[This post is part of “A Bicycle for the Mind.” The complete series can be found here.]
Don Tarbell: A Life in Personal Computing
In August 1968, Stephen Gray, sole proprietor of the Amateur Computer Society (ACS), published a letter in the society newsletter from an enthusiast in Huntsville, Alabama named Don Tarbell. To help other would-be owners of home-built computers, Tarbell offered a mounting board for integrated circuits for sale for $8 from his own hobby-entrepreneur company, Advanced Digital Design. Tarbell worked for Sperry Rand on projects for NASA’s Marshall Space Flight Center, but had gotten hooked on computers through coursework at the University of Alabama at Huntsville, and found the ACS through a contact at IBM.[1]
Over the ensuing years, integrated circuits became far cheaper and easier to come by, and building a real home computer on one’s own thus far more feasible (though still a daunting challenge, demanding a wide range of hardware and software skills). In June 1972, Tarbell had mastered enough of those skills to report to the ACS Newsletter that he (at last) had a working computer system, with an 8-bit processor built from integrated circuits, four-thousand bytes of memory, a text editor and a calculator program, a Teletype for input and output, and an eight-track-tape interface for long-term storage. Not long after this report to ACS, Tarbell decamped from Alabama and moved to the Los Angeles area to work for Hughes Aircraft.[2]
Three years after that, in 1975, the arrival of the Altair 8800 kit announced that anyone with the skills to assemble electronics could have the power of a minicomputer in their own home, and thousands heeded the call. A group of 150 of these personal computer hobbyists met in the commons of the apartment complex where Tarbell lived. They had come on Father’s Day for the inaugural meeting of the Southern California Computer Society (SCCS). Half of the participants already owned Altairs. Tarbell took on the position of secretary for the new society, and served on the board of directors. Within a few months, SCCS began producing its own magazine with a full editorial staff, a far more sophisticated operation than the old hand-typed ACS Newsletter; Tarbell eventually became one of its associate editors.[3]
But an Altair kit by itself was far from a complete computer system like the one Tarbell had back in 1975. It had a piddling 256 bytes of memory, and no devices for reading or writing data other than lights and switches. Dozens of hobbyists founded their own companies to sell other computer buffs the additional equipment that would answer the deficiencies of their newly-purchased Altairs. Don Tarbell was one of them. Among the major problems was the inability to permanently store or load programs and data. Once you shut off the computer, everything you had entered into it was lost. A standard Teletype terminal came equipped with a paper tape punch and reader, but even a heavily used Teletype could cost $1000.
In February 1976, Tarbell offered a much simpler and cheaper solution, the Tarbell cassette interface, a board that would slot into the Altair case and connect the computer to an ordinary cassette recorder, writing or reading data to or from the magnetic tape. Not only was a cassette machine much cheaper than a teletype, cassettes were more durable than paper, could store more data (up to 2200 bits per inch with Tarbell’s controller), and could be rewritten many times. Tarbell’s board sold for $150 assembled, $100 for a kit. He later branched out into floppy disk controllers and an interpreter for the BASIC computer language, and became a minor celebrity of the growing microcomputer scene.[4]
Tarbell’s story offers a microcosm of the transition of personal computers, over the course of the 1970s, from an obscure niche hobby to a national industry. Like Hugo Gernsback in radio half a century before, home-computer tinkerers found themselves new roles in a growing hobby business as community-builders, publishers, and small-scale manufacturers. Like Tarbell, the first wave of these entrepreneurs responded directly to the Altair, offering supplemental hardware to offset its weaknesses or offering a more reliable or more capable hobby computer.
The First Wave: Responding to Altair
The Micro Instrumentation and Telemetry Systems (MITS) Altair came with a lot of potential, but it lay mostly unrealized in the basic kit MITS shipped out. This was partly intentional: the Altair sold on the basis of its exceptionally low price (less than $500), and it simply couldn’t remain so cheap if it had all the features of a full-fledged minicomputer system.
