Mechanics
The stiff disk utilizes rigid rotating platters (disks). For each one platter has the two-dimensional charismatic surface in which digital information can be stored. References is written to the disk by transmitting an electromagnetic flux across an antenna or even read-write head that is very roughly the charismatic lesson, which successively changes its polarization due to the flux. the information may be review back by the page through-write head beinduce the magnetic fields cause electrical vary in the see-write head when it lives on top a platter.

the average strong disk cause project consists of the central axis or even spindle upon which the platters spin at a constant speed. Moving along & between the platters in a commons armature come scroll through-write heads, by having a single head for every platter face. A armature moves a heads radially through a platters when it spin, permitting both head access to the entireness of the platter.

A associated electronics control a movement of a scroll through-write armature & a rotation of the disk, & perform reads & write about require from either the disk controller. Modern cause electronics come capable of scheduling reads & writes with efficiency through a disk & remapping sectors of the disk which use at times failed.

Likewise, virtually all major disk drive & motherboard vender today support S.M.A.R.T. technology, by which at hand failures might typically become predicted, permitting a user to exist as alerted eventually to cease information loss.

A (mostly) sealed enclosure protects a cause internals from either dust, condensation, & more sources of contamination. A strong disk's scan-write heads fly in an air bearing (a cushion of air) sole nanometres above the disk surface. A disk surface & a cause's internal environment must so become saved immaculately filtered to halt damage from either fingerprints, hair, dust, smoke particles, etc. given a submicroscopic gap between a heads & disk.

the select few population suppose the disk cause contains a vacuum — this is incorrect, when a body relies in atmospheric pressure in a cause to trend lines a heads at their proper flying height when a disk is within motion. An additional most common misconception is that the winchester drive is entirely sealed. The stiff disk cause takes the certain range of atmospheric pressure sequentially to work properly. In case a atmospheric pressure is as well moo, a air may non exert plenty click on a flying head, a head may non become at the proper height, & there is a chance of head crashes & information loss. (Specially made sealed & pressurised causes come required for dependable high-high-level operation, above all about 10,000 feet. This doesn't use to pressurized enclosures, such as an airplane cabin.) Modern drives include temperature sensing element & adjust their operation to the operational environment.

Protective disk causes are non airtight. It have the permeable purification (a breather purification) between a top handle & in of a cause, to allow a pressure in & outside the cause to equalize when exclude dust & dirt. A purification as well allows wet in everyone's thoughts to enter a cause. Super high humidness season-year-around may stimulate accelerated get into of the cause's heads (by increasing stiction, or a tendency for the heads to stick to the disk surface, which stimulates physical damage to the disk & spindle motor). That you might look at these breather holes in tons causes -- it unremarkably have a admonitory sticker next to a babies, informing a user does'nt to handle the holes. A air inside a operational cause is constantly moving as well, existence swept in motion by friction sustaining a spinning disk platters. This air lives across an internal purification to dislodge any left contamination from either manufacture, any particles that will st& somehow entered a cause, and any particles generated by head crash.

Due to the highly close spacing of the heads & disk surface, any contamination of the understand-write heads or even disk platters can lead to the head crash — a failure of a disk in which a head scrapes through a platter surface, typically cram the thinly charismatic film. For GMR heads in particular, a minor head crash from either contamination (that doesn't dislodge a charismatic surface of a disk) may however symptom upstairs temporarily overheating, due to friction by having a disk surface, & renders the disk indecipherable until the head temperature stabilizes. Head crashes may be from either electronic failure, the sudden power failure, physical shock, put on & tear, or even ill made disks. Ordinarily, whenever powering down, a stiff disk moves its heads to the safe metropolitan area of the disk, in which there are no information is ever saved (the landing zone). All a same, especially around old system, sudden power interruptions or even a power supply failure potty effect in the cause fold by using the heads in the information zone, which increases the chance of information loss. Recently causes come designed such that a rotational inertia in a platters is utilized to safely park the heads in the outbreak of unexpected power loss. IBM pioneered causes by owning "head unloading" technology that lifts a stave off a platters onto "ramps" instead of getting a children rest on the platters, reducing the chance of stiction. More manufacturers too utilize this technology.

