Through engineers’ never-ending quest for miniaturization, computers and other electronics keep getting smaller. But for many components, the rules change when their size approaches the nanoscale–where parts are just billionths of a meter across. Laws that rule in a gallon or a gram of material no longer apply. That’s the dilemma for the makers of materials such as the iron oxide–coated disks in computer hard drives. These magnetic devices now store 30 million times as many bits of information per square inch as they did when introduced in 1956.