A hard disk drive (HDD), hard disk, hard drive, or fixed disk,[b] is an electromechanical data storage device that uses magnetic storage to store and retrieve digital information using one or more rigid rapidly rotating disks (platters) coated with magnetic material. The platters are paired with magnetic heads, usually arranged on a moving actuator arm, which read and write data to the platter surfaces. Data is accessed in a random-access manner, meaning that individual blocks of data can be stored or retrieved in any order and not only sequentially. HDDs are a type of non-volatile storage, retaining stored data even when powered off.
Introduced by IBM in 1956, HDDs became the dominant secondary storage device for general-purpose computers by the early 1960s. Continuously improved, HDDs have maintained this position into the modern era of servers and personal computers. More than 200 companies have produced HDDs historically, though after extensive industry consolidation most units are manufactured by Seagate, Toshiba, and Western Digital. HDDs dominate the volume of storage produced (exabytes per year) for servers. Though production is growing slowly, sales revenues and unit shipments are declining because solid-state drives (SSDs) have higher data-transfer rates, higher areal storage density, better reliability, and much lower latency and access times.
The revenues for SSDs, most of which use NAND, slightly exceed those for HDDs. Though SSDs have nearly 10 times higher cost per bit, they are replacing HDDs in applications where speed, power consumption, small size, and durability are important.
The primary characteristics of an HDD are its capacity and performance. Capacity is specified in unit prefixes corresponding to powers of 1000: a 1-terabyte (TB) drive has a capacity of 1,000 gigabytes (GB; where 1 gigabyte = 1 billion bytes). Typically, some of an HDD's capacity is unavailable to the user because it is used by the file system and the computer operating system, and possibly inbuilt redundancy for error correction and recovery. Also there is confusion regarding storage capacity, since capacities are stated in decimal Gigabytes (powers of 10) by HDD manufacturers, whereas some operaring systems report capacities in binary Gibibytes, which results in a smaller number than advertised. Performance is specified by the time required to move the heads to a track or cylinder (average access time) adding the time it takes for the desired sector to move under the head (average latency, which is a function of the physical rotational speed in revolutions per minute), and finally the speed at which the data is transmitted (data rate).
The two most common form factors for modern HDDs are 3.5-inch, for desktop computers, and 2.5-inch, primarily for laptops. HDDs are connected to systems by standard interface cables such as PATA (Parallel ATA), SATA (Serial ATA), USB or SAS (Serial Attached SCSI) cables.
|Hard disk drive|
Internals of a 2.5-inch SATA hard disk drive
|Date invented||24 December 1954[a]|
|Invented by||IBM team led by Rey Johnson|
|Parameter||Started with (1957)||Developed to (2018)||Improvement|
|3.75 megabytes||15 terabytes||4-million-to-one|
|Physical volume||68 cubic feet (1.9 m3)[c]||2.1 cubic inches (34 cm3)[d]||56,000-to-one|
|Weight||2,000 pounds (910 kg)||2.2 ounces (62 g)||15,000-to-one|
|Average access time||approx. 600 milliseconds||2.5 ms to 10 ms; RW RAM dependent||about|
|Price||US$9,200 per megabyte (1961)||US$0.032 per gigabyte by 2015||300-million-to-one|
|Data density||2,000 bits per square inch||1.3 terabits per square inch in 2015||650-million-to-one|
|Average lifespan||c. 2000 hrs MTBF||c. 2,500,000 hrs (~285 years) MTBF||1250-to-one|
The first production IBM hard disk drive, the 350 disk storage, shipped in 1957 as a component of the IBM 305 RAMAC system. It was approximately the size of two medium-sized refrigerators and stored five million six-bit characters (3.75 megabytes) on a stack of 50 disks.
In 1962, the IBM 350 was superseded by the IBM 1301 disk storage unit, which consisted of 50 platters, each about 1/-inch thick and 24 inches in diameter. While the IBM 350 used only two read/write heads, the 1301 used an array of heads, one per platter, moving as a single unit. Cylinder-mode read/write operations were supported, and the heads flew about 250 micro-inches (about 6 µm) above the platter surface. Motion of the head array depended upon a binary adder system of hydraulic actuators which assured repeatable positioning. The 1301 cabinet was about the size of three home refrigerators placed side by side, storing the equivalent of about 21 million eight-bit bytes. Access time was about a quarter of a second.
Also, in 1962, IBM introduced the model 1311 disk drive, which was about the size of a washing machine and stored two million characters on a removable disk pack. Users could buy additional packs and interchange them as needed, much like reels of magnetic tape. Later models of removable pack drives, from IBM and others, became the norm in most computer installations and reached capacities of 300 megabytes by the early 1980s. Non-removable HDDs were called "fixed disk" drives.
Some high-performance HDDs were manufactured with one head per track (e.g. IBM 2305 in 1970) so that no time was lost physically moving the heads to a track. Known as fixed-head or head-per-track disk drives they were very expensive and are no longer in production.
In 1973, IBM introduced a new type of HDD code-named "Winchester". Its primary distinguishing feature was that the disk heads were not withdrawn completely from the stack of disk platters when the drive was powered down. Instead, the heads were allowed to "land" on a special area of the disk surface upon spin-down, "taking off" again when the disk was later powered on. This greatly reduced the cost of the head actuator mechanism, but precluded removing just the disks from the drive as was done with the disk packs of the day. Instead, the first models of "Winchester technology" drives featured a removable disk module, which included both the disk pack and the head assembly, leaving the actuator motor in the drive upon removal. Later "Winchester" drives abandoned the removable media concept and returned to non-removable platters.
Like the first removable pack drive, the first "Winchester" drives used platters 14 inches (360 mm) in diameter. A few years later, designers were exploring the possibility that physically smaller platters might offer advantages. Drives with non-removable eight-inch platters appeared, and then drives that used a 5 1⁄4 in (130 mm) form factor (a mounting width equivalent to that used by contemporary floppy disk drives). The latter were primarily intended for the then-fledgling personal computer (PC) market.
As the 1980s began, HDDs were a rare and very expensive additional feature in PCs, but by the late 1980s their cost had been reduced to the point where they were standard on all but the cheapest computers.
