Why classical gates are irreversible?

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SUMMARY

The discussion centers on the irreversibility of classical logic gates, specifically the NAND gate, which loses one bit of information during its operation, leading to increased entropy. Participants clarify that while it is theoretically possible to construct reversible computers using classical components, practical applications remain limited. The distinction between high-impedance inputs and low-impedance outputs in logic gates is emphasized, highlighting the inherent directionality in their function. The conversation also touches on the historical context of reversible computing and its influence on the development of quantum computing.

PREREQUISITES
  • Understanding of classical logic gates, particularly NAND gates
  • Basic knowledge of entropy in information theory
  • Familiarity with high-impedance and low-impedance circuit concepts
  • Awareness of reversible computing principles
NEXT STEPS
  • Research the principles of reversible computing and its theoretical foundations
  • Explore the implications of entropy in digital logic design
  • Study the differences between classical and quantum computing architectures
  • Investigate practical applications of reversible logic gates in modern computing
USEFUL FOR

Electrical engineers, computer scientists, and anyone interested in the theoretical aspects of logic design and the evolution of computing technologies.

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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