Hard disk

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Hard Disk
An IBM hard disk drive with the metal cover removed. The platters are  highly reflective.
Date Invented:	September 13, 1956
Invented By:	Reynold Johnson
Connects to: Motherboard via one of PATA SATA SCSI External enclosure via one of USB 1.1/ 2 FireWire 400/ 800 eSATA
Form Factor: Desktop Laptop

The inside of a hard disk drive displaying the read/write head traveling over the top platter

A hard disk drive (HDD, also commonly shortened to hard drive and  formerly known as a fixed disk) is  a digitally encoded non-volatile storage device which stores data on rapidly rotating platters with magnetic surfaces. Strictly speaking, "drive" refers to an  entire unit containing multiple platters, a read/write head assembly, driver electronics, and  motor while "hard disk" (sometimes "platter") refers to the storage medium itself[1].

Hard disks were originally developed for use with computers. In the 21st century, applications for hard disks have  expanded beyond computers to include video recorders, audio players, digital organizers, and  digital cameras. In 2005 the first cellular telephones to include hard disks were introduced by Samsung and  Nokia. The need for large-scale, reliable storage, independent of a particular device, led to the introduction of configurations such as RAID, hardware such as network attached storage (NAS) devices, and  systems such as storage area networks (SANs) for efficient access to large volumes of data.

[edit] Technology

 is  the read-write arm. In the middle the electromagnets of the platter's motor can be seen."> is  the read-write arm. In the middle the electromagnets of the platter's motor can be seen." width="175" height="123" longdesc="../../../h/a/r/Image%7EHard_disk_dismantled.jpg_d650.html" />

The inside of a hard disk drive with the disk itself removed. To the left is  the read-write arm. In the middle the electromagnets of the platter's motor can be seen.

Hard disks record data by magnetizing a magnetic material in a pattern that represents the data. They read the data back by detecting the magnetization of the material. A typical hard disk design consists of a spindle which holds one or  more flat circular disks called platters, onto which the data is  recorded. The platters are  made from a non-magnetic material, usually glass or  aluminum, 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.

The platters are  spun at very high speeds. Information is  written to a platter as it  rotates past mechanisms called read-and-write heads that fly very close 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 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.

A cross section of the magnetic surface in action. In this case the binary data encoded using frequency modulation.

The magnetic surface of each platter is  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 hard disks each of these magnetic regions is  composed of a few hundred magnetic grains. Each magnetic region forms a magnetic dipole which generates a highly localised magnetic field nearby. The write head magnetizes a magnetic region by generating a strong local magnetic field nearby. Early hard disks used the same inductor that was used to read the data as an  electromagnet to create this field. Later, metal in Gap (MIG) heads were used, and  today thin film heads are  common. With these later technologies, the read and  write head are  separate mechanisms, but are  on the same actuator arm.

Hard disks have  a mostly sealed enclosure that protects the disk internals from dust, condensation, and  other sources of contamination. The hard disk's read-write heads fly on an  air bearing which is  a cushion of air only nanometers above the disk surface. The disk surface and  the disk's internal environment must therefore be kept immaculate to prevent damage from fingerprints, hair, dust, smoke particles and  such, given the sub-microscopic gap between the heads and  disk.

Using rigid platters and  sealing the unit allows much tighter tolerances than in a floppy disk. Consequently, hard disks can store much more  data than floppy disk and  access and  transmit it  faster. In 2006, a typical workstation hard disk might store between 80 GB and  250 GB of data, rotate at 7,200 to 10,800 revolutions per minute (RPM), and  have a sequential media transfer rate of over 50 MB/s. The fastest workstation and  server hard disks spin at 15,000 RPM, and  can achieve sequential media transfer speeds up to and  beyond 80 MB/s. Laptop hard disks, which are  physically smaller than their desktop counterparts, tend to be slower and  have less  capacity. Most spin at only 4,200 RPM or  5,400 RPM, whereas the newest top models spin at 7,200 RPM.

[edit] Capacity

 is  logarithmic, so the fit line corresponds to exponential growth."> is  logarithmic, so the fit line corresponds to exponential growth." width="180" height="132" longdesc="../../../h/a/r/Image%7EHard_drive_capacity_over_time.png_4f20.html" />

PC hard disk capacity (in GB). The plot is  logarithmic, so the fit line corresponds to exponential growth.

