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 personal files. HDDs are known for their large storage capacity and cost-effectiveness compared to other storage options like solid-state drives (SSDs). However, they are generally slower and more prone to mechanical failure due to their moving parts. Despite this, they remain popular for bulk data storage.