A Close Look At A Little Known 8-bit Computer

If you read about the history of personal computing, you hear a few familiar names like Microsoft, Apple, and even Commodore. But there were a host of companies that were well known and well regarded back then that are all but forgotten today. Godbout computing, Ohio Scientific, and Southwest Technical Products (SWTP). SWTP is probably best remembered for having a relatively cheap printer and “TV typewriter”, but they also made a 6800-based computer and [Adrian] takes us inside of one.

The 6800 was Motorola’s entry into the microprocessor fray, competing with the Intel 8080. The computer came out scant months after the introduction of the famous Altair 8800. Although the Altair is often credited as being the first hobbyist-grade computer, there were a few earlier ones based on the 8008, but the Altair was the first to be successful.

The SWTP was notable for its day for its blank appearance. Most computers in those days had lots of switches and lights. The SWTP has a blank front with only a power switch and a reset button. A ROM monitor let you use the machine with a terminal. For about the same price as a bare-bones Altair that had no interfaces or memory, you could pick one of these up with most of the extras you would need. The memory was only 2K, but that was 2K more than you got with an Altair at that price point.

The $450 sounds fairly cheap, but in the early 70s, that was a lot of lawns to mow. Of course, while you’d need to add memory to the Altair, you’d have to add some kind of terminal to the SWTP. However, you’d wind up with something more usable but the total bill was probably going to approach $1,000 to get a working system.

Inside the box were some old-fashioned-looking PC boards and connectors that will look familiar to anyone who has been inside 1970s gear. Will it work? We don’t know yet, but we hope it does. [Adrian] promises that will be in the next video.

It is amazing how far we’ve come in less than 50 years. A postage-stamp sized $10 computer now has enough speed and memory to emulate a bunch of these old machines all at once. The SWTP has been on our pages before. A lot of these old machines and companies are all but forgotten, but not by us!

47 thoughts on “A Close Look At A Little Known 8-bit Computer

    1. I still have an AC-30 dual cassette interface for a SWTP 6800 computer. I interfaced it to a CDP1802 system for program and data storage. Boy, was that a long time ago.

    2. After mowing a lot of lawns, I too, built an 1802 system. The board was from an outfit called Netronics. I soldered everything, assembled it, toggled in the machine code to display the “Enterprise” on my TV monitor, and proved it worked. I did a few more experiments and learned a few more things about programming along the way, but never gained any real traction with it. I sold it shortly thereafter. (I do wish I still had that machine now, though!)

      After that I then mowed a LOT MORE lawns and bought a TRS-80 model I. I added lower case, reverse video, my own RAM upgrades, and a Votrax SC01 speech synth. By the time I gave that machine away, I had added the expansion port, modem and two floppy drives (which back then was a big deal).

      Those two computers really launched my engineering career… By age 17, I was coding for a paycheck.

    3. I was on the team that designed the VIP II right out of college and cut my teeth on the 1802. Programming in assembly on the 1802 was a dream compared with my foray into the z80. 16 general purpose registers where you could change their roles ( change the program counter from register 4 to register 8, etc. ). What tripped me up on the Z80 was that loading the accumulator with a value didn’t set the register flags. I banged my head for days before I realized why testing the zero flag failed after I knew it was loaded with 0. You had to do an xor on itself (or other operation) to get the flags set.

  1. I built one of these kits as a sophomore in high school. The kit cost my dad $350 but I needed a $1000 teletype to talk to it (The downside of no front panel switch register). I rented an ASR33 teletype for $20 bucks a month until my 15 year old savings account went dry. The teletype served as both terminal and mass storage (Paper tape). When the bank account dried up I bought a Kleinschmidt field teletype from a surplus auction and wrote code to convert ASCII to 5 bit Baudot. It was an adventure but it launched my career!

  2. It wasn’t.little known if you were there at the time. SWTP had existed before comouters, and kept going. They offered various peripherals like terminals and a fancy cassette controller, and kept going with the 6809. MITS nevver really got beyond the Altair, fading into some other company after a few years. SWTP was the main company for the 6800/6809. There were others like Gimix, but aimed at a higher end market.

    If you want little known, there’s the MITS 680B, which had a front panel, though I doubt many used it, and never had much penetration. It was similar to the Altair, but used yet another bus structure.

    1. No I agree. I used to drool over all this stuff in the issues of Kilobaud (I still have issue #1). I did build an 1802 around this time and it was actually serviceable, but not like an Altair. I have my eye on an old IMSAI but I’m afraid the guy is going to ask for more than I’m willing to pay for it. We’ll see…

      1. I used to have Tectonics graphics terminal sales brochures with the pages stuck together.

        I’ve thrown away better displays.
        Currently using a 50 inch 4k dumb TV. Cost less than $250 in 2020 money, about $60 in 1980 dollars. Price of about 20 5.25 floppy disks.

