Hard disk drive 13777 225948305 2008-07-16T04:06:33Z 74.12.100.219 {{ infobox computer hardware generic | name = Hard Disk Drive | image = Hard disk platters and head.jpg | caption = A hard disk drive with the metal cover removed. | invent-date = [[September 13]] [[1956]] | invent-name = An [[IBM]] team led by [[Reynold B. Johnson|Rey Johnson]] | conn1 = [[Host adapter]] (on [[personal computer|PCs]] often integrated into [[motherboard]]) | via1_1 = [[AT Attachment|PATA]] ([[AT Attachment|IDE]]) interface | via1_2 = [[SATA]] interface | via1_3 = [[Serial Attached SCSI|SAS]] interface | via1_4 = [[SCSI]] interface (popular on [[Server (computing)|servers]]) | via1_5 = [[Fibre Channel|FC]] interface (almost exclusively found on servers) | class-name = [[Market segment|Market Segments]] | class1 = [[Desktop computer|Desktop]] | class2 = [[Mobile computing|Mobile]] | class3 = Enterprise | class4 = Consumer | class5 = Other/Miscellaneous }} A '''hard disk drive''' ('''HDD'''), commonly referred to as a '''hard drive''', '''hard disk''', or '''fixed disk drive''',<ref>Other terms used to describe hard disk drives include ''disk drive'', ''disk file'', ''DASD (Direct Access Storage Device''), ''fixed disk'', ''CKD disk'' and ''Winchester Disk Drive'' (after the [[Early IBM disk storage|IBM 3340]]).</ref> is a [[non-volatile storage]] device which stores digitally encoded data on rapidly rotating [[hard disk platters|platters]] with [[magnetic]] surfaces. Strictly speaking, "drive" refers to a device distinct from its medium, such as a tape drive and its tape, or a floppy disk drive and its floppy disk. Early HDDs had removable media; however, an HDD today is typically a sealed unit (except for a filtered vent hole to equalize air pressure) with fixed media.<ref>[http://computer.howstuffworks.com/hard-disk1.htm How Hard Disks Work], howstuffworks.com</ref> An HDD is a rigid-disk drive although it is probably never referred to as such. By way of comparison, a so-called "floppy" drive (more formally, a diskette drive) has a disc that is flexible. Originally, the term "hard" was temporary slang, substituting "hard" for "rigid", before these drives had an established and universally-agreed-upon name. Some time ago, IBM's internal company term for a HDD was "file". {{Fact|date=June 2008}} HDDs (introduced in 1956 as data storage for an IBM [[accounting]] computer<ref>[http://www-03.ibm.com/ibm/history/exhibits/storage/storage_350.html] IBM 350 disk storage unit</ref>) were originally developed for use with general purpose [[computer]]s; see [[History of hard disk drives]]. In the 21st century, applications for HDDs have expanded to include [[digital video recorder]]s, [[digital audio player]]s, [[personal digital assistant]]s, [[digital camera]]s and [[video game console]]s. In 2005 the first [[mobile phone]]s to include HDDs were introduced by [[Samsung Electronics|Samsung]] and [[Nokia]].<ref>[http://www.engadget.com/2004/09/06/finally-the-samsung-sph-v5400-worlds-first-cellphone-with-a/ Finally! The Samsung SPH-V5400, world's first cellphone with a hard drive], engadget.com, 6 September 2004</ref> The need for large-scale, reliable storage, independent of a particular device, led to the introduction of configurations such as [[RAID]] arrays, [[network attached storage]] (NAS) systems and [[storage area network]] (SAN) systems that provide efficient and reliable access to large volumes of data. Note that although not immediately recognizable as a computer, all the aforementioned applications are actually [[Embedded system|embedded computing devices]] of some sort. == Technology == [[Image:Hard drive-en.svg|thumb|300px]] HDDs record data by magnetizing [[ferromagnetism|ferromagnetic]] material directionally, to represent either a 0 or a 1 [[binary digit]]. They read the data back by detecting the magnetization of the material. A typical HDD design consists of a spindle which holds one or more flat circular disks called [[Hard disk platter|platters]], onto which the data are recorded. The platters are made from a non-magnetic material, usually aluminum alloy or glass, and are coated with a thin layer of magnetic material. Older disks used [[iron(III) oxide]] as the magnetic material, but current disks use a [[cobalt]]-based alloy. {{Fact|date=June 2008}} [[Image:magneticMedia.png|thumb|left|250px|A cross section of the magnetic surface in action. In this case the binary data is encoded using [[frequency modulation]].]] The platters are spun at very high speeds (details follow). Information is written to a platter as it rotates past devices called [[Disk read-and-write head|read-and-write head]]s that operate very close (tens of nanometers in new drives) over the magnetic surface. The read-and-write head is used to detect and modify the magnetization of the material immediately under it. There is one head for each magnetic platter surface on the spindle, mounted on a common arm. An actuator arm (or access arm) moves the heads on an arc (roughly radially) across the platters as they spin, allowing each head to access almost the entire surface of the platter as it spins. The arm is moved using a [[voice coil]] actuator or (in older designs) a [[stepper motor]]. Stepper motors were outside the head-disk chamber, and preceded voice-coil drives. The latter, for a while, had a structure similar to that of a loudspeaker; the coil and heads moved in a straight line, along a radius of the platters. The present-day structure differs in several respects from that of the earlier voice-coil drives, but the same interaction between the coil and magnetic field still applies, and the term is still used. Older drives read the data on the platter by sensing the rate of change of the magnetism in the head; these heads had small coils, and worked (in principle) much like magnetic-tape playback heads, although not in contact with the recording surface. As data density increased, read heads using [[magnetoresistance]] (MR) came into use; the electrical resistance of the head changed according to the strength of the magnetism from the platter. Later development made use of [[spintronics]]; in these heads, the magnetoresistive effect was much greater that in earlier types, and was dubbed [[Giant magnetoresistance|"giant" magnetoresistance]] (GMR). This refers to the degree of effect, not the physical size, of the head — the heads themselves are extremely tiny, and are too small to be seen without a microscope. GMR read heads are now commonplace.{{Fact|date=March 2008}}<!--This needs a standard <ref> citation, otherwise it is impossible to find the reference that was referred to here--> HD heads are kept from contacting the platter surface by the air that is extremely close to the platter; that air moves at, or close to, the platter speed.{{Fact|date=March 2008}}<!--This boundary layer air should be at a LOWER pressure than the air above the head - what's the idea here?