|Hard Disk Drive|
A hard disk drive with the metal cover removed.
|Date Invented:||September 13, 1956|
|Invented By:||An IBM team led by Rey Johnson|
A hard disk drive (HDD), commonly referred to as a hard drive, hard disk, or fixed disk drive, is a non-volatile storage device which stores digitally encoded data on rapidly rotating platters with magnetic surfaces. Events 509 BC - The Temple of Jupiter on Rome 's Capitoline Hill is dedicated on the ides of September Year 1956 ( MCMLVI) was a Leap year starting on Sunday (link will display full calendar of the Gregorian calendar. International Business Machines Corporation abbreviated IBM and nicknamed "Big Blue", is a multinational Computer Technology Reynold "Rey" Johnson (1906-1998 was an American inventor and computer pioneer In Computer hardware, a host controller, host adapter, or host bus adapter ( HBA) connects a host system (the Computer) to other A personal computer ( PC) is any Computer whose original sales price size and capabilities make it useful for individuals and which is intended to be operated A motherboard is the central or primary Printed circuit board (PCB making up a complex electronic system such as a modern Computer or Laptop AT Attachment with Packet Interface ( ATA/ATAPI) is a standard interface used to connect storage devices such as Hard disks Solid-state AT Attachment with Packet Interface ( ATA/ATAPI) is a standard interface used to connect storage devices such as Hard disks Solid-state Introduction A typical Serial Attached SCSI system consists of the following basic components An Initiator is a device that originates device service A server is a Computer dedicated to providing one or more services over a computer network typically through a request-response routine Fibre Channel, or FC, is a Gigabit -speed network technology primarily used for Storage networking. A market segment is a subgroup of people or organizations sharing one or more characteristics that cause them to have similar product needs A desktop computer is a Personal computer (PC in a form intended for regular use at a single location as opposed to a mobile Laptop or portable computer Mobile computing is a generic term describing one's ability to use technology while moving as opposed to Portable computers which are only practical for use while deployed in Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, is Computer memory that can retain the stored information A hard disk platter (or disk is a component of a Hard disk drive: it is the circular disk on which the magnetic data are stored In Physics, magnetism is one of the Phenomena by which Materials exert attractive or repulsive Forces on other Materials. Strictly speaking, "drive" refers to a device distinct from its medium, such as a tape drive and its tape, or a floppy disk drive and its floppy disk. Early HDDs had removable media; however, an HDD today is typically a sealed unit (except for a filtered vent hole to equalize air pressure) with fixed media. 
A HDD is a rigid-disk drive, although it is probably never referred to as such. By way of comparison, a so-called "floppy" drive (more formally, a diskette drive) has a disc that is flexible. Originally, the term "hard" was temporary slang, substituting "hard" for "rigid", before these drives had an established and universally-agreed-upon name. Some time ago, IBM's internal company term for an HDD was "file".
HDDs (introduced in 1956 as data storage for an IBM accounting computer) were originally developed for use with general purpose computers; see History of hard disk drives. Accountancy or accounting is the measurement statement or provision of assurance about financial information primarily used by Lenders managers, A computer is a Machine that manipulates data according to a list of instructions. The commercial usage of Hard disk drives began in 1956 with the shipment of an IBM 305 RAMAC system including IBM Model 350 disk storage.
In the 21st century, applications for HDDs have expanded to include digital video recorders, digital audio players, personal digital assistants, digital cameras and video game consoles. A digital video recorder ( DVR) or personal video recorder ( PVR) is a device that records video in a digital format to a Disk drive or other A digital audio player, more commonly referred to as an MP3 player, is a Consumer electronics device that stores organizes and plays audio files Some Many compact digital still cameras can record Sound and moving Video as well as still Photograph. In 2005 the first mobile phones to include HDDs were introduced by Samsung and Nokia. Samsung Electronics (SEC Hangul:삼성전자,,,) is the world's largest Consumer electronics company headquartered in Seocho Samsung Town in Nokia Corporation (pronunciation /'nɔkiɑ/),,) is a Finnish multinational Communications Corporation, headquartered  The need for large-scale, reliable storage, independent of a particular device, led to the introduction of configurations such as RAID arrays, network attached storage (NAS) systems and storage area network (SAN) systems that provide efficient and reliable access to large volumes of data. RAID — which stands for Redundant Array of Inexpensive Disks,or alternatively Redundant Array of Independent Disks (a less specific name and thus now the Network-attached storage ( NAS) is file-level Computer data storage connected to a Computer network providing data access to heterogeneous network clients In Information technology, a storage area network ( SAN) is an architecture to attach remote computer storage devices (such as Disk arrays tape libraries Note that although not immediately recognizable as a computer, all the aforementioned applications are actually embedded computing devices of some sort. An embedded system is a special-purpose Computer system designed to perform one or a few dedicated functions often with Real-time computing constraints
HDDs record data by magnetizing ferromagnetic material directionally, to represent either a 0 or a 1 binary digit. Ferromagnetism is the basic mechanism by which certain materials (such as Iron) form Permanent magnets and/or exhibit strong interactions with Magnets it A bit is a binary digit, taking a value of either 0 or 1 Binary digits are a basic unit of Information storage and communication They read the data back by detecting the magnetization of the material. A typical HDD design consists of a spindle which holds one or more flat circular disks called platters, onto which the data are recorded. A hard disk platter (or disk is a component of a Hard disk drive: it is the circular disk on which the magnetic data are stored The platters are made from a non-magnetic material, usually aluminum alloy or glass, and are coated with a thin layer of magnetic material. Older disks used iron(III) oxide as the magnetic material, but current disks use a cobalt-based alloy. Iron(III oxide —also known as ferric oxide, Hematite, red iron oxide, synthetic maghemite, colcothar, or simply Rust —is Cobalt (ˈkoʊbɒlt is a hard lustrous silver-grey Metal, a Chemical element with symbol Co.