Other deficiencies arose by accident, out of the amateurish nature of MITS. The good timing and negotiating skills of Ed Roberts, the company’s owner, had put him at the spearhead of the hobby computer revolution, but no one at his company had exceptional talent in electronics or product design. The Altair took hours to assemble, and the assembled machines often didn’t work. Follow-up accessories came out slowly as MITS technicians struggled to get them working. Tarbell’s cassette interface succeeded because it performed faster and more reliably than MITS’ equivalent. The most urgent need of the hobbyist other than easier input and output was additional memory beyond the scanty 256 bytes included with the base kit: far from enough to run a meaningful program, like a BASIC interpreter. In the spring of 1975, MITS started shipping a 4096-byte (4K) board designed by Roberts, but these boards simply didn’t work.[5]
Unsurprisingly, other hobby-entrepreneurs began to step up quickly to fill the gaps. Several of them came from the most famous of the Altair-inspired hobby communities, the Homebrew Computer Club, which met in Silicon Valley and attracted attendees from around the Bay Area. Processor Technology was founded in Berkeley by Homebrew regular and electronics enthusiast Bob Marsh and his reclusive partner, Gary Ingram. In the spring of 1975, they began offering a 4K memory board for the Altair that actually worked. Later, the company came out with its own tape controller and a display board that would make Altair into a TV Typewriter, which they called VDM-1.[6]
Only one “authorized” Altair board maker existed, Cromemco, also located in the Bay Area. Cromemco founders Harry Garland and Roger Melen met as Ph.D. students in electrical engineering at Stanford (and named their company after their dormitory: Crothers Memorial). They contributed articles to Popular Electronics regularly, and found out about Altair while visiting the magazine’s offices in New York. They originally intended to build an interface board for the Altair that could read data from their “Cyclops” digital camera design. Despite the early partnership, no Cromemco board saw the light of day until 1976.
Their slow start notwithstanding, Garland and Melen created two products of significance to MITS’ business and to the future of personal computing: the “Dazzler” graphics board the “Bytesaver” read-only-memory (ROM). Unlike the TV Typewriter or the VDM-1, which could display only text, the Dazzler could paint arbitrary pixels onto the screen from an eight color palette (though only at a resolution of 64 x 64, or up to 128 x 128 in monochrome mode). Less sexy but equally significant, the Bytesaver board stored a program that would be immediately loaded into the Altair memory on power up; prior to that an Altair could do nothing until basic control instructions were keyed in manually to bootstrap it (instructing it, for example, to load another program from paper tape).[7]
Roberts bristled at the competition from rival card makers. But more aggravating still were the rival computer makers cranking out Altair knock-offs. In 1974, Robert Suding and Deck Bemis had launched Digital Group out of Denver to support the Micro-8. After Altair came out, they decided to make their own, superior computer; Suding happily quit his steady but dull job at IBM to serve as the Woz to Bemis’ Jobs, avant la lettre. Digital Group computers came complete with an eight-kilobyte memory board, a cassette tape controller, and a ROM chip that could boot a program directly from tape. They also had a processor board independent of the backplane into which expansion cards slotted, which meant you could upgrade your processor without replacing any of your other boards. In short, they offered a computer hobbyist’s dream. The catch came in the form of poor quality control and very long waits for delivery, after paying cash up front.[8]
Other would-be Altair-killers entered the market from around the country in 1975. Mike Wise, of Bountiful, Utah, created the Sphere, the first hobby computer with an integrated keyboard and display—although production was so limited that, decades later, vintage computer collectors would doubt whether any were actually built. The SWTPC 6800 came out of San Antonio, built by the same Southwest Technical Products Corporation that had sold parts for Don Lancaster’s TV Typewriter. A pair of Purdue graduate students in West Lafayette, Indiana wrote software for the SWTPC under the moniker of Technical Systems Consultants. A few hundred miles to the east, Ohio Scientific of Hudson, Ohio released a Microcomputer Trainer Board that put it, too, on the hobbyist map.[9]
