Reversible Computing: An Honest Bound on the Total-System Energy Saving

Logically reversible operations need not erase information, and so can in principle avoid the Landauer erasure cost. This paper computes, from published component energies, how large a saving reversible logic could honestly deliver for a complete processor at fixed throughput. The Landauer cost is only 0.0004% of a present-day switching event; logic switching is about a fifth of processor energy, capping any saving at 20% before implementation; adiabatic recovery trades energy for time as RC/tau, so a 100-fold logic-energy reduction caps the clock at 0.25 GHz under four-phase power-clocking; and compute-copy-uncompute overhead multiplies the work by a factor of six to four before the trade begins. Combining the effects at fixed throughput, the largest total-system saving is about 9% under generous assumptions (15% optimistic), obtained only at a six-to-eightfold per-transition slowdown repaid in parallelism; with no credit for leakage suppression there is no saving at any slowdown. All calculations are model calculations, SIMULATED, NOT MEASURED, and are generated by the accompanying computation script from published input values.