15 NOV 2013 by ideonexus

 The World is a Black Box

The world with its quarks and chromosomes, its distant lands and spiral nebulae, is like a vast computer in a black box, forever sealed except for its input and output registers. These we directly observe, and in the light of them we speculate on the structure of the machine, the universe. Thus it is that we think up the quarks and chromosomes, the distant lands and the nebulae; they would account for the observable data. When an observation turns out unexpectedly, we may try modifying our th...
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We don't know how it works, we only see the inputs and outputs and must extrapolate hypotheses from what we see.

03 JAN 2011 by ideonexus

 A Reversible NAND Gate

The great discovery of Bennett and, independently, of Fredkin is that it is possible to do computation with a different kind of fundamental gate unit, namely, a reversible gate unit. I have illustrated their idea--with a unit which I could call a reversible NAND gate. It has thre inputs and thre outputs. Of the outputs, tow, A' and B', are the same as two of the inputs, A and B, but the third input works this way. C' is the same as C unless A and B are both 1, in which case it changes whateve...
Folksonomies: computing
Folksonomies: computing
  1  notes

Feynman describes a reversible logic gate, with three inputs and three outputs, one of which tracks the change in input and output, allowing the computer to reverse its operation and potentially pursue a different route.