This module explains how to build a 4 X 1 Multiplexer.In electronics, a multiplexer or mux is a device that selects one of several analog or digital input signals and forwards the selected input into a single line. Multiplexers were logically designed and used as electronic selector switches. A multiplexer of 2n inputs has n select lines, which are used to select which input line to send to the output. Multiplexers are mainly used to increase the amount of data that can be sent over the network within a certain amount of time and bandwidth. On the other hand, a demultiplexer (or demux) is a device taking a single input signal and selecting one of many data-output-lines, which is connected to the single input. A multiplexer is often used with a complementary demultiplexer on the receiving end.