        1. Those price comparisons don’t really work. It took more work to buy that SWTP computer in 1975 than it does to spend $500 today.

          And you get a way better computer for $500 today than in 1975.

  3. That was still a large amount of money in 1974. I looked it up and you could multiply those prices by 5.75 in today’s dollars.

    There were very few “teen age hackers” in the early and mid 1970’s, unless they built their equipment from complete scratch or they repaired old/broken surplus – which I had to do back then. And I liked it :)

    1. That’s my experience. I was there before the Altair (I didn’t read Radio Electronics so.missed the Mark-8), but I couldn’t afford a computer in 1975. That fall, Godbout advertised a “kit”, an 8080, some RAM, an eprom and maybe some support ICs, and I coukd have scrounged the money. But no monitor, and withiut a comkuter, no means of learning to program to make a monitor. I was fifteen in 1975.

      There were kids at high school who were interested, but it was “older” people buying.

      I didn’t get my KIM-1 until April 1979.

  4. If you go to archive.org and search for Byte Magazine or Creating Computing and look just inside the front cover for issues from the appropriate time period (late 70’s), you’ll see SWTPC’s advertisements.

    1. Yes, I used to read BYTE back then and every time I saw ‘SWTPC’ my brain translated it to ‘Sweatpack’. It still does :)
      To this day I have never seen a real SWTPC machine here in Australia, I am not sure if many were imported.
      I recall reading in a magazine trade column from that era that 100 Sphere machines were (to be?) brought into Oz, but not sure if that really went through.
      Instead we had the famous first one that was beaten by a month on being the worlds first kit computer serialised in a magazine, the EDUC-8, quickly followed by a few homegrown mostly S100, 6800, 2650 single board project machines.
      In turn by 1978 or so these were followed by the TRS80, (the unaffordable) Apple ][, PET, Dick Smith System 80, Sorcerer and so on.

      1. I forgot to add, I started with an F8 Development Kit. It had 1K RAM across 8 2102’s and 1K ROM. I still have it and the box it was posted from the USA in, postmarked October 16 1978.

      2. I’m not sure betting on Sphere, a more less known computer, would have been a good choice.

        But we forget that success was relative. In the beginning lots of interest, but among a subset of the population. It.took time to prime the general population.

        In early 1977, I heard an ad on the radio for a store opening, “Compucentre”. It was evening, but I rushed right down. No computers, just calculators and video games. I always assumed they were getting ready for the future, but computers not there yest.

        Some months later I saw a small ad for a computer store. I rushed right down again, but this was real. Computer magazines and books, and computers. I can’t remember what they sold, but it seemed like an odd collection. I’d go in regularly to check the magazines, and it took a long time befkre I ever saw it crowded. And that was when the kids found it, using the display comouters.

        So a hundred Spheres isn’t much, but it probably satisfied a lot of the buyers there at the time. Somebody had to raise or collect money, organize shipping, and then get them into customer’s hands. Easy in some parts kf the US near the manufacturers, harder even in Canada or further afield.

    2. I used to yearn for the next issue of 68 Micro Journal, very much a magazine dedicated to this era of computing and hardware systems.

      And yes, SWTP, Gimix, TSC were all the rage back then.

  5. “even Commodore”??? Have you looked at Commodore’s sales stats? $450 was easily affordable for this self-employed teenager but as the author points out, I/O was the stumbling block. Hate the lawn, don’t hate the lawn mower.

  6. > The $450 sounds fairly cheap, but in the early 70s, that was a lot of lawns to mow.

    Ohhhh yes!
    Been there…
    …but started with a SC/MP.

    1. I usually only got about $3/mow, maybe $5 for a big one, and being rather rural there weren’t that many available. It couldn’t rain enough. Those shiny things in Kilobaud might as well have been on the moon, at that rate. My rising buying power intersected the falling hardware prices only about ’82, by which time the S-100s and SS-50s and so forth had already given way to the likes of the C64. Always wanted one of those ‘front panel’ machines though.

  7. I owned a SWTPC and I didn’t have to mow any lawns!

    I purchased it complete with two 8″ hard sector floppy drives, 6800 assembler, eprom programmer etc at a auction for about $50 back in 1985.
    I connected it to my Centronics parallel port office dot matrix A3 printer and immediately fell in love with Motorola assembly language.

