back to article Das blinkenlights are back thanks to RPi revival of the PDP-11

Always wanted a PDP-11, but don't have space for the iron? Good news: an obsolete computer enthusiast s offering beta tests of a kit designed to recreate the famous Digital Equipment Corporation box on a Raspberry Pi. As Obsolescence Guaranteed explained here earlier this month, “The PiDP-11 wants to bring back the experience …

  1. bombastic bob Silver badge
    Devil

    I cut my teeth on a PDP-11

    back in the day, 11/34 at my high school, and 11/70 at the university. the 11/34 ran RT-11. The 11/70 ran RSTS/E. I did some interesting things with assembly language, the most useful of which was a re-write of the access program for diskettes [it was tee'd from a terminal on a 9600 baud serial port] that did NOT lose data. The one written by the grad student DID lose data, and was pretty much worthless with more than a handful of people on the system. students were supposed to do backups using that diskette drive, but write-only memory is pretty worthless.

    WIthout my assembly language program, it was 'write only'. that's because the grad student made a n00b mistake: he assumed that the input buffer would never fill up. what I did to fix it: I sent one buffer's worth of data at a time, and polled for the next buffer after receiving it. Also mine had a FAT-like directory instead of skipping through the disk looking for "directory tags" that would fail for binary files. yeah, mine could store binary files, too. But it was generally incompatible with the 'grad student' BASIC version.

    I gave the system operators the source and everything, gave copies to friends, etc. before I left. Thing is, I fear that it was generally unused because nobody understood it... [or they feared I'd put some kind of back door into it, but i thought it was pretty simple ya know? comments read like a book, too]

    1. Anonymous Coward
      Anonymous Coward

      Re: I cut my teeth on a PDP-11

      "Thing is, I fear that it was generally unused because nobody understood it..."

      In my IT career I often took the time to automate tedious manual processes. Getting people to take the time to use the automation was a different matter.

      One example was a BASIC program that merged code patches with the current release's compilation text. Even when there were patches over patches you could still read the final code flow. Which patch changed each location was clearly identified.

      The system at that time was very heavily patched - but the official support team stuck to paper copies of the original listing. They often lost track of how overlaid patches were interacting.

    2. Tom 7 Silver badge

      Re: I cut my teeth on a PDP-11

      nooo nooo nooo. Did my thesis on a PDP11 (after spending a term or so walking into the Uni Mainframe to see the 'Hardware Fault' light illuminating the unused card punches.

      Wow was that a revelation. I went from two lines of code a week to writing atom bomb simulations* (nothing to do with my thesis which was on fibre optic performance).

      To be able to write code and not wait a 1/2 day or so for it to be run by the batch system was a fucking revelation. And now I can do it all again on a Pi. Must resist Must resist.

      *source code deleted after converting from eV to tonnes TNT!

    3. SteveCarr

      Re: I cut my teeth on a PDP-11

      Same here - my first was a PDP 11/05, that had been upgraded from 4KB to 8KB of core RAM. It had a high speed paper tape reader and high speed punch, as well as two, count 'em two, ASR-33 Teletype terminals.

      It lived in the undergraduate room at the University where I studied in the mid to late 70's. You'd start up toggling in the paper tape bootstrap (14 sets of instructions from memory) and then read in the a tape to get it up and running properly - perhaps with the BASIC interpreter (multi user basic, what a buzz!). Writing assembler in the basic stream text editor, loading the (two pass) assembler, then link editing, loading a fresh tape at each step, and voila!

      Ah, the memories!

      1. Daedalus Silver badge

        Re: I cut my teeth on a PDP-11

        Let's not forget the joys of overlay swapping to squeeze the most out of that 64K. I eventually came up with some rather creative tricks that you might call "minimal root" where instead of common code being at the base overlay, there were multiple occurrences out on the ends of branches. This cured the "blob effect" where all the code used by more than one module migrated to the base and used up all the address space before you'd even loaded anything useful. It was also good for making all the init code disappear when no longer needed.

