page_title: Hard disk drive
section_title: Form factors
hierarchical_section_title: Hard disk drive / Form factors
caption_attribution_description: Deutsch: sechs Festplattenlaufwerke in den Baugrößen 8, 5,25 (Gehäusebreite rund 146&#160;mm oder genau 5,75″[1]), 3,5 (101,6&#160;mm oder genau 4″[1]), 2,5 (70&#160;mm[1]), 1,8 (54&#160;mm[1]) und 1&#160;Zoll English: Six hard disk drives with cases opened showing platters and heads; 8, 5.25, 3.5, 2.5, 1.8 and 1 inch disk diameters are represented.
context_page_description: A hard disk drive, hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that uses magnetic storage to store and retrieve digital data using 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 even when powered off.
  Introduced by IBM in 1956, HDDs were the dominant secondary storage device for general-purpose computers beginning in the early 1960s. 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 products. More than 224 companies have produced HDDs historically, though after extensive industry consolidation most units are manufactured by Seagate, Toshiba, and Western Digital. HDDs dominate the volume of storage produced for servers.
context_section_description: IBM's first hard disk drive, the IBM 350, used a stack of fifty 24-inch platters, stored 3.75 MB of data (approximately the size of one modern digital picture), and was of a size comparable to two large refrigerators. In 1962, IBM introduced its model 1311 disk, which used six 14-inch (nominal size) platters in a removable pack and was roughly the size of a washing machine. This became a standard platter size for many years, used also by other manufacturers. The IBM 2314 used platters of the same size in an eleven-high pack and introduced the "drive in a drawer" layout. sometimes called the"pizza oven", although the "drawer" was not the complete drive.  Into the 1970s HDDs were offered in standalone cabinets of varying dimensions containing from one to four HDDs.
  Beginning in the late 1960s drives were offered that fit entirely into a chassis that would mount in a 19-inch rack. Digital's RK05 and RL01 were early examples using single 14-inch platters in removable packs, the entire drive fitting in a 10.5-inch-high rack space (six rack units). In the mid-to-late 1980s the similarly sized Fujitsu Eagle, which used (coincidentally) 10.5-inch platters, was a popular product.
  With increasing sales of microcomputers having built in floppy-disk drives (FDDs), HDDs that would fit to the FDD mountings became desirable. Starting with the Shugart Associates SA1000 HDD Form factors, initially followed those of 8-inch, 5½-inch, and 3½-inch floppy disk drives. Although referred to by these nominal sizes, the actual sizes for those three drives respectively are 9.5″, 5.75″ and 4″ wide.  Because there were no smaller floppy disk drives, smaller HDD form factors developed from product offerings or industry standards.  2½-inch drives are actually 2.75″ wide.
  As of 2019, 2½-inch and 3½-inch hard disks are the most popular sizes.  By 2009, all manufacturers had discontinued the development of new products for the 1.3-inch, 1-inch and 0.85-inch form factors due to falling prices of flash memory, which has no moving parts. While nominal sizes are in inches, actual dimensions are specified in millimeters.
caption: 8-, 5.25-, 3.5-, 2.5-, 1.8- and 1-inch HDDs, together with a ruler to show the size of platters and read-write heads
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