loremipsum-I think that the cost of developing and mass producing an RCO-POW device will probably be hundreds of millions of dollars or even billions of dollars. However, since we do not have reversible computing devices, we do not know what technologies will be best for constructing reversible computing devices, and because I am a mathematician and not an engineer, I am unable to make an accurate estimate about how much it will cost to mass produce this future technology. Let me quote Mike Frank at
https://intelligence.org/2014/01/31/mike-frank-on-reversible-computing/ about the difficulty of manufacturing a reversible computing device whose efficiency surpasses Landauer's limit.
. . .But to actually realize practical, high-quality, high-performance, cost-efficient reversible computing below the Landauer limit is, I would say, one of the most difficult, hard-core engineering challenges of our time. That’s not to say it’s impossible; indeed, there has never been any valid proof from fundamental physics that it’s impossible, and to the contrary, there are many indications, from the research that’s been done to date, that suggest that it will probably be possible to achieve eventually. But it’s certainly not an easy thing to accomplish, given the state of engineering know-how at this point in time. A future computer technology that actually achieves high-quality, efficient reversible computing will require a level of device engineering that’s so precise and sophisticated that it will make today’s top-of-the-line device technologies seem as crude in comparison, to future eyes, as the practice of chiseling stone tablets looks to us today.
It will only be practical to develop these reversible devices if RCO-POW problems take up a significant share of the cryptocurrency mining market. Of course, we do not need to make reversible devices that go beyond Landauer's limit just yet to mine cryptocurrencies. We currently only need to develop reversible devices which are more efficient than conventional devices in order to solve these RCO-POW problems.
I am not worried at all about the cryptographic security of RCO-POW problems since these problems can be made just as secure as SHA-256 simply by adding more rounds to the reversible circuit. Of course, there is always the threat of a 51 percent attack, but the use of 5 different algorithms in the POW will provide the decentralization needed to thwart 51 percent attacks. I currently do not have any funding to develop a cryptocurrency with an RCO-POW problem so I will need a modest amount of funding to launch the cryptocurrency in the first place. Even if I use an ICO, I will definitely need funding to set up the ICO in the first place.
David Rabahy-While all algorithms including SHA-256 can be made reversible, it in general takes more steps to run a computation reversibly than it takes to run the computation irreversibly. Furthermore, after one is done computing SHA-256, one produces much garbage information. In order to clean this information, one either has to uncompute or delete the garbage information (and deleting garbage information after computation defeats the purpose of reversible computation in the first place). I want an RCO-POW problem for cryptocurrencies since these problems will make it as easy as possible for reversible devices to solve. If it is not easy for a reversible device to solve a POW problem, then it is unlikely that such a reversible device will be developed in the first place for a very long time.
A possible problem with using a hybrid of reversibility and irreversiblity is that it may be difficult to make reversible technologies compatible with conventional computing technologies (since reversible computers do not exist, we do not know what technologies will be used to make reversible devices and these technologies could be anything from adiabatic circuits to quantum dot cellular automata to even nano-mechanical devices). Cryptocurrency POW problems should be used to advance new technologies instead of stockpiling current technologies and burning energy.
I do not think an established cryptocurrency like Bitcoin would want to change its POW to an RCO-POW until other cryptocurrencies are using RCO-POW problems.
Joseph Van Name Ph.D.
boolesrings.org/jvanname