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Definition: Boolean gates


Following are illustrations of Boolean AND, OR and NOT gates depicted in mechanical terms because the openings and closings of a mechanical switch are easy to visualize. To understand how these gates work together, see Boolean logic.

In real electronic systems, the mechanical switches in these diagrams are actually a semiconductor material that can normally be in a conductive state (closed) or non-conductive state (open). When pulsed, they switch their states. See transistor.




AND Gates Are Wired in Series
If both inputs are 1 (a pulse, high), both switches close, and the source current reaches the output.






OR Gates Are Wired in Parallel
Any of the two inputs will close their respective switch, and the source current reaches the output.






The NOT Gate Is an Inverter
What comes out of NOT is the opposite of what went in. If the input is 1, the output is 0 and vice versa. There are various electronic approaches to making a NOT gate; however, this illustrates the concept with switch #1 normally open and switch #2 normally closed. If there is an input pulse, switch one is closed causing the source current to reach switch two and open it.






From Gates to Systems
Boolean gates make up circuits, and circuits make up electronic systems.