
MRAM-Like Device Could Make Logic Run Backwards - rbanffy
https://spectrum.ieee.org/nanoclast/semiconductors/devices/mramlike-device-could-make-logic-run-backwards
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jumpkickhit
Shouldn't this be way more efficient for computing?

[https://en.wikipedia.org/wiki/Reversible_computing](https://en.wikipedia.org/wiki/Reversible_computing)

"In other words, we would need to precisely track the state of the active
energy that is involved in carrying out computational operations within the
machine, and design the machine in such a way that the majority of this energy
is recovered in an organized form that can be reused for subsequent
operations, rather than being permitted to dissipate into the form of heat."

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russellsprouts
It is true that reversible computers can solve the issue of necessarily losing
heat due to entropy decreases, but current computers are still far too
inefficient for entropy loss to be a concern.

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ChuckMcM
I am not so sure, all of the heat being dissipated by your typical CMOS
transistor is due to the transistor state going through a linear region as it
switches from fully saturated to fully depleted or fully depleted to fully
saturated.

As I see it, if you're transistors did _not_ dissipate that energy as heat,
and instead 'stashed' it so that it could be re-used. Then you're 4 Ghz CPU
would no longer need a heat sink.

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ben_w
That’s the point. The entropy cost thermodynamically inherent to doing a
calculation is _infintesimal_ compared to the energy cost of current
transistors.

From Wikipedia:

> At 20 °C (room temperature, or 293.15 K), the Landauer limit represents an
> energy of approximately 0.0172 eV, or 2.75 zJ. Theoretically,
> room‑temperature computer memory operating at the Landauer limit could be
> changed at a rate of one billion bits per second with energy being converted
> to heat in the memory media at the rate of only 2.85 trillionths of a watt
> (that is, at a rate of only 2.85 pJ/s). Modern computers use millions of
> times as much energy.

[https://en.m.wikipedia.org/wiki/Landauer%27s_principle](https://en.m.wikipedia.org/wiki/Landauer%27s_principle)

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sitkack
But if we ran blackholes backwards wouldn't they start shooting out wikipedias
all over the universe?

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pavement
An infinite spacefiller that produces a flood of wikipedias in a simulation
will simply trigger out-of-memory exceptions, silly.

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sitkack
Isn't the interior of a black hole already over-committed?

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marshray
Couldn't one implement these functions with ordinary analog circuits?

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nayuki
I have trouble understanding how p-bits can speed up computations. Can't they
be emulated with deterministic logic plus a random number generator?

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jfoutz
Yes absolutely. Prolog would kinda sorta do the same thing. It would be much
faster though. You can build a mechanical computer with gears and cams, but
it’s big and slow.

This style is much quicker than a deterministic computer with an rng. It
wobbles between all the valid states at the ghz range, rather than the
thousands of cycles prolog would need.

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sitkack
Isn't this a stepping stone to same style of computation as a Quantum
Computer?

