10 ms·

How do you measure nuclear warhead yield with a PDP-11?

133 points by segfaultbuserr 6y ago

mhh__ 6y ago
Curious I assume the TDR picks up induced EMF in the cable by the radiation from the Detonation.
- ISL 6y ago
  The "time-domain reflectometer" will send a signal down the line and listen for a reflection from its end. This happens in much the same way a travelling wave will reflect from the free end of a dangling rope. Even though a jiggling rope and an electrical signal seem different, the underlying mathematics (mismatched impedance at the rope/cable end) is essentially the same. The time difference between when the signal is sent and the reflected signal received, multiplied by the speed of the signal (over two), gives the distance to the end of the cable. If the reflectometer can make the measurement quickly-enough, the series of measurements will trace out the decreasing length of the cable as the detonation destroys it.
  - segfaultbuserr 6y ago
    This doesn't answer the original question: How could the experimenter ensure the electromagnetic pulse from the nuclear denotation wouldn't create false readings in the TDR measurements?
    - ISL 6y ago
      It might -- in this context (and always ;) ), I'd guess that experiment is the arbiter of truth. If they set up a few of them, perhaps with differing cable lengths in order to vary the capacitance, the extent to which they all measured similar results would give a measure of how well the method might measure the cable ablation. There's a chance that there's a subtle systematic, but my guess is that either the method would work or the measuring device would get smoked, with not much in between.
    - namibj 6y ago
      You could transmit a chirp, and use that to distinguish it from a nuclear EMP.
    - hwillis 6y ago
      Nuclear reactions don't just make EMPs; it's not like nuclear plants are emitting continuous electromagnetic interference. Nuclear EMPs are created when radiation ionizes susceptible atoms, creating charged particles via Compton scattering. That's why high-altitude nukes create much more intense EMPs; the low-density atmosphere is much easier to ionize. Gases at low pressure are DRAMATICALLY easier to ionize than anything else- think fluorescent tubes, etc. Dirt will not be highly ionized by an underground explosion, although I can't actually find anything about underground EMPs. It is safe to say that the EMP will be very greatly reduced, though. The EMP is dangerous to electronics because it creates a voltage gradient over a large area. A 5 volt gradient across a few inches of ground plane will destroy most electronics permanently. A semiconductor is painstakingly embedded with atoms that create an intrinsic voltage difference across a tiny sliver of silicon; a mild voltage in the wrong direction will erase that gap. It will not destroy wires, since the pulse is extremely short. Forget erroneous measurements. The EMP would kill the computer if it was just a plain wire. You're talking about picking up tens of thousands of volts across any kind of protection circuit. The only possible way this works is with some protection, ideally shielded wire like a coax cable. If that's the case it'll just cause a brief (<10 microsecond, mostly) flash of current to ground. Modern Ethernet is twisted pair, but the first ethernet was coax and the first R58 was sometimes shielded. There are other types and components of nuclear EMPs but they mostly aren't important in this case. There are several highly questionable things about this story- the PDP-11 would need a pretty skookum power supply to not bottom out, the motivation is... strange, the ethernet wire would need to be incredibly long, etc. etc. EMP is probably not one of them, at least as far as the quality of data. EMP becomes irrelevant if you can access raw data or the ping uses anything but the simplest impulse waveform. Assuming you can actually collect data in the first place, anyway.
- fit2rule 6y ago
  It sure does. (I'm pretty sure the cable is in the path of the bomb being tested..)
barbegal 6y ago
There is some truth to this account: https://books.google.co.uk/books?id=6t-wCwAAQBAJ&pg=PA131&lpg=PA131 https://books.google.co.uk/books?id=6t-wCwAAQBAJ&pg=PA131&lp... It's called CORRTEX. And I think you could probably set up a PDP-11 to sample roughly every millisecond so this could work.
- walshemj 6y ago
  The smaller PDP systems 11/03's where often used in Labs - DEC did a Realtime operating system RT11 for this use case and there where some exotic expansion cards for experimental use. Back in my first job we had a custom built 12 bit ADC used for analysing mixing about £3k per channel in early 1980's £
- beamatronic 6y ago
  That doesn’t seem fast enough to be useful...
  - hwillis 6y ago
    The initial fireball of a nuke is caused by xrays absorbed by air and develops in microseconds. Basically all at once, since the xrays move at the speed of light. A spherical region of air just ionizes. The expanding fireball moves quite a bit slower and increases 10s of meters (from an initial ~10-100 m) over several milliseconds[1]. After that it slows down even more, and if you measure every millisecond you'll see the fireball expanding by meters. [1]: https://pbs.twimg.com/media/Dbf8IK9V0AA38po.jpg https://pbs.twimg.com/media/Dbf8IK9V0AA38po.jpg
    - Tehchops 6y ago
      This phenomenon is referred to as a "double flash": http://wordpress.mrreid.org/2015/04/18/the-nuclear-double-flash/ http://wordpress.mrreid.org/2015/04/18/the-nuclear-double-fl...
  - barbegal 6y ago
    A DEQNA ethernet controller card can measure to an accuracy of 100ns which is around 20m at the speed of light. Shockwave velocities in the ground are in the order of 1000 to 10000 m/s or 1 to 10 m/ms so sampling at 1ms intervals should be precise enough. In fact here is a graph produced by CORRTEX https://digital.library.unt.edu/ark:/67531/metadc1200655/m1/6/ https://digital.library.unt.edu/ark:/67531/metadc1200655/m1/... which shows a velocity of ~3 m/ms or 3000 m/s. The sepcialised equipment has much better resolution and samples much faster than every millisecond.
tech-historian 6y ago
FYI, the PDP-11 cost around USD $20,000 when introduced in the early 1970s. That's equivalent to ~$135,000 today.
- dylan604 6y ago
  Oh, so it was developed by SGI? ;-)
  - walshemj 6y ago
    If SGI built systems designed like a tank - I recall helping to install a dual 8 inch floppy drive took two guys to lift it into position
    - JoeAltmaier 6y ago
