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Unformatted text preview: T described computation with idealized,
perfectly elastic balls reﬂecting o↵ barriers. Minimum dissipation, propelled by (conserved) momentum. Unrealistic. Later we will look at it
¶11. They suggested a more realistic implementation involving “charge packets bouncing around along inductive paths between capacitors.”
¶12. Richard Feynman (CalTech) had been interacting with IM group, and
developed “a full quantum model of a serial reversible computer” (Feynman, 1986).
¶13. Adiabatic circuit: Since 1980s there has been work in adiabatic circuits, esp. in 1990s.
An adiabatic process takes place without input or dissipation of energy.
Adiabatic circuits minimize energy use by obeying certain circuit design
rules. “[A]rbitrary, pipelined, sequential logic could be implemented
in a fully-reversible fashion, limited only by the energy coe cients and
leakage currents of the underlying transistors.” 52 CHAPTER II. PHYSICS OF COMPUTATION ¶14. As of 2004, est. cE = 3 meV/kHz, about 250⇥ less than DNA.
¶15. “It is di cult to tell for certain, but a wide variety of post-transistor
device technologies have been proposed . . . that have energy coe cients ranging from 105 to 1012 times lower than present-day CMOS!
This translates to logic circuits that could run at GHz to THz frequencies, with dissipation per op that is still less (in some cases orders of
magnitude less) than the VNL bound of kB T ln 2 . . . that applies to
all irreversible logic technologies. Some of these new device ideas have
even been prototyped in laboratory experiments .”
¶16. “Fully-reversible processor architectures  and instruction sets 
have been designed and implemented in silicon.”
¶17. But this is more the topic of a CpE course. . . C.2 Physical assumptions of computing These lectures are based primarily on Edward Fredkin and Tommaso To↵oli’s
“Conservative logic” (Fredkin & To↵oli, 1982).
C.2.a Dissipative logic ¶1. The following physical principles are implicit in the existing theory of
¶2. P1. The speed of propaga...
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- Fall '13