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Build Technology

Rebuilding the PDP-8 With a Raspberry Pi 92

braindrainbahrain writes: Hacker Oscarv wanted a PDP-8 mini computer. But buying a real PDP-8 was horribly expensive and out of the question. So Oscarv did the next best thing: he used a Raspberry Pi as the computing engine and interfaced it to a replica PDP-8 front panel, complete with boatloads of fully functional switches and LEDs.
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Rebuilding the PDP-8 With a Raspberry Pi

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  • ...so that you can wire up more MSI TTL to add instructions or other features. That's the charm of the old-school PDP-8. (Okay, not the really old-school DTL version, but the version I remember in a friend's dorm room...)

  • by Anonymous Coward on Friday March 27, 2015 @12:42PM (#49355805)

    Anyone have a link to a less sucky version of the article?

    • by Anonymous Coward on Friday March 27, 2015 @04:58PM (#49358021)

      Thank you for that comment.
      Hack-a-Day features great content, but they bastardize it with
      some of the worst presentation skills on the internet.
      If there is a contest for "Worst Presentation" they should win.
      People who read HAD don't want "cool" webpages.
      They want clear and well organized webpages.
      The folks behind HAD have a great product - they just don't know
      how to package it. pity.

    • by Anonymous Coward on Friday March 27, 2015 @06:52PM (#49358567)
      I can't even get that pile of Google.blogblog Javashit to render with Javashit enabled.

      And that's fucking sad. It's a static fucking web page with some text, some images, and at most an embedded YouTube video. Fuck this Web 2.0 shit, and fuck the web designers who made it a default behavior for blogspot.

  • by X10 ( 186866 ) on Friday March 27, 2015 @12:45PM (#49355825) Homepage

    I programmed a PDP8 in Fortran. In the good old days....

    • by kenaaker ( 774785 ) on Friday March 27, 2015 @05:34PM (#49358185)
      We had a PDP 8/I that the EE guys built a high speed paper tape reader for. One I/O addresss made it go forward, the other backward. Watching various sort algorithms run against data on the tape were educational in a unique way.

      We also had a paper tape based 4K 2Pass Algol compiler that worked, it waited until you reloaded the freshly punched tape of intermediate format to start the next pass and gave you an loadable paper table on the final pass.

      Not bad for a machine that had 8 Opcodes.

      • by Thor Ablestar ( 321949 ) on Friday March 27, 2015 @08:50PM (#49359029)

        Oh, the paper tape... When I was a Comsomol member there were FS-1500 tape readers made in Chechoslovakia. They were really high speed - 1500 bytes per second. The tape just flew through them nonstop. When the first Western readers arrived (made in Poland by US license), they were slow as snails. But the Western tape punchers were really good.

        • by hackertourist ( 2202674 ) on Saturday March 28, 2015 @04:10AM (#49360141)

          Interesting; things apparently regressed before they could progress. The first paper tape reader for a computer (Colossus [wikipedia.org]) read at 5000 characters/s in normal operation, and could be cranked up to 9700 char/s (85 km/h), but the tape wasn't strong enough to survive that speed for long.
          Of course, the Official Secrets Act made sure the Colossus design wasn't available on the open market.

  • by Anonymous Coward on Friday March 27, 2015 @12:45PM (#49355837)

    PDP 8/I was the first computer I worked on. Operating system TSS 8.22D, programing language PAL-D (twos complement math) , whopping 16K of memory. We had to use the front panel toggle switches to toggle in a program that when you executed it would read a program stored on paper tape into memory so we could boot off the hard drive. You could use assembler to make the panel lights do funny things to frighten newbs. What a hoot. Hope this person has as much fun as I did.

  • by Camel Pilot ( 78781 ) on Friday March 27, 2015 @12:54PM (#49355895) Homepage Journal

    "Hacker Oscarv wanted a PDP-8 mini computer" the question needs to be asked... why? This is part of humanity I just don't understand. An infinite number of useful potential projects lay before me and the thought of playing around playing with or restoring 'vintage hardware' is just opportunity cost.

    • Re:Why??? (Score:5, Insightful)

      by gstoddart ( 321705 ) on Friday March 27, 2015 @01:02PM (#49355967) Homepage

      I've long since stopped asking why, and just gotten on with "why not?"

      Building a replica of a platform gives you the experience of doing it, the understanding of the process, familiarity with the tools you're using ... and possibly some bragging rights among your fellow nerds.