But the real onslaught came in 1976. By that time hobbyists with entrepreneurial ambition had had time to fully absorb the lessons of the Altair, to hone their own skills at computer building, and to adopt new chips like the MOS Technology 6502 or Zilog Z80. The most significant releases of the year were the Apple Computer, MOS Technology KIM-1, IMSAI 8080, Processor Technology Sol-20, and, in the unkindest cut for Roberts, the Z-1 from former ally Cromemco. Most of these computer makers solved the upgrade problem in a more blunt fashion than the Digital Group’s sophisticated swappable boards: they simply copied the card interface protocol (known as the “bus”) of the Altair. Already own an Altair? Buy a Z-1 or Sol-20 and you could put all of the expansion cards for your old computer into the new. Cromemco founder Roger Melen encouraged the community to disassociate this interface from MITS by calling it the S100 bus, not the Altair bus—another twist of the knife.[10]
Almost all of these businesses (excepting IMSAI, of whom more shortly) continued to exclusively target electronic hobbyists as their customers. The Z-1 looked just like an upmarket Altair, with a front panel now adorned with slightly nicer switches and lights. The Apple Computer and KIM-1 offered no frills at all, just a bare green printed circuit board festooned with chips and other components. Processor Technology’s Sol-20, inflected with Lee Felsenstein’s vision of a “Tom Swift” terminal for the masses, sported a handsome blue case with integrated keyboard and walnut side panels. This represented a major progress in usability from the company’s first memory boards, which came only as a kit the buyer had to assemble), but the Sol-20 was still marketed via Popular Electronics as a piece of hobby equipment.[11]
Software Entrepreneurs
In early 1975, a computer hobbyist who wanted a minicomputer-like system of their own had only one low-price option: buy an Altair; then build, or wait for, or scrounge, the additional components that would make it into a functional system. Eighteen months later, abundance had replaced scarcity in the computer hobby hardware market, with many makes, models, and accessories to choose from.
But what about software? A working computer consisted of metal, semi-conductor, and plastic, but also a certain quantity of “thought-stuff,” program text that would tell the computer what, exactly, to compute. A large proportion of the hobby community had a minicomputer background. They were accustomed to writing some software themselves and getting the rest (compilers, debuggers, math libraries, games, and more) from fellow users, often through organized community exchanges like the DEC user group program library. So, they expected to get microcomputer programs in the same way, through free exchange with fellow hobbyists. Even in the mainframe world, software was rarely sold independently of a hardware system prior to the 1970s.[12]
It came as a shock, then, when, immediately on the heels of Altair, the first software entrepreneurs appeared. Paul Allen and Bill Gates—especially Gates—were roughly a decade younger than most of the early hardware entrepreneurs, at just 22 and 19, respectively. Compare to Ed Roberts of MITS at 33; Lee Felsenstein of Processor Technology, 29; Harry Garland of Cromemco, 28; Chuck Peddle of MOS Technology and Robert Suding of the Digital Group, both 37. These two young men from Seattle had caught the computer bug at the keyboard of their private school’s time-sharing terminal; they had finagled some computer time at a Seattle time-sharing company in exchange for finding bugs, but had no serious work experience that would have immersed them in the practices of the minicomputer world.
For all their youth, though, Gates and Allen brimmed with ambition, and when they saw the Altair on the cover of Popular Electronics, they saw a business opportunity. Of course, everyone knew that a computer would need software to be useful, but it was not obvious that anyone would pay for that software. Gates and Allen, having not yet grown accustomed to getting software for free, had an easier time imagining that they would. They also knew that the first program any self-respecting hobbyist would want to get their hands on was a BASIC interpreter, so that they could run the huge existing library of BASIC software (especially games) and begin writing programs of their own.
Like Cromemco, Gates and Allen started out as partners with MITS—within days of seeing they Altair cover, they contacted Ed Roberts promising a BASIC interpreter. They delivered in March, despite having no Altair, nor even an 8080 processor—they developed the program on a simulator written by Allen for the DEC PDP-10 at Harvard, where Gates was enrolled as a sophomore. In another debt to DEC, Gates based the syntax on Digital’s popular BASIC-PLUS. Allen moved to Albuquerque soon after, to head a new software division at MITS. Gates eventually followed to nurture their independent software venture, Micro-Soft, though he did not completely abandon Harvard until 1977.[13]
Many hobbyists balked at the culture shock of paying for software, and freely exchanged paper tapes of Altair BASIC in defiance of Micro-Soft and MITS, prompting Gates’ famous “Open Letter to Hobbyists,” in February 1976. There he made the case that software writers deserved compensation for their work just as much as hardware builders did, prompting a flurry of amici curiae from various corners of the hobby (with far more weighing in for the defendants than the plaintiff).