The capacity of hard disks has grown dramatically over time. The first commercial disk, the IBM RAMAC introduced in 1956, stored 5 million characters (about 5 megabytes) on fifty 24-inch diameter disks. (See early IBM disk storage.) With early personal computers in the 1980s, a disk with a 20 megabyte capacity was considered large. In the latter half of the 1990s, hard disks with capacities of 1 gigabyte and  greater became available. As of 2006, the "smallest" desktop hard disk still in production has a capacity of 20 gigabytes, while the largest-capacity internal disks are  a 3/4 terabyte (768 gigabytes), with external disks at or  exceeding one terabyte by using multiple internal disks. These new internal disks increased their storage capacities with perpendicular recording.

The exponential increases in disk space and  data access times for hard disks has enabled the commercial viability of consumer products that require large storage capacities, such as the Apple iPod digital music player, the TiVo personal video recorder, and  web-based email programs.^[1] This is  also gradually but significantly altering how programmers think; in many programming tasks there is  a time-space tradeoff, so as space becomes cheaper and  cheaper relative to CPU cycles the appropriate choice about time versus space changes. For instance in database work it  is now common practice to store precomputed views, transitive closures, and  the like on disk in order to speed up queries; 20 years ago such profligate use of disk space would have  been impractical.

A vice president of Seagate projects a future growth in disk density of 40% per year.[2] Access times have  not kept up with throughput increases, which themselves haven't kept up with growth in storage capacity. The main way to increase either is  to increase the number of read-write heads in a hard disk. Since flying heads are  the most expensive component of hard disks, increasing their number per hard disk wouldn't help the situation. Currently, the most promising way to reduce access times and  increase throughput are  to replace rotating disks with nonvolatile random access memory (NVRAM) or, possibly, holographic technology.

[edit] Capacity measurements

Hard disk manufacturers typically specify disk capacity using the SI definition of the prefixes "mega" and  "giga." This is  largely for historical reasons. Disks with multi-million byte capacity have  been used since 1956, long before there were standard binary prefixes. (The IEC only standardized binary prefixes in 1999.) Many practitioners early on in the computer and  semiconductor industries used the prefix kilo to describe 2¹⁰ (1024) bits, bytes or  words because 1024 is  "close enough" to 1000. Similar usage has been applied to the prefixes "mega," "giga," "tera," and  even "peta." Often this non-SI conforming usage is  noted by a qualifier such as "1 kB = 1,024 bytes" but the qualifier is  sometimes omitted, particularly in marketing literature.

Operating systems, such as Microsoft Windows, frequently report capacity using the binary interpretation of the prefixes, which results in a discrepancy between the disk manufacturer's stated capacity and  what the system reports. The difference becomes much more  noticeable in the multi-gigabyte range. For example, Microsoft's Windows 2000 reports disk capacity both in decimal to 12 or  more significant digits and  with binary prefixes to 3 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," 10⁹. However utilities provided by Windows define a gigabyte as 2³⁰, or  1,073,741,824, bytes, so the reported capacity of the disk will be closer to 28.0 GB. For this reason, many utilities that report capacity have  begun to use the aforementioned IEC standard binary prefixes (e.g. KiB, MiB, GiB) since their definitions are  unambiguous.

Some people mistakenly attribute the discrepancy in reported and  specified capacities to reserved space used for file system and  partition accounting information. However, for large (several GiB) filesystems, this data rarely occupies more  than a few MiB, and  therefore cannot possibly account for the apparent "loss" of tens of GBs.

The capacity of a hard disk can be calculated by multiplying the number of cylinders by the number of heads by the number of sectors by the number of bytes/sector (most commonly 512).

[edit] History

Main article: history of hard disks

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IBM 62PC "Piccolo" HDD, circa 1979 - an  early 8" disk

For many years, hard disks were large, cumbersome devices, more  suited to use in the protected environment of a data center or  large office than in a harsh industrial environment (due to their delicacy), or  small office or  home (due to their size and  power consumption). Before the early 1980s, most hard disks had 8-inch (20 cm) or  14-inch (35 cm) platters, required an  equipment rack or  a large amount of floor space (especially the large removable-media disks, which were often referred to as "washing machines"), and  in many cases needed high-current or  even three-phase power hookups due to the large motors they used. Because of this, hard disks were not commonly used with microcomputers until after 1980, when Seagate Technology introduced the ST-506, the first 5.25-inch hard disk, with a capacity of 5 megabytes. In fact, in its factory configuration, the original IBM PC (IBM 5150) was not equipped with a hard disk.

