Why classical gates are irreversible?

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Discussion Overview

The discussion centers on the irreversibility of classical logic gates, specifically the NAND gate, and explores the implications of this irreversibility in the context of computation. Participants examine the relationship between inputs and outputs, entropy, and the potential for reversible computing using classical components.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant states that a NAND gate is irreversible because it loses one bit of information in the output, leading to an increase in entropy.
  • Another participant questions whether considering one of the inputs as an output could render the NAND gate reversible, seeking clarification on this point.
  • A different participant notes that while reversible computers can be built using classical components, they currently lack practical applications and are often used as "toy" systems.
  • There is mention of the direction associated with amplification in logic gates, highlighting the difference between high-impedance inputs and low-impedance outputs.

Areas of Agreement / Disagreement

Participants express differing views on the nature of irreversibility in logic gates and the potential for reversibility, indicating that multiple competing perspectives remain in the discussion.

Contextual Notes

The discussion does not resolve the assumptions regarding the definitions of reversibility and irreversibility in the context of logic gates, nor does it clarify the practical implications of reversible computing.

markoX
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Hi everybody.
I give you an example to clarify my question:
a NAND gate is irreversible because you can not find inputs from outputs and this is because of one bit is lost in output ( Antropy will increase ).the number of inputs and output are not the same in NAND gate.
ok...now my question is that we can consider one of input as output so we can make it reversible.why is'nt this true?

I have graduated in physics. thanks
 
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markoX said:
Hi everybody.
I give you an example to clarify my question:
a NAND gate is irreversible because you can not find inputs from outputs and this is because of one bit is lost in output ( Antropy will increase ).the number of inputs and output are not the same in NAND gate.
ok...now my question is that we can consider one of input as output so we can make it reversible.why is'nt this true?

I have graduated in physics. thanks

There is a direction associated with the amplification that is used for the logic gate function. Look at the equivalent circuit for a logic gate, and it is apparent that the inputs are high-impedance controls (like FET gates), and the outputs are low-impedance drivers.
 
Note that it IS of course possible to build reversible computers (in the computational sense) using classical components.
As far as I know there are no practical applications, but reversible comouters have been used as "toy" systems for a long time (this is one reason why quantum computing took off so quickly, much of the theory for reversible gates has been around for a long time).
 
thanks for your replies.
 

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