Computers often chain logic gates together, by taking the output from one gate and using it as the input to another gate. We call that a logic circuit. Circuits enables computers to do more complex operations than they could accomplish with just a single gate. The smallest circuit is a chain of 2 logic gates.
Logic circuits include such devices as multiplexers, registers, arithmetic logic units (ALUs), and computer memory, all the way up through complete microprocessors, which may contain more than 100 million gates. In modern practice, most gates are made from MOSFETs (metal–oxide–semiconductor field-effect transistors).