Can a hard drive be smaller than a bacterium?

By far! While bacteria may be on the order of 700 microns, the smallest data-storage device in the world is measured in an even smaller unit: the nanometer, which is one-billionth of a meter. The tiniest memory-storage structure is 16 nanometers long and 4 nanometers high— it is 12 iron atoms arranged together. Electric current enables the components to switch back and forth between two states— each atom is 1 bit, the smallest storage unit in computer science. Using this principle, researchers managed to squeeze 8 bits, or 1 byte, into 96 atoms. Thus about 7.5 terabytes could fi t on a square centimeter— room for more than 2 million MP3S.