Most HDDs in the early 1980s were sold to PC end users as an external, add-on subsystem. The subsystem was not sold under the drive manufacturer's name but under the subsystem manufacturer's name such as Corvus Systems and Tallgrass Technologies, or under the PC system manufacturer's name such as the Apple ProFile. The IBM PC/XT in 1983 included an internal 10 MB HDD, and soon thereafter internal HDDs proliferated on personal computers.
External HDDs remained popular for much longer on the Apple Macintosh. Many Macintosh computers made between 1986 and 1998 featured a SCSI port on the back, making external expansion simple. Older compact Macintosh computers did not have user-accessible hard drive bays (indeed, the Macintosh 128K, Macintosh 512K, and Macintosh Plus did not feature a hard drive bay at all), so on those models external SCSI disks were the only reasonable option for expanding upon any internal storage.
Driven by ever increasing areal density, HDDs have continuously improved; a few highlights are listed in the table above. Market applications expanded through the 2000s, from the mainframe computers of the late 1950s to most mass storage applications including computers and consumer applications such as storage of entertainment content.
NAND performance is improving faster than HDDs, and applications for HDDs are eroding. In 2018, the largest hard drive had a capacity of 15TB while the largest capacity SSD had a capacity of 30.72TB or 100TB and HDDs are not expected to reach 100TB capacities until somewhere around 2025. Smaller form factors, 1.8-inches and below, were discontinued around 2010. The price of solid-state storage (NAND), represented by Moore's law, is improving faster than HDDs. NAND has a higher price elasticity of demand than HDDs, and this drives market growth. During the late 2000s and 2010s, the product life cycle of HDDs entered a mature phase, and slowing sales may indicate the onset of the declining phase. Relatively new technologies like HDMR, HAMR and MAMR, Bit patterned media and dual independent actuator arms increase the speed and capacity of HDDs and are expected to make HDDs more competitive with SSDs.
A modern HDD records data by magnetizing a thin film of ferromagnetic material[e] on a disk. Sequential changes in the direction of magnetization represent binary data bits. The data is read from the disk by detecting the transitions in magnetization. User data is encoded using an encoding scheme, such as run-length limited encoding,[f] which determines how the data is represented by the magnetic transitions.
A typical HDD design consists of a spindle that holds flat circular disks, also called platters, which hold the recorded data. The platters are made from a non-magnetic material, usually aluminum alloy, glass, or ceramic. They are coated with a shallow layer of magnetic material typically 10–20 nm in depth, with an outer layer of carbon for protection. For reference, a standard piece of copy paper is 0.07–0.18 mm (70,000–180,000 nm) thick.
The platters in contemporary HDDs are spun at speeds varying from 4,200 rpm in energy-efficient portable devices, to 15,000 rpm for high-performance servers. The first HDDs spun at 1,200 rpm and, for many years, 3,600 rpm was the norm. As of December 2013, the platters in most consumer-grade HDDs spin at either 5,400 rpm or 7,200 rpm.
Information is written to and read from a platter as it rotates past devices called read-and-write heads that are positioned to operate very close to the magnetic surface, with their flying height often in the range of tens of nanometers. The read-and-write head is used to detect and modify the magnetization of the material passing immediately under it.
In modern drives, 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 some older designs a stepper motor. Early hard disk drives wrote data at some constant bits per second, resulting in all tracks having the same amount of data per track but modern drives (since the 1990s) use zone bit recording – increasing the write speed from inner to outer zone and thereby storing more data per track in the outer zones.
In modern drives, the small size of the magnetic regions creates the danger that their magnetic state might be lost because of thermal effects — thermally induced magnetic instability which is commonly known as the "superparamagnetic limit". To counter this, the platters are coated with two parallel magnetic layers, separated by a three-atom layer of the non-magnetic element ruthenium, and the two layers are magnetized in opposite orientation, thus reinforcing each other. Another technology used to overcome thermal effects to allow greater recording densities is perpendicular recording, first shipped in 2005, and as of 2007 used in certain HDDs.
In 2004, a new concept was introduced to allow further increase of the data density in magnetic recording: the use of recording media consisting of coupled soft and hard magnetic layers. So-called exchange spring media magnetic storage technology, also known as exchange coupled composite media, allows good writability due to the write-assist nature of the soft layer. However, the thermal stability is determined only by the hardest layer and not influenced by the soft layer.
A typical HDD has two electric motors; a spindle motor that spins the disks and an actuator (motor) that positions the read/write head assembly across the spinning disks. The disk motor has an external rotor attached to the disks; the stator windings are fixed in place. Opposite the actuator at the end of the head support arm is the read-write head; thin printed-circuit cables connect the read-write heads to amplifier electronics mounted at the pivot of the actuator. The head support arm is very light, but also stiff; in modern drives, acceleration at the head reaches 550 g.
The actuator is a permanent magnet and moving coil motor that swings the heads to the desired position. A metal plate supports a squat neodymium-iron-boron (NIB) high-flux magnet. Beneath this plate is the moving coil, often referred to as the voice coil by analogy to the coil in loudspeakers, which is attached to the actuator hub, and beneath that is a second NIB magnet, mounted on the bottom plate of the motor (some drives have only one magnet).
The voice 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 is wound on a form, making it self-supporting. The portions of the coil along the two sides of the arrowhead (which point to the actuator bearing center) then interact with the magnetic field of the fixed magnet. Current flowing radially outward along one side of the arrowhead and radially inward on the other produces the tangential force. If the magnetic field were uniform, each side would generate opposing forces that would cancel each other out. Therefore, the surface of the magnet is half north pole and half south pole, with the radial dividing line in the middle, causing the two sides of the coil to see opposite magnetic fields and produce forces that add instead of canceling. Currents along the top and bottom of the coil produce radial forces that do not rotate the head.
The HDD'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. Feedback of the drive electronics is accomplished by means of special segments of the disk dedicated to servo feedback. These are either complete concentric circles (in the case of dedicated servo technology), or segments interspersed with real data (in the case of embedded servo technology). The servo feedback optimizes the signal to noise ratio of the GMR sensors by adjusting the voice-coil of the actuated arm. The spinning of the disk also uses a servo motor. Modern disk firmware is capable of scheduling reads and writes efficiently on the platter surfaces and remapping sectors of the media which have failed.