      Oh yeah old computers were heavy. I just cleaned out a cabinet in my basement office, and on the bottom shelf were parts of a 1980's computer. It weighed tons! Broke my back carrying it all upstairs to get rid of.
    - qubex 6y ago
      It’s no joke that SGI machines contain lumps of cast iron. I collected them for a while and I can assure you they are built like tanks.
    - pmiller2 6y ago
      Have you seen a PDP-11? It probably weighs closer to a tank than anything produced by SGI. You wouldn't be lifting a PDP-11 without equipment: it would be the size of a refrigerator or 2.
      - kps 6y ago
        > Have you seen a PDP-11? There's a PDP-11/73 about eight feet to my left; it's a 4U box, much smaller than a little SGI Onyx, let alone an Origin.
qubex 6y ago
There’s a lot of discussion here on how (or even whether) a ‘reflectometer’ (I had to look up what that even meant) works. However, I’m more interested in the things I do understand, and in this case, my question is: considering the fact that there needs to be another (remote) computer to receive the readings, and considering that we’re speaking of processes that ‘degrade’ the cable dangling into the nuclear borehole at an alarming rate, just how does one go about performing an ordinary electrical transmission of data over those distant ranges in those minute times? The latencies are enormous and therefore clearly we’re not talking something like TCP and it’s three-way-handshake SYM/ACK kind of response. And once the blast approaches the surface (assuming it doesn’t breach it)… is it sufficient for the computer to (comparatively) leisurely transmit its findings whilst it’s in the process of falling into the enormous crater that’s opening up beneath it? Can one presume that the power remains stable long enough for this to occur? (Assuming that the power supply has been destroyed and/or the cables jolted loose, how long does the machine “stay up whilst falling down”?)
- cosmiccatnap 6y ago
  This is alot of assumptions in an age of paper pencil and telephone.
- jacobush 6y ago
  The story doesn't say, but one could imagine electrically copying the communication in real-time on another wire back to the bunker or something. Or if the test is deep underground, just walk up to the PDP-11 and load it onto a truck.
  - qubex 6y ago
    > the story doesn’t say [...] electrically copying [the signal] back to the bunker or something That’s precisely my point: how do you reliably “copy a signal back” if one terminus of the cable cannot be relied upon to exist for long?
- raldi 6y ago
  Underground nuclear tests don’t make huge holes in the surface. That’s the whole point. Here’s what they look like at ground level: https://www.atlasobscura.com/articles/heres-what-an-underground-nuclear-test-actually-looks-like https://www.atlasobscura.com/articles/heres-what-an-undergro... Plenty of room for the computer to survive.
antman 6y ago
Related: Fermi's report on estimating yield by dropping small pieces of paper during a nuclear blast and measuring their displacement. http://www.dannen.com/decision/fermi.html http://www.dannen.com/decision/fermi.html
- semi-extrinsic 6y ago
  Also related: G.I. Taylor who developed the theory of blast waves to the point where he could estimate yield from photographs published in newspapers, and wrote papers that published the classified yield of the first US nuclear tests. Edit: His estimate was between 17 and 23 kilotons of TNT, the real yield was 22 kilotons. https://royalsocietypublishing.org/doi/10.1098/rspa.1950.0049 https://royalsocietypublishing.org/doi/10.1098/rspa.1950.004... https://royalsocietypublishing.org/doi/10.1098/rspa.1950.0050 https://royalsocietypublishing.org/doi/10.1098/rspa.1950.005...
  - qubex 6y ago
    This remakrable achievement is often used as the setting-off point to explain dimensional analysis.
    - jedimastert 6y ago
      > This remakrable achievement is often used as the setting-off point to explain dimensional analysis. I was always a fan of dimensional analysis as it tickled "puzzle solving" aspect of my lizard brain, but if it were introduced via nuclear blast analysis in my classes I bet it would have grabbed a lot more attention.
  - ramshanker 6y ago
    This reminded me of the quote "Any science well done, is as good as magic."
_sbrk 6y ago
Great stuff from the golden years of the 'net. Archived websites like this show what it was, before it became infected with consumers.
- Swizec 6y ago
  My favorite was an in depth website about farts. It explained how it was impossible to fart while you sleep because your “don’t pee myself” reflex keeps everything sealed shut. This is why you often let a big one rip soon after waking. I believed that shit for 20 years ... then my girlfriend moved in and lemme tell ya, humans definitely fart in their sleep.
raldi 6y ago
(1992)
eggy 6y ago
I so desperately wanted to get in on this novel personal computing thing, and I couldn't afford a computer. In 1976 I bought a book on machine and assembly language programming not knowing a thing from a bookstore on Wall St. somewhere. It was for the DEC PDP-11. I went through the first third or so of it with pencil and paper and put boxes on the side to show me the status of registers. Not productive, but not a waste of time. I then bought a Commodore PET in 1978 and the rest is history! That early exercise made it easy for me to learn 6502 assembly and work on the Vic-20, C64, C128, and PowerPC Macs.
- nicolashahn 6y ago
  Hey, this is not related to the original submission, but I just wanted to know what keeps someone like you (who's been interested in computers for much longer than I've been alive) going. It seems like it'd be very easy to tire of the industry/hobby after that long, I want to know what you're currently interested in and if you're comfortable sharing, what you're currently working on day-to-day in your job (if you're not retired by now).
  - eggy 6y ago
