Monitor Nib

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Monitor Nib

HDD

History

Main article: History of hard disks

HDDs (introduced in 1956 as data storage accountability for IBM computer) were originally developed for use with general purpose computers. During the 1990s, the need for large, reliable storage, independent of a particular device, led to the introduction of embedded systems such the raids, Network Attached Storage (NAS) systems and storage area network (SAN) systems that provide reliable and efficient access to large volumes of data. In the 21st century, the hard disk usage expanded in consumer applications such as camcorders, cell phones (eg the Nokia N91), digital audio players, digital video players, digital video recorders, personal digital assistants and consoles video games.

Technology

Diagram of a computer's hard disk

save hard drive data by magnetizing ferromagnetic material directionally, to represent a 0 or a binary digit 1. They read back data by detecting the magnetization of the material. A typical design consists of a hard disk spindle that holds one or more circular flat disks called platters on which data are recorded. The dishes are made of nonmagnetic material, usually aluminum alloy or glass and are coated with a thin layer of material magnetic, typically 1020 nm thick reference standard paper may be between 0.07 mm (70 000 nm) and 0.18 mm (180,000 nm) thick. with an outer layer of carbon for protection. Older disks used iron (III) oxide as the magnetic material, but current disks use a cobalt based alloy. [Citation needed]

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

The plates are spun at high speed. Information is written in a flat formerly known rotation devices read and write heads that operate very close (a few tens of nanometers new readers) on the surface magnetic. Reading and writing head is used to detect and modify the magnetization of the material immediately beneath it. There is a head for each magnetic platter surface on the axis, mounted on a common arm. A control arm (or access arm) moves the head in an arc (Roughly radially) across the platters as they spin, allowing each head to access almost the entire surface of the plate while running. The arm is moved using a voice coil actuator or in some older models, a stepper motor.

The magnetic surface of each platter is conceptually divided into several small sub-micron magnetic regions, each of which is used to encode a single binary unit of information. Initially, the regions have been oriented horizontally, but starting around 2005, the orientation was changed to the perpendicular. Due to the polycrystalline nature of the magnetic material each of these magnetic regions is composed of several hundred of magnetic grains. magnetic grains are typically 10 nm size and shape of each single magnetic domain. Each magnetic region forms total magnetic dipole which generates a highly localized magnetic field nearby. A write head magnetized region generating a strong local magnetic field. At the beginning of hard drives used both an electromagnet to magnetize the region and to read his magnetic field using electromagnetic induction. Later versions of inductive heads included metal in Gap (MIG) heads and heads film thin. As the increased density of data, read heads using magnetoresistance (MR) entered service, the electrical resistance of The lead changed depending on the strength of the magnetism of the plateau. Later development made use of spintronics in these heads, the magnetoresistive effect was much greater than in earlier types, and was dubbed "giant" magnetoresistance (GMR). Inside the mind of today read and write elements are separate, but nearby on the head portion of a control arm. The scan element is generally magneto-resistive while the write element is typically thin film inductive.

HD heads are kept in contact with the surface of the plate by the air which is extremely close to the plateau, as the air moves at, or near, the platter speed. [Citation needed] The record and playback head are mounted on a block called a slider, and the surface near the top is shaped to keep it just out of contact. It is a type of air cushion.

In modern disks, the small size of the magnetic regions creates the danger that their magnetic state can be lost due to thermal effects. To counter this, the plates are coated with two parallel magnetic layers separated by a 3-atom layer thick, the non-magnetic element ruthenium, and the two layers are magnetized in opposite direction, reinforcing one another. Another technology used to overcome thermal effects to allow greater recording densities is perpendicular recording, first shipped in 2005 and from 2007 the technology was used in many hard drives.

This section may require cleanup to meet standards quality of Wikipedia. Please improve this section if you can. (December 2009)

The grain boundaries will be very important in the design of hard disk. The grains are very small and close to each other, so that the coupling between adjacent grains is very strong. When a grain is magnetized, adjacent grains tend to be parallel to it or demagnetized. Then both data stability and signal to noise ratio will be sabotaged. A clear grain boundary can weaken the coupling of the grains and subsequently increase the signal to noise ratio. In longitudinal recording, the grains have a single domain uniaxial anisotropy with easy axes lying in the film plane. The consequence of this arrangement is that the magnets repel each other adjacent. Therefore, energy magnetostatics is so great that it is difficult to increase the areal density. perpendicular recording media, on the other hand, has the easy axis of grain oriented perpendicular to the plane of the disk. adjacent magnets attract to each level of energy and other magnetostatic are much lower. Thus, the surface density much higher than can be achieved in perpendicular recording. Another feature Single perpendicular recording is a sub-layer that are embedded in soft magnetic disk recording. This sub-layer is used to conduct writing magnetic flux, so that writing is more effective. This will be discussed in the writing process. Therefore, a film over medium anisotropy, such as L10-FePt and rare earth magnets can be used.

