischer, who produced new S-100/IEEE-696 products and some old IMSAI products at

[IMSAI 8080] Here on the right is an inside view of an original IMSAI 8080, with various cards. On this page we have IMSAI history history and many IMSAI documents available as part of our S-100 document services on this page.

  • IMSAI history;
  • IMSAI and CP/M;
  • Fischer-Freitas and;
  • Fulcrum Computers;
  • WW Component Supply
  • IMSAI parts available
  • IMSAI manuals available

    On other pages, we have the following:
    a few IMSAI front panel switches, click here.
    Here is a list of the IMSAI and Altair bus lines.
    For a list of all S-100 docs click there.
    And here is how to order S-100 stuff and to email @ me.

    IMSAI history

    [IMSAI 8080] Here's the FIRST "clone" computer: the IMSAI 8080, offered by IMS Associates Inc. late in 1975 after the introduction of the MITS Altair 8800. While not a copy of the Altair, it was designed and sold to be card and bus-compatible with the Altair 8800. Consequently over 100 manufacturers created S-100 products and so established a market requirement of compatibility which later became "clones" in the IBM-PC world.

    IMSAI's history preceeded the Altair but it is remembered best for the IMSAI 8080 computer and related products. IMS Associates, Inc. was founded in 1973 by Bill Millard. The company provided engineering and software services. Sometime during 1975-76 it became known as IMSAI. Thomas "Todd" Fischer, an early IMSAI employee who later acquired rights to some IMSAI products and its name, describes on his site that IMSAI was designing a multiple 8080 processor system called the "Hypercube" in 1975. Meanwhile, MITS announced their Altair 8800 late in 1974. IMSAI decided to replicate the Altair for use with this system, and subsequently to offer it as a stand-alone product.

    The IMSAI 8080 was designed by Joe Killian, and advertized in Popular Electronics late in 1975. The first units were shipped sometime in December 1975. The first IMSAI 8080 contained three cards: a motherboard with an Altair-like 100-pin bus connector, a front panel card with switches and lights like mainframe and minicomputers of the day; and a CPU card with a 2MHz 8-bit Intel 8080. This package was sold for the amazing initial price in 1975 of $400. A fourth card for memory was added at some point. The price rose during 1976 at various points, to about $500.

    Most S-100 fans today say the IMSAI is better engineered than the Altair 8800. At the time MITS in their customer magazine called it a "copy". IMSAI ads of the period referred to their bus and cards as "MITS compatible". Subsequent plug-in card manufacturers referred to their products as "MITS/Altair bus compatible". The name "S-100" was created later, a term disliked by MITS management. But that bus cross-compatibility initiated an industry of S-100 compatible cards that led to the formation of over 100 computer companies large and small, producing (more or less) compatible cards and systems. A list of those companies is on my . A subsequent version of the S-100 bus wasthe IEEE-696 design which was in use in the late 1970's but not approved by the IEEE until 1983. S-100 bus history is described in this document.

    IMSAI (or IMS Associates Inc.) went bankrupt in late 1979. A public auction of IMSAI assets occurred Oct 24th 1979; rights to software and intellectual property were sold prior by sealed bid. Meanwhile, in 1976 Bill Millard co-developed and controlled ComputerLand, an early chain of franchised computer stores which did business through the mid-1980's.

    IMSAI and CP/M

    IMSAI was an early adopter of CP/M and floppy disk drives, starting in 1976. Check my Digital Research page for the IMSAI and CP/M story. According to Todd Fischer at IMSAI, "the first disk controller configuration was the two-board IFM/FIB single density only controller that ran IMSAI's CP/M 1.3. The next generation (c. early 1977) was the DIO/PDS board set which ran the enhanced proprietary version of CP/M called IMDOS. First, there was [IMDOS] version 2.02, then 2.05, then 2.07, and finally IMDOS II (Dianne Hijcek's last-ditch effort at propping up the value of the third generation IMSAI hardware." [See my notes below: the IFM/FIB was packaged by IMSAI as the "FIF-1 Disk System". - Herb]