        Of course we now have the Great Blob Object where all the "must have" features migrate up to the godlike object class from which all other object classes must descend. The only cure for that is carefully used multiple inheritance - but nobody knew how to use that safely.

        Those who do not learn from history are doomed to repeat it.

    4. BillG Silver badge
      Holmes

      Re: I cut my teeth on a PDP-11

      bombastic bob wrote: I did some interesting things with assembly language

      Real programmers have programmed in assembly at least once.

      1. jake Silver badge

        Re: I cut my teeth on a PDP-11

        Real programmers use inline assembler often, regardless of language.

        1. ds6 Bronze badge
          Coat

          Re: I cut my teeth on a PDP-11

          According to modern parlance, real programmers use JS.

          And nothing but JS.

          And get jobs for it.

          I'm so very, very sorry.

  2. jake Silver badge

    How noisy are the cooling fans?

    Can't get into the proper zone to toggle front panel switches without cooling fans properly roaring away in the background^W^W my ears. Can I connect my line printer? Acoustically coupled modem? PC11? CR11? RK05? TU56?

    More seriously, this might be an excellent teaching tool. IMNECTHO, DEC kit is the absolute pinnacle for ease of explaining and demonstrating computing concepts to students. Although, in today's world of DevOps App builders, understanding the basics no longer seems to be all that important. Sad that.

    1. Lord Elpuss Silver badge

      Re: How noisy are the cooling fans?

      ”Although, in today's world of DevOps App builders, understanding the basics no longer seems to be all that important.“

      Understanding the basics is still important, it’s just that the definition of ‘basic’ has changed through the years. Much like math or engineering students no longer learn the ‘basic’ skill of using a slide rule - because there’s just no point any more.

      1. jake Silver badge

        Re: How noisy are the cooling fans?

        The definition of basic might have changed in your eyes, but the heap and the stack still exist and knowing how to use them is just as important as it was 40 years ago. Unfortunately, I've interviewed new college graduate so-called programmers who don't even know they exist. Hell, I interviewed one poor kid who couldn't convert from hex to decimal to binary on paper, much less in his head. Worse, he didn't understand why that kind of "skill" might be handy ... in his words "Why should I know that? That's what the computer is for!".

        As for your example, I use sliderules almost every day. Here's my favorite. Now THAT's what I call a Sun Workstation!

        Why? Because a slipstick's more accurate and faster than guestimating for fencing, fertilizer, seed, irrigation, roofing, paint, roadbase, DG, working loads on beams and the like, and a lot easier than firing up a computer. Just to really make you think, I also use an abacus nearly daily. It's in the feed barn. I use it to calculate livestock feed & supplement needs. Electric calculators tend to die in a matter of weeks in that kind of environment.

        Horses for courses and all that ...

        1. Anonymous Coward
          Anonymous Coward

          Re: How noisy are the cooling fans?

          IT "basics" also includes a knowledge of electronics and radio. Most of my colleagues had no idea of how a computer and its associated electronics worked. Therefore they could not double-guess when underlying constraints in the technology might be responsible for intermittent errors in the system.

          Even something as simple as the speed of propagation of electromagnetic waves through various media was a mystery to them.

          I even had an official "network designer" once ask me about speeds - "What does 'mega' mean?".

        2. Peter Gathercole Silver badge

          Re: How noisy are the cooling fans? @Jake

          My slipstick is a Faber Castell log-log slide rule. I would like to say that it is the same one that was bought for me in 1971 when I went to senior school, but that got lost in one of many house moves, and I had to do a like-for-like replacement from eBay.

          Although I think I still know how to use all of the scales (it's got around 20 different ones), I don't do the type of maths that it's best suited for very often.

          I have one of my Grandfather's slide rules, probably dating back to the 1930's that he would have used at the RAE in Farnborough (it was one of the UKs primary aircraft research institutions). It's engraved polished ivory on wooden slides, but feels so fragile that I don't play with it very much.

          When it comes to abacuses, not me. I used a blackboard and chalk and counting gates when counting sheep and hay bales on my father-in-law's farm before he retired.

