At the time, computers were typically built up from a series of "modules", each module containing the electronics needed to perform a single function. A complex circuit like an adder would generally require several modules working in concert. The modules were typically built on printed circuit boards of a standardized size, with a connector on one edge that allowed them to be plugged into the power and signaling lines of the machine, and were then wired to other modules using twisted pair or coaxial cable.