Error Handling

Modern also causes make extensive use of error correcting codes (ECC), in particular the correction of errors Reedolomon. These techniques store additional bits for each block of data that are determined by mathematical formulas. The additional bits allow many errors to correct. Although these additional bits occupy space on the hard drive, they enable higher recording densities to be employed, resulting in more storage capacity important for user data. In 2009, the latest drives, low density parity check codes (LDPC) take precedence over Reed-Solomon. LDPC codes allow execution near the Shannon limit and thus allow the highest density storage available.

Typical hard drives attempt to "redefine" the data into a physical sector which will hurt a spare physical sectoropefully while the number of errors in the bad sector is still small enough that the ECC can completely recover the data without loss. The SMART system counts the total number of errors in the disk entire hard set by ECC, and the total number of remapping, in an attempt to predict hard disk failure.

See also: File System

Architecture

A hard drive with platters and motor hub removed showing the copper coils surrounding the stator colored a bearing in the center of the spindle motor. Orange strip along the side of the arm is a thin cable circuit board. The rolling pin is in the center.

A typical hard drive has two electric motors, one to spin the disks and the position of read / write head assembly. The motor has a rotor connected to an external disk trays, coils stator are fixed in place. The actuator has a read-write head under the tip of its end (near center), a thin wire circuit printed connects the read-write head on the hub of the actuator. A flexible U-shaped 'little', dish cable, seen edge lower and to the left of the control arm in the first picture and more clearly in the second, continues to connect the head to the controller card on the opposite side.

The head support arm is very light but rigid in modern drives, acceleration at the head reaches 550 GS.

Open hard drive with top magnet removed, showing the head of copper coil of the actuator (upper right).

Structure silvery in the upper left of the first image is the top plate of the permanent magnet and moving coil motor that swings the head to the desired position (it is shown off in the second image). The plate carries a thin neodymium-iron-boron (NIB) magnet high flux. Sub This is the voice coil plate, often referred to as the coil by analogy to the coil speakers, which is attached to the actuator hub, and below that is a second NIB magnet mounted on the bottom plate of the engine (some readers have a single magnet).

The coil, itself, is rather shaped like an arrow, and double coated coppmagnet [clarification needed] wire. The inner layer is the insulation and the outer is thermoplastic, linking the coil together after it is wound on a form, making it independent. The parts of the coil along both sides of the arrow (which point to the center bearing actuator) interact with the magnetic field, the development of a tangential force that rotates the actuator. Current flowing radially outward on one side of the arrowhead, and radially inward of the other product of tangential force. (See field # Magnetic Force on a charged particle.) If the magnetic field was uniform, each side would generate opposing forces would cancel out. Therefore, the surface of the magnet is half N pole, half S pole, with the radial line of division in the middle, causing the two sides of the coil see opposite magnetic fields and produce forces that add rather than cancel. The currents along the top and bottom of the coil to produce radial forces that do not turn your head.

Capacity and access speed

PC hard drive capacity (in GB) over time. The axis Vertical is logarithmic, so the fit line corresponds to exponential growth.

Using rigid disks and sealing the unit allows much tighter tolerances than in a floppy drive. Therefore, hard disk drives can store data much more than the disk drives and can access and transmit faster.

In April 2009 [update], the largest capacity hard drives consumption is 2 TB.

A "desktop hard drive" can typically store between 120 GB and 2TB though rarely above 500 GB of data (database on the U.S. market), turn from 5,400 to 15,000 rpm, and a transfer rate of 0.5 Gbit Media / s or more. (1 GB = 109 bytes, 1 Gbit / s = 109 bps)

Hard drives spin faster ompany to 10,000 or 15,000 rpm and can reach speeds sequential transfer medium above of 1.6 Gbit / s. and a sustained transfer rate of up to 1 Gbit / s. Drives running at 10,000 or 15,000 rpm use smaller plates to reduce increased energy needs (as they have less drag from the air) and therefore generally have lower capacity than the highest capacity hard drives office.

