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Digital

Retro Computing Enthusiast Tries Restoring a 1986 DEC PDP-11 Minicomputer (youtube.com) 52

Posted by EditorDavid from the Programmed-Data-Processor dept.
More than half a century ago, Digital Equipment Corporation released the first of their 16-bit PDP-11 minicomputers, continuing the PDP-11 line until 1997.

This week long-time Slashdot reader Shayde writes: I've been working on a 1986 PDP/11 that I basically got as a "barn find" from an estate sale a year ago. The project has absolutely had it's ups and downs, as the knowledgebase for these machines is aging quickly. I'm hoping to restore my own expertise with this build, but it's been challenging finding parts, technical details, and just plain information.

I leaned pretty heavily on the folks at the Vintage Computing Federation, as well as connections I've made in the industry — and made some great progress... Check it out if you're keen on retrocomputing and old minicomputers and DEC gear.
The entire saga is chronicled in three videos titled "Barn Find PDP 11/73 — Will it boot" — part 1, part 2, and this week's latest video. "What started as a curiosity has turned into an almost 10-month-long project," it concludes, creeping up hopefully on the possibility of an awe-struck glimpse at the PDP-11's boot sequence (over two minutes long)

"So cool," responded Jeremiah Cornelius (Slashdot reader #137) in a comment on the submitted Slashdot story. "I have huge affection for these beasts. I cut my teeth in High School on a DEC PDP11/70 and AT&T SysV, and a little RSTS/E in 1979-82. We switched systems by loading different cakelid platters into the washing-machine drives, and toggling the magenta keys.

"I've thought about the Blinkenlights 7/10 scale emulator, tha uses an RPi, but I envy you and hope you have fun."
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Retro Computing Enthusiast Tries Restoring a 1986 DEC PDP-11 Minicomputer More

Retro Computing Enthusiast Tries Restoring a 1986 DEC PDP-11 Minicomputer

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  • DEC Logo used properly first time in 20 years. (Score:5, Funny)

    by Anonymous Coward on Saturday December 09, 2023 @10:08PM (#64069811)
    I'm impressed.

  • Good to hear (Score:5, Interesting)

    by HotNeedleOfInquiry ( 598897 ) on Saturday December 09, 2023 @10:10PM (#64069815)
    I have a PDP 8/L in storage that I'd like to restore. I bought it around 1980 at at the time it would run a simple keyed-in program to rotate a bit in the AC. I'd like to get it going again and at least running FOCAL before I die.

    • Re:Good to hear (Score:5, Interesting)

      by Hans Lehmann ( 571625 ) on Saturday December 09, 2023 @11:29PM (#64069907)
      A PDP-8 was the first computer with which I had actual hands on experience, rather than just remote access through a teletype terminal. Its entire instruction set was only eight or so instructions, and we would write our code on paper before laboriously entering it into the machine through front panel toggle switches. Plus, we had to remember that the light bulbs above the 2nd and 5th toggle switches were long burned out, so we couldn't count on knowing what the state of those bits was.
      I don't recall ever having worked with another machine that used octal as it's number format

  • Oh man (Score:5, Interesting)

    by 93 Escort Wagon ( 326346 ) on Saturday December 09, 2023 @10:39PM (#64069847)

    Fun times. I remember my first real exposure to computing, back in high school advanced placement - a PDP 11/70 at the University of Puget Sound. Happily they had *just* upgraded from punch cards to DECwriters (IIRC - were there other terminals available?) My friends and I had a BASIC class there once a week, but free access to the computing labs... so we'd drive over there most evenings. Some of it was us trying to learn, but I must admit some of it was wasting paper playing Trek.

    My college had an 11/40, also with the DECwriters... each with a paper tape reader/writer, to boot! I still have a few programs saved on spools of paper tape, somewhere...

    I much prefer working in today's computing environment, but still - there was something magical about it back then that doesn't seem to exist anymore, at least for me.

