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A hard disk drive (HDD), hard disk, hard drive, or fixed disk [a] 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 capacity of hard drives has grown exponentially over time. When hard drives became available for personal computers, they offered 5-megabyte capacity. During the mid-1990s the typical hard disk drive for a PC had a capacity in the range of 500 megabyte to 1 gigabyte. [6] As of February 2025 hard disk drives up to 36 TB were available. [7]
Disk storage (also sometimes called drive storage) is a data storage mechanism based on a rotating disk. The recording employs various electronic, magnetic, optical, or mechanical changes to the disk's surface layer. A disk drive is a device implementing such a storage mechanism.
Longitudinal recording and perpendicular recording, two types of writing heads on a hard disk. 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.
2.5-inch hard disk drives often consume less power than larger ones. [12] [13] Low capacity solid-state drives have no moving parts and consume less power than hard disks. [14] [15] [16] Also, memory may use more power than hard disks. [16] Large caches, which are used to avoid hitting the memory wall, may also consume a large amount of power.
In the 1950s, introduction of magnetic tapes and hard disk drives allowed for mass external storage of information, which played the key part of the computer revolution. [6] Initially all external storage, tape and hard disk drives are today available as both internal and external storage.
The term was coined by IBM to describe devices that allowed random access to data, the main examples being drum memory and hard disk drives. [1] Later, optical disc drives and flash memory units are also classified as DASD. [2] [3]
A hard disk drive platter or hard disk is the circular magnetic disk on which digital data is stored in a hard disk drive. [1] The rigid nature of the platters is what gives them their name (as opposed to the flexible materials which are used to make floppy disks). Hard drives typically have several platters which are mounted on the same spindle.