Reversible or adiabatic computing/logic uses processors that can reconstruct a prior state of a computation, from a later state; they are time-invertible, can produce time-reversed version of a process; run it backwards. The main reason to do this to save energy, and lower heat output, by using thermodynamically reversible, energy-recovering circuits and devices. This is a research area which is gaining interest (heating up), as processors grow smaller and faster, and thus hotter per unit area.
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