It should be noted that multiplexers need not be digital. Analog multiplexers have many practical applications as well. Although the selection is done as for a normal multiplexer, using digital signals, the values being switched themselves are analog signals. In other words, take the example of a CD4051. It has three selection inputs, A, B and C. These are digital inputs. It also has eight data inputs, x0 to x7. These are analog -- they need not be 0 or 1, they can be any value. There is a single output, X, which is set to be one of x0 to x7 depending on the values of A, B and C. For instance, if ABC = 001, then X = X1, if ABC = 010, X = X2.