(06-05-2015, 06:26 PM)Bob Jenkins Wrote: Irreversible computing can be done as reversible computing plus bit clearing. Swapping bits is reversible. You don't have to clear bits at the same place that computation consumes zeros. You could clear bits someplace safe to generate heat, toss a bunch of bits to the computation, swap zeros for random bits, then toss the random bits back to be cleared again.

Does that help with making computation compact and low temperature?

Not really.

I'm not sure what you mean by "swapping bits", but writing a bit requires joules per bit, and is an irreversible process.

If you don't write the result of a (classical) computation, you cannot know it.

If we are talking qubits, then reading the result state involves collapse of the wave function, which is also inherently non-reversible. Attempts to evade this by weak measurement run into the problem that until the result is observed, the solution doesn't exist (or rather exists as a multiplicity of possible outcomes which don't allow the quantum algorithm to proceed further).

Even if you wave your hands and invoke Many-Worlds, wave function collapse is still irreversible in our particular branch of reality.

When you write "clear bits someplace safe" you are really discussing information transfer rate, which in temperatures ranging from 10E3 to 10E9K is (in bits per second):

So you haven't fooled nature or otherwise gotten around fundamental limits of computation.

https://cloud.sagemath.com/#projects/970...ion.sagews

As discussed maybe a decade ago on the old Orion's Arm Yahoo lists, reversible computing allows you to reduce the power expenditure of computing an N-step algorithm by for some 0<b<1, but the algorithm will then take longer by the same factor, thus conserving total energy usage.

http://citeseerx.ist.psu.edu/viewdoc/dow...1&type=pdf