The platters are spun at very high speeds (details follow). Information is written to a platter as it rotates past devices called read-and-write heads that operate very close (tens of nanometers in new drives) over the magnetic surface. Disk read/write heads are mechanisms that read Data from or write data to Disk drives The heads have gone through a number of changes over the years The read-and-write head is used to detect and modify the magnetization of the material immediately under it. There is one head for each magnetic platter surface on the spindle, mounted on a common arm. An actuator arm (or access arm) moves the heads on an arc (roughly radially) across the platters as they spin, allowing each head to access almost the entire surface of the platter as it spins. The arm is moved using a voice coil actuator or (in older designs) a stepper motor. A voice coil (consisting of a Bobbin, Collar and Winding) is the Coil of Wire attached to the apex of the cone of a Loudspeaker A stepper motor (or step motor) is a brushless, synchronous Electric Stepper motors were outside the head-disk chamber, and preceded voice-coil drives. The latter, for a while, had a structure similar to that of a loudspeaker; the coil and heads moved in a straight line, along a radius of the platters. The present-day structure differs in several respects from that of the earlier voice-coil drives, but the same interaction between the coil and magnetic field still applies, and the term is still used.
Older drives read the data on the platter by sensing the rate of change of the magnetism in the head; these heads had small coils, and worked (in principle) much like magnetic-tape playback heads, although not in contact with the recording surface. As data density increased, read heads using magnetoresistance (MR) came into use; the electrical resistance of the head changed according to the strength of the magnetism from the platter. Later development made use of spintronics; in these heads, the magnetoresistive effect was much greater that in earlier types, and was dubbed "giant" magnetoresistance (GMR). Spintronics (a Neologism meaning "spin transport electronics" also known as magnetoelectronics is an Emerging technology which exploits the intrinsic This refers to the degree of effect, not the physical size, of the head — the heads themselves are extremely tiny, and are too small to be seen without a microscope. GMR read heads are now commonplace.
HD heads are kept from contacting the platter surface by the air that is extremely close to the platter; that air moves at, or close to, the platter speed. The record and playback head are mounted on a block called a slider, and the surface next to the platter is shaped to keep it just barely out of contact. It's a type of air bearing.
The magnetic surface of each platter is conceptually divided into many small sub-micrometre-sized magnetic regions, each of which is used to encode a single binary unit of information. A micrometre ( American spelling: micrometer; symbol µm) is one millionth of a Metre, or equivalently one thousandth of a Millimetre In today's HDDs, each of these magnetic regions is composed of a few hundred magnetic grains. Each magnetic region forms a magnetic dipole which generates a highly localized magnetic field nearby. In physics there are two kinds of dipoles ( Hellènic: di(s- = two- and pòla = pivot hinge An electric dipole is a In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges The write head magnetizes a region by generating a strong local magnetic field. Early HDDs used an electromagnet both to generate this field and to read the data by using electromagnetic induction. An electromagnet is a type of Magnet in which the Magnetic field is produced by the flow of an electric current. Faraday's law of induction describes an important basic law of electromagnetism which is involved in the working of Transformers Inductors and many forms of Later versions of inductive heads included metal in Gap (MIG) heads and thin film heads. Thin films are thin material layers ranging from fractions of a Nanometre to several Micrometres in thickness In today's heads, the read and write elements are separate, but in close proximity, on the head portion of an actuator arm. The read element is typically magneto-resistive while the write element is typically thin-film inductive. Giant magnetoresistance (GMR is a quantum mechanical effect a type of Magnetoresistance effect observed in thin film structures composed of alternating Ferromagnetic 
In modern drives, the small size of the magnetic regions creates the danger that their magnetic state might be lost because of thermal effects. To counter this, the platters are coated with two parallel magnetic layers, separated by a 3-atom-thick layer of the non-magnetic element ruthenium, and the two layers are magnetized in opposite orientation, thus reinforcing each other. Ruthenium (ruːˈθiːniəm is a Chemical element that has the symbol Ru and Atomic number 44  Another technology used to overcome thermal effects to allow greater recording densities is perpendicular recording, first shipped in 2005, as of 2007 the technology was used in many HDDs. Perpendicular recording (or Perpendicular Magnetic Recording PMR is a technology for data recording on Hard disks It was first proven advantageous in 1976 by Shun-ichi
See File System for how operating systems access data on HDDs and other storage devices. In Computing, a file system (often also written as filesystem) is a method for storing and organizing Computer files and the data they contain to make
The motor has an external rotor; the stator windings are copper-colored. The spindle bearing is in the center. To the left of center is the actuator with a read-write head under the tip of its very end (near center); the orange stripe along the side of the arm, a thin printed-circuit cable, connects the read-write head to the hub of the actuator. The flexible, somewhat 'U'-shaped, ribbon cable barely visible below and to the left of the actuator arm is the flexible section, one end on the hub, that continues the connection from the head to the controller board on the opposite side.