Modern drives make extensive use of error correction codes (ECCs), particularly Reed–Solomon error correction. These techniques store extra bits, determined by mathematical formulas, for each block of data; the extra bits allow many errors to be corrected invisibly. The extra bits themselves take up space on the HDD, but allow higher recording densities to be employed without causing uncorrectable errors, resulting in much larger storage capacity. For example, a typical 1 TB hard disk with 512-byte sectors provides additional capacity of about 93 GB for the ECC data.
In the newest drives, as of 2009, low-density parity-check codes (LDPC) were supplanting Reed–Solomon; LDPC codes enable performance close to the Shannon Limit and thus provide the highest storage density available.
Typical hard disk drives attempt to "remap" the data in a physical sector that is failing to a spare physical sector provided by the drive's "spare sector pool" (also called "reserve pool"), while relying on the ECC to recover stored data while the number of errors in a bad sector is still low enough. The S.M.A.R.T (Self-Monitoring, Analysis and Reporting Technology) feature counts the total number of errors in the entire HDD fixed by ECC (although not on all hard drives as the related S.M.A.R.T attributes "Hardware ECC Recovered" and "Soft ECC Correction" are not consistently supported), and the total number of performed sector remappings, as the occurrence of many such errors may predict an HDD failure.
The "No-ID Format", developed by IBM in the mid-1990s, contains information about which sectors are bad and where remapped sectors have been located.
Only a tiny fraction of the detected errors end up as not correctable. Examples of specified uncorrected bit read error rates include:
The worst type of errors are silent data corruptions which are errors undetected by the disk firmware or the host operating system; some of these errors may be caused by hard disk drive malfunctions while others originate elsewhere in the connection between the drive and the host.
The rate of areal density advancement was similar to Moore's law (doubling every two years) through 2010: 60% per year during 1988–1996, 100% during 1996–2003 and 30% during 2003–2010. Gordon Moore (1997) called the increase "flabbergasting," while observing later that growth cannot continue forever. Price improvement decelerated to −12% per year during 2010–2017, as the growth of areal density slowed. The rate of advancement for areal density slowed to 10% per year during 2010–2016, and there was difficulty in migrating from perpendicular recording to newer technologies.
As bit cell size decreases, more data can be put onto a single drive platter. In 2013, a production desktop 3 TB HDD (with four platters) would have had an areal density of about 500 Gbit/in2 which would have amounted to a bit cell comprising about 18 magnetic grains (11 by 1.6 grains). Since the mid-2000s areal density progress has increasingly been challenged by a superparamagnetic trilemma involving grain size, grain magnetic strength and ability of the head to write. In order to maintain acceptable signal to noise smaller grains are required; smaller grains may self-reverse (electrothermal instability) unless their magnetic strength is increased, but known write head materials are unable to generate a magnetic field sufficient to write the medium. Several new magnetic storage technologies are being developed to overcome or at least abate this trilemma and thereby maintain the competitiveness of HDDs with respect to products such as flash memory–based solid-state drives (SSDs).
In 2013, Seagate introduced one such technology, shingled magnetic recording (SMR). Additionally, SMR comes with design complexities that may cause reduced write performance. Other new recording technologies that, as of 2016, still remain under development include heat-assisted magnetic recording (HAMR), microwave-assisted magnetic recording (MAMR), two-dimensional magnetic recording (TDMR), bit-patterned recording (BPR), and "current perpendicular to plane" giant magnetoresistance (CPP/GMR) heads.
The rate of areal density growth has dropped below the historical Moore's law rate of 40% per year, and the deceleration is expected to persist through at least 2020. Depending upon assumptions on feasibility and timing of these technologies, the median forecast by industry observers and analysts for 2020 and beyond for areal density growth is 20% per year with a range of 10–30%. The achievable limit for the HAMR technology in combination with BPR and SMR may be 10 Tbit/in2, which would be 20 times higher than the 500 Gbit/in2 represented by 2013 production desktop HDDs. Seagate began sampling HAMR HDDs in 2018. They require a different architecture, with redesigned media and read/write heads, new lasers, and new near-field optical transducers.
The capacity of a hard disk drive, as reported by an operating system to the end user, is smaller than the amount stated by the manufacturer for several reasons: the operating system using some space, use of some space for data redundancy, and space use for file system structures. Also the difference in capacity reported in SI decimal prefixed units vs. binary prefixes can lead to a false impression of missing capacity.
Modern hard disk drives appear to their host controller as a contiguous set of logical blocks, and the gross drive capacity is calculated by multiplying the number of blocks by the block size. This information is available from the manufacturer's product specification, and from the drive itself through use of operating system functions that invoke low-level drive commands.
The gross capacity of older HDDs is calculated as the product of the number of cylinders per recording zone, the number of bytes per sector (most commonly 512), and the count of zones of the drive. Some modern SATA drives also report cylinder-head-sector (CHS) capacities, but these are not physical parameters because the reported values are constrained by historic operating system interfaces. The C/H/S scheme has been replaced by logical block addressing (LBA), a simple linear addressing scheme that locates blocks by an integer index, which starts at LBA 0 for the first block and increments thereafter. When using the C/H/S method to describe modern large drives, the number of heads is often set to 64, although a typical hard disk drive, as of 2013, has between one and four platters.
In modern HDDs, spare capacity for defect management is not included in the published capacity; however, in many early HDDs a certain number of sectors were reserved as spares, thereby reducing the capacity available to the operating system.
For RAID subsystems, data integrity and fault-tolerance requirements also reduce the realized capacity. For example, a RAID 1 array has about half the total capacity as a result of data mirroring, while a RAID 5 array with x drives loses 1/x of capacity (which equals to the capacity of a single drive) due to storing parity information. RAID subsystems are multiple drives that appear to be one drive or more drives to the user, but provide fault tolerance. Most RAID vendors use checksums to improve data integrity at the block level. Some vendors design systems using HDDs with sectors of 520 bytes to contain 512 bytes of user data and eight checksum bytes, or by using separate 512-byte sectors for the checksum data.
Some systems may use hidden partitions for system recovery, reducing the capacity available to the end user.