--> The record and playback head are mounted on a block called a slider, and the surface next to the platter is shaped to keep it just barely out of contact. It's a type of air bearing. The magnetic surface of each platter is conceptually divided into many small sub-[[micrometre]]-sized magnetic regions, each of which is used to encode a single binary unit of information. In today's HDDs, each of these magnetic regions is composed of a few hundred magnetic grains. Each magnetic region forms a [[magnetic dipole]] which generates a highly localized [[magnetic field]] nearby. The write head magnetizes a region by generating a strong local magnetic field. Early HDDs used an [[electromagnet]] both to generate this field and to read the data by using [[electromagnetic induction]]. Later versions of inductive heads included metal in Gap (MIG) heads and [[thin film]] heads. In today's heads, the read and write elements are separate, but in close proximity, on the head portion of an actuator arm. The read element is typically [[giant magnetoresistance|magneto-resistive]] while the write element is typically thin-film inductive.<ref>[http://www.hitachigst.com/hdd/technolo/gmr/gmr.htm IBM OEM MR Head | Technology | The era of giant magnetoresistive heads<!-- Bot generated title -->]</ref> In modern drives, the small size of the magnetic regions creates the danger that their magnetic state might be lost because of thermal effects. To counter this, the platters are coated with two parallel magnetic layers, separated by a 3-atom-thick layer of the non-magnetic element [[ruthenium]], and the two layers are magnetized in opposite orientation, thus reinforcing each other.<ref>Brian Hayes, [http://www.americanscientist.org/template/AssetDetail/assetid/14750 Terabyte Territory], ''[[American Scientist]]'', Vol 90 No 3 (May-June 2002) p. 212</ref> Another technology used to overcome thermal effects to allow greater recording densities is [[perpendicular recording]], first shipped in 2005<ref>[http://www.toshiba.co.jp/about/press/2004_12/pr1401.htm Toshiba : Press Releases 14 December, 2004<!-- Bot generated title -->]</ref>, as of 2007 the technology was used in many HDDs<ref>[http://www.seagate.com/www/en-us/products/laptops/momentus/ Seagate Momentus 2½" HDDs per webpage Jan 2008]</ref><ref>[http://www.seagate.com/www/en-us/products/desktops/barracuda_hard_drives/ Seagate Baracuda 3½" HDDs per webpage Jan 2008]</ref><ref>[http://www.wdc.com/en/company/investor/q108remarks.asp Western Digital Scorpio 2½" and Greenpower 3½" HDDs per quarterly conference, July 2007]</ref>. See [[File System]] for how operating systems access data on HDDs and other storage devices. ===Architecture=== [[Image:Hard disk dismantled.jpg|thumb|left|250px|A hard disk drive with the platters and spindle motor hub removed showing the copper colored motor coils surrounding a bearing at the center of the spindle motor.]] The motor has an external rotor; the stator windings are copper-colored. The spindle bearing is in the center. To the left of center is the actuator with a read-write head under the tip of its very end (near center); the orange stripe along the side of the arm, a thin printed-circuit cable, connects the read-write head to the hub of the actuator. The flexible, somewhat 'U'-shaped, ribbon cable barely visible below and to the left of the actuator arm is the flexible section, one end on the hub, that continues the connection from the head to the controller board on the opposite side. The head support arm is very light, but also rigid; in modern drives, acceleration at the head reaches 250 [[g-force|''g''s]]. The silver-colored structure at the upper left is the top plate of the permanent-magnet and moving coil "motor" that swings the heads to the desired position. Beneath this plate is the moving coil, attached to the actuator hub, and beneath that is a thin neodymium-iron-boron (NIB) high-flux magnet. That magnet is mounted on the bottom plate of the "motor". The coil, itself, is shaped rather like an arrowhead, and made of doubly-coated copper magnet wire. The inner layer is insulation, and the outer is thermoplastic, which bonds the coil together after it's wound on a form, making it self-supporting. Much of the coil, sides of the arrowhead, which points to the actuator bearing center, interacts with the magnetic field to develop a tangential force to rotate the actuator. Considering that current flows (at a given time) radially outward along one side of the arrowhead, and radially inward on the other, the surface of the magnet is half N pole, half S pole; the dividing line is midway, and radial. == Capacity and access speed == [[Image:Hard drive capacity over time.png|right|thumb|[[personal computer|PC]] hard disk drive capacity (in [[gigabytes|GB]]). The vertical axis is [[logarithmic scale|logarithmic]], so the fit line corresponds to [[exponential growth]].]] Using rigid disks and sealing the unit allows much tighter tolerances than in a [[floppy disk|floppy disk drive]]. Consequently, hard disk drives can store much more data than floppy disk drives and can access and transmit it faster. As of January 2008: *A typical [[desktop]] HDD, might store between 120 and 500 [[Gigabyte|GB]] of data (based on US market data<ref>PC Magazine comparison of 136 desktops shows 60 in this HDD capacity range with 50 larger and 26 smaller capacities [http://www.pcmag.com/products/0,,qn=Desktops+General+Purpose,00.asp]</ref>), rotate at 7,200 [[revolutions per minute]] (RPM) and have a media transfer rate of 1 Gbit/s or higher. (1 GB = 10<sup>9</sup> B; 1 Gbit/s = 10<sup>9</sup> bit/s) *The highest capacity HDDs are 1.5 [[Terabytes| TB]]<ref name="1500gb">[http://crave.cnet.com/8301-1_105-9987407-1.html Seagate ups ante to 1.5TB with new Barracuda hard drive]</ref>. *The fastest “enterprise” HDDs spin at 10,000 or 15,000 rpm, and can achieve sequential media transfer speeds above 1.6 Gbit/s.<ref name = "erwpnw">Seagate Cheetah 15K.5[http://www.seagate.com/docs/pdf/datasheet/disc/ds_cheetah_15k_5.pdf]</ref> and a sustained transfer rate up to 125MBytes/second.<ref name = "erwpnw"/> Drives running at 10,000 or 15,000 rpm use smaller platters because of air drag and therefore generally have lower capacity than the highest capacity desktop drives. *Mobile, i.e., [[laptop]] HDDs, which are physically smaller than their desktop and enterprise counterparts, tend to be slower and have less capacity. A typical mobile HDD spins at 5,400 rpm, with 7,200 rpm models available for a slight price premium. Because of the smaller disks, mobile HDDs generally have lower capacity than the highest capacity desktop drives. The exponential increases in disk space and data access speeds of HDDs have enabled the commercial viability of consumer products that require large storage capacities, such as [[digital video recorder]]s and [[digital audio player]]s.<ref>{{ cite news | first = Chip | last = Walter | url = http://www.sciam.com/article.cfm?articleID=000B0C22-0805-12D8-BDFD83414B7F0000&ref=sciam&chanID=sa006 | title = Kryder's Law | work = Scientific American | publisher = Verlagsgruppe Georg von Holtzbrinck GmbH | date = [[25 July]] [[2005]] | accessdate = 2006-10-29 }}</ref> In addition, the availability of vast amounts of cheap storage has made viable a variety of web-based services with extraordinary capacity requirements, such as free-of-charge web search, [[web archiving]] and video sharing ([[Google]], [[Yahoo!]], [[YouTube]], etc.). The main way to decrease access time is to increase rotational speed, while the main way to increase [[throughput]] and storage capacity is to increase areal density. A vice president of [[Seagate Technology]] projects a future growth in disk density of 40% per year.