A Scratch-Built Forgotten Classic Of The Early PC Age

All the retrocomputer love for Commodore machines seems to fall on the C64 and Amiga, with a little sprinkling left over for the VIC-20. Those machines were truly wonderful, but what about the Commodore machine that paved their way? What about the machine that was one of the first to be gobbled up in the late 1970s by school districts eager to convert a broom closet into the new “computer lab”?

The PET 2001 might be a little hard to fall in love with given its all-in-one monitor, cassette recorder, and horrible chiclet keyboard, but some still hold a torch for it. [Glen] obviously felt strongly enough about the machine to build a PET from current production parts, and the results are pretty neat. When trying to recreate a 40-year old machine from scratch, some concessions must be made, of course. The case doesn’t attempt to replicate the all-in-one design, and the original keyboard was mercifully replaced by a standard PS/2 keyboard. But other than that the architecture is faithfully replicated using new production 65xx chips and 74HCT family logic chips. [Glen] had to jump through some hoops to get there, but as the video below shows, the finished machine plays a decent game of Space Invaders.

We’ve seen a PET brought back from the grave by FPGA and a C64 emulated on a Raspberry Pi, but going back to basics and building this from scratch was a fitting homage to an important machine in PC history.

33 thoughts on “A Scratch-Built Forgotten Classic Of The Early PC Age

  1. In 30 years I expect that there will be people who care about the early Raspberry Pi computers, but I don’t expect that many will care about the Pi A. The Vic-20 is a similar comparison.

    When the Vic-20 and the C64 first came out, the C64 was about triple the prices of the Vic-20 (IIRC, I was in Jr high at the time), but within a few months (a year at the most), the C64 had dropped below the original price of the Vic-20. So it’s a footnote that had no long term significance.

    1. That’s interesting comment.

      I acquired a Vic 20 when i was I high school – while my mates had 64’s .

      While all they could do was play games I had my Vic 20 running the light show for discos – I could drive 8 channels at 240v up to about 5A I guess.

      1. what interface did the Vic-20 have that the C64 didn’t? I remember the C64 having the same interfaces, but with more computer available to use them

        The C64 was much more than a game machine (even if that’s all some people used it for)

        1. I think the OP’s point was that simplicity begets innovation. The ZX80 (and 81) encouraged similar DIY endeavours straight on the bus (e.g eprom programmers) – whilst interfacing to the BBC micro was more involved — with the cassette “remote” relay often being abused.

          1. IIRC both of them had a card-edge interface on the back that gave you access to the system internals, and this was the era of the fat manual that included wiring diagrams.

            you weren’t limited to the serial interface that was used for floppy drives, etc. (again, IIRC, this was the same for both models)

          2. A major bummer of the C64’s and VIC20’s User and Expansion-port was the nearly complete lack of protection circuitry. I remember “building” a reset switch (the C64 had no built in one) and counting the pins wrong. Magic smoke escaped and it cost 50 Deutsche Mark (about $100 in todays money) to put the magic smoke back in tbe C64.
            Hardware experiments were uber-expensive back then for a 15 year old like me.
            Parts that are a dime a dozen today were serious bucks back then.

    1. I remember a program for the c64 in an 8-bit-magazine which used some low level commands to let the stepper motor in the 1541 disk drive play music.
      The head was quickly thrown out of alignment by that kind of abuse and the drive was basically trashed.

      1. You can not ruin the stepper motor inside an 1541, otherwise every Scratch could ruin it as it slams the head up to 40 times as it has no way to detect where the start and stop is besides brute-forcing it.

  2. Impressive build, and very nicely done! Very clean build and the 19″ rack form factor does add to the appeal.

    Regarding “a little sprinkling left over for the VIC-20”, I must say that there is still a huge interest for the VIC-20. FPGA implementations are made, cartridges are being developed, games are being written even a demonstration of full motion video through the user port has been shown on youtube. I wouldn’t dare to say that the VIC-20 community is smaller than the PET community. Although I fully agree that the PET is much more iconic mostly because of it’s looks.

    For those who aren’t aware of the very active VIC-20 scene, please take a look at one of the forums:
    http://sleepingelephant.com/ipw-web/bulletin/bb/index.php

      1. The Atari 8-bit computers were advanced well before their time. They had several custom chips, each comparable in complexity to the 6502, to handle video, sound, etc. Some of the designers of Atari 8-bit went on to design the Amiga. Surprisingly, people are still innovating using Atari 8-bit, including one clever fellow who developed a screen mode with full interlacing, so double the vertical resolution, instead of the half interlacing native to the hardware. There are motherboards offered where you can plug in the Atari chips into a relatively modern mini-ITX environment with PS/2, SD cards, and banked memory.