        3. Waseem Alkurdi Silver badge

          Re: How noisy are the cooling fans?

          So you work in both farming and computing industries? That's a first for me!

          1. jake Silver badge

            Re: How noisy are the cooling fans?

            Waseem, it actually makes perfect sense. When you think about it, farming is a form of computing ... analog computing, perhaps, but computing nonetheless.

          2. Anonymous Coward
            Anonymous Coward

            Re: How noisy are the cooling fans?

            "[...] work in both farming and computing industries? That's a first for me!"

            Back in the late 1960s many programmers were young women. When they wanted to start a family it would previously have been expected that they would leave work for many years.

            ICL's Hilary Cropper decided that she could employ them as part-time home programmers - now that Teletype devices on interactive services were starting to be available. So began the era of "Hilary's Pregnant Programmers".

            There was at least one guy who joined that crew. He left full time programming to do dairy farming in Wales. He complained that a local manual exchange operator would sometimes disconnect his Teletype connection when she checked on the long-distance call's conversation - "because the line was making funny noises".

            1. bobajob12
              Stop

              Re: How noisy are the cooling fans?

              STOP. DO NOT PASS GO.

              El Reg, we need to know more about this programming group. There's a great story in there, I'm sure.

            2. Steve the Cynic Silver badge

              Re: How noisy are the cooling fans?

              Back in the late 1960s many programmers were young women. When they wanted to start a family it would previously have been expected that they would leave work for many years.

              Early 60s as well. My mother was one of them. And yes, when she started a family (her first-born was someone who might just post here as Steve the Cynic), she left work, the 60s being what they were.

              But she reached the level of Chief Programmer at LEO.

          3. Phil O'Sophical Silver badge

            Re: How noisy are the cooling fans?

            So you work in both farming and computing industries? That's a first for me!

            Cue old joke: Why are experts like farmers? They're both people out standing in their fields...

      2. John H Woods Silver badge

        Re: Basic skill of slide rule

        I used to teach remedial maths to biology undergrads. Nearly all of them had been taught that logs were historic and related to the time before calculators, and they weren't that happy to hear that they were fundamental to science. One day, one of my mature students, who understood the maths back to front but nevertheless dutifully turned up to even the maths tutorials, asked if we'd like to see his slide rule. "I'm an old fossil" he explained apologetically.

        By the end of the hour the three students still struggling with the concept of logs had got it absolutely solid. The "old fossil" gave me the slide rule and I used it for years: some people massively benefit from a degree of "physical learning." I think the same must be true for computing and projects like this are invaluable.

        1. Chemist

          Re: Basic skill of slide rule

          The other advantage of slide-rules was that it was 'necessary' to approx. the order of magnitude answer - which was good brain training.

        2. Steve the Cynic Silver badge

          Re: Basic skill of slide rule

          The "old fossil" gave me the slide rule and I used it for years

          This made me think of the best slide rule I ever saw. Cue: 1977. I'm about to start secondary school, and it's the end of the previous academic year (last at primary school). They sent us to the Comprehensive down the road for a tour, and hanging on the wall in one of the maths classrooms was a slide rule.

          "Hanging on the wall"? Sure. It was six feet long, for teaching slide rule technique.

          1. Unicornpiss Silver badge
            Happy

            Re: Basic skill of slide rule

            "Hanging on the wall"? Sure. It was six feet long, for teaching slide rule technique."

            A local restaurant (one of those that specializes in having kitschy decor with antiques, etc. everywhere) has one of these on the wall. It spans 2 or 3 booths. I doubt many of the younger crowd even knows what it is when dining there. They also have a WWII-era Army Jeep on the wall sideways. I'm always a bit afraid to sit under it..

      3. Charlie van Becelaere

        Re: How noisy are the cooling fans?

        "Much like math or engineering students no longer learn the ‘basic’ skill of using a slide rule - because there’s just no point any more."

        No point? Hardly.

        Keep in mind that batteries die, power grids go down, but slide rules need neither.

        Mine got me through a Physics exam when my HP-45 batteries died back in my undergrad days.

