Why classical gates are irreversible?

AI Thread Summary
A NAND gate is considered irreversible because it loses one bit of information in the output, making it impossible to uniquely determine the inputs from the outputs. This loss increases entropy, as the number of inputs does not equal the number of outputs. The discussion suggests that if one input is treated as an output, it could be made reversible, but this is not feasible due to the inherent properties of the gate. While reversible computing can be achieved with classical components, practical applications remain limited, and such systems are often used for theoretical exploration rather than real-world use. The principles of reversible gates have contributed to the development of quantum computing.
markoX
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Hi everybody.
I give you an example to clarify my question:
a NAND gate is irreversible becuase 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 becuase 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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