Wire wrap is a technique for constructing small numbers of complex electronics assemblies. It is an alternative technique to the use of small runs of printe circuit boards, and has the advantage of being easily changed for prototyping work. It has been used to construct telephone exchanges, computers, control consoles, radios, radars, sonars, and other complex pieces of equipment that are needed in small volumes; the Apollo Guidance Computer, among many other historically relevant computers, was constructed using wire wrap technology.