<ref>[http://www.hardwarezone.com/articles/view.php?cid=1&id=1805&pg=2 Seagate Outlines the Future of Storage :: Articles :: www.hardwarezone.com®<!-- Bot generated title -->]</ref> [[Access time]]s have not kept up with throughput increases, which themselves have not kept up with growth in storage capacity. The first 3.5" HDD marketed as able to store 1 TB was the [[Hitachi Deskstar]] 7K1000. It contains five platters at approximately 200 GB each, providing 935.5 GiB of usable space.<ref name=tomshardwarehitachiterabyte>[http://www.tomshardware.com/2007/04/17/hitachi_7k1000_terabyte_hard_drive/ Hitachi's 7K1000 Terabyte Hard Drive]</ref> Hitachi has since been joined by Samsung (Samsung SpinPoint F1, which has 3 × 334 GB platters), Seagate and Western Digital in the 1 TB drive market.<ref>[http://www.dailytech.com/Article.aspx?newsid=7740 Seagate, Samsung Begin to Ship 1 TB Desktop Hard Drives]</ref><ref>[http://www.tomshardware.com/2007/10/11/wd_caviar_gp/ WD Caviar GP: The "Green" 1 TB Drive]</ref> {| class="wikitable" |- ! Form factor ! Width ! Largest capacity ! Platters (Max) |- | 5.25" [[Drive bay#Full-height|FH]] | 146 [[Millimeter|mm]] | 47 [[gigabyte|GB]]<ref>Seagate Elite 47, shipped 12/97 per 1998 Disk/Trend Report - Rigid Disk Drives</ref> (1998) | 14 |- | 5.25" [[Drive bay#Half-height|HH]] | 146 mm | 19.3 GB<ref>Quantum Bigfoot TS, shipped 10/98 per 1999 Disk/Trend Report - Rigid Disk Drives</ref> (1998) | 4<ref>The Quantum Bigfoot TS used a maximum of 3 platters, other earlier and lower capacity product used up to 4 platters in a 5.25" HH form factor, e.g. Microscience HH1090 circa 1989.</ref> |- | 3.5" | 102 mm | 1.5 [[Terabytes|TB]]<ref name="1500gb"/> (2008) | 5 |- | 2.5" | 69.9 mm | 500 GB<ref>{{cite web|title=Hitachi announces 500GB laptop drive|url=http://www.macworld.com/article/131372/2008/01/hitachi.html}} 080103 http://www.macworld.com</ref> (2008) | 3 |- | 1.8" ([[PCMCIA]]) | 54 mm | 160 GB<ref>{{cite web|title=Samsung unveils 160GB iPod-sized drive |url=http://www.macnn.com/articles/07/08/20/samsung.spinpoint.n2.160gb/}} 070808 macnn.com</ref> (2007) |- | 1.8" (ATA-7 [[Low insertion force|LIF]]<!-- Correct link? -->) | 53.8 mm | | |- | 1.3" | 36.4 mm | 40 GB<ref>[http://www.sdk.co.jp/aa/english/news/2008/aanw_08_0812.html SDK Starts Shipments of 1.3-Inch PMR-Technology-Based HD Media]</ref> (2008) | 1 |} === Capacity measurements === {{Mergefrom|Disk Overhead|Talk:Disk Overhead#Merge proposal|date=March 2008}} [[Image:HardDiskAnatomy.jpg|right|thumb|A disassembled and labeled 1997 hard drive.]] Capacity of a hard disk drive is usually quoted in [[gigabyte]]s and [[terabyte]]s. Older HDDs quoted their smaller capacities in [[megabytes]], the first drives for PCs being just 5 or 10 MB. The capacity of an HDD can be calculated by multiplying the number of [[cylinder (computer)|cylinders]] by the number of heads by the number of [[Cylinder-head-sector|sector]]s by the number of bytes/sector (most commonly 512). Drives with the [[AT Attachment|ATA]] interface and a capacity of eight gigabytes or more behave as if they were structured into 16383 cylinders, 16 heads, and 63 sectors, for compatibility with older operating systems. Unlike in the 1980s, the cylinder, head, sector (C/H/S) counts reported to the CPU by a modern ATA drive are no longer actual physical parameters since the reported numbers are constrained by historic operating-system interfaces and with [[zone bit recording]] the actual number of sectors varies by zone. Disks with [[SCSI]] interface address each sector with a unique integer number; the operating system remains ignorant of their head or cylinder count. The old C/H/S scheme has been replaced by [[logical block addressing]]. In some cases, to try to "force-fit" the C/H/S scheme to large-capacity drives, the number of heads was given as 64, although no drive has anywhere near 32 platters. Hard disk drive manufacturers specify disk capacity using the [[SI prefix]]es ''[[mega-]]'', ''[[giga-]]'' and ''[[tera-]]'', and their abbreviations '''M''', '''G''' and '''T'''. Byte is typically abbreviated '''B'''. Most operating-system tools report capacity using the same abbreviations but actually use [[binary prefix]]es. For instance, the prefix [[mega-]], which normally means 10<sup>6</sup> (1,000,000), in the context of data storage can mean 2<sup>20</sup> (1,048,576), which is nearly 5% more. Similar usage has been applied to prefixes of greater magnitude. This results in a discrepancy between the disk manufacturer's stated capacity and the apparent capacity of the drive when examined through most operating-system tools. The difference becomes even more noticeable (7%) for a gigabyte. For example, [[Microsoft Windows]] reports disk capacity both in decimal-based units to 12 or more significant digits and with binary-based units to three significant digits. Thus a disk specified by a disk manufacturer as a '''30 GB''' disk might have its capacity reported by Windows 2000 both as "'''30,065,098,568 bytes'''" and "'''28.0 GB'''". The disk manufacturer used the [[SI]] definition of "giga", 10<sup>9</sup> to arrive at '''30 GB'''; however, because [[Microsoft Windows]], [[Mac OS]] and some [[Linux distributions]] use "gigabyte" for 1,073,741,824 bytes (2<sup>30</sup> bytes), the operating system reports capacity of the disk drive as (only) '''28.0 GB'''. ==Form factors== [[Image:5.25 inch MFM hard disk drive.JPG|thumb|5¼" full height 110 MB HDD,<br>2½" 8.5 mm 6495 MB HDD,<br>US/UK pennies for comparison.]] [[Image:SixHardDriveFormFactors.jpg|thumb|Six hard drives with 8", 5.25", 3.5", 2.5", 1.8", and 1" disks, partially disassembled to show platters and read-write heads, with a ruler showing inches.]] The earliest “form factor” hard disk drives inherited their dimensions from [[Floppy disk| floppy-disk drives (FDDs)]], so that either could be mounted in chassis slots, and thus the HDD form factors became colloquially named after the corresponding FDD types. "Form factor" compatibility continued after the 3½ in size even though floppy disk drives with new smaller dimensions ceased to be offered. * '''8 inch:''' (9.5 in x 4.624 in x 14.25 in = 241.3 mm x 117.5 mm x 362 mm)<br/>In 1979, [[Shugart Associates]]' SA1000 was the first form factor compatible HDD, having the same dimensions and a compatible interface to the 8" FDD. Both "full height" and "half height" (2.313 in) versions were available. * '''5.25 inch:''' (5.75 in x 1.63 in x 8 in = 146.1 mm x 41.4 mm x 203 mm)<br/>This smaller form factor, first used in an HDD by Seagate in 1980, was the same size as full height 5¼-inch diameter FDD, i.e., 3.25 inches high. This is twice as high as commonly used today; i.e., 1.63 in = 41.4 mm (“half height”). Most desktop models of drives for optical 120 mm disks ([[DVD]], [[CD]]) use the half height 5¼" dimension, but it fell out of fashion for HDDs. The [[Quantum Bigfoot]] HDD was the last to use it in the late 1990s, with “low-profile” (~25 mm) and “ultra-low-profile” (~20 mm) high versions. * '''3.5 inch''' (4 in x 1 in x 5.75 in = 101.6 mm x 25.4 mm x 146 mm)<br/> This smaller form factor, first used in an HDD by [[Rodime]] in 1984, was the same size as the "half height" 3½ FDD, i.e., 1.63 inches high. Today has been largely superseded by 1-inch high “slimline” or “low-profile” versions of this form factor which is used by most desktop HDDs. * '''2.5 inch:''' (2.75 in x 0.374 in x 3.945 in = 69.85 mm x 9.5&ndash;15mm mm x 100 mm)<br/>This smaller form factor was introduced by PrairieTek in 1988; there is no corresponding FDD. It is widely used today for hard-disk drives in mobile devices (laptops, music players, etc.) and [[as of 2008]] replacing 3.5 inch enterprise-class drives. Today, the dominant height of this form factor is 9.5 mm for laptop drives, but high capacity drives have a height of 12.5 mm. Enterprise-class drives can have a height up to 15 mm.