Tyler Muth’s Blog

Technology with a focus on Oracle, Application Express and Linux

Rope Memory

Posted by Tyler Muth on February 27, 2009

I watched the Discovery Science series “Moon Machines” a few weeks ago, as I’m pretty much obsessed with all things space or flying. In the “Navigation Computer” episode, there was a section about the memory they used for the Apollo machines that I found fascinating. They actually sent their programs off to a factory to have them woven into a “rope” of 1’s and 0’s!!!  This makes punch-cards look convenient.

Check out the video on YouTube from about 3:00 to 6:00 min:


10 Responses to “Rope Memory”

  1. ittichai said

    That is amazing. It is unimaginable to think that the 72KB memory of the Apollo’s guidance and Navigational system could accomplish the job. I’ve watched similar Discovery episode saying that there was issue with memory overload (error 1202) during the halfway through its final 12-minute burn that would land them safely on the moon. But they’d decided to ignore error and land it anyway.


  2. Tyler Muth said

    Yeah, the 1202 was due to the fact that Neil Armstrong turned on the rendezvous radar just in case they had to abort and return to the command module. The computer was overloaded with data from both the landing radar and the rendezvous radar. You can understand his reasoning, but next time I would stick to the check-list 😉

  3. Tyler,
    Thanks for sharing!


  4. Kaili said

    First blog I read after wakeup from sleep today!

    FREE Image Converter.!Convert just using right click.

  5. The “Rope” name came from an original Instrumentation Lab concept of using a Jaquard Loom[used to make clothing labels] to weave a “rope” of cores. It never worked. Weaving even ten wires turns into an immovable object after a few cycles. The final version of the “Rope” had 196 wires approach each magnetic core. A wire passing thru the core represented a “one”[or a zero] and a wire bypassing a core made a “zero”[or a one]. The final version consisted of cores in a planer array. The plane was mounted in “Y,Z” NC machine. Each core that needed a wire was presented to the operator who then threaded the particular sense wire thru it.–etc,. etc– Very exspensive but very reliable The final product was most like brick!!!————–BillZ

  6. Almost nobody talks about “Rope Memory” ROM for anything but its use in the Apollo navigation computer. There were other applications.

    While working at Univac, 1969, I did testing on the switches for a keyboard on a punched card machine, probably other uses but I didn’t see them myself. This keyboard used 11 cores to encode ASCII keys into 1 Start, 7 data, 1 parity, and 2 stop bits. The 128 wires were strung through the cores to encode the data bits. As I recall, the sense windings on the 11 cores directly set flip flops made from NPN transistors.

    The keyboard keys actuated special switch assembles made by Micro Switch. When the key was pressed the micro switch was momentarily closed and sent a current pulse down one of the encoding wires. This was quite a robust system with very few electronic components.

    I did some experiments to see if I could make my own computer. I had chosen the rope ROM concept to encode operation of all registers transfers and stuff. The control ROM worked well but was quite slow.

    I found you can do lots of things. I managed to get an 8 bit digital adder to work using Rope Memory. I never did get the computer built though. I really wish I had my notes from that wonderful time.

    This was a “Personal Invention” of mine, later I learned of the Apollo computer which pioneered all this.

    See related stuff:


  7. Nice post… Looks like solid state memory is really beginning to take off. Hopefully we’ll start seeing a drop in solid state harddrive prices real soon. 5 dollar 32 GB Micro SD Cards for your Nintendo DS flash card… imagine that!(Submitted from NewPost for R4i Nintendo DS.)

  8. Tyler, Nice Post

  9. Phil said

    Buzz Aldrin, not Neil Armstrong, turned on the Rendezvous Radar prior to the landing. And it *was* on the checklist — Aldrin had specifically recommended it prior to the mission so the radar would be immediately available if needed for an abort and return to the CSM.

    There was no reason this shouldn’t have been okay. But a design error in the hardware interface between the computer and radar antenna resulted in a flurry of spurious interrupts that stole so much real time from the computer that it didn’t have enough to run all its tasks. Fortunately, the software was written very defensively, and it was able to run the more important tasks while stopping the less important ones.

    The hardware bug was quickly discovered and fixed so that it never happened again on any of the other landing missions.

    • Hugh Blair-Smith said

      Thanks Phil, for getting real close! Exposure to the problem came, not from the RR being “on” in the sense of powered up (though Buzz Aldrin remembered it that way in 2009), but from its being moded to its backup configuration, that is, ready to work with the Abort Guidance System instead of the AGC. That was what Buzz had put into the procedures, and he did perform it as specified. Even then, there was only about a 1% chance of having the problem, based on the exact instant the LM’s Primary GN&C system was powered up. Despite the best efforts of the late George Silver of MIT, this was never considered a hardware bug that needed fixing; instead, a small software upgrade was inserted to reset one of the circuits involved whenever the RR was moded to AGS. See my paper in IEEE’s Aerospace & Electronics Systems, Oct 2011, and the paper by Don Eyles that was my primary reference.

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