        1. Bill Gray

          Re: How noisy are the cooling fans?

          "...batteries die, power grids go down, but slide rules need neither."

          I keep meaning to put my slide rule and tables of logarithmic and trigonometric functions into a little glassed-in case, with a small hammer and sign reading "break glass in case of power failure".

          1. jake Silver badge

            Re: How noisy are the cooling fans?

            About 30 years ago, my daughter subtitled my CRC handbook "Post Apocalypse Science Rebuild Notes" and insisted on shelving it next to the Firefox books, the UBC, and various other bits & bobs :-)

            1. jake Silver badge

              Re: How noisy are the cooling fans?

              That's the Foxfire books, of course. Obvious brain fart is obvious. Mea culpa.

      4. Diginerd

        Re: How noisy are the cooling fans?

        Slide rulers & log tables...

        Having both and knowing how to use them should be mandatory - they still work when there’s no power or internet.

        Not sure if that’s why the VMS admin (yes, still a thing!) ad my old workplace had a 6’ slide rule in his office marked up with a label “Emergency backup CPU”, but it’ll still be usable long after everything else is landfill

  3. Steve Davies 3 Silver badge

    Can't wait

    I've built two of the PDP-8 kits and had great fun with them.

    I'll be ordering a couple of the kits as soon as Oscar opens the ordering.

    Why? Well, I worked for Dec from 1979 to 1999. I have a MicroVax in my Garage so a PDP-11 would make the set. Same that the new one does not have a UniBus. I have an old prototype interface that I'd love to get working.

    1. james_smith

      Re: Can't wait

      I had a working MicroVax (model 3100-80 with two SCSI hard drives) for quite a while in the early 2000s, even using it as a web server with NetBSD running on it. Then I acquired a PDP-11 from the same place - both had been standbys for when similar machines had been installed at client sites for warehouse automation. Never did get the PDP working, so I sold it. When the guy came to collect it he took one look inside and pointed out that the card I had assumed was the RAM was in fact some kind of controller board. Doh.

  4. Ken 16 Silver badge
    Pint

    Completely pointless

    Well done everyone, beers all around!

    1. Anonymous Coward
      Anonymous Coward

      Re: Completely pointless

      I tell you, this post has been far from pointless—I now have an urge to buy a slide rule and touch up on my knowledge of heap logistics.

  5. Alister Silver badge

    an obsolete computer enthusiast

    I say, that's a bit harsh...

    Can't you just call him retired?

    1. Anonymous Coward
      Anonymous Coward

      Re: an obsolete computer enthusiast

      A rather unfortunate turn of phrase methinks.

    2. Spanners Silver badge
      Go

      Re: an obsolete computer enthusiast

      That must be an oxymoron.

      If the computer has an enthusiast, it is not an obsolete device.

    3. Tom 7 Silver badge

      Re: an obsolete computer enthusiast

      "Self unemployed" is my preferred moniker.

  6. jeffdyer

    My first job after leaving the company I did a sandwich course with still used PDP-11, I think an 11/70 and an 11/73 to run stock and order processing systems for a group of steel processing companies. We still had to run backups onto reels of mag tape. After about a year, we started to migrate to MicroVAX, and, having the least experience with the PDPs , I was tasked to convert the processing software over from the PDP version to VAX/VMS. Happy days (1990 ish)

    I don't know what happened to the PDPs, but I was almost scared to touch them with their open cabinets and huge pcbs visible. Very noisy as well.

  7. Thoguht Silver badge

    All this talk about BASIC and not one mention of FOCAL. Back in my PDP-8 days at university, BASIC was a pain because it was too big to fit into the 4k word memory and so it was split into two parts, I'm assuming the parser and the runtime, that had to be loaded separately from paper tape. FOCAL, on the other hand, was half the size and so you could easily load it in one go and get some coursework done in your allocated 1 hour slot.

    But about this PDP-11 emulator, unless it comes with Adventure then I'm not interested.

    1. Steve Davies 3 Silver badge
      Happy

      PDP-11 Adventure

      I'm sure the fortran source is out there somewhere...

