What do the circular platters in a hard disk use to store data?

The circular platters in a hard disk use magnetic particles to store data. Each platter is coated with a magnetic material that allows data to be encoded as magnetized regions on the surface. When the read/write head of the hard disk moves across the surface of these platters, it can detect the magnetic fields of these regions. This process enables the hard disk to read the stored data or write new data by altering the magnetic state of the particles.

This method of data storage is integral to the functionality of traditional hard disk drives (HDDs) and distinguishes them from other storage technologies, such as solid-state drives (SSDs), which utilize flash memory and do not depend on magnetic storage. This fundamental characteristic of magnetic data storage allows hard disks to maintain their historical prominence in data storage, especially for large amounts of information.