(right) has circuits that can be partially or completely changed while it is operating. Scanning electron micrographs to the left (magnification 3,000x) show three fixed-circuit metal layers of a flip-flop cell in a field-programmable gate array. The flip-flop cell contains four memory cells with switches (bottom left, colored areas) that can be opened or closed electronically to produce a conductive path.

Image right: Xilinx. Images left: Integrated Circuit Engineering