But, though this controversy is famous for its retrospective echoes of later debates over free software, Gates and Allen rendered the issue irrelevant almost immediately, by switching to a different business model. They began licensing BASIC to computer manufacturers at a flat fee, instead of a royalty on each copy sold. MITS paid $31,200, for example, for the BASIC for a new Altair model using the Motorola 6800 processor. The licensor could choose to charge for the software or not, Micro-Soft didn’t care, but they typically didn’t. This approach bypassed the cultural conflict altogether; BASIC interpreters and other systems software became a bullet point in a list of advertised features for a given piece of hardware rather than a separate item in the catalog.[14]
Having a BASIC would let you run programs on your computer; but the other crucial linchpin for an easy-to-use microcomputer system was a program to manage your other programs and data. As faster and denser magnetic storage supplanted paper tape, computer users needed a way to quickly and easily move files between memory and their cassettes or floppy disks. By far the most popular tool for this purpose was CP/M, for Control Program for Microcomputers.
CP/M was the creation of Gary Kildall, who got his hands on his first microcomputer directly from the source: Intel. Kildall grew up in Seattle and studied computer science at the University of Washington, where he had a brief run in with Gates and Allen, who at the time were teenagers who worked at a company part-owned by one of his professors, the Computer Center Corporation, in exchange for free computer time. Drafted into the army, Kildall used his connections at the University and his father’s position as a merchant marine instructor to get posted instead to naval officer training, and then a position as a math and computer science teacher at the Naval Postgraduate School in Monterey. After completing his obligations to the Navy in 1972, he stayed on as a civilian instructor.[15]
That same year, Kildall learned about the Intel 4004, and, like so many other computer enthusiasts, became enchanted with the idea of a computer of his own. The most obvious route was to get his hands on Intel’s development kit for the 4004, the SIM4-01, intended to be used by customers to write software for the new chip. So Kildall began talking to people at Intel, and then consulting at Intel, and in exchange for software written for Intel, managed to acquire microprocessor development kits for the 4004, and then later the 8008 and 8080 processors.[16]
The most significant piece of software Kildall provided to Intel was PL/M, Programming Language for Microprocessors, which allowed developers to express code in a higher-level syntax that would then be compiled down to the 4004 (or 8008, or 8080) machine language. But you could not write PL/M on a microcomputer, it didn’t have the necessary mass storage interface or software tools; clients were expected to write programs on a minicomputer and then flash the final result onto a ROM chip that would power whatever microprocessor application they had in mind (a traffic light controller, for example, or a cash register.) What Kildall dreamed of was to “self-host” PL/M: that is, to author PL/M programs on the same computer on which they would run. By 1974 he had assembled everything he needed—a Intellec 8/80 development kit (for the 8080), a used hard drive and teletype, a disk controller board built by a friend—except for a program that could load and store the PL/M compiler, the code to be compiled, and the output of the compilation. It was for this reason, to complete his own personal quest, that he wrote CP/M.[17]
Only after the fact did he think about selling it, just in time to catch the rising wave of hobby computers. Though Kildall later offered direct sales to users, he began with the same flat-fee license model that Micro-Soft had adopted: Kildall sold the software to Omron, a smart terminal maker, and then to IMSAI for their 8080 computer, each at a fee of $25,000. He incorporated his software business as Intergalactic Digital Research (later just Digital Research) in Pacific Grove, just west of Monterey. Gates visited in 1977 to float the idea of a California merger of the two (relative) giants of microcomputer software, but he and Allen decided to relocate to Seattle instead, leaving behind an intriguing what-if.[18]
CP/M soon became the de-facto standard operating system for personal computers. Having an operating system made writing application software far easier, because basic routines like reading data from disk could be delegated to system calls instead of being re-written from scratch every time. CP/M in particular stood out for its quality in an often-slapdash hobby industry, and could easily be adapted to new platforms because of Kildall’s innovation of a Basic Input Output System (BIOS), which acted as a translation layer between the operating system and hardware. But what bootstrapped its initial popularity was the IMSAI deal, which attached Digital Research to the rising star in what up to that point had been Altair’s market to lose.[19]
Getting Serious?
There was one company thinking different about the microcomputer market in 1975: IMSAI, headquartered in San Leandro, California, intended to sell business machines. It had the right name for it, an acronym stuffed wall-to-wall with managerial blather: Information Management Sciences Associates, Inc. William (Bill) Millard was an IBM sales rep, then worked for San Francisco setting up computer systems, and founded IMS Associates to sell his services to companies who needed similar IT help.
