LGP-30 and PDP-8e basement find

Wow, there are still discoveries to be made… and some are indeed lucky to make such a find. Compare the following Reddit post:

I found ancient computers in the basement of my grandparents (LGP-30 and PDP 8e)

Including a nice gallery of the objects in question.

Via HN: https://news.ycombinator.com/item?id=33514399


Spectacular find! From one of the reddit comments:

Owner of an LGP-30 here, undergoing a “long-term” restoration. One thing to be very careful of is the drum. The spacing between the heads and oxide surface is extremely tight and with age, the heads can make contact due to expansion. If the drum turns at all in this condition, you’re SOL.

My preferred method before moving the machine was to cut the v-belt and extract the drum. Then very carefully space all of the head mounting bars off the surface with washers. Only then did I dial them all in individually using brass shim stock.

The functioning LGP-30 in Stuttgart is neat to see; I was able to play Lunar Lander on it a few years ago. AFAIK, it’s the only 100% functioning one on the planet.

Link here to the startup procedure (text, with sound effects.)

From an HN comment, a link to writing polyglot code - a single binary running on many architectures, including the LGP-30:

Instead, we ended up building a polyglot shellcode that really did run on 8 different architectures (64-bit Intel, Royal Precision LGP-30, Donald Knuth’s MIX, PDP-1, PDP-8, PDP-10, DEFCON 2017’s cLEMENCy, and Data General Nova), and really did output a flag on every single one.


Quite a valuable tip, in case a LGP-30 shows up in my basement. :slight_smile:

Meaning, there’s a rather comical contrast in the serious and useful tip on how to handle a unrestored storage drum and the chances of actually encountering one.

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BTW, on a not so serious note, is this a young Elon Musk operating the LGP-30? :wink:

Mind that the same Royal McBee sales brochure for the LGP-30, where this image is from, lists “missile development studies” as one of the “suggested LGP-30 uses in industry”!

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Essential to view this video for the sights of sounds of starting up this machine:


In order to understand the start-up operations (quoting myself from elsewhere, based on the manual):

put the computer into manual input mode (which puts the machine into single instruction mode and prevents any recordings of transient signals onto the drum), press the “Operate“ button on the console and “Power On”, and the computer will engage in an automatic 2-stage startup sequence, lasting 50 seconds each. The first one is an intentionally slow warm-up stage, in order to preserve the filaments and to prolong the life of the vacuum tubes (valves), while the machine is helpfully putting on the “Stand By” light. The second one raises the circuitry to full DC voltages, slowly so for the same reasons. As the lights change from “Standby to Operate” to “Operate”, you probably have the loader program already in memory (since the drum provides nonvolatile memory) and you are ready to go.

If not, it’s time to enter the bootstrap loader. We could enter this either the hard way by the keyboard or run a paper tape instead. Button “Fill Instruction” simply transfers the contents of the accumulator into the instruction register and “Execute Instruction” executes it.

Edit: The description linked above mentions a three-button sequence for entering each of the bootstrap instructions, but I can’t see what the third button may be. “6 Bit Input” for transferring an instruction code into the accumulator?

Also from the Computermuseum der Stuttgarter Informatik, a repair video, where we get a good view of the internals, also another program read-in and execution (I guess, this is in ACT).


(Embedding is disabled for this video.)

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