    Funny, but I took only a few jobs where coding was more than 50% of my day job, but for the most part I've held very eclectic jobs in a predominantly technical or artistic career. I was reading about neural networks and genetic algorithms in the late 80s and programming in Lisp and C. Mark Watson's book (he's on HN) "Common Lisp Modules: Artificial Intelligence in the Era of Neural Networks and Chaos Theory" got me started in coding them rather than just reading the more academic tomes I read in the late 80s. I am glad I didn't just focus on that then, although, I'd probably have more of a savings now and higher salary. But not the adventures I managed to have by meeting people in all different types of jobs. And there's something about physical labor that calms me. Sitting at a desk all day seems so antithetical to actually living a life out in the real world and feeling the earth between your toes, the sun and wind on your body while taking in the green things around you! I was dumpster diving and taking stepper motors out of dot matrix printers in the early 90s down on Wall street while working a 12 to 9 shift taking care of a VAX/VMS and Banyan Vines PC network for an environmental law firm. I used to write reports in Paradox, work on Concordance - a document management system - BRS search routines and queries. I used the steppers for my amateur robotics influenced by Rodney Brooks' subsumption architecture and Mark Tilden's BEAM stuff. I played Doom for the first time at that job! I was an art handler (Brooklyn Museum), paintings conservator's assistant, 3D FX and animation on SGI intern using Prisms (now Houdini) at a NYC Ad agency/FX company, welder, machinist, CNC coder, technical diver and ropework technician (think IRATA/SPRAT), among the memorable items. I remember being one of the early funders for getting Blender3D open sourced way back when (2001/02), and writing a Python script to turn photos into wooden carvings back in 2002/03 with it on my CNC table. The software was based upon a paper by NASA about 'Shape from Shading'. it alsow churned out G-code for our table after downloading the client's file, and gave me an estimate of machine time and overall cost. This is before 3D printers, and tables used to be in the 6 figures, but this was an $8k 4 ft x 8 ft router table. My partner and I used it to cut out kayak designs we made out of 4 mm Okume plywood and the carvings I did in solid maple in bas relief. We did some urns for pets and pet cemeteries (really! http://thewoodenimage.com http://thewoodenimage.com. Used to come up on the Wayback Machine without pics or other content). Sad to say, people loved our carvings at boat shows, etc., but nobody bought them. We had crowds at our table, but not a single purchase. Funny cemeteries were our market, and a gentlemen offered me money for the software to make bronze tombstone plaques from family photos! I worked at a company as a sys admin, and did some coding in C, C#, Java, but mainly my strength was writing front ends for old Italian sheet metal punch machines and translating modern G-code into the 'Octo' machines' proprietary code. This was in C. Putting a temperature sensor in the server room, and have it ping a pager of me and the other sys admins. I did Christmas display window animations for a display company in NYC as a welder and later as the head of their creative technologies. One Christmas (1996-7?). We had pneumatically operated 4 to 5 ft high Nutcrackers whose arms would go up with a bell in it if a child touched the window where there were five large buttons painted on the back of the window with a capacitive sensor behind it, a BasicStamp (think today's Arduino) running it, queuing the music and triggering the pneumatic valves. Remember right up until this, the internet and information from companies was not as accessible. I had to write letters, emails, and phone call for weeks. I will probably never retire. I just put a deposit down on a live/work space to use my desktop cnc mill/lathe, 3D printer and electronics equipment (a CNC sewing/embroidery machine too). I currently work at an engineering firm that specializes in stage machinery and anything entertainment-related. Because I don't code full-time for a living, I code up things in what works best for me and the company I work for. I write them in C, python, factor, J, forth, assembler (micros), and I play with a lot more PLs (Zig, Rust, Haskell, R/RStudio), but I am mainly sticking with C and J for now with Zig as a cross compiler. I avoid python, not because it isn't good or I don't like it, but it doesn't fit in with my preference for terseness and shedding bloat. I am having a renewed interest in C and assembler. I am getting older for some of the more physical work I did, so I am now coding more to try and see if I can make something of it. I was working in Macau for 6-plus years for the The House of Dancing Water show up until the end of 2015. I have hundreds of technical dives working on hydraulics, air FX, and electrical systems under water. It is almost 10 m deep and was the world's largest commercial indoor pool! Programming is not so much a career for me as it is simply a tool. The same for my electronics and metalworking experience, or any other skill. Critical thinking, problem solving, and knowing how to provide what's needed or desired are more important. I've always followed my heart or gut on what's next and it is landed me in a good place at my age. Follow your bliss to quote Joseph Campbell! [1] https://link.springer.com/book/10.1007/978-1-4612-3186-8 https://link.springer.com/book/10.1007/978-1-4612-3186-8
dekhn 6y ago
I'm pretty sure this is apocryphal. It seems more likely that somebody used cables with TDR to measure yield at some point, and somebody noticed that the ethernet interfaces on their PDPs had similar equipment, and made a story that combined them.
kps 6y ago
I read a different version of this story many years ago, but have not been able to find it again. In it, the machine did not send measurements to a more distant location, it recorded them in memory: core memory, with each core individually labelled, in case the machine didn't stay in one piece. (If true, this probably implies the machine was not a QBUS PDP-11, and the reflectometer was not an ethernet card.)
craftinator 6y ago
I feel like this would be right at home in a Neal Stephenson novel.
loph 6y ago
Having a DEQNA was the reason they did not love their PDP-11. They were notoriously buggy. Replaced with DELQA. See http://www.bitsavers.org/pdf/dec/qbus/EK-DELQA-UG-002.pdf http://www.bitsavers.org/pdf/dec/qbus/EK-DELQA-UG-002.pdf
posix_me_less 6y ago
Here is how nuclear explosion vaporizing telephone cables was thought to sound like on the open line in 60's. Absolutely terrifying scene. https://youtu.be/kw5o1eRhSiw?t=83 https://youtu.be/kw5o1eRhSiw?t=83
lmilcin 6y ago
Not likely to be workable. Nuclear explosions generate massive amount of electromagnetic interference which is likely to fry or at least throw off any regular reflectometer that relies on echo of the signal. Don't want to say it is technically impossible but would probably require especially designed instrument.
- pmiller2 6y ago
