Earlier already we have seen: The gate functions, can be performed by switches of any kind.
And we know: Instead of actuating a switch with the hande by a lever or button we can use an electrically actuated relay switch.

Thus all gate functions can be realized by relays instead of semiconductors as it is shown by the example picture aside. In this case it is even possible to actuate the switches by manual pressure instead of electromagnetism.

Therefore by the future we will work only by the gate symbols and not bother about the practical realization.
As well we always should be aware that every logical function can not only be realized by miniaturized semiconductor elements (as by now) but by such "oldfashinoned" relay switches too. The first computers (in the forties) had acted by this way.


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