Storage Devices
A hard disk drive (HDD), hard disk, hard drive or fixed disk is a data storage device used for storing and retrieving digital information using one or more rigid ("hard") rapidly rotating disks (platters) coated with magnetic material. The platters are paired with magnetic heads arranged on a moving actuator arm, which read and write data to the platter surfaces. Data is accessed in a random-access manner, meaning that individual blocks of data can be stored or retrieved in any order rather than sequentially. HDDs retain stored data even when powered off.
As of 2015, the primary competing technology for secondary storage is flash memory in the form of solid-state drives (SSDs), which have higher data transfer rates, better reliability and significantly lower latency and access times, but HDDs remain the dominant medium for secondary storage due to advantages in price per bit and per-device recording capacity. However, SSDs are replacing HDDs where speed, power consumption and durability are more important considerations.