  3. I had an Apple IIe in the mid-1980s and remember envying my Commodore 64-owning friends… the Commodore was clunkier but it seemed like you could do more. Specifically, four-voice audio.

    1. Here in Germany/Europe the killer-feature of the C64 was the abundance of games. There were simply a Gazillion of them. Everybody had (sometimes literally) five feet high stacks of diskettes and tapes.
      80s memories…

  4. In 1972 I got a computer kit, made by an American company called Commodore, and named “Pet” (of which I am absolutely certain!). It was based on on the Intel 8008 and was in many ways similar to the Imsai and and Altair which came afterwards. It did not include a monitor or keyboard and was nothing at all like the better known Commodore Pet. I’ve never been able to find any references to the model I had, perhaps because they only sold about 60 of them and I had to make quite a few corrections to the motherboard to get it working. Anyone else remember that “Pet”?

      1. The Scelbi and Mark-8 were two different computers, but yeah. This definitely sounds like one of them. Doesn’t sound like you still have yours, but if you do, I know Mike Willegal is trying to assemble a list of known Scelbi units. Had around a dozen or so still in existence, I think.

        1. I had to go look those up, I was not familiar with them. But that’s not what I had. Mine was definitely called “Pet” and the logo was a dog with a monitor for a head. The monitor had a large “C” on it in a squared off Micr bank font. If was definitely from a company called “Commodore” although I suspect it may have been just one guy. My father and I ordered it from an ad that was running in more than one magazine at the time, Popular Science and Popular Mechanics I think. We ordered it in early November and received it just in time for Christmas 1972. It used an “engineering sample” of the Intel 8008. It had 1K of memory that was sold separately. It included a stamped aluminum housing for the boards, and plans for building a full case from wood. With the memory and power supply, it sold for about $2000. I was 9 years old at the time. It had to be assembled from a kit, but I was already a skilled solderer at that age. There were numerous mistakes on the printed circuits and we communicated with the company via snail mail to get them all resolved. It wasn’t until February or March that we actually got it functioning. I spent countless hours learning how to program it in assembly, including converting hand-written assembler in notebooks to hex code so I could toggle it in. I also eventually got an old teletype for it which connected with a 20ma current loop, and a 50 baud acoustic coupler modem although I could not find anything/one to connect to in 1973.
          My father was a Master electrical and mechanic engineer, but definitely an Analog guy. He never fully grasped Digital, but he recognized it was the future and always encouraged my interest in computers.

      1. The PET and CBM 30xx keyboard was pretty bad. Fortunately, at the time none of us had proper typing skills anyway so it didnt matter much.

        Gosh, i miss those days in the broom cupboard…

  5. Oh my aching field density equalizers!
    I got my start in BASIC programming on one of those. Updated variety, not the fellows with the ucky keyboard. Years later two things happened, I found a book describing the inside world of the VIC-20 and was enrolled into a program that basically ran one-on-one at a VoTech school in Westchester County, the instructor says he ended up with a big crowd of them. When we were done with things, he would let me do things with an exposed VIC-20 that most other people, read those of us who do not read this blog, would scream foul about.

    He also collected the remains of a Computerland that, ah, was in White Plains at one point, I managed to get a line on Apple’s ProDOS collection even before it got its guts dumped. And that was exploring how the OS for the Apple III managed to do things.

    Despite doing programming in BASIC on the Stamp, and doing equally strange things on the PC world and of course the Raspberry Pi, and Linux in general, I have a soft spot in my hearts for the R6502. If I can find my collection of oddball parts, and it contains somebody from the same line that includes the R6502, I might consider a simple system based on it. But nothing like the Cactus design.

  6. Back in the early ’80s I remember my small-town high-school had a half dozen PET computers networked with a device called a “MUPPET”. I think it was more of a resource sharing tool than a networking device but I can still remember my teacher announcing “The Muppet is dead!” and then we had to follow some procedure to get it up again. Those PETs were horrible compared to the Apple ][+ I had at home. :-) …yes, the Keyboard was truly an obamanation.

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