The head support arm is very light, but also rigid; in modern drives, acceleration at the head reaches 250 gs. g-force (also G-force, g-load) is a measurement of an object's Acceleration expressed in g s
The silver-colored structure at the upper left is the top plate of the permanent-magnet and moving coil "motor" that swings the heads to the desired position. Beneath this plate is the moving coil, attached to the actuator hub, and beneath that is a thin neodymium-iron-boron (NIB) high-flux magnet. That magnet is mounted on the bottom plate of the "motor".
The coil, itself, is shaped rather like an arrowhead, and made of doubly-coated copper magnet wire. The inner layer is insulation, and the outer is thermoplastic, which bonds the coil together after it's wound on a form, making it self-supporting. Much of the coil, sides of the arrowhead, which points to the actuator bearing center, interacts with the magnetic field to develop a tangential force to rotate the actuator. Considering that current flows (at a given time) radially outward along one side of the arrowhead, and radially inward on the other, the surface of the magnet is half N pole, half S pole; the dividing line is midway, and radial.
Using rigid disks and sealing the unit allows much tighter tolerances than in a floppy disk drive. A floppy disk is an increasingly Obsolete data storage medium that is composed of a disk of thin flexible ("floppy" Magnetic storage medium encased Consequently, hard disk drives can store much more data than floppy disk drives and can access and transmit it faster. As of January 2008:
The exponential increases in disk space and data access speeds of HDDs have enabled the commercial viability of consumer products that require large storage capacities, such as digital video recorders and digital audio players. A digital video recorder ( DVR) or personal video recorder ( PVR) is a device that records video in a digital format to a Disk drive or other A digital audio player, more commonly referred to as an MP3 player, is a Consumer electronics device that stores organizes and plays audio files Some  In addition, the availability of vast amounts of cheap storage has made viable a variety of web-based services with extraordinary capacity requirements, such as free-of-charge web search, web archiving and video sharing (Google, Yahoo!, YouTube, etc. Google Inc is an American public corporation, earning revenue from advertising related to its Internet search, e-mail, online YouTube is a video sharing website where users can upload view and share Video clips YouTube was created in February 2005 by three former PayPal employees ).
The main way to decrease access time is to increase rotational speed, while the main way to increase throughput and storage capacity is to increase areal density. In Communication networks, such as Ethernet or Packet radio, throughput is the average rate of successful message delivery over a communication channel A vice president of Seagate Technology projects a future growth in disk density of 40% per year. Seagate ( is the world's largest manufacturer of hard drives and storage solutions  Access times have not kept up with throughput increases, which themselves have not kept up with growth in storage capacity. Access time is the time delay or latency between a request to an electronic system and the access being completed or the requested data returned
The first 3. 5" HDD marketed as able to store 1 TB was the Hitachi Deskstar 7K1000. The Deskstar is the name of a Product line of computer Hard drives It was originally produced by IBM until Hitachi bought IBM 's hard It contains five platters at approximately 200 GB each, providing 935. 5 GiB of usable space.  Hitachi has since been joined by Samsung (Samsung SpinPoint F1, which has 3 × 334 GB platters), Seagate and Western Digital in the 1 TB drive market. 