Spring tension from either a head mounting constantly pushes a heads towards a disk. When a disk is spinning, a heads come supported by an air bearing & case there is no contact have on. a sliders (a sectiin of a heads that come nighest to the disk & contain the pickup coil itself) come designed to dependably exist a total of landings & takeoffs from either the disk surface, though put on & tear on these tiny components in time will require its toll. Virtually all manufacturers project a sliders to live 50,000 call for rounds prior to a risk of damage in startup rises above 50%. Nevertheless, a decompose rate is non linear — while a cause is immature & hwhen fewer start/stop oscillations, it has a better risk of surviving a next startup than an older, higher-mileage cause (as the head literally drags along the cause's surface until a air bearing is established). E.g., a Maxtor DiamondMax series of desktop winchester drive come rated to 50,000 begin-prevent oscillations. This means that there is no failures attributed to the head-disk interface were seen prior to at least 50,000 begin-prevent rounds when you took researching.

Utilizing rigid platters & waterproofing the unit allows good deal tighter tolerances than inside a floppy disk. Consequently, arduous disks might store lot additional information than floppy disk, & access & transmit it sooner. Inside 2005, a average workstation hard disk might store between Eighty GB & 400 GB of information, rotate at 7,200 to 10,000 rpm, and have a serial transport rate of all over Fifty MB/s. A fastest workstation disk drive spin at 15,000 rev. Notebook disc drive, which are then physically little than their desktop counterparts, tend to become slower & use less capacity. Virtually all spin at exclusively 4,200 rev or even 5,400 rev, though a recently top system spin at 7,200 rev.

Access and interfaces
The protective disk is typically accessed ended one of the total of bus types, including ATA (IDE, EIDE), SCSI, FireWire/IEEE 1394, USB, and Fibre Channel. Around late 2002 Serial ATA was introduced.

Back in the times of the ST-506 interface, the information encoding scheme was also significant. A number 1 ST-506 disks utilized Modified Frequency Modulation (MFM) encoding (which is however utilized on the park "1.44 MB" (I.Iv MiB) 3.Fivesome-inch floppy disk), & ran at the information rate of Phoebe megabits per 2nd. Afterward, controllers applying 2,7 RLL (or merely "RLL") encryption increased this by half, to Vii.Pentad megabits by the 2nd; it besides increased cause capacity by half.

Numerous ST-506 interface causes were single qualified per manufacturer to start at a moo MFM information rate, when supplementary system (normally more expensive versions of a equivalent basic cause) were qualified to rerun at the higher RLL information rate. Within a few subjects, a cause was overengineered upright plenty to allow a MFM-qualified model to process at a sooner information rate; nonetheless, this was typically undependable & was non recommended. (An RLL-qualified cause may rerun in the MFM controller, however using 1/3 less information capacity & speed.)

ESDI as well supported multiple information rates (ESDI causes universally utilized 2,7 RLL, yet at Tenner, Fifteen or even even Xx megabits per 2nd), however this was normally negotiated automatically by the cause & controller; virtually all of the instance, however, Fifteen or Twenty megabit ESDI causes weren't downwards compatible (i personally.e. the Xv or even Twenty megabit cause wouldn't dog in the Tenner megabit controller). ESDI causes occasionally likewise experienced jumpers to placed a total of sectors by the track & (around occasionally lawsuits) sector size.

SCSI originally got good of these speed, V MHz (for the utmost information rate of Quint megabytes by the 2nd), however late this was increased dramatically. A SCSI bus speed experienced there are no bearing on the cause's internal speed because of buffering between a SCSI bus & a cause's internal informatiin bus; still, numbers of early causes experienced super little buffers, & so experienced to become reformatted to the different interleave (good like ST-506 causes) after utilized on slow computers, such as early IBM PC compatibles and Apple Macintoshes.

