A hard disk is a data storage device used for storing and retrieving digital information using rapidly rotating disks (platters) coated with magnetic material. The platters are housed inside a sealed unit, with read/write heads on an arm that move across the platters to read and write data. Hard disks are typically larger in storage capacity than other forms of storage like flash drives and memory cards, and are commonly used in computers to store the operating system, applications, and user data