Gate logic

gate is a physical device that implements a Boolean function. If a Boolean function f operates on n variables and returns m binary results, the gate that implements f will have n input pins and m output pins. Just like complex boolean functions can be expressed in terms of simpler functions, complex gates are composed from more elementary gates. The simplest gates of all are made from tiny switching devices, called transistors, wired in a certain topology designed to effect the overall gate functionality.