<ref>[http://www.tomshardware.com/reviews/HDD-SATA-VelociRaptor,1914-6.html One Drive, Multiple Applications - Tom's Hardware : WD's New Raptor Drive Is a Bird of Prey!<!-- Bot generated title -->]</ref> * '''1.8 inch:''' (54 mm × 8 mm × 71 mm)<br/>This form factor, originally introduced by Integral Peripherals in 1993, has evolved into the ATA-7 LIF with dimensions as stated. It is increasingly used in [[digital audio player]]s and [[subnotebook]]s. An original variant exists for 2–5 GB sized HDDs that fit directly into a [[PC card]] expansion slot. These became popular for their use in iPods and other HDD based MP3 players. * '''1 inch:''' (42.8 mm × 5 mm × 36.4 mm)<br/>This form factor was introduced in 1999 as [[IBM]]'s [[Microdrive]] to fit inside a [[Compact Flash|CF]] Type II slot. Samsung calls the same form factor '''"1.3 inch" drive''' in its product literature.<ref>[http://www.samsung.com/global/system/business/hdd/prdmodel/2008/1/25/2469101.3_Inch_Spec_PATA_rev.2.3.pdf 1.3" HDD Product Specification], Samsung, 2008</ref> * '''0.85 inch:''' (24 mm × 5 mm × 32 mm)<br/>[[Toshiba]] announced this form factor in January 2004<ref>[http://www.toshiba.co.jp/about/press/2004_01/pr0801.htm Toshiba's 0.85-inch HDD is set to bring multi-gigabyte capacities to small, powerful digital products], Toshiba press release, 8 January 2004</ref> for use in mobile phones and similar applications, including [[Secure Digital card|SD]]/[[MultiMediaCard|MMC]] slot compatible HDDs optimized for video storage on [[4G]] handsets. Toshiba currently sells a 4 GB (MK4001MTD) and 8 GB (MK8003MTD) version[http://www3.toshiba.co.jp/storage/english/spec/hdd/mk4001.htm] and holds the [[Guinness World Record]] for the smallest harddisk drive.<ref>[http://www.toshiba.co.jp/about/press/2004_03/pr1601.htm Toshiba enters Guinness World Records Book with the world's smallest hard disk drive], Toshiba press release, 16 March 2004</ref> Major manufacturers discontinued the development of new products for the 1-inch (=1.3-inch) and 0.85-inch form factors in 2007, due to falling prices of [[flash memory]]<ref>[http://www.eetasia.com/ART_8800474064_499486_NT_3335be30.HTM Flash price fall shakes HDD market], EETimes Asia, 1 August 2007.</ref>, although Samsung introduced in 2008 with the SpinPoint A1 another 1.3-inch drive. The inch-based nickname of all these form factors usually do not indicate any actual product dimension (which are specified in millimeters for more recent form factors), but just roughly indicate a size relative to disk diameters, in the interest of historic continuity. == Other characteristics == ''Transfer rate'' As of 2008, the data transfer rate at the inner zone ranges from 44.2 [[MB]]/s to 74.5 MB/s, while the transfer rate at the outer zone ranges from 74.0 MB/s to 111.4 MB/s.{{Fact|date=March 2008}} In contrast, the first PC drives could manage only around 40 KiB/s. [[Random access time]] (seek time) currently ranges from just under 5 [[ms]] for high-end server drives, to 15 ms for miniature drives, with the most common desktop type typically being around 9 ms.{{Fact|date=March 2008}} There has not been any significant improvement in this speed for some years. Some early PC drives used a worm-gear to move the heads, and as a result had access times as slow as 80 - 120 ms, but this was quickly improved by voice-coil type actuation in the late 1980s, seeing access times reduce to around 20 ms. [[Power consumption]] has become increasingly important, not just in mobile devices such as laptops but also in server and desktop markets. Increasing data center machine density has led to problems delivering sufficient power to devices, and getting rid of the waste heat subsequently produced, as well as environmental and electrical cost concerns (see [[green computing]]). Similar issues exist for large companies with thousands of desktop PCs. Smaller form factor drives often use less power than larger drives. One interesting development in this area is actively controlling the seek speed so that the head arrives at its destination only just in time to read the sector, rather than arriving as quickly as possible and then having to wait for the sector to come around (i.e. the rotational latency). ''Audible noise'' (measured in [[A-weighting|dBA]]) is significant for certain applications, such as [[PVR]]s digital audio recording and [[quiet PC|quiet computers]]. Low noise disks typically use fluid bearings, slower rotational speeds (usually 5,400rpm) and reduce the seek speed under load (AAM) to reduce audible clicks and crunching sounds. Drives in smaller form factors (e.g. 2.5 inch) are often quieter than larger drives. ''Shock resistance'' is especially important for mobile devices. Some laptops now include a motion sensor that parks the disk heads if the machine is dropped, hopefully before impact, to offer the greatest possible chance of survival in such an event. == Access and interfaces == {{Unreferencedsection|date=May 2008}} Hard disk drives are accessed over one of a number of bus types, including parallel [[Advanced Technology Attachment|ATA]] (PATA, also called IDE or [[EIDE]]), [[Serial ATA]] (SATA), [[SCSI]], [[Serial Attached SCSI]] (SAS), and [[Fibre Channel]]. Bridge circuitry is sometimes used to connect hard disk drives to buses that they cannot communicate with natively, such as [[IEEE 1394]] and [[Universal Serial Bus|USB]]. Back in the days of the [[ST-506]] interface, the data [[encoder|encoding]] scheme was also important. The first ST-506 disks used [[Modified Frequency Modulation]] (MFM) encoding, and transferred data at a rate of 5 [[megabit]]s per second. Later on, controllers using ''2,7 [[Run Length Limited|RLL]]'' (or just "RLL") encoding increased the transfer rate by 50%, to 7.5 megabits per second; this also increased disk capacity by fifty percent. Many ST-506 interface disk drives were only specified by the manufacturer to run at the lower MFM data rate, while other models (usually more expensive versions of the same basic disk drive) were specified to run at the higher RLL data rate. In some cases, a disk drive had sufficient margin to allow the MFM specified model to run at the faster RLL data rate; however, this was often unreliable and was not recommended. (An RLL-certified disk drive could run on a MFM controller, but with 1/3 less data capacity and speed.) [[Enhanced Small Disk Interface]] (ESDI) also supported multiple data rates (ESDI disks always used 2,7 RLL, but at 10, 15 or 20 megabits per second), but this was usually negotiated automatically by the disk drive and controller; most of the time, however, 15 or 20 megabit ESDI disk drives weren't downward compatible (i.e. a 15 or 20 megabit disk drive wouldn't run on a 10 megabit controller). ESDI disk drives typically also had jumpers to set the number of sectors per track and (in some cases) sector size. Modern hard drives present a consistent interface to the rest of the computer, no matter what data encoding scheme is used internally. Typically a [[DSP]] in the electronics inside the hard drive takes the raw analog voltages from the read head and uses [[PRML]] and [[Reed–Solomon error correction]] <ref>[http://gaussianwaves.blogspot.com/2008/06/reed-solomon-codes-introduction.html "Reed Solomon Codes - Introduction"] <!