A hard disk drive (HDD) is a type of data storage device that uses spinning disks coated with magnetic material to read and write information. It stores digital data by changing the magnetization of the disk surface, allowing for the retrieval of files, programs, and operating systems. HDDs are commonly used in computers, servers, and external storage devices. HDDs are known for their large storage capacities 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 archiving and bulk data storage.