Combinational logic defines digital behavior where outputs respond directly to current input values. No clocked storage or previous state is involved. This creates the foundation for fast, deterministic hardware functions built from Boolean operations. Inverters, AND, NAND, OR, NOR, XOR, and XNOR gates establish the basic operation set used to construct larger logic structures. Functional completeness explains how universal gate sets such as NAND and NOR can realize any Boolean function. This principle is essential for gate-level implementation, logic optimization, and technology mapping. Complex combinational behavior can be reduced to smaller gate structures, allowing digital IC functions to be represented, simplified, and synthesized using predictable logic forms. Multiplexers and demultiplexers provide controlled data routing. A multiplexer selects one input from several available data sources and forwards it to a single output based on select signals. A demultiplexer takes one input and routes it to one selected output. These structures are central to datapath selection, conditional routing, bus organization, and efficient signal movement inside digital systems. Decoders an...