-- I wish I had a better reference --> </ref> to decode the sector boundaries and sector data, then sends that data out the standard interface. That DSP also watches the error rate detected by [[error detection and correction]], and performs [[bad sector]] remapping, data collection for [[Self-Monitoring, Analysis, and Reporting Technology]], and other internal tasks. SCSI originally had just one speed, 5 MHz (for a maximum data rate of five megabytes per second), but later this was increased dramatically. The SCSI bus speed had no bearing on the disk's internal speed because of buffering between the SCSI bus and the disk drive's internal data bus; however, many early disk drives had very small buffers, and thus had to be reformatted to a different interleave (just like ST-506 disks) when used on slow computers, such as early [[IBM PC compatible]]s and early [[Apple Macintosh]]es. ATA disks have typically had no problems with interleave or data rate, due to their controller design, but many early models were incompatible with each other and couldn't run in a master/slave setup (two disks on the same cable). This was mostly remedied by the mid-1990s, when ATA's specification was standardised and the details began to be cleaned up, but still causes problems occasionally (especially with CD-ROM and DVD-ROM disks, and when mixing [[Ultra DMA]] and non-UDMA devices). Serial ATA does away with master/slave setups entirely, placing each disk on its own channel (with its own set of I/O ports) instead. FireWire/IEEE 1394 and USB(1.0/2.0) HDDs are external units containing generally ATA or SCSI disks with ports on the back allowing very simple and effective expansion and mobility. Most FireWire/IEEE 1394 models are able to [[Daisy chain#Information technology|daisy-chain]] in order to continue adding peripherals without requiring additional ports on the computer itself. === Disk interface families used in personal computers === Notable families of disk interfaces include: * Historical '''bit serial interfaces''' — connected to a hard disk drive controller with three cables, one for data, one for control and one for power. The HDD controller provided significant functions such as serial to parallel conversion, data separation and track formatting, and required matching to the drive in order to assure reliability. ** ST506 used [[Modified Frequency Modulation|MFM]] (Modified Frequency Modulation) for the data encoding method. ** ST412 was available in either MFM or [[Run Length Limited|RLL]] (Run Length Limited) variants. ** [[Enhanced Small Disk Interface]] (ESDI) was an interface developed by Maxtor to allow faster communication between the PC and the disk than MFM or RLL. *Modern '''bit serial interfaces''' — connect to a host bus adapter (today typically integrated into the "[[Southbridge (computing)|south bridge]]") with two cables, one for data/control and one for power. ** [[Fibre Channel]] (FC), is a successor to parallel SCSI interface on enterprise market. It is a serial protocol. In disk drives usually the [[Fibre Channel Arbitrated Loop]] (FC-AL) connection topology is used. FC has much broader usage than mere disk interfaces, it is the cornerstone of [[storage area network]]s (SANs). Recently other protocols for this field, like [[iSCSI]] and [[ATA over Ethernet]] have been developed as well. Confusingly, drives usually use ''copper'' twisted-pair cables for Fibre Channel, not fibre optics. The latter are traditionally reserved for larger devices, such as servers or [[disk array controller]]s. ** [[Serial ATA]] (SATA). The SATA data cable has one data pair for differential transmission of data to the device, and one pair for differential receiving from the device, just like [[EIA-422]]. That requires that data be transmitted serially. The same [[differential signaling]] system is used in [[RS485]], [[LocalTalk]], [[USB]], [[Firewire]], and differential [[SCSI]]. ** [[Serial Attached SCSI]] (SAS). The SAS is a new generation serial communication protocol for devices designed to allow for much higher speed data transfers and is compatible with SATA. SAS uses serial communication instead of the parallel method found in traditional SCSI devices but still uses SCSI commands. * '''Word serial interfaces''' — connect to a host bus adapter (today typically integrated into the "[[Southbridge (computing)|south bridge]]") with two cables, one for data/control and one for power. The earliest versions of these interfaces typically had a 16 bit parallel data transfer to/from the drive and there are 8 and 32 bit variants. Modern versions have serial data transfer. The word nature of data transfer makes the design of a host bus adapter significantly simpler than that of the precursor HDD controller. ** [[Integrated Drive Electronics]] (IDE), later renamed to ATA, and then later to PATA ("parallel ATA", to distinguish it from the new [[Serial ATA]]). The original name reflected the innovative integration of HDD controller with HDD itself, which was not found in earlier disks. Moving the HDD controller from the interface card to the disk drive helped to standardize interfaces, including reducing the cost and complexity. The 40 pin IDE/ATA connection of PATA transfers 16 bits of data at a time on the data cable. The data cable was originally 40 conductor, but later higher speed requirements for data transfer to and from the hard drive led to an "ultra DMA" mode, known as UDMA, which required an 80 conductor variant of the same cable; the other conductors provided the [[Ground (electricity)|grounding]] necessary for enhanced high-speed signal quality. The interface for 80 conductor only has 39 pins, the missing pin acting as a key to prevent incorrect insertion of the connector to an incompatible socket, a common cause of disk and controller damage. ** EIDE was an unofficial update (by Western Digital) to the original IDE standard, with the key improvement being the use of [[direct memory access]] (DMA) to transfer data between the disk and the computer without the involvement of the [[CPU]], an improvement later adopted by the official ATA standards. By directly transferring data between memory and disk, DMA does not require the CPU/program/operating system to leave other tasks idle while the data transfer occurs. ** [[Small Computer System Interface]] (SCSI), originally named SASI for Shugart Associates System Interface, was an early competitor of ESDI. SCSI disks were standard on servers, workstations, and [[Apple Macintosh]] computers through the mid-90s, by which time most models had been transitioned to IDE (and later, SATA) family disks. Only in 2005 did the