Data is stored on a hard drive in a series of logical blocks. Each block is delimited by markers identifying its start and end, error detecting and correcting information, and space between blocks to allow for minor timing variations. These blocks often contained 512 bytes of usable data, but other sizes have been used. As drive density increased, an initiative known as Advanced Format extended the block size to 4096 bytes of usable data, with a resulting significant reduction in the amount of disk space used for block headers, error checking data, and spacing.
The process of initializing these logical blocks on the physical disk platters is called low-level formatting, which is usually performed at the factory and is not normally changed in the field. High-level formatting writes data structures used by the operating system to organize data files on the disk. This includes writing partition and file system structures into selected logical blocks. For example, some of the disk space will be used to hold a directory of disk file names and a list of logical blocks associated with a particular file.
Examples of partition mapping scheme include Master boot record (MBR) and GUID Partition Table (GPT). Examples of data structures stored on disk to retrieve files include the File Allocation Table (FAT) in the DOS file system and inodes in many UNIX file systems, as well as other operating system data structures (also known as metadata). As a consequence, not all the space on an HDD is available for user files, but this system overhead is usually small compared with user data.
|Capacity advertised by manufacturers[g]||Capacity expected by some consumers[h]||Reported capacity|
|Windows[h]||macOS ver 10.6+[g]|
|100 GB||100,000,000,000||107,374,182,400||7.37%||93.1 GB||100 GB|
|1 TB||1,000,000,000,000||1,099,511,627,776||9.95%||931 GB||1,000 GB, 1,000,000 MB|
The total capacity of HDDs is given by manufacturers using SI decimal prefixes such as gigabytes (1 GB = 1,000,000,000 bytes) and terabytes (1 TB = 1,000,000,000,000 bytes). This practice dates back to the early days of computing; by the 1970s, "million", "mega" and "M" were consistently used in the decimal sense for drive capacity. However, capacities of memory are quoted using a binary interpretation of the prefixes, i.e. using powers of 1024 instead of 1000.
Software reports hard disk drive or memory capacity in different forms using either decimal or binary prefixes. The Microsoft Windows family of operating systems uses the binary convention when reporting storage capacity, so an HDD offered by its manufacturer as a 1 TB drive is reported by these operating systems as a 931 GB HDD. Mac OS X 10.6 ("Snow Leopard") uses decimal convention when reporting HDD capacity. The default behavior of the df command-line utility on Linux is to report the HDD capacity as a number of 1024-byte units.
The difference between the decimal and binary prefix interpretation caused some consumer confusion and led to class action suits against HDD manufacturers. The plaintiffs argued that the use of decimal prefixes effectively misled consumers while the defendants denied any wrongdoing or liability, asserting that their marketing and advertising complied in all respects with the law and that no class member sustained any damages or injuries.
HDD price per byte improved at the rate of −40% per year during 1988–1996, −51% per year during 1996–2003, and −34% per year during 2003–2010. The price improvement decelerated to −13% per year during 2011–2014, as areal density increase slowed and the 2011 Thailand floods damaged manufacturing facilities.
IBM's first hard drive, the IBM 350, used a stack of fifty 24-inch platters and was of a size comparable to two large refrigerators. In 1962, IBM introduced its model 1311 disk, which used six 14-inch (nominal size) platters in a removable pack and was roughly the size of a washing machine. This became a standard platter size and drive form-factor for many years, used also by other manufacturers. The IBM 2314 used platters of the same size in an eleven-high pack and introduced the "drive in a drawer" layout, although the "drawer" was not the complete drive.
Later drives were designed to fit entirely into a chassis that would mount in a 19-inch rack. Digital's RK05 and RL01 were early examples using single 14-inch platters in removable packs, the entire drive fitting in a 10.5-inch-high rack space (six rack units). In the mid-to-late 1980s the similarly sized Fujitsu Eagle, which used (coincidentally) 10.5-inch platters, was a popular product.
Such large platters were never used with microprocessor-based systems. With increasing sales of microcomputers having built in floppy-disk drives (FDDs), HDDs that would fit to the FDD mountings became desirable. Thus HDD Form factors, initially followed those of 8-inch, 5.25-inch, and 3.5-inch floppy disk drives. Although referred to by these nominal sizes, the actual sizes for those three drives respectively are 9.5″, 5.75″ and 4″ wide. Because there were no smaller floppy disk drives, smaller HDD form factors developed from product offerings or industry standards. 2.5-inch drives are actually 2.75″ wide.
As of 2012, 2.5-inch and 3.5-inch hard disks were the most popular sizes. By 2009, all manufacturers had discontinued the development of new products for the 1.3-inch, 1-inch and 0.85-inch form factors due to falling prices of flash memory, which has no moving parts. While nominal sizes are in inches, actual dimensions are specified in millimeters.
The factors that limit the time to access the data on an HDD are mostly related to the mechanical nature of the rotating disks and moving heads.
Seek time is a measure of how long it takes the head assembly to travel to the track of the disk that contains data. The first HDD had an average seek time of about 600 ms. Some early PC drives used a stepper motor to move the heads, and as a result had seek times as slow as 80–120 ms, but this was quickly improved by voice coil type actuation in the 1980s, reducing seek times to around 20 ms. Seek time has continued to improve slowly over time. The fastest server drives today have a seek time around 4 ms. The average seek time is strictly the time to do all possible seeks divided by the number of all possible seeks, but in practice is determined by statistical methods or simply approximated as the time of a seek over one-third of the number of tracks.
Rotational latency is incurred because the desired disk sector may not be directly under the head when data transfer is requested. Average rotational latency is shown in the table, based on the statistical relation that the average latency is one-half the rotational period.
The bit rate or data transfer rate (once the head is in the right position) creates delay which is a function of the number of blocks transferred; typically relatively small, but can be quite long with the transfer of large contiguous files.
Delay may also occur if the drive disks are stopped to save energy.
Defragmentation is a procedure used to minimize delay in retrieving data by moving related items to physically proximate areas on the disk. Some computer operating systems perform defragmentation automatically. Although automatic defragmentation is intended to reduce access delays, performance will be temporarily reduced while the procedure is in progress.
