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More than 200 companies have produced HDDs historically, though after extensive industry consolidation most current units are manufactured by Seagate, Toshiba, and Western Digital.
HDD unit shipments and sales revenues are declining, though production (exabytes per year) is growing.
is a data storage device that uses magnetic storage to store and retrieve digital information using one or more rigid rapidly rotating disks (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.
The two most common form factors for modern HDDs are 3.5-inch, for desktop computers, and 2.5-inch, primarily for laptops.
The first IBM drive, the 350 RAMAC in 1956, was approximately the size of two medium-sized refrigerators and stored five million six-bit characters (3.75 megabytes), the 1301 used an array of heads, one per platter, moving as a single unit.
Cylinder-mode read/write operations were supported, and the heads flew about 250 micro-inches (about 6 µm) above the platter surface.
The latter were primarily intended for the then-fledgling personal computer (PC) market.
As the 1980s began, HDDs were a rare and very expensive additional feature in PCs, but by the late 1980s their cost had been reduced to the point where they were standard on all but the cheapest computers.