capacity of SCSI disks fall behind IDE disk technology, though the highest-performance disks are still available in SCSI and Fibre Channel only. The length limitations of the data cable allows for external SCSI devices. Originally SCSI data cables used single ended data transmission, but server class SCSI could use differential transmission, either low voltage differential (LVD) or high voltage differential (HVD). {| class="wikitable" |- ! [[Acronym]] or abbreviation !! Meaning !! Description |- |[[Shugart Associates System Interface|SASI]]||Shugart Associates System Interface ||Historical predecessor to SCSI. |- |[[SCSI]]||Small Computer System Interface ||[[Computer bus|Bus]] oriented that handles [[concurrent]] operations. |- |[[Serial Attached SCSI|SAS]]||Serial Attached SCSI||Improvement of SCSI, uses serial communication instead of parallel. |- |[[ST-506]]|| ||Historical Seagate interface. |- |[[ST-412]]|| ||Historical Seagate interface (minor improvement over ST-506). |- |[[Enhanced Small Disk Interface|ESDI]]||Enhanced Small Disk Interface ||Historical; backwards compatible with ST-412/506, but faster and more integrated. |- |[[Advanced Technology Attachment|ATA]]||Advanced Technology Attachment ||[[Successor]] to ST-412/506/ESDI by integrating the disk controller completely onto the device. Incapable of concurrent operations. |- |[[Serial ATA|SATA]]||Serial ATA||Modification of ATA, uses serial communication instead of parallel. |} == Integrity == [[Image:hdhead.jpg|thumb|right|An IBM HDD head resting on a disk platter. Since the drive is not in operation, the head is simply pressed against the disk by the suspension.]] [[Image:Hard disk head.jpg|thumb|right|Close-up of a hard disk head resting on a disk platter, and its suspension. A reflection of the head and suspension are visible beneath on the mirror-like disk.]] Due to the extremely close spacing between the heads and the disk surface, any contamination of the read-write heads or platters can lead to a [[head crash]] — a failure of the disk in which the head scrapes across the platter surface, often grinding away the thin magnetic film and causing data loss. Head crashes can be caused by electronic failure, a sudden power failure, physical shock, wear and tear, corrosion, or poorly manufactured platters and heads. The HDD's spindle system relies on air pressure inside the enclosure to support the heads at their proper ''flying height'' while the disk rotates. An HDD requires a certain range of air pressures in order to operate properly. The connection to the external environment and pressure occurs through a small hole in the enclosure (about 0.5 mm in diameter), usually with a carbon filter on the inside (the ''breather filter,'' see below). If the air pressure is too low, then there is not enough lift for the flying head, so the head gets too close to the disk, and there is a risk of head crashes and data loss. Specially manufactured sealed and pressurized disks are needed for reliable high-altitude operation, above about 3,000 m (10,000 feet). Note that modern commercial [[aircraft]] have a [[pressurized cabin]], whose [[pressure altitude]] does not normally exceed 2,600 m(8,500 feet) - thus, ordinary hard drives can safely be used in flight. Modern disks include temperature sensors and adjust their operation to the operating environment. Breather holes can be seen on all disks — they usually have a sticker next to them, warning the user not to cover the holes. The air inside the operating disk is constantly moving too, being swept in motion by friction with the spinning platters. This air passes through an internal recirculation (or "recirc") filter to remove any leftover contaminants from manufacture, any particles or chemicals that may have somehow entered the enclosure, and any particles or outgassing generated internally in normal operation. Very high humidity for extended periods can corrode the heads and platters. For [[giant magnetoresistive effect|giant magnetoresistive]] (GMR) heads in particular, a minor head crash from contamination (that does not remove the magnetic surface of the disk) still results in the head temporarily overheating, due to friction with the disk surface, and can render the data unreadable for a short period until the head temperature stabilizes (so called "thermal asperity," a problem which can partially be dealt with by proper electronic filtering of the read signal). The hard disk's electronics control the movement of the actuator and the rotation of the disk, and perform reads and writes on demand from the [[disk controller]]. Modern disk firmware is capable of scheduling reads and writes efficiently on the platter surfaces and remapping sectors of the media which have failed. === Landing zones and load/unload technology=== [[Image:Rwheadmicro.JPG|thumb|right|[[Micrograph|Microphotograph]] of a hard disk head. The size of the front face (which is the "trailing face" of the slider) is about 0.3 mm × 1.0 mm. The (not visible) bottom face of the slider is about 1.0 mm × 1.25 mm (so called "nano" size) and faces the platter. One functional part of the head is the round, orange structure in the middle - the [[photolithography|lithographically]] defined copper coil of the write [[transducer]]. Also note the electric connections by wires bonded to gold-plated pads.]] Most HDDs prevent power interruptions from shutting the drive down with its heads landing in the data zone by either moving the heads to a '''landing zone''' or unloading (i.e., '''load/unload''') the heads. A '''landing zone''' is an area of the platter usually near its inner diameter (ID), where no data is stored. This area is called the Contact Start/Stop (CSS) zone. Disks are designed such that either a spring or, more recently, rotational [[inertia]] in the platters is used to park the heads in the case of unexpected power loss. In this case, the spindle motor temporarily acts as a generator, providing power to the actuator. Spring tension from the head mounting constantly pushes the heads towards the platter. While the disk is spinning, the heads are supported by an air bearing and experience no physical contact or wear. In CSS drives the sliders carrying the head sensors (often also just called ''heads'') are designed to survive a number of landings and takeoffs from the media surface, though wear and tear on these microscopic components eventually takes its toll. Most manufacturers design the sliders to survive 50,000 contact cycles before the chance of damage on startup rises above 50%. However, the decay rate is not linear: when a disk is younger and has had fewer start-stop cycles, it has a better chance of surviving the next startup than an older, higher-mileage disk (as the head literally drags along the disk's surface until the air bearing is established). For example, the Seagate Barracuda 7200.10 series of desktop hard disks are rated to 50,000 start-stop cycles, in other words no failures attributed to the head-platter interface were seen before at least 50,000 start-stop cycles during testing.