      So, what did PLUGGH do then?

      1. Phil O'Sophical Silver badge

        Re: PDP-11 Adventure

        I'm sure the fortran source is out there somewhere...

        In many forms:

        http://rickadams.org/adventure/e_downloads.html

        https://www.dwheeler.com/adventure/

        are just two I have bookmarked.

    2. PhilBuk

      @Thoguht

      I once loaded up the 8K BASIC interpreter on our 12K PDP-8/E (slowly, as we only had the tape reader on an ASR33) hoping that it would allow me to get round some of the limitations of 8K FOCAL. No such luck. The BASIC was almost identical to FOCAL in functionality - they just swapped the commands over and made it much less efficient!

      Phil.

    3. Unicornpiss Silver badge
      Pint

      Adventure

      "But about this PDP-11 emulator, unless it comes with Adventure then I'm not interested."

      The local university had an 11/40, an 11/70, and a VAX as I recall. I remember playing Zork I on it when I was perhaps 9 or 10 years old, using both a VT-100 terminal and a Decwriter. (Was Zork I part of the Adventure series at the time?) Long story as to why I even got to be in the lab. Somewhere I may even have one of the printouts on 140-column green bar paper from one of those sessions. As I recall, it was written in FORTRAN to run on the 11/70. (or it may have been the 11/40, I don't remember)

  8. Nicko

    Happy, happy days...

    Happy days. We had an 11/34A at school, running RSTS/E (can't remember the version) - my first ever commercial product (written with another EE at the same university) was a BASIC+ Decompiler.- very popular product,=.

    I loved RSTS/E, RT-11, RSX-11,... I still have a J11 chip on on "Shelf of Doom", along with my Sinclair Scientific calculator (still works), my British Thornton slide rule and a set of PDP-8 manuals (among much other detritus).

    Somewhere in the loft is an AXP-433 workstation running Windows 2000...

    (ex. DECUS Europe OpenVMS Chairman, ex-DEC employee in France, UK & Switzerland).

  9. Doctor Syntax Silver badge

    “The PiDP-11 wants to bring back the experience of PDP-11 Blinkenlights, with its pretty 1970s Magenta/Red colour scheme.”

    That magenta; it's going to get them into trouble with T-Mobile.

    1. jake Silver badge

      Nah.

      Prior art.

  10. sawatts

    Painful

    Many years ago in a house share we had a PDP-11 and WinchesterDisk stacked on the landing, by the bathroom.

    It is very painful to collide with these devices when trying to get to the toilet in the dark. I still have a dent in my kneecap...

  11. TRT Silver badge

    A thing of beauty...

    is a joy forever.

  12. james_smith

    Oh wow! I read a little bit about this project but had assumed it was a one off - it did seem an amazing amount of effort so I guess I shouldn't be surprised that it's now available as a kit. Would definitely like to build one of these, as the PDP-11 had a wonderfully elegant instruction set.

    1. Anonymous Coward
      Anonymous Coward

      wonderfully elegant instruction set. (@james_smith)

      "the PDP-11 had a wonderfully elegant instruction set."

      Programmers Cards were a Thing back in the day. Here's one DEC prepared earlier:

      https://archive.org/details/bitsavers_decpdp11PDul75_1582192

      or direct to theappropriate PDF at

      https://archive.org/download/bitsavers_decpdp11PDul75_1582192/PDP-11_Programming_Card_Jul75_text.pdf

      Also available via Bitsavers (and/or archive.org) are DEC (and other) Processor Handbooks and such other outdated stuff (e.g. diagnostics) as are generally considered irrelevant in the 'modern' world. Bitsavers is a great resource for such things, though for DEC stuff there are often other places to look.

  13. Paul Ward

    Brings back memories...

    Of my first 'real' job in IT. It was on the Isle of Man working for a small company that did systems software ('C' compilers, assemblers etc). They had a PDP 11/23 and an 11/34 running RSX11 (? - it's been 30 years...). They had the PDPs to develop and test cross-compilers so you could code on a PDP11 and compile for a new-fangled 68K processor, for example. 'C' compiler used was Whitesmiths...