|Form factor||Width||Largest capacity||Platters (Max)|
|5. 25" FH||146 mm||47 GB (1998)||14|
|5. A drive bay is a standard-sized area for adding hardware to a computer The Millimetre ( American spelling: millimeter, symbol mm) is a unit of Length in the Metric system, equal to A gigabyte (derived from the SI prefix Giga-) is a unit of Information or Computer 25" HH||146 mm||19. A drive bay is a standard-sized area for adding hardware to a computer 3 GB (1998)||4|
|3. 5"||102 mm||1 TB (2007)||5|
|2. A terabyte (derived from the prefix Tera- and commonly abbreviated TB) is a measurement term for data storage capacity. 5"||69. 9 mm||500 GB (2008)||3|
|1. 8" (PCMCIA)||54 mm||160 GB (2007)|
|1. 8" (ATA-7 LIF)||53. Low-insertion-force sockets (LIF are integrated circuit sockets that are designed so the force required to insert or remove a package is low 8 mm|
|1. 3"||36. 4 mm||40 GB (2008)||1|
Capacity of a hard disk drive is usually quoted in gigabytes and terabytes. A gigabyte (derived from the SI prefix Giga-) is a unit of Information or Computer A terabyte (derived from the prefix Tera- and commonly abbreviated TB) is a measurement term for data storage capacity. Older HDDs quoted their smaller capacities in megabytes, the first drives for PCs being just 5 or 10 MB. A megabyte is a unit of Information or Computer storage equal to either 106 (1000000 Bytes or 220 (1048576 bytes depending on
The capacity of an HDD 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). Cylinder-head-sector, also known as CHS, was an early method for giving addresses to each physical block of data on a Hard disk drive. Drives with ATA interface bigger and more than eight gigabytes behave as if they were structured into 16383 cylinders, 16 heads, and 63 sectors, for compatibility with older operating systems. AT Attachment with Packet Interface ( ATA/ATAPI) is a standard interface used to connect storage devices such as Hard disks Solid-state Unlike in the 1980s, the cylinder, head, sector (C/H/S) counts reported to the CPU by a modern ATA drive are no longer actual physical parameters since the reported numbers are constrained by historic operating-system interfaces and with zone bit recording the actual number of sectors varies by zone. Zone Bit Recording ( ZBR) is used by Disk drives to store more sectors per track on outer tracks than on inner tracks Disks with SCSI interface address each sector with a unique integer number; the operating system remains ignorant of their head or cylinder count.
The old C/H/S scheme has been replaced by logical block addressing. Logical block addressing (LBA is a common scheme used for specifying the location of blocks of data stored on Computer storage devices generally Secondary storage In some cases, to try to "force-fit" the C/H/S scheme to large-capacity drives, the number of heads was given as 64, although no drive has anywhere near 32 platters.
Hard disk drive manufacturers specify disk capacity using the SI prefixes mega-, giga- and tera-, and their abbreviations M, G and T. An SI prefix (also known as a metric prefix) is a name or associated symbol that precedes a unit of measure (or its symbol to form a Decimal multiple or Mega- (symbol M) is an SI prefix in the SI system of units denoting a factor of 106, 1000000 (one Million For other meanings see Giga (disambiguation Giga- (symbol G is a prefix in the SI system of units denoting 109 teras- (symbol T) is a prefix in the SI system of units denoting 1012, or 1000000000000 (1 trillion Byte is typically abbreviated B.
Most operating-system tools report capacity using the same abbreviations but actually use binary prefixes. In computing binary prefixes are names or associated symbols that can precede a unit of measure (such as a Byte) to indicate multiplication by a power of two For instance, the prefix mega-, which normally means 106 (1,000,000), in the context of data storage can mean 220 (1,048,576), which is nearly 5% more. Mega- (symbol M) is an SI prefix in the SI system of units denoting a factor of 106, 1000000 (one Million Similar usage has been applied to prefixes of greater magnitude. This results in a discrepancy between the disk manufacturer's stated capacity and the apparent capacity of the drive when examined through most operating-system tools. The difference becomes even more noticeable (7%) for a gigabyte. For example, Microsoft Windows reports disk capacity both in decimal-based units to 12 or more significant digits and with binary-based units to three significant digits. Microsoft Windows is a series of Software Operating systems and Graphical user interfaces produced by Microsoft. 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 to arrive at 30 GB; however, because the utilities provided by Windows, Mac and some Linux distributions define a gigabyte as 1,073,741,824 bytes (230 bytes, often referred to as a gibibyte, or GiB), the operating system reports capacity of the disk drive as (only) 28. A gibibyte (a contraction of gi ga bi nary byte) is a unit of Information or Computer storage, abbreviated GiB. 0 GB.
The earliest “form factor” hard disk drives inherited their dimensions from floppy-disk drives (FDDs), so that either could be mounted in chassis slots, and thus the HDD form factors became colloquially named after the corresponding FDD types. A floppy disk is an increasingly Obsolete data storage medium that is composed of a disk of thin flexible ("floppy" Magnetic storage medium encased "Form factor" compatibility continued after the 3½ in size even though floppy disk drives with new smaller dimensions ceased to be offered.
Major manufacturers discontinued the development of new products for the 1-inch (=1. 3-inch) and 0. 85-inch form factors in 2007, due to falling prices of flash memory, although Samsung introduced in 2008 with the SpinPoint A1 another 1. 3-inch drive.
The inch-based nickname of all these form factors usually do not indicate any actual product dimension (which are specified in millimeters for more recent form factors), but just roughly indicate a size relative to disk diameters, in the interest of historic continuity.
Transfer rate As of 2008, the data transfer rate at the inner zone ranges from 44. 2 MB/s to 74. 5 MB/s, while the transfer rate at the outer zone ranges from 74. 0 MB/s to 111. 4 MB/s. In contrast, the first PC drives could manage only around 40 KiB/s.
