A NOT gate (also often called Inverter) is a logic gate. Each NOT gate has only one input signal. Logically with NOT gates, the input and the output swap, so if you input 1 it outputs as 0; likewise if you input 0 it outputs as 1.The NOT gate negates the values of data or signal in its input. It will always output the opposite signal. Its main function is to interchange logic.
In the 20th century an inverter was often made of a discrete transistor with other components, or several inverters were packaged in an integrated circuit.
Symbols
There are three symbols for the NOT gate: