4 ms·

Reminds me of a scene from Cryptonomicon that may or may not have been inspired by history. It describes the RAM from a fictionalized 1940s computer: >The pipe

Reminds me of a scene from Cryptonomicon that may or may not have been inspired by history. It describes the RAM from a fictionalized 1940s computer: >The pipes are laid out horizontally, like a rank of organ pipes that has been knocked flat. Stuck into one end of each pipe is a little paper speaker ripped from an old radio. >“The speaker plays a signal—a note—that resonates in the pipe, and creates a standing wave,” Waterhouse says. “That means that in some parts of the pipe, the air pressure is low, and in other parts it is high.” He is backing down the length of one of the pipes, making chopping motions with his hand. “These U-tubes are full of mercury.” He points to one of several U-shaped glass tubes that are plumbed into the bottom of the long pipe. >[...] >“If the air pressure in the organ pipe is high, it pushes the mercury down a little bit. If it’s low, it sucks the mercury up. I put an electrical contact into each U-tube—just a couple of wires separated by an air gap. If those wires are high and dry (like because high air pressure in the organ pipe is shoving the mercury down away from them), no current flows. But if they are immersed in the mercury (because low air pressure in the organ pipe is sucking the mercury up to cover them), then current flows between them, because mercury conducts electricity! So the U-tubes produce a set of binary digits that is like a picture of the standing wave—a graph of the harmonics that make up the musical note that is being played on the speaker. We feed that vector back to the oscillator circuit that is driving the speaker, so that the vector of bits keeps refreshing itself forever, unless the machine decides to write a new pattern of bits into it.” Mechanical computing in general is fascinating. People also used to use precisely-machined drums and cams to perform complex realtime calculations.

nullc 6y ago
https://en.wikipedia.org/wiki/Delay_line_memory https://en.wikipedia.org/wiki/Delay_line_memory
- deleted 6y ago
  [deleted]
- m4rtink 6y ago
  From what I've heard this was really sensitive to any changes in environment - temperature, vibration or possibly even air pressure. All of which were likely to change where you were about to demonstrate your new mainframe to a delegation of important people! :-) IIRC it was even named "the general syndrome" in some places.
- avianlyric 6y ago
  What’s described above isn’t quite the same as delay line memory. Delay line memory relies on the speed of sound through a medium. You put a signal in at one end, and it propagates “slowly” to the other, where you receive the signal, and immediately replay it at the start. Creating a kind of never ending echo. What’s described above relies on a standing wave in a tube, with sensors along the length of the tube to detect nodes and anti-nodes. Then encoding data into that by changing the signal input to change the locations of the nodes and anti-nodes. I don’t think such a system would actually work, because your stuck using only the harmonics of your tube as possible states, and there’s gonna be a pretty limited number that you could realistically produce.
  - hwillis 6y ago
    You're correct- mercury delay lines read/write in a set order and you have to wait for your address to come back around in order to access it. Standing wave memory would mostly defeat the point of having memory, since you'd need to address every single antinode individually. You might as well just have a bunch of latches. The real point of delay lines, shift registers, or core memory is to reduce the address space: you store bits in a way that is slower but simpler to access, which means you can store more things. Mercury standing waves would not make it any easier to store bits, so there's no advantage. Still, you could make a device like that. Only 2/3rds of the tube can store memory- the rest is a quarter-wave transformer, which basically makes the tube act as if it was open at both ends. You can construct arbitrary patterns with fourier decompositions: https://en.wikipedia.org/wiki/Periodic_summation https://en.wikipedia.org/wiki/Periodic_summation
    - klyrs 6y ago
      > Standing wave memory would mostly defeat the point of having memory This is a common theme in sci-fi. Authors tend to know enough to make something sound plausible; but it's pretty rare for their inventions to pass the sniff test. I'd say "they're not writing patents, after all" but Salvatore Pais took that away from me: https://www.thedrive.com/the-war-zone/31798/the-secretive-inventor-of-the-navys-bizarre-ufo-patents-finally-talks https://www.thedrive.com/the-war-zone/31798/the-secretive-in...
scsilver 6y ago
A visual representation of standing waves on air pressure along the tube. You could set up a similar mechanical ram with a temperature or light sensor on each fire hole along the tube https://youtu.be/pWekXMZJ2zM https://youtu.be/pWekXMZJ2zM

nullc 6y ago

https://en.wikipedia.org/wiki/Delay_line_memory https://en.wikipedia.org/wiki/Delay_line_memory

deleted 6y ago
[deleted]
m4rtink 6y ago
From what I've heard this was really sensitive to any changes in environment - temperature, vibration or possibly even air pressure. All of which were likely to change where you were about to demonstrate your new mainframe to a delegation of important people! :-) IIRC it was even named "the general syndrome" in some places.
avianlyric 6y ago
What’s described above isn’t quite the same as delay line memory. Delay line memory relies on the speed of sound through a medium. You put a signal in at one end, and it propagates “slowly” to the other, where you receive the signal, and immediately replay it at the start. Creating a kind of never ending echo. What’s described above relies on a standing wave in a tube, with sensors along the length of the tube to detect nodes and anti-nodes. Then encoding data into that by changing the signal input to change the locations of the nodes and anti-nodes. I don’t think such a system would actually work, because your stuck using only the harmonics of your tube as possible states, and there’s gonna be a pretty limited number that you could realistically produce.
- hwillis 6y ago
  You're correct- mercury delay lines read/write in a set order and you have to wait for your address to come back around in order to access it. Standing wave memory would mostly defeat the point of having memory, since you'd need to address every single antinode individually. You might as well just have a bunch of latches. The real point of delay lines, shift registers, or core memory is to reduce the address space: you store bits in a way that is slower but simpler to access, which means you can store more things. Mercury standing waves would not make it any easier to store bits, so there's no advantage. Still, you could make a device like that. Only 2/3rds of the tube can store memory- the rest is a quarter-wave transformer, which basically makes the tube act as if it was open at both ends. You can construct arbitrary patterns with fourier decompositions: https://en.wikipedia.org/wiki/Periodic_summation https://en.wikipedia.org/wiki/Periodic_summation
  - klyrs 6y ago
    > Standing wave memory would mostly defeat the point of having memory This is a common theme in sci-fi. Authors tend to know enough to make something sound plausible; but it's pretty rare for their inventions to pass the sniff test. I'd say "they're not writing patents, after all" but Salvatore Pais took that away from me: https://www.thedrive.com/the-war-zone/31798/the-secretive-inventor-of-the-navys-bizarre-ufo-patents-finally-talks https://www.thedrive.com/the-war-zone/31798/the-secretive-in...

scsilver 6y ago

A visual representation of standing waves on air pressure along the tube. You could set up a similar mechanical ram with a temperature or light sensor on each fire hole along the tube https://youtu.be/pWekXMZJ2zM https://youtu.be/pWekXMZJ2zM