Random access time (seek time) currently ranges from just under 5 ms for high-end server drives, to 15 ms for miniature drives, with the most common desktop type typically being around 9 ms. There has not been any significant improvement in this speed for some years. Some early PC drives used a worm-gear to move the heads, and as a result had access times as slow as 80 - 120 ms, but this was quickly improved by voice-coil type actuation in the late 1980s, seeing access times reduce to around 20 ms.
Power consumption has become increasingly important, not just in mobile devices such as laptops but also in server and desktop markets. In Electrical engineering, power consumption often refers to the Electrical energy over Time supplied to operate an Electrical appliance, although Increasing data center machine density has led to problems delivering sufficient power to devices, and getting rid of the waste heat subsequently produced, as well as environmental and electrical cost concerns (see green computing). Green computing is the study and practice of using computing resources efficiently Similar issues exist for large companies with thousands of desktop PCs. Smaller form factor drives often use less power than larger drives. One interesting development in this area is actively controlling the seek speed so that the head arrives at its destination only just in time to read the sector, rather than arriving as quickly as possible and then having to wait for the sector to come around (i. e. the rotational latency).
Audible noise (measured in dBA) is significant for certain applications, such as PVRs digital audio recording and quiet computers. A-weighting is the most commonly used of a family of curves defined in the International standard IEC616722003 and various national standards relating to the measurement of sound A quiet PC is a Personal computer that makes little Noise. Common uses for quiet PCs include video editing sound mixing home servers, and Home Low noise disks typically use fluid bearings, slower rotational speeds (usually 5,400rpm) and reduce the seek speed under load (AAM) to reduce audible clicks and crunching sounds. Drives in smaller form factors (e. g. 2. 5 inch) are often quieter than larger drives.
Shock resistance is especially important for mobile devices. Some laptops now include a motion sensor that parks the disk heads if the machine is dropped, hopefully before impact, to offer the greatest possible chance of survival in such an event.
Hard disk drives are accessed over one of a number of bus types, including parallel ATA (PATA, also called IDE or EIDE), Serial ATA (SATA), SCSI, Serial Attached SCSI (SAS), and Fibre Channel. AT Attachment with Packet Interface ( ATA/ATAPI) is a standard interface used to connect storage devices such as Hard disks Solid-state AT Attachment with Packet Interface ( ATA/ATAPI) is a standard interface used to connect storage devices such as Hard disks Solid-state Introduction A typical Serial Attached SCSI system consists of the following basic components An Initiator is a device that originates device service Fibre Channel, or FC, is a Gigabit -speed network technology primarily used for Storage networking. Bridge circuitry is sometimes used to connect hard disk drives to buses that they cannot communicate with natively, such as IEEE 1394 and USB. The IEEE 1394 interface is a serial bus Interface standard for high-speed communications and Isochronous real-time data transfer frequently
Back in the days of the ST-506 interface, the data encoding scheme was also important. The ST-506 was the first 525 inch Hard disk drive. Introduced in 1980 by Seagate Technology (then Shugart An encoder is a device used to change a signal (such as a Bitstream) or Data into a Code. The first ST-506 disks used Modified Frequency Modulation (MFM) encoding, and transferred data at a rate of 5 megabits per second. This article is about Modified Frequency Modulation For other uses of MFM see the MFM (disambiguation A megabit is a unit of Information or computer storage abbreviated Mbit (or Mb) Later on, controllers using 2,7 RLL (or just "RLL") encoding increased the transfer rate by 50%, to 7. Run length limited or RLL coding is a technique that is used to store data on recordable media 5 megabits per second; this also increased disk capacity by fifty percent.
Many ST-506 interface disk drives were only specified by the manufacturer to run at the lower MFM data rate, while other models (usually more expensive versions of the same basic disk drive) were specified to run at the higher RLL data rate. In some cases, a disk drive had sufficient margin to allow the MFM specified model to run at the faster RLL data rate; however, this was often unreliable and was not recommended. (An RLL-certified disk drive could run on a MFM controller, but with 1/3 less data capacity and speed. )
Enhanced Small Disk Interface (ESDI) also supported multiple data rates (ESDI disks always used 2,7 RLL, but at 10, 15 or 20 megabits per second), but this was usually negotiated automatically by the disk drive and controller; most of the time, however, 15 or 20 megabit ESDI disk drives weren't downward compatible (i. Enhanced Small Disk Interface (ESDI was a disc interface designed by Maxtor Corporation in the early 1980s to be a follow-on to the ST-506 interface e. a 15 or 20 megabit disk drive wouldn't run on a 10 megabit controller). ESDI disk drives typically also had jumpers to set the number of sectors per track and (in some cases) sector size.
SCSI originally had just one speed, 5 MHz (for a maximum data rate of five megabytes per second), but later this was increased dramatically. The SCSI bus speed had no bearing on the disk's internal speed because of buffering between the SCSI bus and the disk drive's internal data bus; however, many early disk drives had very small buffers, and thus had to be reformatted to a different interleave (just like ST-506 disks) when used on slow computers, such as early IBM PC compatibles and early Apple Macintoshes. IBM PC compatible computers are those generally similar to the original IBM PC, XT, and AT. Macintosh, commonly nicknamed Mac is a Brand name which covers several lines of Personal computers designed developed and marketed by Apple Inc
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). AT Attachment with Packet Interface ( ATA/ATAPI) is a standard interface used to connect storage devices such as Hard disks Solid-state
Serial ATA does away with master/slave setups entirely, placing each disk on its own channel (with its own set of I/O ports) instead.