ATA causes keep close at h& generally experienced there are no problems by using interleave or even information rate, imputable their controller project, however numerous early system were incompatible by using every more and couldn't dog inside the master/slave setup (deuce causes on the equivalent cable). This was mostly remedied per mid-1990s, whenever ATA's specfication was standardised & a details begun to exist as filtered higher, however however stimulates problems at times (especially sustaining Video-ROM & DVD-ROM causes, & whenever mixing Ultra DMA & non-UDMA equipment).

Serial ATA does away by using master/slave setups totally, placing both cause in its have channel (using its have placed of I/O ports) instead.

FireWire/IEEE 1394 & USB(I.0/2.Cypher) difficult disks come external units containing usually ATA or even SCSI causes using ports on the back leaving super elementary & efficacious expansion & mobility. Virtually all FireWire/IEEE 1394 system come suspire to daisy-chain in order to continue adding peripheral device while forgoing requiring extra ports on the computer itself.

Other characteristics
Capacity (measured around g) Physical size (inches) About altogether strong disks in todays world come of either a Triad.Phoebe", used in desktops, or 2.5", utilized around laptop computer, kind. Two.Fivesome" drives are usually slower and have less capacity but use less power and are more tolerant of movement. Additionally, there is the CF form factor microdrive which is usually used as storage for portable devices such as mp3 players and digital cameras. The size designations can be slightly confusing, for example a 3.5" disk cause has the pack that is Quaternion" wide. Reliability: Mean Time Between Failures (MTBF) SATA 1.0 drives support speeds up to 10,000 rpm and mean time between failure (MTBF) levels up to 1 million hours under an eight-hour, low-duty cycle. Fibre Channel (FC) drives support up to 15,000 rpm and an MTBF of 1.4 million hours under a 24-hour duty cycle. Number of I/O operations per second Modern disks can perform around 50 random or 100 sequential OPS Power consumption (especially important in battery-powered laptops) audible noise (in dBA) G-shock rating (surprisingly high in modern drives)

Addressing modes
There are two modes of addressing the data blocks on more recent hard disks. The older mode is CHS addressing (Cylinder-Head-Sector), used on old ST-506 and ATA drives and internally by the PC BIOS. The more recent mode is the LBA (Logical Block Addressing), used by SCSI drives and newer ATA drives (ATA drives power up in CHS mode for historical reasons).

CHS describes the disk space in terms of its physical dimensions, data-wise; this is the traditional way of accessing a disk on IBM PC compatible hardware, and while it works well for floppies (for which it was originally designed) and small hard disks, it caused problems when disks started to exceed the design limits of the PC's CHS implementation. The traditional CHS limit was 1024 cylinders, 16 heads and 63 sectors; on a drive with 512-byte sectors, this comes to 504 MiB (528 megabytes). The origin of the CHS limit lies in a combination of the limitations of IBM's BIOS interface (which allowed 1024 cylinders, 256 heads and 64 sectors; sectors were counted from 1, reducing that number to 63, giving an addressing limit of 8064 MiB or 7.8 GiB), and a hardware limitation of the AT's hard disk controller (which allowed up to 65536 cylinders and 256 sectors, but only 16 heads, putting its addressing limit at 2^28 bits or 128 GiB).

When drives larger than 504 MiB began to appear in the mid-1990s, many system BIOSes had problems communicating with them, requiring LBA BIOS upgrades or special driver software to work correctly. Even after the introduction of LBA, similar limitations reappeared several times over the following years: at 2.1, 4.2, 8.4, 32, and 128 GiB. The 2.1, 4.2 and 32 GiB limits are hard limits: fitting a drive larger than the limit results in a PC that refuses to boot, unless the drive includes special jumpers to make it appear as a smaller capacity. The 8.4 and 128 GiB limits are soft limits: the PC simply ignores the extra capacity and reports a drive of the maximum size it is able to communicate with.

SCSI drives, however, have always used LBA addressing, which describes the disk as a linear, sequentially-numbered set of blocks. SCSI mode page commands can be used to get the physical specifications of the disk, but this is not used to read or write data; this is an artifact of the early days of SCSI, circa 1986, when a disk attached to a SCSI bus could just as well be an ST-506 or ESDI drive attached through a bridge (and therefore having a CHS configuration that was subject to change) as it could be a native SCSI device. Because PCs use CHS addressing internally, the BIOS code on PC SCSI host adapters does CHS-to-LBA translation, and provides a set of CHS drive parameters that tries to match the total number of LBA blocks as closely as possible.

