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4 networks propagation delays are not explicitly associated with individual gates or wires; rather, they are
¶3.mplicitly lumped this related to "delay elements." Yet, in thesethan to timing delay elements already have
However, in the so-called proper causal ordering rather networks (which (would1980). This
garbage cannot be thrown away the per se Toffoli, dissipate
an explicit formal role,
confusion about the role must be logic avoided insome explicitly consider the distributed
energy), so it of delay elements is force conservative logic.
composition rules of conservative recycled in one to way. The
encountered in routing a signal from one processing element to the next. In conventional sequential
networks propagation delays are not explicitly associated with individual gates or wires; rather, they are
implicitly lumped in the so-called "delay elements." Yet, in these networks the delay elements already have
an explicit C.7 role, related to proper causal ordering rather than to timing per se (Toffoli, 1980). This
confusion about the role of delay elements is avoided in conservative logic. ¶1. OR, NOT, and FAN-OUT: Fig. II.15 shows Fredkin realizations of
other common gates. C. REVERSIBLE COMPUTING 59 ¶2. Demultiplexer example: Fig. II.16 shows a 1-line to 4-line demultiplexer.
¶3. Hence you can convert conventional logic circuits into conservative circuits, but the process is not very e cient. It’s better to design the
conservative circuit from scratch.
¶4. Universality: “any computation that can be carried out by a conventional sequential network can also be carried out by a suitable
conservative-logic network, provided that an external supply of constants and an external drain for garbage are available.”
(Will see how to relax these constraints: Sec. C.8) C.8 Garbageless conservative logic ¶1. To reuse the apparatus for a new computation, we will have to throw
away the garbage and provide fresh constants, both of which will dissipate energy.
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