A hard disk drive (HDD), hard disk, hard drive, or fixed disk, is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magnetic material. The platters are paired with magnetic heads, usually 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 and retrieved in any order. HDDs are a type of non-volatile storage, retaining stored data when powered off. Modern HDDs are typically in the form of a small rectangular box.
A partially disassembled IBM 350 hard disk drive (RAMAC)
2.5-inch hard disk drive with cover removed
The end of a 3.5 inch hard disk drive with a Serial ATA (SATA) interface
Destroyed hard disk, glass platter visible
Magnetic storage or magnetic recording is the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetisation in a magnetizable material to store data and is a form of non-volatile memory. The information is accessed using one or more read/write heads.
The programmable calculators of the HP-41-series (from 1979) could store data via an external magnetic tape storage device on microcassettes.
Hard drives use magnetic memory to store giga- and terabytes of data in computers.