<ref>[http://www.seagate.com/support/disc/manuals/sata/100402371a.pdf Barracuda 7200.10 Serial ATA Product Manual]</ref> Around 1995 IBM pioneered a technology where a landing zone on the disk is made by a precision laser process (''Laser Zone Texture'' = LZT) producing an array of smooth nanometer-scale "bumps" in a landing zone, thus vastly improving [[stiction]] and wear performance. This technology is still largely in use today (2007), predominantly in desktop and enterprise (3.5 inch) drives. In general, CSS technology can be prone to increased stiction (the tendency for the heads to stick to the platter surface), e.g. as a consequence of increased humidity. Excessive stiction can cause physical damage to the platter and slider or spindle motor. '''Load/Unload''' technology relies on the heads being lifted off the platters into a safe location, thus eliminating the risks of wear and stiction altogether. The first HDD [[RAMAC]] and most early disk drives used complex mechanisms to load and unload the heads. Modern HDDs use ramp loading, first introduced by Memorex in 1967<ref>Pugh et al; "IBM's 360 and Early 370 Systems;" MIT Press, 1991, pp.270</ref>, to load/unload onto plastic "ramps" near the outer disk edge. All HDDs today still use one of these two technologies. Each has a list of advantages and drawbacks in terms of loss of storage area on the disk, relative difficulty of mechanical tolerance control, cost of implementation, etc. Addressing shock robustness, [[IBM]] also created a technology for their [[ThinkPad]] line of laptop computers called the [[Active Protection System]]. When a sudden, sharp movement is detected by the built-in [[accelerometer]] in the Thinkpad, internal hard disk heads automatically unload themselves to reduce the risk of any potential data loss or scratch defects. [[Apple Inc.|Apple]] later also utilized this technology in their [[PowerBook]], [[iBook]], [[MacBook Pro]], and [[MacBook]] line, known as the [[Sudden Motion Sensor]]. [[Toshiba]] has released similar technology in their laptops.<ref>[http://eu.computers.toshiba-europe.com/Contents/Toshiba_teg/EU/WORKSHOP/files/EXP-2005-04-HDD-Protection-EN.pdf Toshiba HDD Protection measures.]</ref> ===Disk failures and their metrics=== <!-- NOTE: Some articles link to this exact section name. Do not change it. --> {{wikibooks|Minimizing hard disk drive failure and data loss}} Most major hard disk and motherboard vendors now support [[Self-Monitoring, Analysis, and Reporting Technology|self-monitoring, analysis and reporting technology]] (S.M.A.R.T.), which attempts to alert users to impending failures. However, not all failures are predictable. Normal use eventually can lead to a breakdown in the inherently fragile device, which makes it essential for the user to periodically back up the data onto a separate storage device. Failure to do so will lead to the loss of data. While it may sometimes be possible to recover lost information, it is normally an extremely costly procedure, and it is not possible to guarantee success. A 2007 study published by [[Google]] suggested very little correlation between failure rates and either high temperature or activity level; however, the correlation between manufacturer/model and failure rate was relatively strong. Google did not publish the manufacturer's names along with their respective failure rates. <ref name=google>Barroso, L.A., et al. [http://labs.google.com/papers/disk_failures.pdf Failure Trends in a Large Disk Drive Population]. February 2007.</ref> While several S.M.A.R.T. parameters have an impact on failure probability, a large fraction of failed drives do not produce predictive S.M.A.R.T. parameters.<ref name=google/> S.M.A.R.T. parameters alone may not be useful for predicting individual drive failures.<ref name=google/> A common misconception is that a colder hard drive will last longer than a hotter hard drive. The Google study showed the reverse -- "lower temperatures are associated with higher failure rates". Hard drives with S.M.A.R.T.-reported average temperatures below 27 C had failure rates worse than hard drives with the highest reported average temperature of 50 C, failure rates at least twice as high as the optimum S.M.A.R.T.-reported temperature range of 36 C to 47 C.<ref name=google/> SCSI, SAS and FC drives are typically more expensive and are traditionally used in [[server]]s and [[disk array]]s, whereas inexpensive ATA and SATA drives evolved in the [[home computer]] market and were perceived to be less reliable. This distinction is now becoming blurred. The [[mean time between failures]] (MTBF) of SATA drives is usually about 600,000 hours (some drives such as [[Western Digital Raptor]] have rated 1.2 million hours MTBF), while SCSI drives are rated for upwards of 1.5 million hours.{{Fact|date=July 2007}} However, independent research indicates that MTBF is not a reliable estimate of a drive's longevity.<ref>{{cite web |url=http://storagemojo.com/?p=383 |title=Everything You Know About Disks Is Wrong |publisher=StorageMojo |date=February 20, 2007 |accessdate=2007-08-29}}</ref> MTBF is conducted in laboratory environments in test chambers and is an important metric to determine the quality of a disk drive before it enters high volume production. Once the drive product is in production, the more valid{{Fact|date=October 2007}} metric is [[annualized failure rate]] (AFR). AFR is the percentage of real-world drive failures after shipping. SAS drives are comparable to SCSI drives, with high MTBF and high {{Fact|date=July 2007}} reliability. Enterprise SATA drives designed and produced for enterprise markets, unlike standard SATA drives, have reliability comparable to other enterprise class drives.{{Fact|date=October 2007}} Typically enterprise drives (all enterprise drives, including SCSI, SAS, enterprise SATA and FC) experience between 0.70%-0.78% annual failure rates from the total installed drives.{{Fact|date=October 2007}} == Manufacturers == [[Image:Hdd.jpg|thumb|right|A [[Western Digital]] 3.5 inch 250 GB [[Serial ATA|SATA]] HDD. This drive has an optional 4-pin Molex power connector typically used for the older ATA standard, and SATA typically uses its own, proprietary power connector.]] :''See also [[List of defunct hard disk manufacturers]] The technological resources and know-how required for modern drive development and production mean that as of 2007, over 98% of the world's HDDs are manufactured by just a handful of large firms: [[Seagate Technology|Seagate]] (which now owns [[Maxtor]]), [[Western Digital]], [[Samsung Electronics|Samsung]], and [[Hitachi Ltd.