Most microcomputer hard disks in the early 1980s were not sold under their manufacturer's names, but by OEMs as part of larger peripherals (such as the Corvus Disk System and  the Apple ProFile). The IBM PC/XT had an  internal hard disk, however, and  this started a trend toward buying "bare" disks (often by mail order) and  installing them directly into a system. Hard disk makers started marketing to end users as well as OEMs, and  by the mid-1990s, hard disks had become available on retail store shelves.

While internal disks became the system of choice on PCs, external hard disks remained popular for much longer on the Apple Macintosh and  other platforms. Every Mac made between 1986 and  1998 has a SCSI port on the back, making external expansion easy. External SCSI disks were also popular with older microcomputers such as the Apple II series, and  were also used extensively in servers, a usage which is  still popular today. The appearance in the late 1990s of high-speed external interfaces such as USB and  FireWire has made external disk systems popular among PC users once again, especially for users who move large amounts of data between two or  more locations, and  most hard disk makers now make their disks available in external cases.

[edit] Hard disk characteristics

5.25" MFM 110 MB hard disk (2.5" IDE 6495 MB hard disk, US & UK pennies for comparison)

• Capacity, usually quoted in gigabytes. (older hard disks used to quote their smaller capacities in megabytes)
• Physical size, usually quoted in inches:
  • Almost all hard disks today are  of either the 3.5" or  2.5" varieties, used in desktops and  laptops, respectively. 2.5" disks are  usually slower and  have less  capacity but use less  power and  are more  tolerant of movement. an  increasingly common size is  the 1.8" disks used in portable MP3 players and  subnotebooks, which have  very low power consumption and  are highly shock-resistant. Additionally, there is  the 1" form factor designed to fit the dimensions of CF Type II, which is  also usually used as storage for portable devices including digital cameras. 1" was a de facto form factor led by IBM's Microdrive, but is  now generically called 1" due to other manufacturers producing similar products. There is  also a 0.85" form factor produced by Toshiba for use in mobile phones and  similar applications. The size designations are  more nomenclature than descriptive: for example, a 3.5" drive is  named for the size of the floppy disk whose drive bay size it  was originally designed to occupy; the drive itself is  actually 4" wide. Server-class hard disks also come in both 3.5" and  2.5" form factors.
• Reliability, usually given in terms of mean time between failure (MTBF):
  • SATA 1.0 disks support speeds up to 10,000 RPM and  MTBF levels up to 1 million hours under an  eight-hour, low-duty cycle.^{[citation needed]} Fibre Channel (FC) disks support up to 15,000 RPM and  an MTBF of 1.4 million hours under a 24-hour duty cycle.^{[citation needed]}
• Number of I/O operations per second:
  • Modern disks can perform around 50 random access or  100 Sequential access operations per second.^{[citation needed]}
• Power consumption (especially important in battery-powered laptops).
• audible noise in dBA (although many still report it  in bels, not decibels).
• G-shock rating (surprisingly high in modern disks).
• Transfer Rate:
  • Inner Zone: from 44.2 MB/s to 74.5 MB/s.
  • Outer Zone: from 74.0 MB/s to 111.4 MB/s.
• Random access time: from 5 ms to 15 ms.

[edit] Integrity

Close-up of a hard disk head suspended above the disk platter together with its mirror image in the smooth surface of the magnetic platter.

The hard disk's spindle system relies on air pressure inside the enclosure to support the heads at their proper flying height while the disk is  in motion. A hard disk 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 1/2 mm in diameter), usually with a carbon filter on the inside (the breather filter, see below). If the air pressure is  too low, there will not be enough lift for the flying head, the head will not be at the proper height, 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 10,000 feet (3,000 m). This does not apply to pressurized enclosures, like an  airplane pressurized cabin. Modern disks include temperature sensors and  adjust their operation to the operating environment.

Very high humidity for extended periods can cause accelerated wear of the heads and  platters by corrosion. If the disk uses "Contact Start/Stop" (CSS) technology to park its heads on the platters when not operating, increased humidity can also lead to increased stiction (the tendency for the heads to stick to the platter surface). This can cause physical damage to the platter and  spindle motor and  can also lead to head crash. Breather holes can be seen on all disks — they usually have  a warning sticker next to them, informing 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.

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. For giant magnetoresistive (GMR) heads in particular, a minor head crash from contamination (that does not remove the magnetic surface of the disk) will still result 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). Head crashes can be caused by electronic failure, a sudden power failure, physical shock, wear and  tear, corrosion, or  poorly manufactured platters and  heads. In most desktop and  server disks, when powering down, the heads are  moved to a landing zone, an  area of the platter usually near its inner diameter (ID), where no data is  stored. This area is  called the CSS (Contact Start/Stop) zone. However, especially in old models, sudden power interruptions or  a power supply failure can sometimes result in the device shutting down with the heads in the data zone, which increases the risk of data loss. In fact, it  used to be procedure to "park" the hard disk before shutting down your computer. Newer disks are  designed such that either a spring (at first) or  (more recently) rotational inertia in the platters is  used to safely park the heads in the case of unexpected power loss.

