Hundreds of types of electrical connectors are manufactured for power, signal and control applications. Connectors may join two lengths of flexible copper wire or cable, or connect a wire or cable to an electrical terminal. In computing, an electrical connector can also be known as a physical interface (compare physical layer in OSI model of networking). It is usually desirable for a connector to be easy to identify visually, rapid to assemble, require only simple tooling, and be inexpensive. In some cases an equipment manufacturer might choose a connector specifically because it is not compatible with those from other sources, allowing control of what may be connected.