  I guess I wasn't the only one thinking the PDP-11 would likely be electrically fried before it got blown to smithereens here.
hazeii 6y ago
I have a number of PDP11's (that escaped nuclear obliteration) and have the skills to keep your nuclear plant running until 2050 [0]. The instruction set is really worth studying to this day, and the fact it has both pre and post-increment/decrement surely informed the design of C (and its predecessors). So orthogonal a single instruction could replicate itself through memory:- MOV (-PC),(-PC) As the instruction counter (PC, AKA R7) auto-incremented on each instruction, that instruction first decrements the PC (so it points back to the current instruction) and then copies the contents of the memory location (i.e. the current instruction) to the next lower memory address. And since the PC has now been decremented twice, the operation can repeat until it hits somewhere without any physical RAM (as PDP-11's have a bus signal to tell them whether the addressed memory exists or not). Also easy to program in octal; knowing that MOV is 01MRMR, addressing mode M is 4 for pre-decrement and R is the register number, no-one even needed an assembler to write that instruction as:- 014747 The ultra-regular ISA made it easy to learn and remember bootstraps, it'd just take a few passes along the toggle switches to key in a loader. It became rather easier with boot ROMs and serial terminals, e.g. on the LSI-11 just typing '173000G' was enough to bring up the system (back then I got to code a boot loader for 5" disk drives, 2 different 8" disk driver and a user interface with a prompt into 256 words of ROM). Those were the days, my friend. Funnily enough I booted one of the PDP's a few days ago and it wasn't even hard to remember op-codes learnt 40+ years ago. [0] https://news.ycombinator.com/item?id=5904191 https://news.ycombinator.com/item?id=5904191
- giardini 6y ago
  from the stackoverflow topic titled: "What are the historical reasons C languages have pre-increments and post-increments?": https://stackoverflow.com/questions/30429753/what-are-the-historical-reasons-c-languages-have-pre-increments-and-post-increme https://stackoverflow.com/questions/30429753/what-are-the-hi... A quote from that topic: >'Ritchie, The Development of the C Language: "People often guess that they [ED. the increment and decrement operators] were created to use the auto-increment and auto-decrement address modes provided by the DEC PDP-11 on which C and Unix first became popular. This is historically impossible, since there was no PDP-11 when B was developed." The PDP-7 seems to have some features that might have played a role, albeit I don't think it's entirely clear from the document that they were the main reason for the existence of both prefix and postfix ++'<
pnw_hazor 6y ago
At LANL they put many experiments/sensors in the bomb stack. A group I was with ran an experiment called PINEX (Pinhole Imaging Neutron Experiment), they used high speed video cameras to capture light/photons from a light intensifier. A meter diameter lead sphere was placed between the bomb and the light intensifier to attenuate the neutron signal. The length of the video cable (coax) was measured in time units. They could get about a frame and half of video off the CCD and out of the bomb hole before everything was vaporized. The video was captured using analog-to-digital signal converters and then interpreted later. The ADC, memory, pulse generators (to trigger light intensifier, start the CCD sweep, etc.) were sitting in a CAMAC crate attached to a customized VAX. They even has a customized VAX and monitor to visualize or analyze the captured data. The captured frame would be rendered into a gray scale image of a concentric circles that meant something to the bomb physicists. My intern project involved showing how the ridiculously expensive and fragile VAX setup could be replaced by a modern workstation running off the shelf software. Of course, this was not well received, that is why my mentor had me do the work and presentation - he would never have gotten away with it himself. No matter though, bomb testing was stopped soon enough.
WalterBright 6y ago
My fluid mechanics professor showed how to measure the yield just by examining a movie of the blast frame by frame, i.e. the size and rate of expansion of the cloud. A professor did this in the late 1940s and got himself investigated by the military for espionage, until he showed them how to do the calculation.
WalterBright 6y ago
I had a PDP-11 in the form of a Heathkit H11. I sorely regret selling it.
ChuckMcM 6y ago
BTW, this is article is not actually correct[1]. The technique is however. The measurement used an HP pulse generator to send a pulse down a piece of coax and that pulse, and the "echo" or return were both attached to Ch1 and Ch2 of an oscilloscope in the measurement trailer. When a pulse was fired a Polaroid picture was taken of the screen at the same time. By measuring the difference between the leading edge of the initial pulse and the returning pulse the length of the cable could be computed. With a lot of pulse generators and oscilloscopes you could synchronize them to each fire slightly later than the next and get a number of solid data points on the cable being vaporized. The Polaroids all included on the picture the rack and rack slot where they were located, and the sequencing was known, so you could digitize the pictures and extract the data. [1] I actually worked in one of these trailers as part of a summer job during college writing code on said PDP 11/34.
- kps 6y ago
  This paper lists the gear used (at some point) for the measurements, on p16: https://www.osti.gov/biblio/7352892 https://www.osti.gov/biblio/7352892 2 - 1.5 MHz tape recorders 2 - Oscilloscopes with cameras (HP-180 w/1805A and 1821A) 2 - Digital freq. and time interval counters/dig. volt meters HP5326B 2 - Sandia SLIFER chassis, shop made 2 - Pulse generators, HP214A 2 - Engine generators, 25 kW 1 - Trailer or shelter, portable, with utilities 2 - Time code generator 2 - WWV receivers 4 - Radios for local communication 2 - Countdown receivers 2 - Hi potters, HP4329A 1 - Time mark generator (Cal scopes) HP226A 2 - Variable oscillators, HP3312A 2 - Time delay generators, Rutherford 3 - Counter (HP5345A) 2 - Program timer, shop made
  - ChuckMcM 6y ago
    Wow, that is awesome. I wish they had a picture from inside the trailer. Basically a Decwriter + PDP-11/34 at one end, and two back to back rows of 19" "telco" racks with scopes, pulse generators, and cameras.

