A serial interface is a communication interface between two digital systems that transmits data as a series of voltage pulses down a wire. A "1" is represented by a high logical voltage and a "0" is represented by a low logical voltage. Essentially, the serial interface encodes the bits of a binary number by their "temporal" location on a wire rather than their "spatial" location within a set of wires. Encoding data bits by their "spatial" location is referred to as a parallel interface and encoding bits by their "temporal" location is referred to as a serial interface. Figure 3 graphically illustrates the difference between these two communication methods.