    Todd updated the above description, in a comp.os.cpm post for Jan 29 2007, quoted with permission here. "The IMSAI DIO series of memory mapped controllers handled Double Density just fine with the MPU-C 8085-based processor running at 3 MHz., and just as well with the original IMSAI MPU-A running at 2 MHz. We sold a boatload of disk subsystems to first and second generation IMSAI system owners. Our double-density formats included 256, 512, and 1024 (long sector) sector lengths. The mid-1977 second generation controllers closely followed the IBM 3740 formats and subsequent variants for media read/write compatibility. The original DIO-A of early 1977 used a proprietary double density format which was unique to IMSAI.

    Todd continued: "For the record, the original IMSAI IFM/FIB intelligent DMA disk controller of mid-1976 was debugged and rendered eminently usable and reliable by Glen Ewing, consultant to IMSAI and fellow instructor with Gary Kildall at the Naval Postgraduate school in Monterey, CA." More of Todd's comments are on my Digital Research Web page.

    notes:In 2010 I reviewed my docs to create this description: The IMSAI "FIF-1 Disk System" consists of one IFM and one or more sets of other boards, cabinets and drives depending on the number of drives. The IFM has an 8080 processor and ROM and RAM, to perform DMA to the system and to control the FIB. The System CPU sees the IFM as "memory-mapped ports". The FIB provides hardware logic to the IFM through a common 26-pin cable; and to the floppy drives through a 50 pin cable to the drives. The FIB is controlled by the FIF. The FIB only has an interrupt line, power and ground to the S-100 bus.

    Fischer-Freitas and

    Todd says IMSAI was in business until October of 1979, when its assets were sold at a bankruptcy auction, and its and intellectual property and manufacturing rights were acquired by Fischer-Freitas Corporation. Some items were acquired by Fulcrum, later known as WW Component Supply. The IMSAI product line continued to be offered as a division of Fischer-Freitas Corporation for some time thereafter, says Todd. In 1998 Fischer-Freitas Company announced some new products based on the IMSAI and opened a Web site at

    By 2001 their products, information and services included some of the original IMSAI systems and cards. In 2003 they had new products based on a new IMSAI using the IEEE-696 bus standard and some IMSAI bus lines as well; and an IEEE-696 I/O card which supports mass storage. Since (about) 2005-06 Todd is the owner of the "IMSAI" trademark and the Web site.

    (Note: Info from Todd Fischer is from Todd's Web site, and from private and public correspondence. It is referenced here with his permission. More info on the history of IMSAI and Fischer-Freitas, and these newer products, can be found on their site. I'm pleased with the good will I've received from Todd Fischer and his company. - Herb Johnson)

    Fulcrum computers

    Todd Fischer of IMSAI, about Fulcrum

    In private communications from 2004, Todd Fischer of IMSAI told me a bit about the history of "Fulcrum" computers, as follows. A company called "W.W. Component Supply" of San Jose, California acquired and sold some goods from the (original) IMSAI Inc. bankruptcy and auction. They advertised IMSAI products for a short period of time. Threatened with a law suit for trademark infringement, W.W. Component changed the name of their products to "Fulcrum", and continued in business until the late 1980's.

    In 2006 I acquired a 1981 "Fulcrum" catalog by WW Component which refers to their "exclusive" IMSAI/Fulcrum product line.

