What is digital circuit and system ?

A digital circuit is one in which the voltage levels assume a finite number of distinct values.
Digital circuits are often called switching circuits, because the voltage levels in a digital circuit are assumed to be switched from one value to another instantaneously, that is the transition time is assumed to be zero.
Digital circuits are also called logic circuits, because each type of digital circuit obeys a certain set of logic rules. The manner in which a logic circuit responds to an input is referred to the circuit's logic.
All of us are familiar with the impact of modern digital computers, communication systems, digital display systems, internet, e-mail, etc on society. One ofthe main of this revolution is the advent of integrated circuits (ICs ) which became possible because of the tremendous progress in emiconductor technology in recent years. Most of us may not be familiar ith the principles ofworking ofcomputers, communication systems, internet e-mail, etc. even though these have become an important part ofour daily life The operaton isbased m the ofthese sysems an many otersysems principles of digital techniques and these are referred to as digital systems.