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I’m curious about what is happening in the field of reversable computing. I haven’t heard much about it at all in the last 20 years. Basic information theory te

I’m curious about what is happening in the field of reversable computing. I haven’t heard much about it at all in the last 20 years. Basic information theory tells us that it takes energy to destroy information, so building ALUs that limit destroying information seems like a bit of a no brainer for attempting to create lower power (and heat) computing. The basic premise is that for any operation that loses info you store enough bits to allow the operation to run backwards. If you were clever about it, you could design your chips to only destroy bits in places that can be effectively as well. I’m sure reality gets in the way of pure theory, but I was sure that people were spending enough effort on the concept to have heard more about it.

zozbot234 3y ago
Reversible computing doesn't help wrt. static or leakage power, which is an increasing fraction of power draw in recent device nodes. It does help wrt. dynamic power, and can be implemented via charge-recovery logic - but this comes at a cost in area which increases static power.
pillusmany 3y ago
Our power problems today are far away from the theoretical limits you described. But reversible computing is inevitable in quantum computers, so it's researched in that context.
sgdpk 3y ago
I have worked on this aspect on quantum computation [1]. The main problem is that reversibility is a feature of isolated quantum systems. In practice, they are not isolated. Why? It's not just because of small interactions with the environment that we cannot control. It's that even the apparatuses that we use to control/drive the logical instructions (lasers, electrical transmission lines) should be taken into account if the computer is to be considered isolated. But usually they aren't, and this leads to inevitable losses of reversiblity in the data register. In other words, unitary (reversible) operations do not come for free. I think that in quantum computers it is more likely that energy-efficiency will come from some sort of algorithmic advantage. [1] https://arxiv.org/abs/2210.10470 https://arxiv.org/abs/2210.10470

zozbot234 3y ago

Reversible computing doesn't help wrt. static or leakage power, which is an increasing fraction of power draw in recent device nodes. It does help wrt. dynamic power, and can be implemented via charge-recovery logic - but this comes at a cost in area which increases static power.

pillusmany 3y ago

Our power problems today are far away from the theoretical limits you described. But reversible computing is inevitable in quantum computers, so it's researched in that context.

sgdpk 3y ago

I have worked on this aspect on quantum computation [1]. The main problem is that reversibility is a feature of isolated quantum systems. In practice, they are not isolated. Why? It's not just because of small interactions with the environment that we cannot control. It's that even the apparatuses that we use to control/drive the logical instructions (lasers, electrical transmission lines) should be taken into account if the computer is to be considered isolated. But usually they aren't, and this leads to inevitable losses of reversiblity in the data register. In other words, unitary (reversible) operations do not come for free. I think that in quantum computers it is more likely that energy-efficiency will come from some sort of algorithmic advantage. [1] https://arxiv.org/abs/2210.10470 https://arxiv.org/abs/2210.10470