A hard disk drive (HDD) is a type of storage device used in computers to store and retrieve digital information. It consists of one or more spinning disks coated with magnetic material, which allows data to be written and read using a moving arm. HDDs are commonly used for storing operating systems, applications, and files due to their large capacity and relatively low cost. HDDs are different from solid-state drives (SSDs), which use flash memory and have no moving parts. While HDDs typically offer more storage space for the price, they are generally slower and more susceptible to physical damage. Both types of drives are essential for modern computing, with each serving specific needs.