Despite the anodyne name he gave to his company, Millard, too, felt the influence of the ideologies of personal liberation that seemed to rise from San Francisco Bay like a fog. But unlike a Lee Felsenstein or a Bob Albrecht, he though mainly of liberating himself, not others: he was a devotee of Erhard Seminars Training, or est, a self-help seminar which promised paying customers access to an understanding of the world-changing power of their will in just two weekends; according to Erhard, “If you keep saying it \ the way it really is \ eventually your word \ is law in the universe.”[20]
Neither Millard nor either of his technical employees (part-time programmer Bruce Van Natta and physicist-cum-electrical engineer Joseph Killian), had any prior interest or experience in home computers; they stumbled into the business almost by accident. Their primary contract, to build a computer networking hub for car dealerships based on a DEC computer, had begun spiraling towards failure. Casting about for some solution, they latched onto the news of Altair’s success: here was an inexpensive alternative to the DEC. When Altair refused to deliver on their timetable, they decided, in late summer of 1975, to clone it instead. And, to get cash flow going to pay their expenses and loans, they would sell their clone direct to consumers as well, while working to complete the big contract. When orders from hobbyists began to pour in, they abandoned the automotive scheme altogether to go all-in on their Altair clone.[21]
The IMSAI 8080 began shipping in December 1975, at a kit price of $439. Millard cultivated an est culture at the company; employees with the “training” were favored, and total commitment to the work was expected. Some employees considered Millard a “genius or a prophet,” spouses and children of employees showed up after school to help assemble computers. By April, they were doing hundreds of thousands of dollars per month in sales. IMSAI was board-compatible with MITS but made improvements that stood out to the connoisseur: a more efficient internal layout, a cleaner and more professional exterior, and a seriously beefed-up power supply that could support a case fully loaded with expansion boards. These advantages appealed enough to buyers to make it Altair’s top competitor in 1976.[22]
But what most set IMSAI apart in 1976 was the fact that it was not led by hobby entrepreneurs, but by a business man who wanted to build business machines. An advertisement in the May 1976 issue of BYTE magazine described the IMSAI as a “rugged, reliable, industrial computer with high commercial-type performance,” as opposed to “Altair’s hobbyist kit” (the IMSAI was of course also sold as a kit), along with obscure allusions to expensive IMSAI business products (Hypercube and Intelligent Disk) that never materialized. This was an odd pretense to put on while advertising in BYTE—a publication featuring articles such as “More to Blinking Lights than Meets the Eye” and “Save Money Using Mini Wire Wrap.” This is not to say that IMSAI (or its contemporaries) had no commercial customers or applications. Alan Cooper, known later for creating Visual Basic, wrote a basic accounting program for the IMSAI in 1976 called General Ledger. But these applications remained a small minority among the mass of buyers who were computer-curious.[23]
In 1977, IMSAI began advertising a “megabyte micro,” another fantasy. Such a powerful and expensive machine could sell in the higher end of the minicomputer market, but not to IMSAI’s actual buyers, hobbyists who were buying kits for less than a thousand dollars out of retail storefronts.IMSAI tried again to attract serious business customers with its second major product, the all-in-one VDP-80, which began shipping in late 1977 with an integrated keyboard, display, and dual disk drives, but it was plagued with quality defects, and lacked any application software for its would-be business customers to use.[24]
Those customers did arrive in large numbers in good time, but only after a second wave of all-in-one computers appeared, aimed at the mass-market, and after the emergence of useful application software to run on them.
[1] Don Tarbell, “Mounting DIL ICs,” ACS Newsletter, August 1968; Sheila Clarke, “A Home Computer Pioneer …profile of Don Tarbell,” 133-136.
[2] Don Tarbell “A Working Computer,” ACS Newsletter, June 1972.
[3] “Computer Retailing ‘Father’ Reflects and Projects,” Infoworld (April 13, 1981), 20; “Looking Back – June 1975,” Kilobaud (June 1977), 20; “Officers” and “Board of Directors,” SCCS Interface 1, 1 (December 1975), 1; Larry Press “Thank You For Waiting!”, SCCS Interface 1, 9 (December 1976), 1.
[4] “New Products,” SCCS Interface 1, 3 (February 1976), 29.