Curious I assume the TDR picks up induced EMF in the cable by the radiation from the Detonation.

ISL 6y ago
The "time-domain reflectometer" will send a signal down the line and listen for a reflection from its end. This happens in much the same way a travelling wave will reflect from the free end of a dangling rope. Even though a jiggling rope and an electrical signal seem different, the underlying mathematics (mismatched impedance at the rope/cable end) is essentially the same. The time difference between when the signal is sent and the reflected signal received, multiplied by the speed of the signal (over two), gives the distance to the end of the cable. If the reflectometer can make the measurement quickly-enough, the series of measurements will trace out the decreasing length of the cable as the detonation destroys it.
- segfaultbuserr 6y ago
  This doesn't answer the original question: How could the experimenter ensure the electromagnetic pulse from the nuclear denotation wouldn't create false readings in the TDR measurements?
  - ISL 6y ago
    It might -- in this context (and always ;) ), I'd guess that experiment is the arbiter of truth. If they set up a few of them, perhaps with differing cable lengths in order to vary the capacitance, the extent to which they all measured similar results would give a measure of how well the method might measure the cable ablation. There's a chance that there's a subtle systematic, but my guess is that either the method would work or the measuring device would get smoked, with not much in between.
  - namibj 6y ago
    You could transmit a chirp, and use that to distinguish it from a nuclear EMP.
  - hwillis 6y ago
    Nuclear reactions don't just make EMPs; it's not like nuclear plants are emitting continuous electromagnetic interference. Nuclear EMPs are created when radiation ionizes susceptible atoms, creating charged particles via Compton scattering. That's why high-altitude nukes create much more intense EMPs; the low-density atmosphere is much easier to ionize. Gases at low pressure are DRAMATICALLY easier to ionize than anything else- think fluorescent tubes, etc. Dirt will not be highly ionized by an underground explosion, although I can't actually find anything about underground EMPs. It is safe to say that the EMP will be very greatly reduced, though. The EMP is dangerous to electronics because it creates a voltage gradient over a large area. A 5 volt gradient across a few inches of ground plane will destroy most electronics permanently. A semiconductor is painstakingly embedded with atoms that create an intrinsic voltage difference across a tiny sliver of silicon; a mild voltage in the wrong direction will erase that gap. It will not destroy wires, since the pulse is extremely short. Forget erroneous measurements. The EMP would kill the computer if it was just a plain wire. You're talking about picking up tens of thousands of volts across any kind of protection circuit. The only possible way this works is with some protection, ideally shielded wire like a coax cable. If that's the case it'll just cause a brief (<10 microsecond, mostly) flash of current to ground. Modern Ethernet is twisted pair, but the first ethernet was coax and the first R58 was sometimes shielded. There are other types and components of nuclear EMPs but they mostly aren't important in this case. There are several highly questionable things about this story- the PDP-11 would need a pretty skookum power supply to not bottom out, the motivation is... strange, the ethernet wire would need to be incredibly long, etc. etc. EMP is probably not one of them, at least as far as the quality of data. EMP becomes irrelevant if you can access raw data or the ping uses anything but the simplest impulse waveform. Assuming you can actually collect data in the first place, anyway.
fit2rule 6y ago
It sure does. (I'm pretty sure the cable is in the path of the bomb being tested..)

There is some truth to this account: https://books.google.co.uk/books?id=6t-wCwAAQBAJ&pg=PA131&lpg=PA131 https://books.google.co.uk/books?id=6t-wCwAAQBAJ&pg=PA131&lp... It's called CORRTEX. And I think you could probably set up a PDP-11 to sample roughly every millisecond so this could work.

walshemj 6y ago
The smaller PDP systems 11/03's where often used in Labs - DEC did a Realtime operating system RT11 for this use case and there where some exotic expansion cards for experimental use. Back in my first job we had a custom built 12 bit ADC used for analysing mixing about £3k per channel in early 1980's £
beamatronic 6y ago
That doesn’t seem fast enough to be useful...
- hwillis 6y ago
  The initial fireball of a nuke is caused by xrays absorbed by air and develops in microseconds. Basically all at once, since the xrays move at the speed of light. A spherical region of air just ionizes. The expanding fireball moves quite a bit slower and increases 10s of meters (from an initial ~10-100 m) over several milliseconds[1]. After that it slows down even more, and if you measure every millisecond you'll see the fireball expanding by meters. [1]: https://pbs.twimg.com/media/Dbf8IK9V0AA38po.jpg https://pbs.twimg.com/media/Dbf8IK9V0AA38po.jpg
  - Tehchops 6y ago
    This phenomenon is referred to as a "double flash": http://wordpress.mrreid.org/2015/04/18/the-nuclear-double-flash/ http://wordpress.mrreid.org/2015/04/18/the-nuclear-double-fl...
- barbegal 6y ago
  A DEQNA ethernet controller card can measure to an accuracy of 100ns which is around 20m at the speed of light. Shockwave velocities in the ground are in the order of 1000 to 10000 m/s or 1 to 10 m/ms so sampling at 1ms intervals should be precise enough. In fact here is a graph produced by CORRTEX https://digital.library.unt.edu/ark:/67531/metadc1200655/m1/6/ https://digital.library.unt.edu/ark:/67531/metadc1200655/m1/... which shows a velocity of ~3 m/ms or 3000 m/s. The sepcialised equipment has much better resolution and samples much faster than every millisecond.

tech-historian 6y ago

FYI, the PDP-11 cost around USD $20,000 when introduced in the early 1970s. That's equivalent to ~$135,000 today.