Time to access data can be improved by increasing rotational speed (thus reducing latency) or by reducing the time spent seeking. Increasing areal density increases throughput by increasing data rate and by increasing the amount of data under a set of heads, thereby potentially reducing seek activity for a given amount of data. The time to access data has not kept up with throughput increases, which themselves have not kept up with growth in bit density and storage capacity.
|Average rotational latency|
As of 2010, a typical 7,200-rpm desktop HDD has a sustained "disk-to-buffer" data transfer rate up to 1,030 Mbit/s. This rate depends on the track location; the rate is higher for data on the outer tracks (where there are more data sectors per rotation) and lower toward the inner tracks (where there are fewer data sectors per rotation); and is generally somewhat higher for 10,000-rpm drives. A current widely used standard for the "buffer-to-computer" interface is 3.0 Gbit/s SATA, which can send about 300 megabyte/s (10-bit encoding) from the buffer to the computer, and thus is still comfortably ahead of today's disk-to-buffer transfer rates. Data transfer rate (read/write) can be measured by writing a large file to disk using special file generator tools, then reading back the file. Transfer rate can be influenced by file system fragmentation and the layout of the files.
HDD data transfer rate depends upon the rotational speed of the platters and the data recording density. Because heat and vibration limit rotational speed, advancing density becomes the main method to improve sequential transfer rates. Higher speeds require a more powerful spindle motor, which creates more heat. While areal density advances by increasing both the number of tracks across the disk and the number of sectors per track, only the latter increases the data transfer rate for a given rpm. Since data transfer rate performance tracks only one of the two components of areal density, its performance improves at a lower rate.
Other performance considerations include quality-adjusted price, power consumption, audible noise, and both operating and non-operating shock resistance.
The Federal Reserve Board has a quality-adjusted price index for large-scale enterprise storage systems including three or more enterprise HDDs and associated controllers, racks and cables. Prices for these large-scale storage systems improved at the rate of ‒30% per year during 2004–2009 and ‒22% per year during 2009–2014.
Current hard drives connect to a computer over one of several bus types, including parallel ATA, Serial ATA , SCSI, Serial Attached SCSI (SAS), and Fibre Channel. Some drives, especially external portable drives, use IEEE 1394, or USB. All of these interfaces are digital; electronics on the drive process the analog signals from the read/write heads. Current drives present a consistent interface to the rest of the computer, independent of the data encoding scheme used internally, and independent of the physical number of disks and heads within the drive.
Typically a DSP in the electronics inside the drive takes the raw analog voltages from the read head and uses PRML and Reed–Solomon error correction to decode the 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.
Modern interfaces connect the drive to the host interface with a single data/control cable. Each drive also has an additional power cable, usually direct to the power supply unit. Older interfaces had separate cables for data signals and for drive control signals.
Due to the extremely close spacing between the heads and the disk surface, HDDs are vulnerable to being damaged by 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, contamination of the drive's internal enclosure, wear and tear, corrosion, or poorly manufactured platters and heads.
The HDD's spindle system relies on air density inside the disk enclosure to support the heads at their proper flying height while the disk rotates. HDDs require a certain range of air densities to operate properly. The connection to the external environment and density occurs through a small hole in the enclosure (about 0.5 mm in breadth), usually with a filter on the inside (the breather filter). If the air density 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 (9,800 ft). Modern disks include temperature sensors and adjust their operation to the operating environment. Breather holes can be seen on all disk drives – they usually have a sticker next to them, warning the user not to cover the holes. The air inside the operating drive 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 present for extended periods of time can corrode the heads and platters.
For 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).
When the logic board of a hard disk fails, the drive can often be restored to functioning order and the data recovered by replacing the circuit board with one of an identical hard disk. In the case of read-write head faults, they can be replaced using specialized tools in a dust-free environment. If the disk platters are undamaged, they can be transferred into an identical enclosure and the data can be copied or cloned onto a new drive. In the event of disk-platter failures, disassembly and imaging of the disk platters may be required. For logical damage to file systems, a variety of tools, including fsck on UNIX-like systems and CHKDSK on Windows, can be used for data recovery. Recovery from logical damage can require file carving.
A common expectation is that hard disk drives designed and marketed for server use will fail less frequently than consumer-grade drives usually used in desktop computers. However, two independent studies by Carnegie Mellon University and Google found that the "grade" of a drive does not relate to the drive's failure rate.
More than 200 companies have manufactured HDDs over time, but consolidations have concentrated production to just three manufacturers today: Western Digital, Seagate, and Toshiba. Production is mainly in the Pacific rim.
Worldwide revenue for disk storage declined 4% per year, from a peak of $38 billion in 2012 to $27 billion in 2016. Production of HDDs grew 16% per year, from 335 exabytes in 2011 to 693 exabytes in 2016. Shipments declined 7% per year during this time period, from 620 million units to 425 million. Seagate and Western Digital each have 40–45% of unit shipments, while Toshiba has 13–17%. The average sales price for the two largest manufacturers was $60 per unit in 2015.
HDDs are being superseded by SSDs in markets where their higher speed (up to 3500 megabytes per second for m.2 SSDs or 2500 megabytes per second for PCIe drives), ruggedness and lower power are more important than price since SSDs are sill twice as expensive than an HDD of the same capacity. They also have a relatively short lifespan (Enterprise HDDs can be rated for up to 550TB of read and/or write endurance per year of warranty where as SSDs are usually not) and their performance drops over time, because NAND flash memory, on which most SSDs are based, degrades with every write operation. The lifespan or write endurance of SSDs is measured by either Terabytes Written (TBW) or Drive Writes Per Day (DWPD). In the case of the latter, if a 1 TB drive is rated for 1 DWPD, and the drive has a 1-year warranty, the Terabytes Written will be equal to 365. Some SSDs offer larger capacities (up to 100 TB) than the largest HDD and/or higher storage densities (100 TB and 30 TB SSDs are housed in 2.5 inch HDD cases but with the same height as a 3.5-inch HDD ), although their cost remains prohibitive.
The maximum areal storage density for flash memory used in solid state drives (SSDs) is 2.8 Tbit/in2 in laboratory demonstrations as of 2016, and the maximum for HDDs is 1.5 Tbit/in2. The areal density of flash memory is doubling every two years, similar to Moore's law (40% per year) and faster than the 10–20% per year for HDDs. As of 2018, the maximum possible capacity was 16 terabytes for an HDD, and 100 terabytes for an SSD. HDDs were used in 70% of the desktop and notebook computers produced in 2016, and SSDs were used in 30%. The usage share of HDDs is declining and could drop below 50% in 2018–2019 according to one forecast, because SSDs are replacing smaller-capacity (less than one-terabyte) HDDs in desktop and notebook computers and MP3 players.