    Chris Raymond of Fulcrum

    In late 2004 I was contacted by Chris Raymond. He designed a Fulcrum product, the Fulcrum VIO-X, first sold in late 1981. He wanted that card from me as a momento of that work. I asked about his VIO-X design versus the IMSAI VIO card, and what he knew of Fulcrum. He wrote:

    Hi Herb, as I recall the VIO is an IMSAI product, is that correct?  The
    VIO-X was a completely different design, not an IMSAI product, although it
    shared the 80x24 format.
    If I remember correctly, the VIO was a memory mapped design which required
    a software driver to keep track of cursor position etc., and handle scrolling,
    which was slow because the driver had to move all the characters around
    one by one in the screen buffer.  I think it produced glitches on the display
    whenever the software wrote to it.  The VIO-X on the other hand was designed
    to look like a UART to the software - it responded to escape sequences and
    commands the same as a Lear Siegler ADM-2 terminal.  There were no screen
    glitches, scrolling was virtually instantaneous, and the software driver
    was identical to a serial port.  The board had an 8085 microprocessor with
    about 2K of software in EPROM to accomplish this.  The design was based on an
    Intel 8275 [video processor chip] app note and worked pretty well, IMHO.
    I designed the board at the suggestion of my friend Dave Needle who needed
    a video terminal as part of his video game development system.  Although he
    only needed TTY capability, I decided to implement conversational and
    block modes compatible with the ADM-2 (which I used daily at my job at Tandem
    Computers).  In addition, I took advantage of the invisible character
    attribute feature of the 8275 chip which allow attributes such as
    blinking, underline or inverse video to be turned on and off without a blank
    character in front of the field, although the default mode used visible attributes
    for ADM-2 compatibility.
    The original design generated a monochrome video signal reasonably close
    to the NTSC standard.  Brent Wright (WW Component Supply, later called
    Fulcrum), who manufactured the board, asked me to change the design to
    work with a Ball Brothers monitor (he had a lot of them on hand), which
    required different timing of the HSYNC signal.  As I recall, the board was
    configurable either way although I don't remember for sure.  Brent took my
    original design, which I implemnted on a wirewrap board, and layed out a
    PCB.  He sold a number of them but I don't know how many.
    I also wrote the original manual which I understand was fairly worthless.
    Hopefully the extended version (which I didn't write) is more useful.
    So anyway, if you have a board lying around let me know how much you want
    for it.   I don't know the business relationship between IMSAI and Fulcrum,
    sorry I can't shed any light there.  I don't have a web site to link to
    either, unless people want to look at baby pictures... thanks for your
    interest in this stuff, it brings back some fun memories.  Cheers, [and]

    WW Component Supply

    Rae Stiening of WW Component Supply

    See also "Fulcrum computers" above. Fulcrum was the previous company name for WW Component Supply. Some Fulcrum manuals have in fine print "distributed by WW Component Supply Inc.".

    In August of 2006 I was contacted by Rae Stiening, who discussed WW Component Supply, and his design of the Omniram for Brent Wright. If anyone has information about Mr. Wright, contact me so I can pass it along to Rae. - Herb Johnson

    Brent Wright was one of the W's in W&W Component Supply. Brent got his start
    in the component business by working for Mike Quinn at Oakland Airport's
    North Field. It was a good start because Brent was the best components man I
    ever met. I do know that the Omniram came after the VIO-X because the first
    job I did for Brent was to write code for the
    VIO-X so that it emulated the Bee terminal used by Cromemco.
    I enjoyed visiting W&W's store at 1776 Junction Avenue in San Jose CA
    on weekends. I don't know when W&W opened but would guess that it was around
    1980. At some point Brent told me that he had located a supply of
    inexpensive 2K static ram chips and that 32 of them would just barely fit on
    an S100 card. I agreed to wire wrap a prototype and we agreed on terms. The
    contract was a few words on the corner of a paper napkin that happened to be
    nearby. W&W sold lots of Omnirams because Brent's choice of memory chip
    permitted it to be sold a price far below that of competing boards.
    From "contract" to first production Omniram's was
    about six weeks. Brent worked really fast. There was a single page ad in
    Byte magazine when we were ready to ship.
    By the time the Omniram was produced neither S100 bus products nor W&W
    Component Supply had long to live as viable commercial enterprises. 
    W&W [later] moved to another location in San Jose and closed down
    in approximately 1988. W&W's building is now (2006) a print shop
    and a Fry's Electronics megastore occupies the entire block across the street.
    At the time of the Omniram I was interested in the application of
    microcomputers to astronomical data acquisition. The most recent project
    that I managed is described at [this Web page].  
    Regards, Rae Stiening, in MA

    Rae provided this photo of WW Component Supply taken in the mid-1980's, at their Junction Avenue address in San Jose, CA.