FireWire/IEEE 1394 and USB(1. 0/2. 0) HDDs are external units containing generally ATA or SCSI disks with ports on the back allowing very simple and effective expansion and mobility. Most FireWire/IEEE 1394 models are able to daisy-chain in order to continue adding peripherals without requiring additional ports on the computer itself.
Notable families of disk interfaces include:
|Acronym or abbreviation||Meaning||Description|
|SASI||Shugart Associates System Interface||Historical predecessor to SCSI. Acronyms, initialisms, and alphabetisms are Abbreviations that are formed using the initial components in a phrase or name|
|SCSI||Small Computer System Interface||Bus oriented that handles concurrent operations. In Computer architecture, a bus is a subsystem that transfers data between computer components inside a Computer or between computers|
|SAS||Serial Attached SCSI||Improvement of SCSI, uses serial communication instead of parallel. Introduction A typical Serial Attached SCSI system consists of the following basic components An Initiator is a device that originates device service|
|ST-506||Historical Seagate interface. The ST-506 was the first 525 inch Hard disk drive. Introduced in 1980 by Seagate Technology (then Shugart|
|ST-412||Historical Seagate interface (minor improvement over ST-506). The ST-506 was the first 525 inch Hard disk drive. Introduced in 1980 by Seagate Technology (then Shugart|
|ESDI||Enhanced Small Disk Interface||Historical; backwards compatible with ST-412/506, but faster and more integrated. Enhanced Small Disk Interface (ESDI was a disc interface designed by Maxtor Corporation in the early 1980s to be a follow-on to the ST-506 interface|
|ATA||Advanced Technology Attachment||Successor to ST-412/506/ESDI by integrating the disk controller completely onto the device. AT Attachment with Packet Interface ( ATA/ATAPI) is a standard interface used to connect storage devices such as Hard disks Solid-state Incapable of concurrent operations.|
|SATA||Serial ATA||Modification of ATA, uses serial communication instead of parallel.|
Due to the extremely close spacing between the heads and the disk surface, any contamination of the read-write heads or platters can lead to a head crash — a failure of the disk in which the head scrapes across the platter surface, often grinding away the thin magnetic film and causing data loss. A head crash is a specific type of Hard disk failure, and occurs when the read-write head of a Hard disk drive touches its rotating platter Head crashes can be caused by electronic failure, a sudden power failure, physical shock, wear and tear, corrosion, or poorly manufactured platters and heads.
The HDD's spindle system relies on air pressure inside the enclosure to support the heads at their proper flying height while the disk rotates. An HDD requires a certain range of air pressures in order to operate properly. The connection to the external environment and pressure occurs through a small hole in the enclosure (about 0. 5 mm in diameter), usually with a carbon filter on the inside (the breather filter, see below). If the air pressure is too low, then there is not enough lift for the flying head, so the head gets too close to the disk, and there is a risk of head crashes and data loss. Specially manufactured sealed and pressurized disks are needed for reliable high-altitude operation, above about 3,000 m (10,000 feet). Note that modern commercial aircraft have a pressurized cabin, whose pressure altitude does not normally exceed 2,600 m(8,500 feet) - thus, ordinary hard drives can safely be used in flight. Cabin pressurization is the active pumping of compressed Air into an Aircraft cabin when flying at altitude to maintain a safe and comfortable environment for crew In Aviation, pressure altitude is the indicated altitude when an Altimeter is set to an agreed baseline pressure setting Modern disks include temperature sensors and adjust their operation to the operating environment. Breather holes can be seen on all disks — they usually have a sticker next to them, warning the user not to cover the holes. The air inside the operating disk is constantly moving too, being swept in motion by friction with the spinning platters. This air passes through an internal recirculation (or "recirc") filter to remove any leftover contaminants from manufacture, any particles or chemicals that may have somehow entered the enclosure, and any particles or outgassing generated internally in normal operation. Very high humidity for extended periods can corrode the heads and platters.
For giant magnetoresistive (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). Giant magnetoresistance (GMR is a quantum mechanical effect a type of Magnetoresistance effect observed in thin film structures composed of alternating Ferromagnetic
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. The disk controller (or "hard disk controller" is the circuit which allows the CPU to communicate with a Hard disk, Floppy disk or Modern disk firmware is capable of scheduling reads and writes efficiently on the platter surfaces and remapping sectors of the media which have failed.
Most HDDs prevent power interruptions from shutting the drive down with its heads landing in the data zone by either moving the heads to a landing zone or unloading (i. e. , load/unload) the heads.
