How do hard drives store data?

Hard drives store data in binary form, as ones and zeros, on a platter coated with a magnetic layer. An electromagnet, called a head, scans over the spinning disc. To write data, the head changes the magnetization of specific sections on the platter. To read data, the head measures the changes in the magnetic poles. A change in polarity creates a voltage spike, which represents a “one,” while no spike represents a “zero.”