dylan604 6y ago
Oh, so it was developed by SGI? ;-)
- walshemj 6y ago
  If SGI built systems designed like a tank - I recall helping to install a dual 8 inch floppy drive took two guys to lift it into position
  - JoeAltmaier 6y ago
    Oh yeah old computers were heavy. I just cleaned out a cabinet in my basement office, and on the bottom shelf were parts of a 1980's computer. It weighed tons! Broke my back carrying it all upstairs to get rid of.
  - qubex 6y ago
    It’s no joke that SGI machines contain lumps of cast iron. I collected them for a while and I can assure you they are built like tanks.
  - pmiller2 6y ago
    Have you seen a PDP-11? It probably weighs closer to a tank than anything produced by SGI. You wouldn't be lifting a PDP-11 without equipment: it would be the size of a refrigerator or 2.
    - kps 6y ago
      > Have you seen a PDP-11? There's a PDP-11/73 about eight feet to my left; it's a 4U box, much smaller than a little SGI Onyx, let alone an Origin.

qubex 6y ago

There’s a lot of discussion here on how (or even whether) a ‘reflectometer’ (I had to look up what that even meant) works. However, I’m more interested in the things I do understand, and in this case, my question is: considering the fact that there needs to be another (remote) computer to receive the readings, and considering that we’re speaking of processes that ‘degrade’ the cable dangling into the nuclear borehole at an alarming rate, just how does one go about performing an ordinary electrical transmission of data over those distant ranges in those minute times? The latencies are enormous and therefore clearly we’re not talking something like TCP and it’s three-way-handshake SYM/ACK kind of response. And once the blast approaches the surface (assuming it doesn’t breach it)… is it sufficient for the computer to (comparatively) leisurely transmit its findings whilst it’s in the process of falling into the enormous crater that’s opening up beneath it? Can one presume that the power remains stable long enough for this to occur? (Assuming that the power supply has been destroyed and/or the cables jolted loose, how long does the machine “stay up whilst falling down”?)

cosmiccatnap 6y ago
This is alot of assumptions in an age of paper pencil and telephone.
jacobush 6y ago
The story doesn't say, but one could imagine electrically copying the communication in real-time on another wire back to the bunker or something. Or if the test is deep underground, just walk up to the PDP-11 and load it onto a truck.
- qubex 6y ago
  > the story doesn’t say [...] electrically copying [the signal] back to the bunker or something That’s precisely my point: how do you reliably “copy a signal back” if one terminus of the cable cannot be relied upon to exist for long?
raldi 6y ago
Underground nuclear tests don’t make huge holes in the surface. That’s the whole point. Here’s what they look like at ground level: https://www.atlasobscura.com/articles/heres-what-an-underground-nuclear-test-actually-looks-like https://www.atlasobscura.com/articles/heres-what-an-undergro... Plenty of room for the computer to survive.

antman 6y ago

Related: Fermi's report on estimating yield by dropping small pieces of paper during a nuclear blast and measuring their displacement. http://www.dannen.com/decision/fermi.html http://www.dannen.com/decision/fermi.html

semi-extrinsic 6y ago
Also related: G.I. Taylor who developed the theory of blast waves to the point where he could estimate yield from photographs published in newspapers, and wrote papers that published the classified yield of the first US nuclear tests. Edit: His estimate was between 17 and 23 kilotons of TNT, the real yield was 22 kilotons. https://royalsocietypublishing.org/doi/10.1098/rspa.1950.0049 https://royalsocietypublishing.org/doi/10.1098/rspa.1950.004... https://royalsocietypublishing.org/doi/10.1098/rspa.1950.0050 https://royalsocietypublishing.org/doi/10.1098/rspa.1950.005...
- qubex 6y ago
  This remakrable achievement is often used as the setting-off point to explain dimensional analysis.
  - jedimastert 6y ago
    > This remakrable achievement is often used as the setting-off point to explain dimensional analysis. I was always a fan of dimensional analysis as it tickled "puzzle solving" aspect of my lizard brain, but if it were introduced via nuclear blast analysis in my classes I bet it would have grabbed a lot more attention.
- ramshanker 6y ago
  This reminded me of the quote "Any science well done, is as good as magic."

_sbrk 6y ago

Great stuff from the golden years of the 'net. Archived websites like this show what it was, before it became infected with consumers.

Swizec 6y ago
My favorite was an in depth website about farts. It explained how it was impossible to fart while you sleep because your “don’t pee myself” reflex keeps everything sealed shut. This is why you often let a big one rip soon after waking. I believed that shit for 20 years ... then my girlfriend moved in and lemme tell ya, humans definitely fart in their sleep.

raldi 6y ago

(1992)

eggy 6y ago

I so desperately wanted to get in on this novel personal computing thing, and I couldn't afford a computer. In 1976 I bought a book on machine and assembly language programming not knowing a thing from a bookstore on Wall St. somewhere. It was for the DEC PDP-11. I went through the first third or so of it with pencil and paper and put boxes on the side to show me the status of registers. Not productive, but not a waste of time. I then bought a Commodore PET in 1978 and the rest is history! That early exercise made it easy for me to learn 6502 assembly and work on the Vic-20, C64, C128, and PowerPC Macs.

