A Modern Day PDP-11 Front End

Hands up if you feel your spiritual home is in front of a terminal with a “DIGITAL” logo on it.  It’s a name that has long ago been subsumed into first Compaq and then by extension HP, but it’s one with a lot of history when it comes to computing.

From the start of the electronic computing age, there were the computers we’d probably now describe as mainframes. Big computers that cost the GDP of a small country, filled an entire floor of a building, and could only be found in government departments, universities, and large companies. By the 1960s, the technologies existed to build computers that broke this mould, could be bought within the budget of a smaller organisation, and for which you didn’t need a huge air-conditioned basement to house. These so-called minicomputers were the great revolution of that era because they bought the fruits of computing into everyday business, and probably the most successful of the companies that produced them was the Maynard, Massachusetts-based Digital Equipment Corporation, or DEC.

DEC produced a succession of minicomputers in their PDP line, of which the most successful was their PDP-11 series. These were 16-bit minicomputers that remained in their product line from their launch in 1970 through to the early 1990s, and were available in a succession of configurations and physical form factors. The famous view of a PDP-11 is of a set of floor-to-ceiling racks, but there were also standalone terminal models, and desktop models. One of these, a PDP-11/03 from 1975, has come into the hands of [Joerg], and he’s used it to craft his LSIbox, the PDP11/03 card frame packaged with a BeagleBone for access via a modern-day interface. It’s a build in the vein of modern tube audio amplifiers that feature the retro hardware on the top of their cases, the card frame is exposed as a feature on top of a white case that is featureless except for a genuine PDP-11/03 front panel.

You might ask why anyone would do this in order to run PDP-11 software when the BeagleBone could almost certainly emulate the vintage hardware much faster than the real thing. But to take that view is to miss the point; the PDP-11 series are a seminal part of computing history, and to have genuine PDP-11 hardware on your desk is quite an achievement.

We’ve shown you a few PDP-11 projects in the past. There was this minimalist PDP-11 implementation using one of the later integrated PDP-11 processors, and we’ve seen a faithful reproduction of an earlier PDP-11 front panel powered by a Raspberry Pi.

26 thoughts on “A Modern Day PDP-11 Front End

  1. Gotta love the names of the companies that took their names directly from the product they made. Digital Equipment Corporation made digital equipment. VLSI made Very Large Scale Integration chipsets for IBM clones. SouthWest Technical Products made technical products in the American Southwest. Radio Corporation of America, shouldn’t need to explain that one… Motorola? Who the heck could figure out what they made simply by reading the name? Was it motors? Nope.

    The Computing-Tabulating-Recording Company was a conglomerate of several companies that had variously made things that Computed, Tabulated, and Recorded – mostly with boring yet self descriptive names. Eventually the company changed its name to International Business Machines, which was still pretty much self descriptive, in a general way, as they made various machines for use in businesses and made and marketed them in more than one country.

    Being the first to start doing business under such an “exactly what it says on the tin” name could give a company a big advantage, if the ones in charge weren’t exceptionally stupid about marketing and money management. It also helped identify the clueless customers who’d read the name of the company – then ask what they make.

    1. (wikipedia: “Paul Galvin wanted a brand name for [their] new car radio, and created the name “Motorola” by linking “motor” (for motorcar) with “ola” (from Victrola), which was also a popular ending for many companies at the time, e.g. Moviola, Crayola”)

      Perhaps not obvious now, but it seems likely that it would have been obvious in the time in which it was formed.

    2. They took the name “Digital Equipment Corp” because their first product line was little logic cards that you could plug into backplanes and create complex functions with. Those Flip-Chip modules were used to create some of the early mini-computers, which – by the way – were called “Programmed Data Processors” because they could not obtain venture capitol to build computers. The investors were happy to front money for these profitable PDP machines that were absolutely not computers (LOL). I enjoyed working there on VAXen and Alpha based machines till they sold out…

      1. Yeah… There was certainly an era where if it didn’t take a whole room, or didn’t come from Sperry-Rand or IBM… It wasn’t a “legitimate” computer… HP used to market their HP9825 and other similar machines as “calculators”… Despite having a 10 MHz 16 bit CPU with multiple I/O expansions, a QWERTY keyboard, a single line alphanumeric LED dot matrix display, and large (for the time) RAM, the HP9825 was marketed in 1976 as a calculator, not a computer. Many government and businesses required a lot of red tape to requisition a computer, but little more than a business expense request to acquire a calculator. By labeling the HP9825 as a calculator, and not as a computer, they were able to streamline the supply of Apple II sized, 10 MHz, 16-bit, all in one computers to the desktops of engineers, with minimal red tape.