    Happy days...

    1. DHR

      Re: Brings back memories...

      Hmm. Isle of Man, Developed C compilers? That made me think of Manx Software Systems, developers of Aztec C. But it turns out that they were a New Jersey (not even the channel island) company named after the breed of cat.

      Odd segue: one of my first programs (in the late 1960s) was to help with breeding Jersey cattle. This links in with the farming and computing theme.

      1. jake Silver badge

        Re: Brings back memories...

        That's odd. In my experience, Jerseys don't need help when breeding. All you gotta do is turn 'em out into a field with a bull, and sure as sunrise, 9 months later you've either got another heifer or a bunch of proto-steaks. Computer programs certainly never come into the equation ...

  14. cdilla

    I too found my career path due to using a PDP-11 at Uni as part of a physics course (which I ditched in favour of programming soon after).

    I also have one of Oscar's most excellent PDP-8 kits, a blinken fine piece of computer history.

  15. Anonymous Coward
    Anonymous Coward

    Grammatical point

    Das Blinkenlight or Die Blinkenlights (or Blinkenlichte if you want to go all Teutonic)

    And don't forget to capitalise your nouns.

    1. Phil O'Sophical Silver badge

      Re: Grammatical point

      In real German, perhaps so, but the original text was not exactly correct: http://www.blinkenlights.nl/

      ...so relaxen und watchen das blinkenlights.

      1. Anonymous Coward
        Anonymous Coward

        Re: Grammatical point

        > In real German, perhaps so

        No. The above is *not* real German because, as someone else has pointed out, where would be the fun in that?

        The above convincing but not real German ist.

        German humour is a serious matter, my friend.

    2. jake Silver badge

      Re: Grammatical point

      Here's the definitive blinkenlights page:

      http://catb.org/~esr/jargon/html/B/blinkenlights.html

    3. allthecoolshortnamesweretaken Silver badge

      Re: Grammatical point

      If you really want to go all Teutonic: Blinklichter.

      Das Blinklicht. Die Blinklichter.

      But where's the fun in that? Blinkenlights is a perpfectly cromulent word in German; use 'der', 'die' or 'das' according to your own liking.

  16. Kevin Johnston

    Glorious memories (pun intended)

    I was an apprentice learning all abut Radar and the processing was handled by a PDP 11/34. I watched in fascination as an engineer loaded up a program on one system before shutting it down and unplugging the memory card (magnetic core store). He then plugged it into a different system, powered it up and ran the program...

    Mind...blown

    1. Dwarf Silver badge

      Re: Glorious memories (pun intended)

      The good old bubble memory board (bb0:) - just an early form of memory stick

  17. Antron Argaiv Silver badge
    Thumb Up

    The PDP-11 lives on

    ...in the Motorola 68000. Much of the same addressing modes, the paired registers, etc. It's not identical, but there's definitely a family resemblance.

    1. Peter Gathercole Silver badge

      Re: The PDP-11 lives on

      A regular instruction set was really a requirement in the early days of computing, as grouping the instructions allowed you to reduce the amount of logic in the instruction decoder, as did using the same addressing modes for different instructions.

      What I found really interesting with the PDP11 instruction set was that the stack pointer and program counter were just implemented the same as general purpose registers, a fact that became obvious if you looked at the generated op. codes that the machine code for jump and stack manipulation instructions generated.

      Remember that the CPU of the PDP11/70 and others of the same generation were mainly constructed from 7400 series TTL in normal DIL packages, which explains why there were so many boards. IIRC, the CPU on 'my' 11/34a was four boards for the CPU, one of which was an FP-11 floating point processor, and another of which was the 22-bit memory controller (it was a SYSTIME special, PDP11/34s did not normally have 22-bit addressing).