[5] Freiberger and Swaine, Fire in the Valley, 52, 55-58, 61.
[6] Processor Technology used “static” memory chips (SRAM), which was more expensive than the “dynamic” memory (DRAM) used by MITS, but did not require additional circuitry to periodically refresh the memory bits. This made it simpler to build with. Freiberger and Swaine, Fire in the Valley, 62.
[7] Freiberger and Swaine, Fire in the Valley, 62-63; Stan Veit, Stan Veit’s History of the Personal Computer (Asheville, NC: Worldcomm, 1993), 103-106.
[8] Robert Suding, “digital group computers – the real story,” 2004, https://web.archive.org/web/20040415171330/http://www.ultimatecharger.com/dg.html; Bryan Blackburn, “The Digital Group,” Byte Collector, 2004, https://bytecollector.com/the_digital_group.htm. t
[9] Freiberger and Swaine, Fire in the Valley, 78-81; “Sphere 1,” Vintage Computer Federation Forums, June 22, 2011, https://web.archive.org/web/20230319210822/https://forum.vcfed.org/index.php?threads/sphere-1.26154/; Scientific Instruments, “The 6000 Series Computer Family,” Byte (December 1975), 102.
[10] Freiberger and Swaine, Fire in the Valley, 66. Apple and the KIM-1 did not use the S100 bus, which was based on the 8080 microprocessor pin interface, because they used the MOS Technology 6502 processor, which had a quite different design.
[11] Robert M. Marsh and Lee Felsenstein, “Build SOL: An Intelligent Computer Terminal,” Popular Electronics (July 1976), 35.
[12] Martin Campbell-Kelly, From Airline Reservations to Sonic the Hedgehog
A History of the Software Industry (Cambridge: MIT Press, 2003), 89-119. Campbell-Kelly reports the estimated total of software sales at $20-50 million in 1969, versus about $4 billion in total mainframe computer sales: Marcus E. Einstein and James C. Franklin, “Computer Manufacturing Enters a New Era of Growth,” Monthly Labor Review (September 1986), 10.
[13] Stephen Manes and Paul Andres, Gates: How Microsoft’s Mogul Reinvented an Industry—and Made Himself the Richest Man in America (New York: Touchstone, 1994), 63-76.
[14] Manes and Andres, Gates, 88-97.
[15] Gary Kildall, Computer Connections: People, Places, and Events in the Evolution of the
Personal Computer Industry (unpublished: 1994), 26-30.
[16] Kildall, Computer Connections, 40-41, 46.
[17] Kildall, Computer Connections, 49-55.
[18] Manes and Andrews, Gates, 120-121. Four years later, as we will (I hope) get to an in a later installment, in another great “what-if,” Kildall would miss out on an IBM PC operating system deal that Gates closed.
[19] Kildall, Computer Connections, 59-61; David Laws, “Fifty Years of the Personal Computer Operating System,” Computer History Museum Blog (April 18, 2024), https://computerhistory.org/blog/fifty-years-of-the-personal-computer-operating-system.
[20] Quoted in Jonathan Littman, Once Upon a Time in Computerland: The Amazing, Billion-Dollar Tale of Bill Millard (New York: Simon & Schuster, 1990), 39.
[21] Littman, Once Upon a Time in Computerland, 29-35.
[22] Littman, 36-42, 60; Veit, 58-60. A report from Electronic News evidently estimated Altair at 25% of the market in 1976 and IMSAI at 17%, but I have been unable to track down the original source. Manes Paul Andres, Gates, 101 and 480.
[23] IMS Associates, “If you thought a rugged…,” Byte (May 1976), 97; Veit, Stan Veit’s History of the Personal Computer, 65; “In the Queue,” Byte (January 1976) 3; “In the Queue,” Byte (April 1976), 3; “Oral History of Alan Cooper,” Computer History Museum (March 13, 2017), 19-20. According to Cooper, his accounting software business made $50,000 in its second year (presumably 1977, so significantly less in 1976), compared to an estimated $25 million microcomputer industry in 1976 per Manes and Andrews, Gates, 101.
[24] Rob Barnaby, an IMSAI programmer, had proposed to write a word processor for the VDP but was rebuffed by Willard; he later went on to write the very successful Word Star. Veit, 61, 69-70; Littman, 144-146.