    Rae says more information about Mike Quinn, a well-known surplus and electronics dealer in Oakland since the 1960's, is described on a section of the Web site. The site said Quinn's shop is still in business as of the 21st century. HOwever, I was told that the store closed in the fall of 2006.

    Rebadged IMSAI's

    A number of companies bought IMSAI computers and put their own company name and model numbers on them. This practice is sometimes called "rebadging" as the name and corporate symbols are a kind of badge afixed to the product. For the IMSAI front panel, one only needed to change out the black (photographic) film mask behind the front panel. I'll list a few of these as I find out about them.

    One company was Alpha Micro. They produced a line of PDP-11 like microcomputers, but started out by rebadging an IMSAI chassis and designed S-100-like boards (some oversized in height) for their AM-100 computer. Check my S-100 home page for Alpha Micro listed there as a S-100 company.

    I have/had an IMSAI with a "Cromemco" name on the front. I don't know if Cromemco did this themselves, or if some prior owner did this.

    Another company was Science Dynamics Corporation. Here's details on their rebadged IMSAI as part of their medical office data services. Thanks to Sherman Foy for showing me his Science Dynamics IMSAIs in May 2024.

    IMSAI and Fulcrum Documentation S-100 docs list

    This list copyright Herbert R. Johnson 2007.
    Price, my email @ address, and other information can be found in this notice.
    To return to the document index click here.
    Some IMSAI or related documentation and hardware may have company names like Fulcrum, or W. W. Component Supply, or Fischer-Freitas Corp.

    Note: I do not offer "sets" of manuals. I offer manuals individually or in some cases I'll identify sections of manuals available seperately. By and large most companies created "sets" of docs from individual manuals for cards and software. Also it's cheaper to YOU if you don't buy docs for card or software you don't have anyway! I only offer copies, by the way, not originals.

    I may have some IMSAI parts or related parts: check my S-100 items for sale page accordingly.

    IMSAI parts available

    Check my S-100 items Web page for S-100 items.

    IMSAI and related documentation available (copies)

