Hard Disk

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. An HDD retains its data even when powered off.