Printed circuit board (PCB). The numerous light lines are where a metal conductor has been printed on an insulating material base. These metal lines form a complex circuit for connecting electronic components that will be attached to the board. The electronic components have not yet been added, but will attach at the numerous small holes all over the PCB. The larger holes (such as in the bottom right and top right corners) are used to fix the whole PCB inside an electronic device. PCBs are used in many products, ranging from computers to cars.