    • Re:Oh man (Score:5, Interesting)

      by az-saguaro ( 1231754 ) on Sunday December 10, 2023 @06:37AM (#64070329)

      I know exactly how you feel. My first computer exposure was 1968, summer after 9th grade, participated in an NSF funded computer program at Univ of Pennsylvania. Some of the classes were in the room where the ENIAC was built. We used IBM 360/65's and RCA Spectra 70's as mainframes, but got to play on a PDP-8 running an oscilloscope trying to make it function as a graphical display. Back in high school, we got a PDP-S, with an added high speed tape reader. To boot the machine, you turned it, then from the front panel toggled in address and data for a (as I recall) 7-instruction program that read a slow speed tape reader from the teletype machine. That permitted feeding in a paper tape coil with a short program (I am only guessing now, but maybe 50-100 codes) which enabled interface to the high speed tape reader which read a long folded tape which filled up much of the 8K memory. That was the OS and Fortran. After that, we could play. In the late 70's, I was at a university hospital clinical studies center where the patients in that unit were plugged into a PDP-11, which was an advanced achievement for that time. It had the same general boot sequence, but we got to interface the machine to a lot of home grown hardware.

      I feel that same way that there was something exhilarating about it all. We all looked forward to coming decades when machines would be more capable, but no one thought that personal computing would advance as much as it has. What we now take for granted, in ease of use and productivity, was replaced back then by a sense of pioneering excitement. Your last sentence "I much prefer ... something magical ...", you said it perfectly.

    • "...there was something magical about it back then that doesn't seem to exist anymore, at least for me."

      I suspect today's budding little hackers may be finding the same magic with ChatGPT and its ilk.

    • Re: (Score:2)

      by twosat ( 1414337 )

      We did programming for our 7th Form Applied Maths class at the Christchurch Polytechnic. It was across the road from my school and we used two PDP 11 computers running RT-11. We learnt to program numerical methods using BASIC. The computers were prone to overheating and "crashing" in summer, so I had to "bootstrap" them a few times using their front panel switches and some instructions taped above them. I spent many hours using them on my private projects, oblivious to the fact that the school was being cha

  • Minicomputer and microcomputer at once?

    • You've got a point. (I went in and changed it to just "minicomputer.")
      • A Slashdot Editor Edits?!

        Is this a sign of the beginning of the end times ?
        • If so, and before we all go to hell, I have a list of 17,832 other grossly erroneous stories that you could maybe take a look it.
        • Greytree says

          A Slashdot Editor Edits?!

          But, from your submissions page :

          Submission Summary: 0 pending, 1 declined, 0 accepted (1 total, 0.00% accepted)

          I think, if you'd actually tried submitting a few stories, you'd know that the editors at Slashdot do generally edit the submissions.

          FYI, about 1 in 4 of submissions get accepted. So dipping your toe in the water just the once isn't likely to teach you anything about the submissions process.

          Now, I have frequently disagreed with the editing of my submission

  • In 1981, I went to work after college programming on a PDP 11/34. They later added a PDP 11/44. Both ran RSTS-E. Across the hall was a Cat scan serial #2,with a PDP 11/45 that we upgraded to a PDP 11/44 to save maintenance costs.

  • Cool hobby (Score:4, Interesting)

    by wyattstorch516 ( 2624273 ) on Saturday December 09, 2023 @10:59PM (#64069873)
    I wonder if anybody has ever brought back the Data General Eclipse MV/8000 from Soul of a New Machine. Sounds like a great way to spend your retirement.
    • Thought the same ( without knowing the name of the machine ).

      Do you know, I think I might go and reread Soul of a New Machine!

    • Re: (Score:3)

      by Dadoo ( 899435 )

      I wonder if anybody has ever brought back the Data General Eclipse MV/8000 from Soul of a New Machine.

      An MV/8000 is a significantly more complex (and more powerful) machine than a PDP/11. I imagine that would be a lot more work.

  • Vax assembly = Hell (Score:5, Interesting)

    by iAmWaySmarterThanYou ( 10095012 ) on Saturday December 09, 2023 @11:07PM (#64069879)

    We had pdp11 and microvax (fuck you autocorrect, I won) which were kind cool except for having to do projects in Vax assembly which was fucking nutso. The guys who came up with that just have been the first crack heads or were heavy lsd users.