    To say that SWTP changed my life would be a understatement and 38 years later, even tho I have moved on to STM32, MSP430 and Forth, that box is the centrepiece of my embedded memories.


    I designed and sold one embedded project with it, a motorised carriage which rapidly moved to one of 8 positions, controlled by a analog servomotor.

    However no SWTP fan can write glowing ownership reports without mentioning the built in nemesis, namely a large, less than solid motherboard and removable card system that used low cost MOLEX connectors.

    Up until ‘Dupont Cables’ took over as the worlds most horrifically unreliable connection system, that honour belonged to MOLEX pcb connectors which on the SWTP were often cracking the solder joints and going opencircuit because of all the flexing.

    So about once a month I would resolder all the connectors on the boards I would often reconnect, such as the EPROM programmer.


    1. Outside of the main frames at my college we accessed remotely and used punchcards with, the computer club at Texas A&M University had one of these. We shared a community floppy disk and wrote on the jacket which sectors we saved our files to. My first exposure to hard versus soft sector floppies.

    2. I mad some wooden “spatula” and very long “pry-wedges” that prevented any problems. On the large OSI systems the backplane is mounted on the side and from the top you can slide anything along the entire length of the connectors. Ha, I just remembered. I also made wood strips affixed under the backplane so that pressure on it did not flex the PCB!

    3. But the SWTP had an interesting bus structure. Some sockets with full access to the bus, then some I/O sockets for peripherals. The latter, the boards could be smaller, and decoding done on the motherboard.

      Thiscontrasts with the S-100 where if you added a UART, it would take up an expansion slot andwaste most if the board.

        1. But I recall the Altair didn’t have enough bus connectors. So either MITS had an upgrade, or someone else offered a mod, or maybe both. And then the linear power supply wasn’t big enough.

  8. I used to have two rocks. They cost my as much as a small car at the time. Id bang them together to produce 1 bit sounds and I could count to three with them as well.

  9. I built a pretty big chemistry spectrophotometer for florescence lifetimes around the big OSI box with 18 slots. The Molex pin connectors were so much cheaper than S100 type edge connectors but I had to make some wood tools to seat and remove the boards safely. The attraction was 6502, good RAM costs, affordable dual 8″ floppy box, and big affordable proto-boards. IIRC boards were used to add stepper controllers, 12 bit ADC for photon counters, 12 bit DACs for X-Y CRT display, ADM9511 floating point processor, and a plotter driver. It was used for a couple decades. (And all written in Forth!)

  10. I remember the ads in those pop- elect- zines at the time and also an interesting audio device that they also made. SWTPC Ambience Synthesizer 2AS-A, sounded like a real cool device at the time. When I saw one at Dayton Hamfest I grabbed It up. It can do Forbidden Planet soundtrack all on it’s own. One very prized audio effect.

  11. Wow, this brings back some fond memories. A SWTP 6809 mulitiuser computer with a 10 MB 14″ hard drive was my first foray into selling computer timeshare. I had one customer for a while, who then left because he was embarrassed he couldn’t log on because he turned the handset the wrong direction in the acoustical modem. I also had a system at work that I used in the test engineering department at Qume (Daisy wheel printer company).

    1. As you must know, SWTP expanded beyond 64K by using a 7489 RAM as an MMU. Really pretty neat. So the extra RAM coukd be anywhere, while most other 8bit computers used bankswitching to get beyond 64K. It helped that the 6809 made it easy to write programs that coukd be anywhere in RAM, all references couod be relative.

  12. I built several of these from kit to supply Central Michigan University with the first microcomputers that they had. So yes, this article definitely brings back memories!

  13. A few of us managed to persuade our school to pay for one, justifying that it would be so much more productive coding for this than punching cards and sending them off to be batch processed. Came with a teletype and 8K BASIC on punched tape. Found it was less hassle to program in assembler than to load up the tape. My first even DIY PCB was a RAM expansion board for it (single sided, with an etch resist pen, and it even showed the symptoms of working too).
    Ah, nostalgia ain’t what it used to be….

  14. My university chemistry department used one of these to run its hand built nuclear magnetic resonance machine back in the late 70s/early 80s. Working with it is one of the reasons I switched majors from chemistry to computer science.

  15. In the mid 1980’s a company I worked for had a SWTP computer but it ran on a MC6809. I think they bought an upgrade from the 6800 directly from SWTP. It ran Uniflex and the order tracking software was written in basic. We hung a LOT of terminals off it so high schools could keypad in film envelop numbers into accounts. There were over a dozen, maybe 2 dozen terminals hooked up. I helped with upgrading the system to a 20 megabyte hard drive.

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