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. Also, most major hard disk and  motherboard vendors now support  and  Reporting Technology">self-monitoring, analysis, and  reporting technology (S.M.A.R.T.), by which impending failures can be predicted, allowing the user to be alerted to prevent data loss.

[edit] Landing zones

 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 lithographically defined copper coil of the write transducer. Also note the electric connections by wires bonded to gold-plated pads."> 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 lithographically defined copper coil of the write transducer. Also note the electric connections by wires bonded to gold-plated pads." width="180" height="121" longdesc="../../../r/w/h/Image%7ERwheadmicro.JPG_2134.html" />

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 lithographically defined copper coil of the write transducer. Also note the electric connections by wires bonded to gold-plated pads.

Around 1995 IBM pioneered a technology where the landing zone is  made by a precision laser process (Laser Zone Texture = LZT) producing an  array of smooth nanometer-scale "bumps" in the ID landing zone, thus vastly improving stiction and  wear performance. This technology is  still widely in use today (2006). A few years after LZT, initially for mobile applications (i.e. laptop etc.), and  later also for the other HDD types, IBM introduced "head unloading" technology, where the heads are  lifted off the platters onto plastic "ramps" near the outer disk edge, thus eliminating the risk of stiction altogether and  greatly improving non-operating shock performance. All HDD manufacturers use these two technologies to this day. Both have  a list of advantages and  drawbacks in terms of loss of storage space, relative difficulty of mechanical tolerance control, cost of implementation, etc.

IBM 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 motion sensor in the Thinkpad, internal hard disk heads automatically unload themselves into the parking zone to reduce the risk of any potential data loss or  scratches made. Apple later also utilized this technology in their Powerbook, iBook, MacBook Pro, and  MacBook line, known as the Sudden Motion Sensor.

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 reliably 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 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 Maxtor DiamondMax series of desktop hard disks are  rated to 50,000 start-stop cycles. This means that no failures attributed to the head-platter interface were seen before at least 50,000 start-stop cycles during testing.

[ and  interfaces">edit] Access and  interfaces

Hard disks are  generally accessed over one of a number of bus types, including ATA (IDE, EIDE), Serial ATA (SATA), SCSI, SAS, IEEE 1394, USB, and  Fibre Channel.

Back in the days of the ST-506 interface, the data encoding scheme was also important. The first ST-506 disks used Modified Frequency Modulation (MFM) encoding (which is  still used on the common "1.44 MB" (1440 KiB) 3.5-inch floppy), and  transferred data at a rate of 5 megabits per second. Later on, controllers using 2,7 RLL (or just "RLL") encoding increased the transfer rate by half, to 7.5 megabits per second; it  also increased disk capacity by half.

Many ST-506 interface disks were only certified by the manufacturer to run at the lower MFM data rate, while other models (usually more  expensive versions of the same basic disk) were certified to run at the higher RLL data rate. In some cases, the disk was overengineered just enough to allow the MFM-certified model to run at the faster data rate; however, this was often unreliable and  was not recommended. (An RLL-certified disk 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 and  controller; most of the time, however, 15 or  20 megabit ESDI disks weren't downward compatible (i.e. a 15 or  20 megabit disk wouldn't run on a 10 megabit controller). ESDI disks typically also had jumpers to set the number of sectors per track and  (in some cases) sector size.

SCSI originally had just one speed, 5 MHz (for a maximum data rate of 5 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's internal data bus; however, many early disks 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 compatibles and  early Apple Macintoshes.

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) hard disks 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 in order to continue adding peripherals without requiring additional ports on the computer itself.

[edit] Disk families used in personal computers

Notable disk families include:

• MFM (Modified Frequency Modulation) disks required that the controller electronics be compatible with the disk electronics.
• RLL (Run Length Limited) disks were named after the modulation technique that made them an  improvement on MFM. They required large cables between the controller in the PC and  the hard disk, the disk did not have  a controller, only a modulator/demodulator.

• ESDI (Enhanced Small Disk Interface) was an  interface developed by Maxtor to allow faster communication between the PC and  the disk than MFM or  RLL.