nicolashahn 6y ago
Hey, this is not related to the original submission, but I just wanted to know what keeps someone like you (who's been interested in computers for much longer than I've been alive) going. It seems like it'd be very easy to tire of the industry/hobby after that long, I want to know what you're currently interested in and if you're comfortable sharing, what you're currently working on day-to-day in your job (if you're not retired by now).
- eggy 6y ago
  Funny, but I took only a few jobs where coding was more than 50% of my day job, but for the most part I've held very eclectic jobs in a predominantly technical or artistic career. I was reading about neural networks and genetic algorithms in the late 80s and programming in Lisp and C. Mark Watson's book (he's on HN) "Common Lisp Modules: Artificial Intelligence in the Era of Neural Networks and Chaos Theory" got me started in coding them rather than just reading the more academic tomes I read in the late 80s. I am glad I didn't just focus on that then, although, I'd probably have more of a savings now and higher salary. But not the adventures I managed to have by meeting people in all different types of jobs. And there's something about physical labor that calms me. Sitting at a desk all day seems so antithetical to actually living a life out in the real world and feeling the earth between your toes, the sun and wind on your body while taking in the green things around you! I was dumpster diving and taking stepper motors out of dot matrix printers in the early 90s down on Wall street while working a 12 to 9 shift taking care of a VAX/VMS and Banyan Vines PC network for an environmental law firm. I used to write reports in Paradox, work on Concordance - a document management system - BRS search routines and queries. I used the steppers for my amateur robotics influenced by Rodney Brooks' subsumption architecture and Mark Tilden's BEAM stuff. I played Doom for the first time at that job! I was an art handler (Brooklyn Museum), paintings conservator's assistant, 3D FX and animation on SGI intern using Prisms (now Houdini) at a NYC Ad agency/FX company, welder, machinist, CNC coder, technical diver and ropework technician (think IRATA/SPRAT), among the memorable items. I remember being one of the early funders for getting Blender3D open sourced way back when (2001/02), and writing a Python script to turn photos into wooden carvings back in 2002/03 with it on my CNC table. The software was based upon a paper by NASA about 'Shape from Shading'. it alsow churned out G-code for our table after downloading the client's file, and gave me an estimate of machine time and overall cost. This is before 3D printers, and tables used to be in the 6 figures, but this was an $8k 4 ft x 8 ft router table. My partner and I used it to cut out kayak designs we made out of 4 mm Okume plywood and the carvings I did in solid maple in bas relief. We did some urns for pets and pet cemeteries (really! http://thewoodenimage.com http://thewoodenimage.com. Used to come up on the Wayback Machine without pics or other content). Sad to say, people loved our carvings at boat shows, etc., but nobody bought them. We had crowds at our table, but not a single purchase. Funny cemeteries were our market, and a gentlemen offered me money for the software to make bronze tombstone plaques from family photos! I worked at a company as a sys admin, and did some coding in C, C#, Java, but mainly my strength was writing front ends for old Italian sheet metal punch machines and translating modern G-code into the 'Octo' machines' proprietary code. This was in C. Putting a temperature sensor in the server room, and have it ping a pager of me and the other sys admins. I did Christmas display window animations for a display company in NYC as a welder and later as the head of their creative technologies. One Christmas (1996-7?). We had pneumatically operated 4 to 5 ft high Nutcrackers whose arms would go up with a bell in it if a child touched the window where there were five large buttons painted on the back of the window with a capacitive sensor behind it, a BasicStamp (think today's Arduino) running it, queuing the music and triggering the pneumatic valves. Remember right up until this, the internet and information from companies was not as accessible. I had to write letters, emails, and phone call for weeks. I will probably never retire. I just put a deposit down on a live/work space to use my desktop cnc mill/lathe, 3D printer and electronics equipment (a CNC sewing/embroidery machine too). I currently work at an engineering firm that specializes in stage machinery and anything entertainment-related. Because I don't code full-time for a living, I code up things in what works best for me and the company I work for. I write them in C, python, factor, J, forth, assembler (micros), and I play with a lot more PLs (Zig, Rust, Haskell, R/RStudio), but I am mainly sticking with C and J for now with Zig as a cross compiler. I avoid python, not because it isn't good or I don't like it, but it doesn't fit in with my preference for terseness and shedding bloat. I am having a renewed interest in C and assembler. I am getting older for some of the more physical work I did, so I am now coding more to try and see if I can make something of it. I was working in Macau for 6-plus years for the The House of Dancing Water show up until the end of 2015. I have hundreds of technical dives working on hydraulics, air FX, and electrical systems under water. It is almost 10 m deep and was the world's largest commercial indoor pool! Programming is not so much a career for me as it is simply a tool. The same for my electronics and metalworking experience, or any other skill. Critical thinking, problem solving, and knowing how to provide what's needed or desired are more important. I've always followed my heart or gut on what's next and it is landed me in a good place at my age. Follow your bliss to quote Joseph Campbell! [1] https://link.springer.com/book/10.1007/978-1-4612-3186-8 https://link.springer.com/book/10.1007/978-1-4612-3186-8

dekhn 6y ago

I'm pretty sure this is apocryphal. It seems more likely that somebody used cables with TDR to measure yield at some point, and somebody noticed that the ethernet interfaces on their PDPs had similar equipment, and made a story that combined them.

kps 6y ago

I read a different version of this story many years ago, but have not been able to find it again. In it, the machine did not send measurements to a more distant location, it recorded them in memory: core memory, with each core individually labelled, in case the machine didn't stay in one piece. (If true, this probably implies the machine was not a QBUS PDP-11, and the reflectometer was not an ethernet card.)

craftinator 6y ago

I feel like this would be right at home in a Neal Stephenson novel.

loph 6y ago

Having a DEQNA was the reason they did not love their PDP-11. They were notoriously buggy. Replaced with DELQA. See http://www.bitsavers.org/pdf/dec/qbus/EK-DELQA-UG-002.pdf http://www.bitsavers.org/pdf/dec/qbus/EK-DELQA-UG-002.pdf

posix_me_less 6y ago

Here is how nuclear explosion vaporizing telephone cables was thought to sound like on the open line in 60's. Absolutely terrifying scene. https://youtu.be/kw5o1eRhSiw?t=83 https://youtu.be/kw5o1eRhSiw?t=83

lmilcin 6y ago

Not likely to be workable. Nuclear explosions generate massive amount of electromagnetic interference which is likely to fry or at least throw off any regular reflectometer that relies on echo of the signal. Don't want to say it is technically impossible but would probably require especially designed instrument.