      1. SteveCarr

        Re: The PDP-11 lives on

        Another extremely elegant machine was the PDP-10 aka DecSystem-10/DecSystem-20. With a 36 bit word length and variable byte size (six bit was most often used, but was by no means the only one), each instruction took up one word/36 bits. Every instruction consists of a 9-bit opcode, a 4-bit register code, and a 23-bit effective address field, which consists in turn of a 1-bit indirect bit, a 4-bit register code, and an 18-bit offset or alternatively an immediate value. Early machines used ferrite core memory, meaning they could be run at arbitrary clock speeds, down as low as one instruction cycle per second or so, all controlled by two knobs on the console. Great fun to watch the lights slowly cycle through as a program ran.

        1. jake Silver badge

          Re: The PDP-11 lives on

          "Another extremely elegant machine was"

          Was? WAS?? WAS??? My TOPS-10 and TOPS-20 boxen are still alive and doing useful work. For values of "useful work" that includes "supporting a couple long term contracts that should probably have been ported to more modern equipment over two decades ago" ... Hey, don't blame me, I can only give advice, I can't force 'em. And as long as they're willing to pay the bills ...

    2. Anonymous Coward
      Anonymous Coward

      Re: The PDP-11 lives on

      " The PDP-11 lives on

      ...in the Motorola 68000"

      Really? I posted a PDP11 programmers card link earlier. Readers familiar with 68K family at this level of detail can have a look at the consistency of the PDP11 instruction encodings and the address modes available and then tell me that the 68K comes anywhere close.

      I liked the 68K family, but the relationship between its approach and instruction set architecture and those of the PDP11 family is arms length at best.

  18. Stevie Silver badge

    Bah!

    Pfft!

    Now if it had been a 1901T with a mini Westrex and a tape reader I'd have been impressed.

    Seriously, I approve of this and the tone adopted by those who brought it into being.

  19. Daedalus Silver badge

    Feature needed

    A true PDP-11 clone requires a feature where you can pay a huge amount of money to somebody to pull a jumper off a board, granting you access to more memory.

    1. Anonymous Coward
      Anonymous Coward

      Re: Feature needed

      True of many systems. The "upgrade" for a feature to a mainframe or a peripheral was often just a case of the engineer adding or removing a link to enable it.

      Even mainframe speeds were facilitated by "slugs" of the fastest possible. Some IBM compatible mainframes had a floppy to load their extended instruction set and to establish how many MIPs you would get. It was useful to plan a project with at least one more performance step available for a delayed painless upgrade if/when needed.

    2. Anonymous Coward
      Anonymous Coward

      Re: Feature needed

      The term is "golden screwdriver", thank you.

  20. gormful

    Wow. I lost both of my PDP-11s (and a couple of MicroVAXen) in a house fire in 2010, and I've missed the blinkenlights ever since. Gotta get one of these.

    And I ALSO have to get one of the PiDP-8 kits. I cut my teeth on a PDP-8 in 1970. Still remember the thrill when I first got to use a "high-speed" fanfold paper tape reader back in 1973.

    Looking forward to displaying both kits, with lights a-blinking, in my old VAX 2000 short rack.

  21. GlenP Silver badge

    I'm another who started with DEC kit. We had a PDP 11/45 and 11/70 but they were turned off* (still didn't stop me having to insert the manual updates in the folders each month). Main computing was a couple of VAXes, a 780 and a 750. There were then several PDP 11/23 boxes around for experiment work so mainly running RT-11.

    *It was a civil service job and at the time all government computing was supposed to be ICL unless you could justify otherwise. The 11/23s were mainly bought as part of a package, e.g. they'd come with a cheap microphone and sound input board so weren't "computers". The larger PDPs had been justified on the grounds of compatibility and then the VAXes as being compatible with those.

  22. Joe Gurman

    About those lights

    You young whippersnappers may have a hard time believing this, but the lights behind the front panel were originally incandescents. A sys admin I worked with on a machine at 2800 m above sea level was ecstatic when LEDs began to come in colors (well, three, then) in the mid-70s so he could replace the ones on his 11/20 with Xmas light-like LEDs. The original bulbs appeared to fail more frequently at that altitude than at sea level.

    1. Anonymous Coward
      Anonymous Coward

      Re: About those lights

      "The original bulbs appeared to fail more frequently at that altitude than at sea level."

      Although the tiny pea bulb failures were a fact of life on the ICL System 4-72 mainframe - I never noticed any particular difference at 1500m in Pretoria.

      The second generation technology EELM KDF9 prototype had had no engineers' panel because "these mainframes will be so reliable". They also said that about not needing parity on the ferrite bead memory. The production design had to add a small engineer's panel.

      When the engineers moved on to design the third generation technology System 4-70 series they made sure that there was a glorious cpu panel including a 36x10*** matrix of green, red, and yellow illuminated squares.

      There were also 109 illuminated push buttons - and a total of 62 lever switches in four rows to cater for setting 32 bit address/data words. People who used the panel regularly developed a callous on the top edge of their fingers from clearing all the switches in one long sweep. Oh - and there was a rotating knob for some forgotten purpose.

      The whole display was about 2x3 feet (60x100cm) on the end of a standard 6' (1.8m) tall cabinet.

      IIRC the incandescent bulbs of the matrix were multiplexed fast enough that the eye couldn't see the flicker.

      ***The matrix was definitely 36 columns - but probably bigger than 10 rows. I've just counted as best I could. The home movie image is a vertical pan shot lasting only a few seconds - and unlit rows are subjective in the blank space. The (by then rather dusty) Standard 8 film was eventually transcribed to VHS tape - which in turn was eventually transcribed to DVD.

  23. Anonymous Coward
    Anonymous Coward

    These things are older than I am but this project is awesome nonetheless. I want one, but I wouldn't know what to do with it.

  24. Unicornpiss Silver badge
    Pint

    Before my time, but..

    ..when I went to school for electronics training, we had a donated 11/70. (this was 1990-ish) I did a bit of assembly programming, but also learned to troubleshoot the beast using an oscilloscope and the miles of schematics for the thing, with dates on them only shortly after I was born. I used to think that if I could be transported back to the early 70s, that I would have had a decent paying job as a technician working on these things. I got relatively fluent at it. Anyway, it was a good way to learn how a microprocessor worked, when the processor was spanned across a dozen or so cards. I remember interfacing a Radio Shack speech chip with it for a project. I got it to actually talk, though not particularly well.

    Ah well, that was about 5 lifetimes ago now, it seems.

  25. George of the Jungle

    I have the PDP-8 (PiDP-8) version of this and will probably spring for the -11. I worked mostly with the PDP-8 in university.

    My first job out of uni was working for DEC and working on the design of the PDP-11/44, the last of the discrete-logic PDP-11s. The 44 was designed to have the wider address space of the 11/70 but in the price footprint of the 11/34.

    I remember we had to change some of the memory management microcode to have the same errors as the 11/70 (mostly certain addressing modes involving the push from user space to K space or S space - it's 40 years ago and don't remember the specifics). Without the changes, some of the operating systems wouldn't run correctly.

    It also allowed me to learn something about a Bell Labs OS... something called Unix... they were a huge customer of DEC so it was paramount that things worked properly for them. That little bit of learning helped my career immensely - getting in at the Unix ground floor was a good thing!

  26. Anonymous Coward
    Anonymous Coward

    pdp-11/70

    Wow. This brings back a lot of (many good, some not so good) memories from the late 70's. I have (some not so) fond memories of doing backups on a Tape Stretcher-11, trying to remember where I put the box of bus terminators, and running out of wrap wire halfway through a change...

  27. JaitcH
    Unhappy

    I Still Have . . .

    callouses from flipping all those damn switches on the PDP-8 and PDP-11.

    But Digital sure built good equipment.

  28. zumbruk

    My PiDP11 arrived a couple of days ago. The Raspi shipped this morning. I am excited and terrified in equal measure (I am useless at building electronics "stuff").

  29. Mike Swann

    Fond memories

    The best machine was the PDP11/60, a real engineer's system. Programmable microcode! With a couple of RK07 disk drives attached it was an absolute dream. The story was that they took the 11/60, made the 16-bit a 32-bit system and called it a VAX.

    I looked after a number of them in the Oxford area.

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