• Integrated Drive Electronics (IDE) was later renamed to ATA, and  then PATA.

The name comes from the way early families had the hard disk controller external to the disk. Moving the hard disk controller from the interface card to the disk helped to standardize interfaces, including reducing the cost and  complexity. In 2005/2006 parlance, the 40 pin IDE/ATA is  called "PATA" or  parallel ATA, which means that there are  16 bits of data transferred in parallel at a time on the data cable.

The data cable was originally 40 conductor, but UDMA modes from the later disks requires using an  80 conductor cable (note that the 80 conductor cable still uses a 40 position connector.)

The interface changed from 40 pins to 39 pin. The missing pin acts as a key to prevent incorrect insertion of the connector, a common cause of disk and  controller damage.

• SCSI (Small Computer System Interface) was an  early competitor with ESDI, originally named SASI for Shugart Associates. 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, and  then Fibre Channel (FC) interface, and  then more  specifically the Fibre Channel Arbitrated Loop (FC-AL), connected SCSI hard disks using fibre optics. FC-AL is  the cornerstone of storage area networks, although other protocols like iSCSI and  ATA over Ethernet have  been developed as well.

• SATA (Serial ATA). 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.

• SAS (Serial Attached SCSI). 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 for interacting with SAS

• EIDE was an  unofficial update (by Western Digital) to the original IDE standard, with the key improvement being the use of DMA to transfer data between the disk and  the computer, an  improvement later adopted by the official ATA standards. DMA is  used to transfer data without the CPU or  program being responsible to transfer every word. That leaves the CPU/program/operating system to do other tasks while the data transfer occurs.

[edit] Manufacturers

Hitachi 2.5 inch laptop hard disk

As of 2005, over 98% of the world's hard disks are  manufactured by just a handful of large firms: Seagate, Maxtor (acquired by Seagate in May 2006), Western Digital, Samsung, and  Hitachi which owns the former disk manufacturing division of 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.

Dozens of former hard disk manufacturers have  gone out of business, merged, or  closed their hard disk divisions; as capacities and  demand for products increased, profits became hard to find, and  there were shakeouts 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.^[2] CMI's reputation never recovered, and  they exited the hard disk business in 1987. Another notable failure was MiniScribe, who went bankrupt in 1990 after it  was found that they had "cooked the books" and  inflated sales numbers for several years. Many other smaller companies (like Kalok, Microscience, LaPine, Areal, Priam and  PrairieTek) also did not survive the shakeout, and  had disappeared by 1993; Micropolis was able to hold on until 1997, and  JTS, a relative latecomer to the scene, lasted only a few years and  was gone by 1999, after attempting to manufacture hard disks in India using a second hand factory.^{[citation needed]} 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 hard disks.

• 1988: Tandon sold its disk manufacturing division to Western Digital (WDC), which was then a well-known controller designer.
• 1989: Seagate Technology bought 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 bought DEC's storage division, giving it  a high-end disk range to go with its more  consumer-oriented ProDrive range, as well as the DLT tape drive range.
• 1995, Conner Peripherals, which was founded by one of Seagate Technology's cofounders 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 drives and  backup equipment.
• 2003: Following the controversy over mass failures of its Deskstar 75GXP range, hard disk pioneer IBM sold the majority of its disk division to Hitachi, who renamed it  Hitachi Global Storage Technologies (HGST).
• 2005: Seagate and  Maxtor announce their intent to merge. US DoJ approval was given for Maxtor to be acquired by Seagate for US$1.9 billion,^[3] and  the merger closed in mid-2006.
• May 22, 2006: Seagate finally announced the completion of its acquisition of Maxtor. Seagate retains its name and  continues to be listed on the New York Stock Exchange as "STX." Maxtor common stock has ceased to trade on the NYSE. Somehow the acquisition created a temporary shortage of Maxtor-based hard disk globally.^[4]

[edit] See also

• Early IBM disk storage
• File system
• Hybrid drive
• PRML
• RK05
• Superparamagnetic effect
• Common Manufacturers: Seagate, Maxtor, Western Digital, Hitachi
• NCQ
• IDE
• SATA
• SCSI
• Data recovery

[edit] References

[edit] External links

Wikimedia Commons has media related to: Hard disk

• The Hard Disk That Changed The World
• TechEncyclopedia about Hard Disks
• Hard disk interfaces pinouts
• How Hard Disks Work
• Digest 2005 - State of the art hard disk drives in 2005
• War of the Disks: Hard Disk Drives vs. Flash Solid State Disks Despatches from the magneto / flash wars