|Hitachi]] (which owns the former disk manufacturing division of [[International Business Machines|IBM]]). [[Fujitsu]] continues to make mobile- and server-class disks but exited the desktop-class market in 2001. [[Toshiba]] is a major manufacturer of 2.5-inch and 1.8-inch notebook disks. [[ExcelStor]] is a small HDD manufacturer. Dozens of former HDD manufacturers have gone out of business, merged, or closed their HDD divisions; as capacities and demand for products increased, profits became hard to find, and the market underwent significant [[consolidation]] in the late 1980s and late 1990s. The first notable casualty of the business in the PC era was [[Computer Memories Inc.]] or CMI; after an incident with faulty 20 MB AT disks in 1985,<ref>Apparently the CMI disks suffered from a higher soft error rate than IBM's other suppliers (Seagate and MiniScribe) but the bugs in Microsoft's DOS Operating system may have turned these recoverable errors into hard failures. At some point, possibly [[MS-DOS]] 3.0, soft errors were reported as disk hard errors and a subsequent Microsoft patch turned soft errors into corrupted memory with unpredictable results ("crashes"). MS-DOS 3.3 apparently resolved this series of problems but by that time it was too late for CMI. See also, "IBM and CMI in Joint Effort to Rehab AT Hard-Disk Rejects," PC Week, v.2 n.11, p.1, March 19, 1985</ref> CMI's reputation never recovered, and they exited the HDD business in 1987. Another notable failure was [[MiniScribe]], who went bankrupt in 1990 after it was found that they had engaged in accounting fraud and inflated sales numbers for several years. Many other smaller companies (like [[Kalok]], [[Microscience International Corporation|Microscience]], LaPine, Areal, Priam and PrairieTek) also did not survive the shakeout, and had disappeared by 1993; [[Micropolis Corporation|Micropolis]] was able to hold on until 1997, and [[JT Storage|JTS]], a relative latecomer to the scene, lasted only a few years and was gone by 1999, after attempting to manufacture HDDs in [[India]]. Their claim to fame was creating a new 3" form factor drive for use in laptops. Quantum and Integral also invested in the 3" form factor; but eventually gave up as this form factor failed to catch on.{{Fact|date=February 2007}} [[Rodime plc|Rodime]] was also an important manufacturer during the 1980s, but stopped making disks in the early 1990s amid the shakeout and now concentrates on technology licensing; they hold a number of patents related to 3.5-inch form factor HDDs. {{incomplete-list}} * 1988: [[Tandon Corporation]] sold its disk manufacturing division to Western Digital (WDC), which was then a well-known controller designer.<ref name="tandon-nyt"> {{cite web | last = | first = | authorlink = | coauthors = | title = COMPANY NEWS; Tandon Sells Disk Drive Unit | work = [[The New York Times]] | publisher = | date = 1988-03-09 | url = http://query.nytimes.com/gst/fullpage.html?res=940DE7DC1139F93AA35750C0A96E948260 | format = | doi = | accessdate = 2008-02-22}} </ref> * 1989: [[Seagate Technology]] bought [[Control Data Corporation|Control Data]]'s high-end disk business, as part of CDC's exit from hardware manufacturing. * 1990: Maxtor buys [[MiniScribe]] out of bankruptcy, making it the core of its low-end disk division. * 1994: [[Quantum Corporation|Quantum]] bought [[Digital Equipment Corporation|DEC]]'s storage division, giving it a high-end disk range to go with its more consumer-oriented ''ProDrive'' range, as well as the [[Digital Linear Tape|DLT]] tape drive range. * 1995: [[Conner Peripherals]], which was founded by one of Seagate Technology's co-founders along with personnel from MiniScribe, announces a merger with Seagate, which was completed in early 1996. * 1996: JTS merges with [[Atari]], allowing JTS to bring its disk range into production. Atari was sold to [[Hasbro]] in 1998, while JTS itself went bankrupt in 1999. * 2000: Quantum sells its disk division to Maxtor to concentrate on [[tape drive]]s and [[backup]] equipment. * 2003: Following the controversy over mass failures of its [[Deskstar 75GXP]] range, HDD pioneer IBM sold the majority of its disk division to Hitachi, who renamed it ''Hitachi Global Storage Technologies'' (HGST). * [[December 21]], [[2005]]: [[Seagate Technology|Seagate]] and [[Maxtor]] announced an agreement under which Seagate would acquire Maxtor in an all stock transaction valued at $1.9 billion. The acquisition was approved by the appropriate regulatory bodies, and closed on [[May 19]], [[2006]]. *2007 ** July: Western Digital (WDC) acquires Komag U.S.A, a thin-film media manufacturer, for USD 1 Billion.<ref>{{cite web|url=http://www.engadget.com/2007/07/01/western-digital-buys-komag-for-1-billion/|title=Western Digital buys Komag for $1 Billion|accessdate=2007-08-18}}</ref> ''' ==See also== *[[Click of death]] *[[Disk Usage]] *[[Disk formatting]] *[[External hard disk drive]] *[[Hybrid drive]] *[[Automatic Acoustic Management]] *[[Solid-state drive]] *[[Disk Size Manager]] == Notes and References == {{Refimprove|date=June 2008}} {{reflist|2}} == External links == {{commons|Hard disk}} * [http://www.IASForensics.com/HD2_Wiki.jpg Magnetic image of 120MB hard drive / Image And Sound Forensics(TM)] * http://www.youtube.com/watch?v=9eMWG3fwiEU Video of opened hard drive performing several operations. * [http://news.bbc.co.uk/2/hi/technology/6677545.stm Factfile: Hard disk drive] - How they work from the [[BBC]] * [http://www.newsweek.com/id/46300 The Hard Disk That Changed The World] [re: RAMAC], Newsweek, August 7, 2006 * [http://www.techweb.com/encyclopedia/defineterm.jhtml?term=harddisk TechEncyclopedia about Hard Disks] * [http://pinouts.ru/pin_HD.shtml Hard disk interfaces pinouts] * [http://www.storagesearch.com/bitmicro-art3.html War of the Disks: Hard Disk Drives vs. Flash Solid State Disks] Despatches from the magneto / flash wars * [http://www.pcdoctor-guide.com/wordpress/?p=595 PC Doctor takes you inside a hard drive] * [http://labs.google.com/papers/disk_failures.pdf Failure Trends in a Large Disk Drive Population] : Disk Failures report by [[Google Labs]] * [http://www.techarp.com/showarticle.aspx?artno=84&pgno=0 Hard Disk Myths] TecHarp / [http://www.snopes.com/photos/technology/storage.asp Photo Myth] Snopes Urban Legend Archive * [http://gizmodo.com/archives/would-that-be-internal-or-external-technically-018574.php Describing a c.1975 HDD] * [http://www.tomshardware.com/reviews/15-years-of-hard-drive-history,1368.html 15 Years Of Hard Drive History: Capacities Outran Performance] at [[Tom's Hardware Guide]]. * [http://www.tomshardware.com/reviews/understanding-hard-drive-performance,1557.html Understanding Hard Drive Performance] at [[Tom's Hardware Guide]]. *[http://www.datarecoveryadvice.org/index.htm datarecoveryadvice.org] - Data Recovery Tips and Advice for the Public. {{Magnetic storage media}} [[Category:Computer storage devices]] [[Category:Rotating disc computer storage media]] [[Category:Non-volatile memory]] {{Link FA|af}} [[af:Hardeskyf]] [[ar:قرص صلب]] [[be:Цвёрды дыск]] [[bn:হার্ড ডিস্ক]] [[bs:Tvrdi disk]] [[br:Pladenn galet]] [[bg:Твърд диск]] [[ca:Disc dur]] [[cs:Pevný disk]] [[da:Harddisk]] [[de:Festplatte]] [[et:Kõvaketas]] [[el:Σκληρός δίσκος]] [[es:Disco duro]] [[eo:Diskaparato]] [[eu:Disko gogor]] [[fa:دیسک سخت]] [[fr:Disque dur]] [[fy:Fêste skiif]] [[gl:Disco ríxido]] [[ko:하드 디스크]] [[hr:Tvrdi disk]] [[id:Cakram keras]] [[ia:Disco dur]] [[is:Harður diskur]] [[it:Disco rigido]] [[he:כונן קשיח]] [[ka:მყარი დისკი]] [[kk:Тұрғылықты дискі]] [[sw:Kiendeshi diski kuu]] [[lv:Cietais disks]] [[lt:Kietasis diskas]] [[ln:Diski ebómbelo enéne]] [[hu:Merevlemez]] [[mk:Хард диск]] [[ml:ഹാര്‍ഡ് ഡിസ്ക് ഡ്രൈവ്]] [[ms:Cakera keras]] [[nl:Harde schijf]] [[ja:ハードディスクドライブ]] [[no:Platelager]] [[nn:Platelager]] [[nds:Fastplaat]] [[pl:Dysk twardy]] [[pt:Disco rígido]] [[ro:Hard disc]] [[ru:Жёсткий диск]] [[sq:Hard disk]] [[simple:Hard disk]] [[sk:Pevný disk]] [[sl:Trdi disk]] [[sr:Тврди диск]] [[sh:Tvrdi disk]] [[fi:Kiintolevy]] [[sv:Hårddisk]] [[te:హార్డ్ డిస్క్ డ్రైవు]] [[th:ฮาร์ดดิสก์]] [[vi:Ổ đĩa cứng]] [[tr:Sabit disk]] [[uk:Жорсткий диск]] [[vec:Disco duro]] [[yi:הארטדיסק]] [[zh-yue:硬碟]] [[diq:Hard disk]] [[zh:硬盘]]