A landing zone is an area of the platter usually near its inner diameter (ID), where no data is stored. This area is called the Contact Start/Stop (CSS) zone. Disks are designed such that either a spring or, more recently, rotational inertia in the platters is used to park the heads in the case of unexpected power loss. The vis insita or innate force of matter is a power of resisting by which every body as much as in it lies endeavors to preserve in its present state whether it be of rest or of moving In this case, the spindle motor temporarily acts as a generator, providing power to the actuator.
Spring tension from the head mounting constantly pushes the heads towards the platter. While the disk is spinning, the heads are supported by an air bearing and experience no physical contact or wear. In CSS drives the sliders carrying the head sensors (often also just called heads) are designed to survive a number of landings and takeoffs from the media surface, though wear and tear on these microscopic components eventually takes its toll. Most manufacturers design the sliders to survive 50,000 contact cycles before the chance of damage on startup rises above 50%. However, the decay rate is not linear: when a disk is younger and has had fewer start-stop cycles, it has a better chance of surviving the next startup than an older, higher-mileage disk (as the head literally drags along the disk's surface until the air bearing is established). For example, the Seagate Barracuda 7200. 10 series of desktop hard disks are rated to 50,000 start-stop cycles, in other words no failures attributed to the head-platter interface were seen before at least 50,000 start-stop cycles during testing. 
Around 1995 IBM pioneered a technology where a landing zone on the disk is made by a precision laser process (Laser Zone Texture = LZT) producing an array of smooth nanometer-scale "bumps" in a landing zone, thus vastly improving stiction and wear performance. Stiction is an informal Portmanteau of the term "static Friction " ( μ s perhaps also influenced by the verb " stick This technology is still largely in use today (2007), predominantly in desktop and enterprise (3. 5 inch) drives. In general, CSS technology can be prone to increased stiction (the tendency for the heads to stick to the platter surface), e. g. as a consequence of increased humidity. Excessive stiction can cause physical damage to the platter and slider or spindle motor.
Load/Unload technology relies on the heads being lifted off the platters into a safe location, thus eliminating the risks of wear and stiction altogether. The first HDD RAMAC and most early disk drives used complex mechanisms to load and unload the heads. The IBM 305 RAMAC was the first commercial computer that used a moving head hard disk drive (magnetic Disk storage) for Secondary storage. Modern HDDs use ramp loading, first introduced by Memorex in 1967, to load/unload onto plastic "ramps" near the outer disk edge.
All HDDs today still use one of these two technologies. Each has a list of advantages and drawbacks in terms of loss of storage area on the disk, relative difficulty of mechanical tolerance control, cost of implementation, etc.
Addressing shock robustness, IBM also created a technology for their ThinkPad line of laptop computers called the Active Protection System. International Business Machines Corporation abbreviated IBM and nicknamed "Big Blue", is a multinational Computer Technology ThinkPad is a brand of portable Laptop and Notebook Personal computers originally designed manufactured and sold by IBM. When a sudden, sharp movement is detected by the built-in accelerometer in the Thinkpad, internal hard disk heads automatically unload themselves to reduce the risk of any potential data loss or scratch defects. An accelerometer is a device for measuring Acceleration and gravity induced reaction forces Apple later also utilized this technology in their PowerBook, iBook, MacBook Pro, and MacBook line, known as the Sudden Motion Sensor. Apple Inc, ( formerly Apple Computer Inc, is an American Multinational corporation with a focus on designing and manufacturing Consumer electronics The PowerBook is a line of Macintosh Laptop Computers that was designed manufactured and sold by Apple Computer Inc The iBook is a line of Laptop computer that was developed and sold by Apple Computer Inc The MacBook Pro is a line of Macintosh portable Computers by Apple Inc The MacBook is a Macintosh Notebook computer by Apple Inc that replaced the iBook G4 series The Sudden Motion Sensor (SMS is Apple 's patent-pending motion-based hardware and data-protection system used in their notebook computer systems. Toshiba has released similar technology in their laptops. ( is a multinational conglomerate manufacturing company headquartered in Tokyo, Japan. 
Most major hard disk and motherboard vendors now support self-monitoring, analysis and reporting technology (S. M. A. R. T. ), which attempts to alert users to impending failures.
However, not all failures are predictable. Normal use eventually can lead to a breakdown in the inherently fragile device, which makes it essential for the user to periodically back up the data onto a separate storage device. Failure to do so will lead to the loss of data. While it may sometimes be possible to recover lost information, it is normally an extremely costly procedure, and it is not possible to guarantee success. A 2007 study published by Google suggested very little correlation between failure rates and either high temperature or activity level. Google Inc is an American public corporation, earning revenue from advertising related to its Internet search, e-mail, online  While several S. M. A. R. T. parameters have an impact on failure probability, a large fraction of failed drives do not produce predictive S. M. A. R. T. parameters.  S. M. A. R. T. parameters alone may not be useful for predicting individual drive failures. 