The market for silicon-based flash memory (NAND) chips, used in SSDs and other applications, is growing rapidly. Worldwide revenue grew 12% per year during 2011–2016. It rose from $22 billion in 2011 to $39 billion in 2016, while production grew 46% per year from 19 exabytes to 120 exabytes.
External hard disk drives typically connect via USB; variants using USB 2.0 interface generally have slower data transfer rates when compared to internally mounted hard drives connected through SATA. Plug and play drive functionality offers system compatibility and features large storage options and portable design. As of March 2015, available capacities for external hard disk drives ranged from 500 GB to 10 TB.
External hard disk drives are usually available as pre-assembled integrated products, but may be also assembled by combining an external enclosure (with USB or other interface) with a separately purchased drive. They are available in 2.5-inch and 3.5-inch sizes; 2.5-inch variants are typically called portable external drives, while 3.5-inch variants are referred to as desktop external drives. "Portable" drives are packaged in smaller and lighter enclosures than the "desktop" drives; additionally, "portable" drives use power provided by the USB connection, while "desktop" drives require external power bricks.
Features such as biometric security or multiple interfaces (for example, Firewire) are available at a higher cost. There are pre-assembled external hard disk drives that, when taken out from their enclosures, cannot be used internally in a laptop or desktop computer due to embedded USB interface on their printed circuit boards, and lack of SATA (or Parallel ATA) interfaces.
IBM 350 disk drive held 3.75 MB
Gordon Moore: ... the ability of the magnetic disk people to continue to increase the density is flabbergasting--that has moved at least as fast as the semiconductor complexity.
It can't continue forever. The nature of exponentials is that you push them out and eventually disaster happens.
The 2011 Thai floods almost doubled disk capacity cost/GB for a while. Rosenthal writes: 'The technical difficulties of migrating from PMR to HAMR, meant that already in 2010 the Kryder rate had slowed significantly and was not expected to return to its trend in the near future. The floods reinforced this.'
'PMR CAGR slowing from historical 40+% down to ~8-12%' and 'HAMR CAGR = 20-40% for 2015–2020'
Shingled Magnetic Technology is the First Step to Reaching a 20 Terabyte Hard Drive by 2020
A 'shingled magnetic recording' (SMR) drive is a rotating drive that packs its tracks so closely that one track cannot be overwritten without destroying the neighboring tracks as well. The result is that overwriting data requires rewriting the entire set of closely-spaced tracks; that is an expensive tradeoff, but the benefit—much higher storage density—is deemed to be worth the cost in some situations.
15–30% CAGR (est.) 2015 through early 2020s; HAMR, TDMR, BPM
page 11: Areal Density (Gbits/in^2) HDD Products 2010–2022 10-20%/year?
Annual Areal Density Growth Rate Scenarios: HDD 20%/yr 2012–2017
a slowing areal density curve … that slowed around 2010 and will advance areal density 25% annually till 2020.
Unfortunately, mass production of actual hard drives featuring HAMR has been delayed for a number of times already and now it turns out that the first HAMR-based HDDs are due in 2018. ... HAMR HDDs will feature a new architecture, require new media, completely redesigned read/write heads with a laser as well as a special near-field optical transducer (NFT) and a number of other components not used or mass produced today.
The LBAs on a logical unit shall begin with zero and shall be contiguous up to the last logical block on the logical unit.
Most disk drives use 512-byte sectors. [...] Enterprise drives (Parallel SCSI/SAS/FC) support 520/528 byte 'fat' sectors.
Example of a pre-assembled external hard disk drive without its enclosure that cannot be used internally on a laptop or desktop due to the embedded interface on its printed circuit board
The Amiga 600, also known as the A600 (codenamed "June Bug" after a B-52s song), is a home computer that was introduced at the CeBIT show in March 1992. The A600 is Commodore International's final model based on the Motorola 68000 CPU and the ECS chipset. It is essentially a redesign of the Amiga 500 Plus, with the option of an internal hard disk drive and a PCMCIA port. A notable aspect of the A600 is its small size. Lacking a numeric keypad, the A600 is only slightly larger than a standard PC keyboard (14" wide by 9.5" long by 3" high and weighing approximately 6 pounds). It shipped with AmigaOS 2.0, which was generally considered more user-friendly than earlier versions of the operating system.
Like the A500, the A600 was aimed at the lower end of the market, with the higher end being dominated by the Amiga 3000. It was intended by Commodore to revitalize sales of the A500-related line before the introduction of the 32-bit Amiga 1200. According to Dave Haynie, the A600 "was supposed to be 50–60 US$ cheaper than the A500, but it came in at about that much more expensive than the A500." This is supported by the fact that the A600 was originally to have been numbered the A300, positioning it as a lower-budget version of the A500+. In the event, the cost led the machine to be marketed as a replacement for the A500+, requiring a change of number. Early models feature motherboards and power supplies with the A300 designation.
The managing director of Commodore UK, David Pleasance, described the A600 as a "complete and utter screw-up". In comparison to the popular A500 it was considered unexpandable, did not improve on the A500's CPU, was more expensive, and lacked a numeric keypad meaning that some existing software such as flight simulators (such as Electronic Arts' F/A-18 Interceptor) and application software cannot be used without a numerical pad emulator.
An "A600HD" model was sold with an internal 2.5" ATA hard disk drive of either 20 or 40 MB. This model was marketed as a more "scholarly" version of a home computer, previously best known for its extensive range of games, and retailed at almost double the price of a standard A600. However, this hard disk support introduced some issues with existing Amiga software because the memory used for hard disk control prevented some memory-intensive titles from launching without disabling the hard drive (via the machine's inbuilt boot menu). Later models sold without a hard disk drive in the "Wild, Weird, and Wicked" bundle contained the A600HD label, but with the HD cradle and HD missing. These all have ROM version 37.350.
