Global InformationHard disk drive information
| Computer memory and Computer data storage types |
|---|
| Volatile |
| Non-volatile |
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 platters are paired with magnetic heads, usually arranged on a moving actuator arm, which read and write data to the platter surfaces.[1] 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.[2][3][4] Modern HDDs are typically in the form of a small rectangular box.
Hard disk drives were introduced by IBM in 1956,[5] and 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 mobile phones and tablets, rely on flash memory storage devices. 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 (exabytes per year) for servers. Though production is growing slowly (by exabytes shipped[6]), sales revenues and unit shipments are declining, because solid-state drives (SSDs) have higher data-transfer rates, higher areal storage density, somewhat better reliability,[7][8] and much lower latency and access times.[9][10][11][12]
The revenues for SSDs, most of which use NAND flash memory, slightly exceeded those for HDDs in 2018.[13] Flash storage products had more than twice the revenue of hard disk drives as of 2017[update].[14] Though SSDs have four to nine times higher cost per bit,[15][16] they are replacing HDDs in applications where speed, power consumption, small size, high capacity and durability are important.[11][12] As of 2019[update], the cost per bit of SSDs is falling, and the price premium over HDDs has narrowed.[16]
The primary characteristics of an HDD are its capacity and performance. Capacity is specified in unit prefixes corresponding to powers of 1000: a 1-terabyte (TB) drive has a capacity of 1,000 gigabytes, where 1 gigabyte = 1 000 megabytes = 1 000 000 kilobytes (1 million) = 1 000 000 000 bytes (1 billion). Typically, some of an HDD's capacity is unavailable to the user because it is used by the file system and the computer operating system, and possibly inbuilt redundancy for error correction and recovery. There can be confusion regarding storage capacity, since capacities are stated in decimal gigabytes (powers of 1000) by HDD manufacturers, whereas the most commonly used operating systems report capacities in powers of 1024, which results in a smaller number than advertised. Performance is specified as the time required to move the heads to a track or cylinder (average access time), the time it takes for the desired sector to move under the head (average latency, which is a function of the physical rotational speed in revolutions per minute), and finally, the speed at which the data is transmitted (data rate).
The two most common form factors for modern HDDs are 3.5-inch, for desktop computers, and 2.5-inch, primarily for laptops. HDDs are connected to systems by standard interface cables such as SATA (Serial ATA), USB, SAS (Serial Attached SCSI), or PATA (Parallel ATA) cables.
Cite error: There are <ref group=lower-alpha> tags or {{efn}} templates on this page, but the references will not show without a {{reflist|group=lower-alpha}} template or {{notelist}} template (see the help page).
- ^ Arpaci-Dusseau, Remzi H.; Arpaci-Dusseau, Andrea C. (2014). "Operating Systems: Three Easy Pieces, Chapter: Hard Disk Drives" (PDF). Arpaci-Dusseau Books. Archived (PDF) from the original on February 16, 2015. Retrieved March 7, 2014.
- ^ Patterson, David; Hennessy, John (1971). Computer Organization and Design: The Hardware/Software Interface. Elsevier. p. 23. ISBN 9780080502571.
- ^ Domingo, Joel. "SSD vs. HDD: What's the Difference?". PC Magazine UK. Archived from the original on March 28, 2018. Retrieved March 21, 2018.
- ^ Mustafa, Naveed Ul; Armejach, Adria; Ozturk, Ozcan; Cristal, Adrian; Unsal, Osman S. (2016). "Implications of non-volatile memory as primary storage for database management systems". 2016 International Conference on Embedded Computer Systems: Architectures, Modeling and Simulation (SAMOS). IEEE. pp. 164–171. doi:10.1109/SAMOS.2016.7818344. hdl:11693/37609. ISBN 978-1-5090-3076-7. S2CID 17794134.
- ^ Cite error: The named reference
IBM350was invoked but never defined (see the help page). - ^ Shilov, Anton (November 18, 2019). "Demand for HDD Storage Booming: 240 EB Shipped in Q3 2019". AnandTech. Archived from the original on August 27, 2023.
- ^ Cite error: The named reference
BBRel2021was invoked but never defined (see the help page). - ^ "Validating the Reliability of Intel Solid-State Drives" (PDF). Intel. July 2011. Archived (PDF) from the original on October 19, 2016. Retrieved February 10, 2012.
- ^ Fullerton, Eric (March 2014). "5th Non-Volatile Memories Workshop (NVMW 2014)" (PDF). IEEE. Archived from the original (PDF) on September 28, 2018. Retrieved February 21, 2023.
- ^ Handy, James (July 31, 2012). "For the Lack of a Fab..." Objective Analysis. Archived from the original on January 1, 2013. Retrieved November 25, 2012.
- ^ a b Hutchinson, Lee. (June 25, 2012) How SSDs conquered mobile devices and modern OSes Archived July 7, 2017, at the Wayback Machine. Ars Technica. Retrieved January 7, 2013.
- ^ a b Santo Domingo, Joel (May 10, 2012). "SSD vs HDD: What's the Difference?". PC Magazine. Archived from the original on March 19, 2017. Retrieved November 24, 2012.
- ^ Hough, Jack (May 14, 2018). "Why Western Digital Can Gain 45% Despite Declining HDD Business". Barron's. Archived from the original on May 15, 2018. Retrieved May 15, 2018.
- ^ Mellor, Chris (July 31, 2017). "NAND that's that... Flash chip industry worth twice disk drive biz". The Register. Retrieved November 21, 2019.
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jcmit 2019was invoked but never defined (see the help page). - ^ a b Mellor, Chris (August 28, 2019). "How long before SSDs replace nearline disk drives?". Retrieved November 15, 2019.