In this chapter, reversible means electrically reversible; this implies a system that does not dissipate energy. Since energy can be related to information, an electrically reversible computer must not lose any information, so it may be designed to be logically reversible. Electrically reversible implies an adiabatic computer. There are plenty of adiabatic gate designs based on charge recovery, such as the SCRL of Chapter 7, but very few adiabatic computer designs.

One fundamental roadblock to the design of adiabatic computers is memory. Memory in the usual sense of RAM generally overwrites old data with new data, thereby losing information; energy is dissipated. The same is true of data registers. But in view of biological memory in the savant, the hypothesis of toggle memory opens new possibilities for hardware design. With care, toggle circuits can be designed to be logically reversible and thus conservative of information; this implies something new, the possibility of an adiabatic computer.

Nanoprocessors based on toggle memory are designed in this chapter, not just functional blocks, but circuits using generic CMOS as an example technology. Translation into other technologies should be easy. Eventually, these designs may be transferred into molecular-sized logic circuits sometimes termed nanobrains. These devices are experimental, with the goal of vastly reducing the size of computers for gadgets such as microscopic ...

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