Re: Theoretical minimum # of logic operations to perform double iterated SHA256?
As I understand it, (and I could be wrong here) what is actually absolutely required to spend energy for, is the output. IOW, you could at least in theory design a system that answers the one-bit question, "is there a nonce meeting the difficulty target within " by actually spending the energy to write exactly one bit. Everything else can be reversible, so the greater the amount of computation you can do without any external effects required the more of it can be done "free" (albeit at ridiculously high complexity) but no matter what, you have to write the output.
In theory yes but even proponents of reversible computing don't believe leakage will be that low. There is the energy cost required to perfectly isolate the circuit from the outside environment so even if your raw circuit was perfectly reversible the total system energy cost will be much higher.
Also theory is just theory. In theory it is possible for someone to make a miner with 5,000,000 G/J (instead of 1 G/J) using plain boring classical computing. Granted you aren't going to do it with 20nm silicon but in theory it can be done. Now 5,000,0000 PH/s well we know that is not possible without a massive reduction in the "work" needed to complete a single hash. "In theory" is a nice way of saying nobody has proved it impossible.
