HDDs dominate the volume of storage produced ( exabytes per year) for servers. More than 224 companies have produced HDDs historically, though after extensive industry consolidation most units are manufactured by Seagate, Toshiba, and Western Digital. HDDs maintained this position into the modern era of servers and personal computers, though personal computing devices produced in large volume, like cell phones and tablets, rely on flash memory storage devices. Introduced by IBM in 1956, HDDs were the dominant secondary storage device for general-purpose computers beginning in the early 1960s.
Modern HDDs are typically in the form of a small rectangular box. HDDs are a type of non-volatile storage, retaining stored data even when powered off. Data is accessed in a random-access manner, meaning that individual blocks of data can be stored and retrieved in any order. The platters are paired with magnetic heads, usually arranged on a moving actuator arm, which read and write data to the platter surfaces. 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 and one or more rigid rapidly rotating platters coated with magnetic material.