A common misconception is that a colder hard drive will last longer than a hotter hard drive. The Google study showed the reverse -- "lower temperatures are associated with higher failure rates". Hard drives with S. M. A. R. T. -reported average temperatures below 27 C had failure rates worse than hard drives with the highest reported average temperature of 50 C, failure rates at least twice as high as the optimum S. M. A. R. T. -reported temperature range of 36 C to 47 C. 
SCSI, SAS and FC drives are typically more expensive and are traditionally used in servers and disk arrays, whereas inexpensive ATA and SATA drives evolved in the home computer market and were perceived to be less reliable. A disk array is a Disk storage system which contains multiple Disk drives It is differentiated from a Disk enclosure, in that an array has Cache A home computer was a class of Personal computer entering the market in 1977 and becoming common during the 1980s This distinction is now becoming blurred.
The mean time between failures (MTBF) of SATA drives is usually about 600,000 hours (some drives such as Western Digital Raptor have rated 1. Mean time between failures (MTBF is the Mean (average time between Failures of a system and is often considered the "useful life" of the device i The Western Digital Raptor (often marketed as WD Raptor) is an Upmarket, enterprise-class Hard disk drive series produced by Western Digital 2 million hours MTBF), while SCSI drives are rated for upwards of 1. 5 million hours. However, independent research indicates that MTBF is not a reliable estimate of a drive's longevity.  MTBF is conducted in laboratory environments in test chambers and is an important metric to determine the quality of a disk drive before it enters high volume production. Once the drive product is in production, the more valid metric is annualized failure rate (AFR). Annualized failure rate ( AFR) is the relation between the mean time between failure ( MTBF) and the assumed hours that a device is run per year expressed in percent AFR is the percentage of real-world drive failures after shipping.
SAS drives are comparable to SCSI drives, with high MTBF and high reliability.
Enterprise SATA drives designed and produced for enterprise markets, unlike standard SATA drives, have reliability comparable to other enterprise class drives.
Typically enterprise drives (all enterprise drives, including SCSI, SAS, enterprise SATA and FC) experience between 0. 70%-0. 78% annual failure rates from the total installed drives.
The technological resources and know-how required for modern drive development and production mean that as of 2007, over 98% of the world's HDDs are manufactured by just a handful of large firms: Seagate (which now owns Maxtor), Western Digital, Samsung, and Hitachi (which owns the former disk manufacturing division of IBM). It has been estimated that over 200 companies were hard disk drive manufacturers at one time or another Seagate ( is the world's largest manufacturer of hard drives and storage solutions Maxtor Corporation was an American manufacturer of computer Hard disk drives founded in 1982 and acquired by Seagate in 2006 Western Digital Corporation ( (often abbreviated to WD) is a manufacturer of computer hard disk drives, and has a long history in the electronics industry as Samsung Electronics (SEC Hangul:삼성전자,,,) is the world's largest Consumer electronics company headquartered in Seocho Samsung Town in () is a Multinational corporation specializing in high-technology and services headquartered in Marunouchi Itchome Chiyoda, Tokyo, Japan. International Business Machines Corporation abbreviated IBM and nicknamed "Big Blue", is a multinational Computer Technology Fujitsu continues to make mobile- and server-class disks but exited the desktop-class market in 2001. is a Japanese company specializing in Semiconductors Computers ( Supercomputers Personal computers, servers, Telecommunications Toshiba is a major manufacturer of 2. ( is a multinational conglomerate manufacturing company headquartered in Tokyo, Japan. 5-inch and 1. 8-inch notebook disks. ExcelStor is a small HDD manufacturer. ExcelStor ( Chinese:易拓 is a small Hard disk drive manufacturer established in 2000
Dozens of former HDD manufacturers have gone out of business, merged, or closed their HDD divisions; as capacities and demand for products increased, profits became hard to find, and the market underwent significant consolidation in the late 1980s and late 1990s. The first notable casualty of the business in the PC era was Computer Memories Inc. or CMI; after an incident with faulty 20 MB AT disks in 1985, CMI's reputation never recovered, and they exited the HDD business in 1987. Computer Memories Inc (CMI was a Chatsworth California manufacturer of Hard disks during the early 1980s Another notable failure was MiniScribe, who went bankrupt in 1990 after it was found that they had engaged in accounting fraud and inflated sales numbers for several years. MiniScribe was a manufacturer of Disk storage products founded in Longmont Colorado in 1980. 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 HDDs in India. Kalok was a Hard disk drive manufacturer which went bankrupt in 1994. Micropolis Corporation was a disk drive company located in Chatsworth California. JT Storage (also known as JTS Corporation) was a maker of inexpensive IDE Hard drives for Personal computers based in San Jose California India, officially the Republic of India (भारत गणराज्य inc-Latn Bhārat Gaṇarājya; see also other Indian languages) is a country Their claim to fame was creating a new 3" form factor drive for use in laptops. Quantum and Integral also invested in the 3" form factor; but eventually gave up as this form factor failed to catch on. 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. Rodime was an Electronics company specialising in Hard disks based in Glenrothes, Scotland. 5-inch form factor HDDs.