ATA drives can either use their native CHS parameters (only on very early drives; hard drives made since the early 1990s use zone bit recording, and thus don't have a set number of sectors per track), use a "translated" CHS profile (similar to what SCSI host adapters provide), or run in ATA LBA mode, as specified by ATA-2. To maintain some degree of compatibility with older computers, LBA mode generally has to be requested explicitly by the host computer. ATA drives larger than 8 GiB are always accessed by LBA, due to the 8 GiB limit described above.

See also: hard disk drive partitioning, master boot record, file system, drive letter assignment, boot sector.

Manufacturers
Hitachi 2.5 inch laptop hard drive]] Most of the world's hard disks are now manufactured by just a handful of large firms: Seagate, Maxtor, Western Digital, Samsung, and the former drive manufacturing division of IBM, now owned by Hitachi. Fujitsu continues to make specialist notebook and SCSI drives but exited the mass market in 2001. Toshiba is a major manufacturer of 2.5-inch and 1.8-inch notebook drives.

Firms that have come and gone
Dozens of former hard drive manufacturers have gone out of business, merged, or closed their hard drive 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 International or CMI; after the 1985 incident with the faulty 20MB AT drives, CMI's reputation never recovered, and they exited the hard drive business in 1987. Another notable failure was MiniScribe, who went bankrupt in 1990 after it was found that they had "cooked a 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. Rodime was also an important manufacturer during the 1980s, but stopped making drives 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 drives.

There have also been a number of notable mergers in the hard disk industry: Tandon sold its disk manufacturing division to Western Digital (which was then a controller maker and ASIC house) in 1988; by the early 1990s Western Digital disks were among the top sellers. Quantum bought DEC's storage division in 1994, and later (2000) sold the hard disk division to Maxtor to concentrate on tape drives. In 1995, Conner Peripherals announced a merger with Seagate (who had earlier bought Imprimis from CDC), which completed in early 1996. JTS infamously merged with Atari in 1996, giving it the capital it needed to bring its drive range into production. In 2003, following the controversy over the mass failures of the Deskstar 75GXP range (which resulted in lost sales of its follow-ons), hard disk pioneer IBM sold the majority of its disk division to Hitachi, who renamed it Hitachi Global Storage Technologies.

"Marketing" capacity versus true capacity
It is important to note that hard drive manufacturers often use the metric definition of the prefixes "giga" and "mega." However, nearly all operating system utilities report capacities using binary definitions for the prefixes. This is largely historical, since when storage capacities started to exceed thousands of bytes, there were no standard binary prefixes (the IEC only standardized binary prefixes in 1999), so 2¹⁰ (1024) bytes was called a kilobyte because 1024 is "close enough" to the metric prefix kilo, which is defined as 10³ or 1000. This trend became habit and continued to be applied to the prefixes "mega," "giga," and even "tera." Obviously the discrepancy becomes much more noticeable in reported capacities in the multiple gigabyte range, and users will often notice that the volume capacity reported by their OS is significantly less than that advertised by the hard drive manufacturer. For example, a drive advertised as 200 GB can be expected to store close to 200 x 10⁹, or 200 billion, bytes. This uses the proper SI definition of "giga," 10⁹ and cannot be considered as incorrect. Since utilities provided by the operating system probably define a Gigabyte as 2³⁰, or 1073741824, bytes, the reported capacity of the drive will be closer to 186.26 GB (actually, GiB), a difference of well over ten gigabytes. For this very 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 not ambiguous.

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

Hard disk usage
From the original use of a hard drive in a single computer, techniques for guarding against hard disk failure were developed such as the redundant array of independent disks (RAID). Hard disks are also found in network attached storage (NAS) devices, but for large volumes of data are most efficiently used in a storage area network (SAN). Applications for hard disk drives expanded to include personal video recorders, digital audio players, digital organizers and digital cameras. In 2005 the first cellular telephones to include hard disk drives were introduced by Samsung and Nokia.