    384 unique instructions, multiple modes, instructions created specifically for certain languages (cobol), and other craziness. It's no wonder the next big thing was RISC.

    • Xtension (Score:4, Informative)

      by JBMcB ( 73720 ) on Sunday December 10, 2023 @12:03AM (#64069953)

      VAX set was designed as a 32-bit extension to the PDP-11, so you had x86 style instruction and mode creep.

      The next big thing wasn't RISC, it was 68000 assembler designed for 32-bit from the ground up

      • In my world it was RISC. YMMV. We never even looked at 68k because it wasn't interesting academically.

      • Re: (Score:2)

        by Dadoo ( 899435 )

        The next big thing wasn't RISC, it was 68000 assembler designed for 32-bit from the ground up

        Yeah, the first RISC machine I'd ever seen was a SPARC server, but that was probably in 1988. By that time, 68K machines had been around for nearly a decade. In fact, the SPARC server replaced a 68K-based 3/280. (The professor who owned it was doing Navier-Stokes computation for the Navy and always had to have the latest and greatest.)

    • Re: (Score:2)

      by kmoser ( 1469707 )
      In college I wrote assembly on a VAX-11/780 and I remember a few of the operators had something like four or five operands. Nuts!

      • Yup, we did the 11/780 too, thanks for reminding me and bringing back the nightmares. I gotta call a psychiatrist and a team of therapists now.

        • Re: (Score:2)

          by kmoser ( 1469707 )
          As long as you knew what the operators were and each of the expected operands, it wasn't much different than any other kind of assembly. I already knew 6502 assembly so moving to the VAX was just moving to a more powerful instruction set.

      • Re: (Score:2)

        by Dadoo ( 899435 )

        a few of the operators had something like four or five operands

        Wasn't there a VAX instruction to evaluate a polynomial?

    • Compared with other instruction sets of its day, the VAX instruction set was pretty consistent and most of the various addressing modes (which were based on those of the PDP/11) were available as operands with most of the instructions. Some of its specific instructions (like the queue instructions that manipulated doubly-linked lists) were integral to the design of the operating system. It was quite common for computers of the day to have instructions for dealing with packed decimal arithmetic - that's how

    • I loved PDP11/Vax assembly, the instruction patterns were so consistent and their macro language turned programming in assembly into something much closer to 3GL programming than assembler. Because it was so consistent I got to the point where I could read an octal dump of PDP assembler as code. It was easily the most productive assembly programming language I have ever worked in for a real system -- 6502 was easier, but your 6502 SLOC was 3-10X VMS assembler SLOC for the same logic.

      What I never liked

  • Seems Like (Score:5, Funny)

    by Skjellifetti2 ( 7600738 ) on Sunday December 10, 2023 @12:25AM (#64069981)
    the poor guy is lost in a twisty little maze of passages.

  • A bunch of Dec Hardware (Score:4, Interesting)

    by Required Snark ( 1702878 ) on Sunday December 10, 2023 @06:10AM (#64070309)
    On YouTube at Usagi Electric [youtube.com] there are examples of multiple DEC machines, including a PDP-11/83 and a DEC Rainbow [youtube.com]. The collection also includes a Bendix G15 Vacuum Tube Computer [youtube.com]. The G15 has rotating drum memory.

    Seeing this old hardware being restored and running is really interesting. It's a tangible example of how much computing has changed.

  • He had to order a part to connect female to female floppy drive power cables.

    Am I missing something, or could one simply cut and splice the cables to do that?

    https://youtu.be/dh52fhCBt0A?t=243
  • The video gave me flashbacks to the PDP-11/7's used by the University of Texas for print servers in the early 80s. When they crashed or there was a power outage, you had to hand-toggle in the bootstrap program using the switches on the front. This program in turned read the printer server boot from the serial line. So before hitting run you would call the main RJE site and get them to queue up the binary; then they would hit send; and you would hit the Start button and hoped there weren't any bit errors.

  • Nice to see an 11/73 getting some love, but there are no doubt thousands of those out there in industrial use today.

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