      Why pimp out your CPU case with neon? Why put spinners on your rims? Hell, why have cars anything other than black, which should suffice for anybody? Why play video games? Why watch TV?

      None of these accomplishes anything other than filling in time or soothing your own need for something you think is cool.

      To you, it's opportunity cost. To someone else, it's "why the hell not?" It's something to do they find amusing.

      Compared to half the crap you see on YouTube or anywhere else with humans ... I don't see this as being worse than anything else.

      With all the dumb crap humans do every day, there's at least some coolness to this.

      And I'm betting you can identify at least 10 things you do every week which you couldn't answer "why" if pressed on the issue.

      • by Anonymous Coward on Friday March 27, 2015 @01:14PM (#49356077)

        Why pimp out your CPU case with neon?

        Because you are an idiot.

        Why put spinners on your rims?

        Because you are an idiot.

        • by gstoddart ( 321705 ) on Friday March 27, 2015 @01:27PM (#49356225) Homepage

          Because you are an idiot.

          Snark from an anonymous coward is about as useful and purposeful as any of my examples.

          Ergo, by your own logic, you are an idiot.

          • Re:Why??? (Score:4, Insightful)

            by TWX ( 665546 ) on Friday March 27, 2015 @01:52PM (#49356511)
            He's snarky, but there's a point when 'additions' start to harm the machine rather than to improve it. Neon tubes with their associated high voltage and extremely high cycling rate draw a lot of power for not real benefit and introduce electromagnetic noise into the computer. Spinners on car wheels mess with the rotational and steering dynamics of the vehicle and remove one cue to other drivers as to what the vehicle is doing as they can no longer look at the wheels to see if the car is starting to pull forward or not.

            There are tradeoffs between aesthetics and functionality. Sometimes the majority of the population feels that those aesthetics are worthwhile and sometimes they don't. Personally I want the indicators on my computer to actually convey something, so having a huge light behind a large transparent open panel in the side that's on just because the computer is powered on doesn't help me while individual indicators for fans and disks could. On the other hand, if I spent considerable time and skill dremelling-out a logo through the side panel, then perhaps the powerful light might actually add something to the experience.

            If someone wants to reimplement some antiquated hardware for their own kicks that's fine. I've got dumb RS-232 terminals on my desks at both work and home, so I am not immune to this either. I don't expect others to find it cool either though, as there aren't that many people that grew up pre-GUI or in the BBS days in this hobby anymore, so I do it for myself, not for anyone else's approval.
            • by kenai_alpenglow ( 2709587 ) on Friday March 27, 2015 @08:19PM (#49358933)
              I remember one of my EE classes (microprocessors class? it's been several decades) was basically "how to design and build a PDP-8 using logic gates". One of the more interesting classes I took. Building up the thing from various blocks gave good insight. So, yes, it can be valuable to "resurrect" old hardware.
          • by Anonymous Coward on Friday March 27, 2015 @03:11PM (#49357177)

            He isn't wrong.

      • by Chris Katko ( 2923353 ) on Friday March 27, 2015 @03:30PM (#49357395)
        "Why?" is the goto card for people who don't achieve anything.

        The things you learn re-inventing the wheel can be applied in various parts of your future projects.

        It's like asking why solve a math problem? Obviously, to learn how to do math for the chance that you see a problem that you DON'T have an easy answer already available. Hell, that's what an entire engineering degree is. It's not "can you solve problem X" because problem X will almost never occur in real life in an isolated environment. The purpose is "can you solve these kinds of problems." And how do you learn to solve problems? By looking at ones people have already solved.
      • by trumpetplayer ( 520581 ) on Friday March 27, 2015 @07:20PM (#49358701)

        > Hell, why have cars anything other than black, which should suffice for anybody?

        You don't live in a hot, sunny place, do you? :-D

      • by Bing Tsher E ( 943915 ) on Friday March 27, 2015 @08:12PM (#49358913) Journal

        Hell, why have cars anything other than black, which should suffice for anybody?

        Ahem. I drive a stripped-model black Ford Ranger. It's about as equivalent a Ford to the Model T as was made in 2006.

    • by rochrist ( 844809 ) on Friday March 27, 2015 @01:04PM (#49355985)
      Why would someone want an antique car?
    • by Anonymous Coward on Friday March 27, 2015 @01:08PM (#49356027)
      You're looking at it wrong. You are trying to understand it using economics, and of course it wouldn't make sense from that standpoint. He is probably looking at it from an emotional or respect standpoint, or a desire to understand those people that came before him, and that is worth more to him.