History
The first computer with a hard disk drive as standard was the IBM 350 Disk File, introduced in 1955 with the IBM 305 computer. This drive had fifty 24 inch platters, with a total capacity of five million characters. In 1952, an IBM engineer named Reynold Johnson developed a massive hard disk consisting of fifty platters, each two feet wide, that rotated on a spindle at 1200 rpm with read/write heads for the first database running RCAs Bismark computer.

In 1973, IBM introduced the 3340 "Winchester" disk system (the 30MB + 30 millisecond access time led the project to be named after the Winchester 30-30 rifle), the first to use a sealed head/disk assembly (HDA). Almost all modern disk drives now use this technology, and the term "Winchester" became a common description for all hard disks, though generally falling out of use during the 1990s.

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 or 14-inch platters, required an equipment rack or a large amount of floor space (especially the large removable-media drives, which were often referred to as "washing machines"), and in many cases needed special power hookups for 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 drive, with a capacity of 5 megabytes. In fact, in its factory configuration the original IBM PC (IBM 5150) was not equipped with a hard drive.

Most microcomputer hard disk drives 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" drives (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 drives became the system of choice on PCs, external hard drives 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; also, "toaster" Macs did not have easily accessible hard drive bays (or, in the case of the Mac Plus, any hard drive bay at all), so on those models, external SCSI disks were the only reasonable option. External SCSI drives were also popular with older microcomputers such as the Apple II series and the Commodore 64, 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 IEEE 1394 (FireWire) has made external disk systems popular among regular users once again, especially for users that move large amounts of data between two or more locations, and most hard disk makers now make their disks available in external cases.

The capacity of hard drives has grown exponentially over time. With early personal computers, a drive with a 20 megabyte capacity was considered large. In the latter half of the 1990s, hard drives with capacities of 1 gigabyte and greater became available. As of early 2005, the "little" desktop hard disk in production has a capacity of 40 gigabytes, while the largest-capacity internal drives are a half terabyte (500 gigabytes), with external drives at or exceeding one terabyte. As far as PC history is concerned, the major drive families have been MFM, RLL, ESDI, SCSI, IDE and EIDE, and now SATA. MFM drives required that the electronics on the "controller" be compatible with the electronics on the card — disks and controllers had to be compatible. RLL (Run Length Limited) was a way of encoding bits onto the platters that allowed for better density. Most RLL drives also needed to be "compatible" with the controllers that communicated with them. ESDI was an interface developed by Maxtor. It allowed for faster communication between the PC and the disk. SCSI (originally named SASI for Shugart (sic) Associates) or Small Computer System Interface was an early competitor with ESDI. When the price of electronics dropped (and because of a demand by consumers) the electronics that had been stored on the controller card was moved to the disk drive itself. This advance was known as "Integrated Cause Electronics" or IDE. Eventually, IDE manufacturers wanted the speed of IDE to approach the speed of SCSI drives. IDE drives were slower because they did not have as big a cache as the SCSI drives, and they could not write directly to RAM. IDE manufacturers attempted to close this speed gap by introducing Logical Block Addressing (LBA). These drives were known as EIDE. While EIDE was introduced, though, SCSI manufacturers continued to improve SCSI's performance. The increase in SCSI performance came at a price — its interfaces were more expensive. In order for EIDE's performance to increase (while keeping the cost of the associated electronics low), it was realized that the only way to do this was to move from "parallel" interfaces to "serial" interfaces, the result of which is the SATA interface. However, as of 2005, performance of SATA and PATA disks is comparable. Fibre channel (FC) interfaces are left to discussions of server drives.

Timeline of capacity and other technical improvements
(CS) denotes an improvement in the consumer market. 1950s
5KB hard drive 1960s
1970s
1980s
198? - 12 megabyte hard drive (CS) 1990s
1991 - 100 megabyte hard drive (CS) 1995 - 2 gigabyte hard drive (CS)

2000s
2005 - 0.5 terabyte hard drive (CS)