The A600 is the first Amiga model that was manufactured in the UK. The factory was in Irvine, Scotland, although some later examples were manufactured in Hong Kong. It was also manufactured in the Philippines.Apple ProFile
The ProFile was the first hard disk drive produced by Apple Computer, initially for use with the Apple III personal computer. The original model had a formatted capacity of 5 MB and connected to a special interface card that plugged into an Apple III slot. In 1983, Apple offered a ProFile interface card for the Apple II, with software support for Apple ProDOS and Apple Pascal.
Also in 1983, Apple introduced the Lisa computer, which was normally sold with a ProFile. The ProFile could be connected to the built-in parallel port of the Lisa, or to a port on an optional dual-port parallel interface card. Up to three such interface cards could be installed, so in principle up to seven ProFile drives could be used on a Lisa.
The 5 MB ProFile was Apple's first hard drive, and was introduced in September 1981 at a price of US$3,499. Later a 10 MB model was offered, but required an upgraded PROM/interface card to recognize the additional 5 MB.Internally, the ProFile consisted of a bare Seagate ST-506 stepper motor drive and mechanism, without the usual Seagate electronics, a digital and an analog circuit board designed and manufactured by Apple, and a power supply.
Later Lisa models could be configured with an internal 10 MB "Widget" voice-coil drive with a proprietary controller designed and built entirely by Apple, but the Widget was never offered as an external product for use with other Apple computers.
Apple did not offer another hard drive until it released the Hard Disk 20 designed specifically for the Macintosh 512K in September 1985 which could not be used on the Apple II or III families, or Lisa series. The ProFile could not be used on the Macintosh or the Apple IIc computer (for which Apple never offered an external hard disk drive of any kind).
By September 1986, the ProFile would be superseded by the introduction of the first cross-platform Hard Disk 20SC SCSI-based drive for the Macintosh and interface card for the Apple II family (excluding the IIc series, which had no SCSI interface of any kind) and Lisa/XL series.Disk image
A disk image, in computing, is a computer file containing the contents and structure of a disk volume or of an entire data storage device, such as a hard disk drive, tape drive, floppy disk, optical disc, or USB flash drive. A disk image is usually made by creating a sector-by-sector copy of the source medium, thereby perfectly replicating the structure and contents of a storage device independent of the file system. Depending on the disk image format, a disk image may span one or more computer files.
The file format may be an open standard, such as the ISO image format for optical disc images, or a disk image may be unique to a particular software application.
The size can be huge because it contains the contents of an entire disk. To reduce storage requirements, if an imaging utility is filesystem-aware it can omit copying unused space, and it can compress the used space.Disk partitioning
Disk partitioning or disk slicing is the creation of one or more regions on secondary storage, so that each region can be managed separately. These regions are called partitions. It is typically the first step of preparing a newly installed disk, before any file system is created. The disk stores the information about the partitions' locations and sizes in an area known as the partition table that the operating system reads before any other part of the disk. Each partition then appears to the operating system as a distinct "logical" disk that uses part of the actual disk. System administrators use a program called a partition editor to create, resize, delete, and manipulate the partitions.. Partitioning allows the use of different filesystems to be installed for different kinds of files. Separating user data from system data can prevent the system partition from becoming full and rendering the system unusable. Partitioning can also make backing up easier. A disadvantage is that it can be difficult to properly size partitions resulting in having one partition with much free space and another nearly totally allocated.Disk storage
Disk storage (also sometimes called drive storage) is a general category of storage mechanisms where data is recorded by various electronic, magnetic, optical, or mechanical changes to a surface layer of one or more rotating disks. A disk drive is a device implementing such a storage mechanism. Notable types are the hard disk drive (HDD) containing a non-removable disk, the floppy disk drive (FDD) and its removable floppy disk, and various optical disc drives (ODD) and associated optical disc media.
(The spelling disk and disc are used interchangeably except where trademarks preclude one usage, e.g. the Compact Disc logo. The choice of a particular form is frequently historical, as in IBM's usage of the disk form beginning in 1956 with the "IBM 350 disk storage unit").Hard disk drive failure
A hard disk drive failure occurs when a hard disk drive malfunctions and the stored information cannot be accessed with a properly configured computer.
A hard disk failure may occur in the course of normal operation, or due to an external factor such as exposure to fire or water or high magnetic fields, or suffering a sharp impact or environmental contamination, which can lead to a head crash.
Hard drives may also be rendered inoperable through data corruption, disruption or destruction of the hard drive's master boot record, or through malware deliberately destroying the disk's contents.Hard disk drive performance characteristics
Higher performance in hard disk drives comes from devices which have better performance characteristics. These devices include those with rotating media, hereby called rotating drives, i.e., hard disk drives (HDD), floppy disk drives (FDD), optical discs (DVD-RW / CD-RW), and it also covers devices without moving parts like solid-state drives (SSD). For SSDs, most of the attributes related to the movement of mechanical components are not applicable, but the device is actually affected by some other electrically based element that still causes a measurable delay when isolating and measuring that attribute. These performance characteristics can be grouped into two categories: access time and data transfer time (or rate).Hard disk drive platter
A hard disk drive platter (or disk) is the circular disk on which magnetic data is stored in a hard disk drive. The rigid nature of the platters in a hard drive is what gives them their name (as opposed to the flexible materials which are used to make floppy disks). Hard drives typically have several platters which are mounted on the same spindle. A platter can store information on both sides, requiring two heads per platter.Hybrid drive
In computing, a hybrid drive (solid state hybrid drive – SSHD) is a logical or physical storage device that combines a faster storage medium such as solid-state drive (SSD) with a higher-capacity hard disk drive (HDD). The intent is adding some of the speed of SSDs to the cost-effective storage capacity of traditional HDDs. The purpose of the SSD in a hybrid drive is to act as a cache for the data stored on the HDD, improving the overall performance by keeping copies of the most frequently used data on the faster SSD.