        Not a bad machine either, for 1976!

    1. The smell isn’t that hard to duplicate. It came from machine oil used in teletypes, line printers, and card readers, phenolic and/or epoxy resin from printed circuit boards, a bit of polyester from magnetic tapes, and a trace of blue smoke from the most recent breakdown. Which was yesterday.

      1. Don’t forget the stale ashtray smell from the chain smoking operators. I’m pretty sure DEC replaced the VT-52 terminals with the seminal VT-100 because the 52s were cream colored and they all developed a tobacco colored patina over time. 100s were black/grey. (Well, that and the detached keyboard.)

        Ah, memories!

        1. So, so true on the smokers! It was especially bad at newspapers, which usually had the VT6x/7x series units (some with the glorious electrostatic printer on the side). When you worked on one, you had to use a Texwipe to get the nicotine off of the screen. The keyboards would last forever (until coffee was introduced into them) and if the user was a long-nailed women, you’d see wear marks from the nails. Except for the paper logic boards, they were great! :)

  2. Nooo, my minicomputer first love was an HP 2100A, complete with illuminated pushbutton switch register and controls.
    The binary display register was laid out in octal groups, which I still find easier to read than 4-bit groupings.
    If you corrupted the boot loader (which read from the paper tape reader), you had to re-enter it by hand.
    The memory was 980 nS cycle-time ferrrite core, and our Elec. Eng. dept. had all of 32k words of it.

    1. Data General Supernova. RISC before there was such a thing. Semiconductor memory with 300 ns access time when most minis were using core memory in the 800-1200 ns range. Also one of the highest switches + lamps per square inch densities ever.

  3. Personally, I’d say the VAX series outshone the PDP’s,I’ve worked with PDP-8s in college, PDP-11 in my college job, PDP-11s, DEC-10s and VAXen of various sorts in my first post-college job.

    Until he reproduces the Tape-Stretch-11 (TS-11), and line printers that need an anti-static fabric softener lozenge dropped in the box of paper, it won’t be the authentic experience.

    1. Well the ‘TS-11’ comment brought back some BAD memories! Being a DEC FE, I’ve had the pleasure to stretch, rip and tear the media in everything from DECtape on up. :)

      AND it always seemed that if you had on a long-sleeve white shirt (we started out having to wear suits) you were going to get an LP0x service call. I don’t miss having to take the drum out and clean it either!

      I do miss the lights and switches though on the front panels!

  4. It feels like I was looking at some PDP-11’s just yesterday. Oh wait!! I WAS just looking at some PDP-11’s yesterday! There were stacks of VT101, VT220 and VT320 terminals. RX02 drives everywhere. It was like a DEC wonderland!

  5. Wow did I love my first “personal” computer – a PDP-11/05! It had two 4Kx16 planar memory “flip” chip modules plus a KSR-33 Teletype interface with a paper punch tape mech for loading and recording programs. Great memories of writing spaghetti code in BASIC.

  6. My first *real* industry job was working for Emulex as a field tech, maintaining the drive arrays at Southwestern Bell Publications (the Yellow Pages). They had a massive data center separated into three rooms – one full of VAX 5xxx, 6xxx, and even a massive pair of 9440s; one with two rows of 12 HSC90s (each with a terminal on top) and dozens of drive cabinets (my domain); and one full of tape drives and a robotic tape silo. We also had a MicroVAX III that belonged to our company, and a brand new 486DX PC with AutoCAD which we used to maintain the datacenter drawing. The “biggest” drives we had there were about 500mb, 8U high behemoths that you had to affix a bracket to to lock down the head and another to lock the spindle before you shipped them off for repair. The “smallest” were 500mb, 4U half-width drives. All of them connected back to the HSCs through a pair of SDI cables – essentially quad-coax cables. Two per drive, for redundancy, so if one controller failed, the other could take over the drive.

    That job ended after DEC sued Emulex for the DA01 – the Emulex-built HSC drive controllers that kinda apparently infringed a bit on DEC’s turf.

  7. Back in the early 80’s I was in a navy spook unit and I installed a pdp 11/73 in our p3’s we had six terminals and two printers I had to fab everything keyboard cases 10″ monitor s and make a new chassis for proscessor and card​ rack we used a 5mb hard drive in a hallburtan zero briefcase to transfer data from the scif to the plane do the mission then download the shit back to the briefcase and back to the acid

    Cool stuff good memories

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