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#reading-together
Title
# reading-together
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alltom

01/20/2024, 4:06 PM
@Ivan Reese, in episode 9 of a podcast I can’t tell if I’m supposed to know about or not, you asked, “Where is [data] going when you’re throwing it away, and when you rewind, how does it come back?” And I don’t think it has answers that you’d want to apply directly to your situation, but Feynman’s Lectures on Computing comes back to the idea of reversible computing again and again with various playful metaphorical lenses. I think that at the very least it might be a nice way to take a break and think about the problem from a physicist’s perspective now and then, if this is still a problem you’re working on.
An extremely low-power computer needs to run just as easily forward as it does backward, so that the slightest touch can send it in one direction or the other. In fact, it will rock forward and backward just based on random fluctuations, and you try to bias it just enough so that it runs forwards more often than backwards. To do that, no part of it can ever create or destroy information. Every operation propagates the “waste” information forward so that if it rolls backward, it returns to its initial state. It’s fun. :)
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Ivan Reese

01/21/2024, 4:07 AM
I love reversible computing! Your 2nd message has a lovely description of it, painting it in a way that I'd not quite pictured before. Thank you for sharing that!
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Konrad Hinsen

01/21/2024, 10:44 AM
Reversible computing is attracting a lot of interest recently because it is the only possible approach to quantum computing. I'd expect the "green computing" people to explore it as well, but I haven't seen any references to it. Something that ought to be obvious but is rarely said is that "never deleting data" also means "never adding data". A perfectly reversible computing system is useless for information processing. But searching for a good compromise ought to be an interesting engineering challenge.
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Peter Abrahamsen

01/21/2024, 11:32 PM
That’s not obvious to me. Why can’t data be added?
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alltom

01/22/2024, 1:37 AM
There’s just an energy cost to changing the inputs, AFAIK?
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Konrad Hinsen

01/22/2024, 7:09 AM
Exactly. Adding data means changing the inputs. That entails the same energetic cost as deleting the prior input values. If you look into reversible computing from an energy-saving point of view, it really matters to look at a complete usable system.