These specialized electronic circuits are known as Logic Gates and are considered to be the Basic Building Blocks of any Digital circuit. The commonly used Logic Gates are the AND gate, the OR gate, the Inverter or NOT Gate. Other gates that are frequently used include NOR, NAND, XOR XNOR.
Each of these gates is designed to perform a unique operation on the input information which is known as a logical or Boolean operation. These basic building blocks are available in the form of Integrated Circuit or ICs. These gates are implemented using standard CMOS and TTL technologies thatdetermine the operational characteristics of the gates such as the power dissipation, operational voltages (3.3v or 5 v), frequency response etc.
Digital circuits to perform specific functions are available as Integrated Circuits for use. Implementing a Digital system in terms of these dedicated functional units makes the system more economical and reliable.
Different gates are combined to build a circuit that is capable of performing some useful operation like adding three numbers. Such circuits are known as Combinational Logic Circuits or Combinational Circuits.