      Now go kill your gramps because frankly he's outdated and society's resources could better be spent on someone younger.
      • by jythie ( 914043 ) on Friday March 27, 2015 @04:00PM (#49357641)
        Economics is generally a terrible way to try to understand a motivation since, broken down to its roots, it has no value judgements in it. Every economic model or approach takes an outside value preference as an input.
    • by Anonymous Coward on Friday March 27, 2015 @01:15PM (#49356089)

      Why did you waste time on Slashdot asking that question when you could have done something useful that had objective return?

      No everybody needs to answer to your particular idea of what their time, effort or money should be used for. People are allowed to do things because it makes them happy. They don't need a reason, they only need to enjoy it. Do you partake in any particular form of entertainment? Being entertained is not particularly useful, it just "wastes" time.

      Here's some advice: If you don't understand why somebody would want or do something, then maybe it's not for you. It's ok to not understand but don't act like the person who does is a complete idiot for not feeling the same way about it. To most of the rest of the world, being really into computers is a waste of time.

      Time you enjoyed wasting isn't wasted.

    • by Anonymous Coward on Friday March 27, 2015 @01:18PM (#49356115)

      Same reason why some pilots prefer flying Piper Cubs over flying jets.

      Or why folks prefer old muscle cars over today's cars.

      Or why many photographers prefer film over digital.

      I used a PDP-11 and I actually kind of miss it. Booting it up by flipping orange and white switches and hitting "Run" and "Halt" on the front panel ...

      Writing a program and just a program and not having to worry about UI, bells (OK We did have bells), eye candy, "user experience", yadda yadda yadda ...

      We wrote a program to help solve a problem. We had to actually think about hardware - it wasn't an abstraction like it is today.

      Computers weren't a toy or gadget - they were a piece of expensive hardware that you used because you needed it.

      And this guy ... jeeze, some of that old shit is on the scrap heap. I don't know why he found it to be expensive.

      And ... oooooo Matlock is on!

      • by TWX ( 665546 ) on Friday March 27, 2015 @01:57PM (#49356577)
        Yeah, I almost bought a surplus PDP-11 from my college surplus about fifteen years ago. Held off because I'd have had to unplug my stove to power it, and my small apartment was not suited to having a minicomputer in it. It would have cost me less than $100 for two racks worth of equipment.
        • by Thor Ablestar ( 321949 ) on Friday March 27, 2015 @09:22PM (#49359157)

          Same for me. But you could install a memory rack over the i/o rack in processor box and find a HDD controller instead of removable packet drives. It would give you an usable PDP-11 in a half-height 19-inch rack (Processor/memory, FDD and HDD in it, magtape controller). I fed my PDP-11 from a simple outlet while the electricians invented the special attachment.

    • by Anonymous Coward on Friday March 27, 2015 @01:30PM (#49356269)

      I just lump these guys in with the Civil War reenactment bunch.

      • by Anonymous Coward on Saturday March 28, 2015 @11:26AM (#49361293)

        “We are on earth to fart around. Don’t let anybody tell you any different.” – Kurt Vonnegut, A Man Without a Country

        "If it makes them happy, and it makes me happy, why should anyone care?" – Linus Van Pelt

    • by Virtucon ( 127420 ) on Friday March 27, 2015 @01:55PM (#49356555)

      Nostalga. I used to have a beer fridge sitting inside of an old S/370 system cabinet. Sure it took up 20 times the space but it was still cool to look at in the garage.

    • by jythie ( 914043 ) on Friday March 27, 2015 @03:57PM (#49357609)
      'Useful' is subjective, esp living in a society where our basic needs are so easily met (at least for the type of person who is likely posting here).

      While people might wrap up their reasons in something with more authority or social support behind it, ultimately, most projects we do are 'because it is cool'.
    • by Anonymous Coward on Saturday March 28, 2015 @09:04AM (#49360827)

      Because not everyone is a soulless accountant?

      • by Anonymous Coward on Sunday March 29, 2015 @11:05AM (#49365361)

        > Because not everyone is a soulless accountant?

        Ironic because the hippies back in the '60s called people who loved computers "soulless accountants."

  • by ArcadeMan ( 2766669 ) on Friday March 27, 2015 @12:55PM (#49355909)

    I don't know anything about the PDP-8, but isn't using a Raspberry PI completely overkill? Wouldn't a much more basic ATmega328P be enough for the task?

