Wires are used in a digital system to communicate signals from one place to another and to distribute power and clock. In these capacities wires dominate a modern digital system in terms of speed, power, and cost. The time required to drive wires and for signals to propagate over wires is often the largest factor in determining cycle time. The bulk of the power in many systems is dissipated driving wires, on-chip and off. The amount of wiring, not the number of transistors or gates, usually determines the amount of area required by a function on a chip. The number of terminals required is a major factor in the area and cost of chips, packages, and circuit boards. Economically achievable wire density is a major influence on the architecture of a system. One can envision many organizations that simply cannot be wired economically.

Despite the importance of wires in a digital system, they are usually all but ignored in most courses on digital electronics. Too often such courses, and real designers, treat wires as ideal equipotential regions that present no load to the driver and change value instantaneously at all points along their length. Real wires are not ideal but rather have parasitic capacitance, resistance, and inductance. If not handled properly, these parasitic circuit elements will add delay, degrade signal quality, and even cause oscillations. With proper engineering techniques, however, they are easily tamed.