The most of the components in a computer are mounted on printed circuit boards. The motherboards are largest printed circuit. Memory chips and Expansion cards plug into the motherboard. The memory chips are in grouped together on a small circuit boards to create the dual in-line memory modules, (DIMMs). The printed circuits eliminate the need for individual wires that are connect components and also greatly reduce the time and cost of building a system by doing away with hand-soldering of most connections. Instead of the wire, metallic traces-usually aluminium or copper are printed onto sheets of a hard plastic.
The design of a printed circuit board might require traces to cross over the other traces without actually touching each other, which would be cause a misrouting of electrical signals. In this case, one of the traces goes through the board to the opposite side surface, where it can continue on its path without intersecting the other trace.