    • by rochrist ( 844809 ) on Friday March 27, 2015 @01:05PM (#49355993)
      He should have gone for a PDP-11! As an aside, simh is a really awesome piece of software.
      • by Anonymous Coward on Sunday March 29, 2015 @11:08AM (#49365365)

        >> I don't know anything about the PDP-8, but isn't using a Raspberry PI completely overkill?
        > He should have gone for a PDP-11! As an aside, simh is a really awesome piece of software.

        But it's just as hard to find a working PDP-11, and even if simh runs on it, would it be fast enough to emulate a PDP-8? :)

    • by Anonymous Coward on Friday March 27, 2015 @01:06PM (#49356007)

      Are you kidding? That machine had as many as 8 instructions! And 12-bit memory. And, uh, that's all I remember.

    • by Darinbob ( 1142669 ) on Friday March 27, 2015 @03:56PM (#49357601)

      Ya, it's kind of a non-story really. Ok, he used a replica panel, and you can't just buy those online easily. But a raspberry pi running an emulator is just decidedly not geeky. I can run Unix version 1 and 6 and BSD 2.9 on my Mac and PC, but I don't tell people I rebuilt a PDP-7 or PDP-11 or VAX.

      Meanwhile there ARE people out there who have built real computers and CPUs from scratch as a hobby, without any emulators behind the scenes. Check out the http://members.iinet.net.au/~d... [iinet.net.au] web ring. Those are infinitely cooler I think.

  • FPGAs (Score:4, Interesting)

    by jones_supa ( 887896 ) on Friday March 27, 2015 @01:18PM (#49356127)

    We really should be preserving old computers in HDL in a form as loyal as possible to the original. Then we could always reimplement them in FPGA and make "real" hardware cheaply enough until the sun burns out.

    It's doable, although these are big efforts.

    There is already this Japanese guy who has done it for the SNES [at-ninja.jp].

    • by trumpetplayer ( 520581 ) on Friday March 27, 2015 @07:31PM (#49358743)

      I was about to post this. In fact, I bet the resulting HDL code for this particular computer can be implemented in a technology that's cheaper than FPGA, like perhaps commercial flash PLD. Also things seem to be moving towards OpenCL which is behavioural and C-like, which may help people who are used to that paradigm, like people who do MCUs including the Raspberry Pi.

  • Fond Memories (Score:5, Interesting)

    by Gim Tom ( 716904 ) on Friday March 27, 2015 @01:21PM (#49356155)
    My first "personal computer" was a PDP-8i at Georgia Tech in the late 1960's. The ISy school had one in a small room in the basement with an ASR TTY (33 I think). There was another room with at least one more TTY with punch and you would code on that machine and after signing up for time on the PDP-8i you would take your paper tape in and after toggling in the boot sequence and loading the BIN tape then the Assembler you would run your tape to punch out your assembled program to run on the machine. I may be leaving out a number of steps since that was a while back.

    in any case that was my first taste of writing any code in a machines assembly language and even then I dreamed of having my very own PDP-8.

    This is a cool project and even for an Old Man I can fully relate to why it was done. I think this experience led to a life long career working with computers ranging from Big Iron mainframes to PC's networks and a variety of internal and Internet facing Servers. Yes, even though retired, I have a couple of Arduinos and Raspberry Pi's around to play with! Learning new things has kept me going all these years.
    • by Anonymous Coward on Wednesday April 01, 2015 @09:53AM (#49386279)

      We had a PDP-8i in my high school in 1977. I think it had 4 or 8K RAM. I remember manually toggling in the bootstrap code on those front panel switches (7737, 3377, etc) before the paper tape would load in the ASR-33 teletype. We had a choice of two languages: Basic or FOCAL. After loading Basic, you had about one or two typed pages of memory left for writing your program, which you could then save on the paper tape.

      After basic started up, you could choose not to load the floating point support. That would get you up to about 4 pages worth of code.

      By 1978, the school went all high-tech and added an optical paper tape reader.