    IMSAI 8080 System User's Manual and chapters
           IMSAI 8080 Microcomputer Systems User's Manual, 
            rev 1 1976, also see rev 4
                intro, cabinet, motherboard, CPA (front panel), MPU (processor card). 146 pgs
                (This is the manual for the processor card, front panel, case
                power supply, and motherboard for the "IMSAI 8080"!)
                Schematics included for items noted. Includes mechanical
                drawings and assembly, IMSAI bus description, test code.
            If you only want individual chapters of the System Users Manual:
                Introduction, overall description and testing, component assembly: 44 pgs
                MOtherboard, 20 pgs
                Power Supply, many photos, 24 pages
                CPA (front panel), 40 pgs with updates
                MPU (CPU card) 14 pages
           additional System User Manual chapters on other cards, with schematics, are extra as below:
                chapter on PROM-4, 14 pgs
                chapter on PIO, 20 pgs                                  
                chapter on SIO, 30 pgs; also see rev 4
                chapter on PIC-8, 20 pgs
                chapter on CRI, w/source listings, 32 pgs
                chapter on SCS (Self-contained op sys), source, 74 pgs
                chapter on RAM 4A, 10 pgs; also see rev 4
                chapter on RAM 4, 10 pgs
          later version schematics, layouts:
                CPA rev 4, 4 pgs
                SIO 2-2 rev 3, 4 pgs
                MPU-A rev 4, 3 pgs
                RAM 4A-4 rev 3, 2 pgs
                PS-C-D rev 1, 2 pgs
    Other IMSAI product manuals
          IMSAI MIO manual (from copy), 70 pgs
          IMSAI PIO-6 manual (from copy), 30 pgs
          IMSAI RAMIII reference man, 50 pgs
          IMSAI Dynamic Ram system User Man (RAM-16, RAM-32, RAM-65), 120 pgs
                sections for ONE model only (RAM-16 OR -32 OR -65), 68 pgs
          IMSAI VIO Users manual, 200 pgs
              schematics, source listing, video character bitmaps
    Other IMSAI system manuals (PCS or VDP systems)
          PCS 80/30 reference manual, 185 pgs
                MPU-B, VIO, IKB-1, PS-28U. CP/M 1.33 references!
          IMSAI PCS-4X Microcomputer Sys Users Man
                CDIO, MDIO, DIO-D, RAMIII, MPU-B, PCS-44; 200 pgs
                RAM III chapter only, 36 pgs
                MDIO chapter only, 34 pgs; other chapters available seperately
          PCS 80/15 reference manual (MPU-B) - ask for details
          IMSAI VDP-80 Users and Ref Man (VIO, MPU-B), 250 pgs
          VDP-80 user manual, 70 pgs
          VDP-80 reference manual, 120 pgs
          VDP-40 Operating manual, 70 pgs
          VDP-4X operators manual, 90 pgs
    IMSAI floppy and hard drive manuals - FIF, FIB, FPS, FLB
    	"IMSAI System, Floppy Disk System User Manual", 1976, updates to Rev. 3, April 1977, approx 200 pages
    	FIF-1 Disk System, see notes above 
    	I will provide individual chapters, contact me with specific needs.
    	Chapters on overall theory, assembly, user (programming)
    	Chapters on similar topics for each of the following items:
    		IFM Interface Master (S-100 card with dedicated 8080 CPU)
    		FIB Floppy Interface Board (S-100 card to floppy drive, one per drive)
    		"FIB Firmware" (source listing for IFM ROM's)
    		FPS power supply for floppy, one per drive cabinet
    		FLB Floppy Light Board in drive cabinet, one per drive	
    		Calcomp 140 floppy drive with PLO data seperator board
    		Floppy Drive cabinet - cables and mechanical
    IMSAI floppy and hard drive manuals - DIO, PDS, PerSci drives
    IMSAI DIO Controller User Manual (cover) for 
    IMSAI DIO Controller Reference Manual (inside title page) NOv 1977
         --  DIO, PDS rev 1 11/77 w/ 14 pages of 5/78 eratta sheets, 120 pgs
         --  schematic for DIO, layout for PDS and DIO, parts, descriptions
         --  System Manual included in manual below.
         --  DIO docs included in manual below except for assembly instructions, layout
         --  PDS docs included in manual below except for assembly instructions, layout
    IMSAI Floppy Disk system User Manual DIO(c) Controller, from May 1978, 125 pgs
    AKA IMSAI PCS-80/21(22) Floppy Disk System - User manual.
          Also see manual above "DIO Controller Reference Manual).
          The front cover has the "floppy disk" title, the inside cover the "PCS-80" title