There are two main configurations for implementing hybrid drives: dual-drive hybrid systems and solid-state hybrid drives. In dual-drive hybrid systems, physically separate SSD and HDD devices are installed in the same computer, having the data placement optimization performed either manually by the end user, or automatically by the operating system through the creation of a "hybrid" logical device. In solid-state hybrid drives, SSD and HDD functionalities are built into a single piece of hardware, where data placement optimization is performed either entirely by the device (self-optimized mode), or through placement "hints" supplied by the operating system (host-hinted mode).List of Linux distributions that run from RAM
This is a list of Linux distributions that can be run entirely from the computer's RAM. That ability allows them to be very fast, since reading and writing data from/to RAM is much faster than on a hard disk drive. Many of these operating systems will load from a removable media such as a Live CD or a Live USB stick. A "frugal" install can also often be completed, allowing boot up from a hard disk drive instead.
This feature is implemented in live-initramfs and allows the user to run a live distro that does not run from ram by default by adding toram to the kernel boot parameters.Additionally some distributions can be configured to run from RAM, such as Ubuntu using the toram option included in the Casper scripts.List of defunct hard disk manufacturers
At least 221 companies were hard disk drive manufacturers in the past. Most of that industry has vanished through bankruptcy or mergers and acquisitions. None of the first four entrants continue in the industry today. As shown in the graphic surviving manufacturers are Seagate, Toshiba and Western Digital (WD) all of whom grew at least in part through mergers and acquisitions.Live CD
A live CD (also live DVD, live disc, or live operating system) is a complete bootable computer installation including operating system which runs directly from a CD-ROM or similar storage device into a computer's memory, rather than loading from a hard disk drive. A Live CD allows users to run an operating system for any purpose without installing it or making any changes to the computer's configuration. Live CDs can run on a computer without secondary storage, such as a hard disk drive, or with a corrupted hard disk drive or file system, allowing data recovery.
As CD and DVD drives have been steadily phased-out, live CD's have become less popular, being replaced by live USBs, which are equivalent systems written onto USB flash drives, which have the added benefit of having write-able storage. The functionality of a live CD is also available with a bootable live USB flash drive, or an external hard disk drive connected by USB. Many live CDs offer the option of persistence by writing files to a hard drive or USB flash drive.
Many Linux distributions make ISO images available for burning to CD or DVD. While open source Operating Systems can be used for free, some commercial software, such as Windows To Go requires a license to use. Many Live CDs are used for data recovery, computer forensics, disk imaging, system recovery and malware removal. The Tails operating system is aimed at preserving privacy and anonymity of its users, allowing them to work with sensitive documents without leaving a record on a computer's hard drive.Page cache
In computing, a page cache, sometimes also called disk cache, is a transparent cache for the pages originating from a secondary storage device such as a hard disk drive (HDD) or a solid-state drive (SSD). The operating system keeps a page cache in otherwise unused portions of the main memory (RAM), resulting in quicker access to the contents of cached pages and overall performance improvements. A page cache is implemented in kernels with the paging memory management, and is mostly transparent to applications.
Usually, all physical memory not directly allocated to applications is used by the operating system for the page cache. Since the memory would otherwise be idle and is easily reclaimed when applications request it, there is generally no associated performance penalty and the operating system might even report such memory as "free" or "available".
When compared to main memory, hard disk drive read/writes are slow and random accesses require expensive disk seeks; as a result, larger amounts of main memory bring performance improvements as more data can be cached in memory. Separate disk caching is provided on the hardware side, by dedicated RAM or NVRAM chips located either in the disk controller (in which case the cache is integrated into a hard disk drive and usually called disk buffer), or in a disk array controller. Such memory should not be confused with the page cache.PlayStation 2 Expansion Bay
The PlayStation 2 Expansion Bay is a 3.5" drive bay introduced with the model 30000 and 50000 PlayStation 2 (replacing the PCMCIA slot used in the models 10000, 15000, and 18000, and no longer present as of the model 70000) designed for the network adaptor and internal hard disk drive (HDD). These peripherals enhance the capabilities of the PS2 to allow online play and other features that were shown at E3 2001.PowerBook Duo 210
The PowerBook Duo 210 is a portable Notebook Personal Computer, manufactured by Apple Computer Inc and introduced in October 1992. Priced at US$2250, the PowerBook Duo 210 was the low end model of the 2 simultaneously released PowerBook Duos. (The other one, PowerBook Duo 230 was priced US$2610). PowerBook 160's specs are almost same for PowerBook Duo 210, except PowerBook Duo 210 has a smaller display (9.1 inch). Its case design is identical to PowerBook Duo 230, but it shipped with 25 MHz 68030, differs from 33 MHz 68030 (PowerBook Duo 230). The PowerBook Duo 210 had a 80MB SCSI Hard Disk Drive. It was Discontinued on October 21, 1993.PowerBook Duo 230
The PowerBook Duo 230 is a subnotebook personal computer introduced on October 19, 1992 by Apple Computer, Inc. Priced at US $2,610, the PowerBook Duo 230 was the high end model of the two simultaneously released PowerBook Duos, the lower end being the US $2,250 PowerBook Duo 210. With a 33 MHz Motorola 68030 microprocessor, 4 MB of RAM and an 80 or 120 MB SCSI hard disk drive, the PowerBook Duo 230 was nearly identical to the simultaneously released PowerBook 180 except for the smaller 9.1 inch greyscale "supertwist" passive-matrix LCD and the lack of a 68882 floating-point unit.
With the October 1993 introduction of the PowerBook Duo 250 and 270c, the 230 replaced the 210 in the entry level, eventually being discontinued entirely on July 27, 1994 shortly after the introduction of the 68040-based PowerBook Duo 280 and 280c.Volatile memory
Volatile memory, in contrast to non-volatile memory, is computer memory that requires power to maintain the stored information; it retains its contents while powered on but when the power is interrupted, the stored data is quickly lost.
Volatile memory has several uses including as primary storage. In addition to usually being faster than forms of mass storage such as a hard disk drive, volatility can protect sensitive information, as it becomes unavailable on power-down. Most of the general-purpose random-access memory (RAM) is volatile.Western Digital
Western Digital Corporation (abbreviated WDC, commonly known as Western Digital and abbreviated WD) is an American computer hard disk drive manufacturer and data storage company. It designs, manufactures and sells data technology products, including storage devices, data center systems and cloud storage services.
Western Digital has a long history in the electronics industry as an integrated circuit maker and a storage products company. It is also one of the larger computer hard disk drive manufacturers, along with its primary competitor Seagate Technology.