  • Yuo fai7 +it.. (Score:-1, Redundant)

    by Anonymous Coward on Friday March 27, 2015 @01:35PM (#49356337)
    be in a sce\ne and BSD culminated in = 36400 FreeBSD come Here but now Member. GNNA (GAY The reaper BSD's shout the loudest all parties it's Stupid. To the consider that right
  • by cruff ( 171569 ) on Friday March 27, 2015 @01:43PM (#49356419)
    The SBC6120 uses a Harris 6120 CPU chip which is a PDP-8/e-like microprocessor. It has a companion FP6120 front panel with switches and lights, which is a scaled down version of an older modle rack mount PDP-8 front panel. You built them from kits, loads of fun for those who like that sort of thing. Mine has a CF card for the hard drives (a whole whopping 2 MB each under OS/8!). You may be able to find an unbuilt kit, as the maker of the kit, Spare TIme Gizmos, will not be making any new ones going forward.
  • by Virtucon ( 127420 ) on Friday March 27, 2015 @01:53PM (#49356527)

    The 8 was a great system but the 11 was far better.

    Just checking ebay, this guy selling the 8E is smoking something [ebay.com]. He thinks it's a mainframe.

    However this PDP-11 [ebay.com] can be had for a reasonable price.

    The point being, you can run emulation software [vandermark.ch] on commodity hardware but I guess as the TFA indicates he wanted the nostalgia look. He could have easily just mounted an LEDs behind the panel with small pattern generator circuit instead of using the Pi.

  • by trenobus ( 730756 ) on Friday March 27, 2015 @02:14PM (#49356721)

    I first learned machine language on a PDP-5, which was similar to the PDP-8, but limited to 4KB of memory. Mostly I just used it to toggle in small programs through the console switches, but I think we got the FOCAL [wikipedia.org] interpreter running on it at one point. Those were the days. To think now there is a generation of programmers who have known nothing but JavaScript.

  • by Anonymous Coward on Friday March 27, 2015 @02:59PM (#49357069)

    Of the old Unix fortune cookie program: One of the fortunes was:

    Q: What is the biggest problem implementing a Jerry Ford emulator in 8K memory on a PDP8?
    A: Figuring out what to do with the other 4K.

  • by Ralph Spoilsport ( 673134 ) on Friday March 27, 2015 @03:10PM (#49357163) Journal
    My cellphone has more storage and processing power. You would think a PDP8 would be worth little more than scrap at this point.
  • by Anonymous Coward on Friday March 27, 2015 @03:20PM (#49357283)

    I would have given him a PDP-8 and a couple of 11s (11/24, 11/34) if he'd asked me three or four years ago. Scrapped now!

  • by cnaumann ( 466328 ) on Friday March 27, 2015 @04:39PM (#49357879)

    Are old PDP8s really expensive? But I bet no one saved the boxes they came in...

  • by Anonymous Coward on Friday March 27, 2015 @05:11PM (#49358081)

    More like PTSD 11 if you dropped that shoe box of punch cards on your way to the computer lab...

    (PRO TIP: Clearly number the BACK of your cards so that if they do get mixed up you can sort them without an aneurism!)

  • by jpellino ( 202698 ) on Friday March 27, 2015 @07:25PM (#49358721)
    Wait, no, that was the boot loader address for the PDP-11. Never mind.
  • For people who want to build a real hardware silicon PDP-8 computer, there exists an LSI version of it, the Harris/Intersil 6100 processor [wikipedia.org]. It's a standard 40-pin package integrated circuit.

    It's a static CMOS processor that can be clocked down to zero hertz if you like (the registers don't need 'refreshing' so it can be clocked as slow as you like) and it's a 12 bit processor and implements the PDP-8 Instruction set.

    They haven't been made for years but they exist in NOS (new old stock) quantities and can be purchased at times.

    It's certainly more interesting to have a real hardware implementation of a PDP-8 and the 'cheap' way is with a 6100 processor.

  • by Thor Ablestar ( 321949 ) on Friday March 27, 2015 @09:28PM (#49359183)

    I'd like to make a BESM-6 emulator with PIC18. But nobody knows it's privileged instructions for now which means that it's impossible to recreate it fully.

  • by evanak ( 796723 ) on Friday March 27, 2015 @10:55PM (#49359439)
    Oscar is exhibiting his PiDP-8, along with 10 or so other people showing * real * PDP-8s, at next month's Vintage Computer Festival East [vintage.org] -- and they'll all be up-and-running, including an original 1965 "Straight-8". Slashdot published a video about the event just a few weeks ago [slashdot.org].
  • by g4ugm ( 4054675 ) on Saturday March 28, 2015 @02:18AM (#49359949)
    Whilst buying one may be out of the question, it is possible to build a PDP-8 "clone" from raw TTL. I know this was done on at least one college course, and there are books out there to support it...

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