          chapters for "Theory of operation"  and "System Programming Manual", plus
          chapters for DIO, PDS (data separator), FPS (Floppy Power Supply), 
          the FLB (Floppy Light Board, an LED with a 74S04 as driver), 
          Floppy Cabinet, and  DCC (interconnect) board between the FPS and the DIO. 
          Also 16 or so pages on the CalComp 142M. The introduction also says this board set
          will interface with a Shugart (SA400) mini drive.
          Schematics for PDS, DIO, cabling, power supply.
    IMSAI Diskette System Reference Manual, Nov 1978, 160 pgs
          overall descriptions of disk SYSTEMS, no schematics (in this copy)
          rewrite of Floppy Disk System and DIO Controller manuals above.
          DIO: -C and -D covered in detail
             DIO-A "original" IBM 3740 and Format V
             DIO-B different step rate for CalComp 142
             DIO-C replaces -A and -B, Formats II, III, IV
             DIO-D replace -C and supports "minidrives" (Shugart 400)
             DIO Theory of Opertation looks very similar to above-noted manuals.
             IFM interface master
             FIB floppy interface board
             1771 based controller
          PDS II:
             supports DIO, data/clock seperator 
             PDS-II/S for 8" drives, -II/M for "minidrives"
    PERSCI manuals associated with DIO/PDS:
         PerSci Logic and Schematic Diagram, Diskette Drive models 270/272/277
         -- 35 pages, schematics and assemblies
         PerSCi Product Specifications, Diskette Drive model 70, 30 pages
         -- diskette format, signals, no schematics
         (Imsai) PerSci/IMSAI 270/277 runnup procedure, May 1978, 75 pgs
         (Imsai) PerSci 277 Maintenance manual (cover page), Jan 78
         --Product Specification model 277 Diskette Drive, 24 pages
         -- PerSci Installation And Maintenance Manual, 
          Dual Diskette Drive Model   277, 50 pages
         Persci data sheets, prices, w/cover note 1977
         -- model 277 dual Spec sheet, 2 pages, 2-color  1977
         -- model 70 Spec sheet, 2 pages, 2-color 1977
         -- model 270 dual Spec sheet, 2 pages, 2-color 1977
         -- 1070 Intelligent Diskettte Drive Controller (summary), 16 pages text
         ----- includes 2-page data sheets on model 70 model 270 floppy drive. No schematics
         ----- controller has parallel interface plus serial interface for commands.
         -- Price lists, 8/76, for 70, 270, 1070 3 pages text
    IMSAI HD-10 (CDC 9427H cartridge disk drive) reference manual, 200 pgs
          includes HD-10, DCFIO controller / formatter
          DA-01 S-100 bus adapter,
          Control Data copies of info on CDC 9427H drive
    IMSAI and related software documentation available (copies)
          IMDOS V2.05 Users manual, dates mid-1978
    	514 pgs as follows:
    	   IMDOS System User guide 92 pgs
    	   IMDOS ED editor User Guide 26 pgs
    	   IMDOS NED user guide 44 pgs
    	   IMDOS ASM assembler user guide 32 pgs
    	   IMDOS DDT users guide 28 pgs
    	   PIP users guide 14 pgs
    	   IMDOS programming guide 88 pgs
    	   IMDOS System Alteration guide & BIOS 52 pgs
    	   SHAKDOWN floppy disk system diagostic guide
    	      16 pgs
    	   BASIC-E User's 12 pgs, ref 82 pgs 
          IMSAI Fortran IV user manual V1.0, 100 pgs
          FORTRAN IV V3.05, 155 pgs
          IMSAI CBASIC user manual, 40 pgs
          IMDOS BIOS listings, 16 pgs
          IMDOS Users Manual, 340 pgs
          IMDOS BASIC-E manual, 80 pgs
          IMSAI 8K BASIC, 100 pgs
          CBASIC users manual, 80 pgs
    Fulcrum & WW Component Supply documentation
          MPU-Z Z80 User's Manual, June 1984 prelim. 12 pgs
          MPU-Z Z80 Ref. Manual, Mar 86 prelim.  27 pgs
          OMNIDISK Unit DMA Disk Controller Tech Ref, June 86, 140 pgs
          VIO-X user manual A1.1 8/81, w/addendum C1 11/81, 56 pgs
          Monitor program for MPU-Z and OMNIDISK, Mar 1986, 20 pgs
                 paper listing only, ZILOG Z80 source for M80 assembler
                     two columns of listings per page, many comments
          OMNIDISK Firmware source listing, "AA1.ASM", 50 pages
                two columns of listings per page, 2 years of fixes from
                1983 initial source date
    	WW Component Supply "Fulcrum" product catalog, 1981, 12 pages

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

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