pmiller2 6y ago
I guess I wasn't the only one thinking the PDP-11 would likely be electrically fried before it got blown to smithereens here.

hazeii 6y ago

I have a number of PDP11's (that escaped nuclear obliteration) and have the skills to keep your nuclear plant running until 2050 [0]. The instruction set is really worth studying to this day, and the fact it has both pre and post-increment/decrement surely informed the design of C (and its predecessors). So orthogonal a single instruction could replicate itself through memory:- MOV (-PC),(-PC) As the instruction counter (PC, AKA R7) auto-incremented on each instruction, that instruction first decrements the PC (so it points back to the current instruction) and then copies the contents of the memory location (i.e. the current instruction) to the next lower memory address. And since the PC has now been decremented twice, the operation can repeat until it hits somewhere without any physical RAM (as PDP-11's have a bus signal to tell them whether the addressed memory exists or not). Also easy to program in octal; knowing that MOV is 01MRMR, addressing mode M is 4 for pre-decrement and R is the register number, no-one even needed an assembler to write that instruction as:- 014747 The ultra-regular ISA made it easy to learn and remember bootstraps, it'd just take a few passes along the toggle switches to key in a loader. It became rather easier with boot ROMs and serial terminals, e.g. on the LSI-11 just typing '173000G' was enough to bring up the system (back then I got to code a boot loader for 5" disk drives, 2 different 8" disk driver and a user interface with a prompt into 256 words of ROM). Those were the days, my friend. Funnily enough I booted one of the PDP's a few days ago and it wasn't even hard to remember op-codes learnt 40+ years ago. [0] https://news.ycombinator.com/item?id=5904191 https://news.ycombinator.com/item?id=5904191

giardini 6y ago
from the stackoverflow topic titled: "What are the historical reasons C languages have pre-increments and post-increments?": https://stackoverflow.com/questions/30429753/what-are-the-historical-reasons-c-languages-have-pre-increments-and-post-increme https://stackoverflow.com/questions/30429753/what-are-the-hi... A quote from that topic: >'Ritchie, The Development of the C Language: "People often guess that they [ED. the increment and decrement operators] were created to use the auto-increment and auto-decrement address modes provided by the DEC PDP-11 on which C and Unix first became popular. This is historically impossible, since there was no PDP-11 when B was developed." The PDP-7 seems to have some features that might have played a role, albeit I don't think it's entirely clear from the document that they were the main reason for the existence of both prefix and postfix ++'<

pnw_hazor 6y ago

At LANL they put many experiments/sensors in the bomb stack. A group I was with ran an experiment called PINEX (Pinhole Imaging Neutron Experiment), they used high speed video cameras to capture light/photons from a light intensifier. A meter diameter lead sphere was placed between the bomb and the light intensifier to attenuate the neutron signal. The length of the video cable (coax) was measured in time units. They could get about a frame and half of video off the CCD and out of the bomb hole before everything was vaporized. The video was captured using analog-to-digital signal converters and then interpreted later. The ADC, memory, pulse generators (to trigger light intensifier, start the CCD sweep, etc.) were sitting in a CAMAC crate attached to a customized VAX. They even has a customized VAX and monitor to visualize or analyze the captured data. The captured frame would be rendered into a gray scale image of a concentric circles that meant something to the bomb physicists. My intern project involved showing how the ridiculously expensive and fragile VAX setup could be replaced by a modern workstation running off the shelf software. Of course, this was not well received, that is why my mentor had me do the work and presentation - he would never have gotten away with it himself. No matter though, bomb testing was stopped soon enough.

WalterBright 6y ago

My fluid mechanics professor showed how to measure the yield just by examining a movie of the blast frame by frame, i.e. the size and rate of expansion of the cloud. A professor did this in the late 1940s and got himself investigated by the military for espionage, until he showed them how to do the calculation.

WalterBright 6y ago

I had a PDP-11 in the form of a Heathkit H11. I sorely regret selling it.

ChuckMcM 6y ago

BTW, this is article is not actually correct[1]. The technique is however. The measurement used an HP pulse generator to send a pulse down a piece of coax and that pulse, and the "echo" or return were both attached to Ch1 and Ch2 of an oscilloscope in the measurement trailer. When a pulse was fired a Polaroid picture was taken of the screen at the same time. By measuring the difference between the leading edge of the initial pulse and the returning pulse the length of the cable could be computed. With a lot of pulse generators and oscilloscopes you could synchronize them to each fire slightly later than the next and get a number of solid data points on the cable being vaporized. The Polaroids all included on the picture the rack and rack slot where they were located, and the sequencing was known, so you could digitize the pictures and extract the data. [1] I actually worked in one of these trailers as part of a summer job during college writing code on said PDP 11/34.

kps 6y ago
This paper lists the gear used (at some point) for the measurements, on p16: https://www.osti.gov/biblio/7352892 https://www.osti.gov/biblio/7352892 2 - 1.5 MHz tape recorders 2 - Oscilloscopes with cameras (HP-180 w/1805A and 1821A) 2 - Digital freq. and time interval counters/dig. volt meters HP5326B 2 - Sandia SLIFER chassis, shop made 2 - Pulse generators, HP214A 2 - Engine generators, 25 kW 1 - Trailer or shelter, portable, with utilities 2 - Time code generator 2 - WWV receivers 4 - Radios for local communication 2 - Countdown receivers 2 - Hi potters, HP4329A 1 - Time mark generator (Cal scopes) HP226A 2 - Variable oscillators, HP3312A 2 - Time delay generators, Rutherford 3 - Counter (HP5345A) 2 - Program timer, shop made
- ChuckMcM 6y ago
  Wow, that is awesome. I wish they had a picture from inside the trailer. Basically a Decwriter + PDP-11/34 at one end, and two back to back rows of 19" "telco" racks with scopes, pulse generators, and cameras.