A logic gate is a device that performs one or all the Boolean logic operations AND, NAND, NOR, NOT, OR, XNOR, and XOR. All types of logic gate, except NOT, accept two binary digits as input, and produce one binary digit as output. NOT gates accept only one input digit.
Two of the logic gate types, NAND ("not and") and NOR ("not or"), are referred to as universal logic gates. Either of these gates may be used in conjunction with itself to create any other type of logic gate.
In a CPU, logic gates are implemented using semiconductors, either as transistors or diodes. However, they can be constructed and implemented using a wide array of technologies based on natural phenomena, including optics, vacuum tubes, pneumatics, or even architected molecules.
In the diagram at right, A and B are the input power sources and Y is the output power, 1 represents power or "on," and 0 indicates "off" (no power). In the first example of the Not gate, if A had no power, then the output would turn on. If A had power, the output would turn off.