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 …

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    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 ...

  1. 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.

  2. 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

      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.

  3. 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

      Re: Glorious memories (pun intended)

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

  4. 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.

  5. Stevie

    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.

  6. Daedalus

    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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. Unicornpiss
    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.

  12. 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!

  13. 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...

  14. 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.

  15. 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").

  16. 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.

  17. Flywheel
    Thumb Up

    Lights

    As a PFY and noob trainee operator I always found the blinkenlights fascinating - I always felt that I'd "arrived" when I walked into the computer room!

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