Hard Drives "Mobile Hard Drives", ie, laptop, which are physically smaller than their desktop counterparts and corporate tend to be slower and lower capacity. A typical mobile hard drive running at 4200rpm is, 5400rpm, 7200rpm, or at 5400 rpm is the first plan. 7200 rpm tend to be more expensive and have a lower capacity, while the 4200rpm models generally have storage capacities very high. Because physically smaller board (s), mobile hard drives generally have lower capacity than their larger desktop counterparts.

The exponential growth of disk space and data access speeds of hard drives have enabled the commercial viability of consumer products that require large storage capacities, such as digital video recorders and digital audio players. In addition, the availability of large quantities cheap storage has made viable a variety of Web services to the needs of extraordinary ability, such as free web search to the indictment, archiving Web and video sharing (Google, Internet Archive, YouTube, etc.).

The main way to reduce the access time is to increase speed, thus reducing the time of rotation, while the main way to increase throughput and storage capacity is to increase areal density. Based on historical trends, analysts expect future growth in bit density of hard disk (and therefore capacity) of about 40% per year. Access times have not kept up with increases in speed, which have not kept pace with growth in storage capacity.

Capacity should random IOPS from any hard drive can be calculated by dividing the sum by 1000 ms average seek time and average latency of rotation.

The first HDD marketed as 3.5 can store 1 TB was the Hitachi Deskstar 7K1000. It contains five platters at approximately 200 GB each, with 1 TB (935.5 GiB) of usable space, note the difference between its capacity in decimal units (1 TB = 1012 bytes) and the binary units (1 TiB = 1024 GiB = 240 bytes). Hitachi has since been joined by Samsung (Samsung SpinPoint F1, which has 3 334 GB platters), Seagate and Western Digital 1 TB in the market discs.

In September 2009, Showa Denko has announced improvements in the capacity of the plates that they manufacture for those responsible for hard disk. One 2.5 "tray can hold 334 GB worth of data results, and preliminary for 3.5" indicates a capacity of 750 GB per platter.

Form Factor

Width

The largest capacity

Platters (Max)

5.25 FH

146 mm

47 GB (1998)

25.5 HH

146 mm

19.3 GB (1998)

3.5 "SATA

102 mm

2 TB (2009)

3.5 PATA

102 mm

750 GB (2006)

2.5 SATA

69.9 mm

1 TB (2009)

2.5 PATA

69.9 mm

320 GB (2009)

1.8 SATA

54 mm

320 GB (2009)

1.8 PATA / LIF

54 mm

240 GB (2008)

1.3

43 mm

40 GB (2007)

1 (CFII / ZIF / IDE-Flex)

42 mm

20 GB (2006)

0.85

24 mm

8 GB (2004)

Capacity measures

A disassembled and labeled 1997 disk drive. All major components have been placed on a mirror, which created the symmetric reflections.

Raw unformatted capacity a disk drive is usually quoted with SI prefixes (prefixes metric system), the increment by powers of 1000, and Today, it usually means gigabytes (GB) and terabytes (TB). This is standard for data speeds and memory sizes that are not intrinsically produced power of two sizes, the RAM and flash memory are. Hard drives, however not inherent in size binary capacity is determined by the number of heads, tracks and sectors.

This may cause some confusion, because some systems can signal the operating capacity of a hard disk formatted using binary prefix units that increase skills of 1024.

A one terabyte (1 TB) hard disk would be expected to hold about 1 trillion bytes (1,000,000,000,000) or 1000 GB, and most drives of 1TB hard indeed contain slightly more than that number. But some utilities operating system would be to report this around 931 GB or 953 674 MB, whereas the correct units would be 931 Gio or 953,674 million. (The actual number for a formatted capacity will be somewhat smaller still, as the file system). Here are the correct ways of information a terabyte.

SI prefixes (HDD)

equivalent

Binary prefixes (OS)

equivalent

1 TB (terabytes)

1 * 10 004 B

0.9095 TiB (tebibytes)

0.9095 * 10 244 B

1000 GB (gigabytes)

1000 B * 10003

931.3 MiB (gibibytes)

931.3 B * 10243

1,000,000 MB (megabytes)

1000000 * 10002 B

953,674.3 MiB (Mebibytes)

B * 10242 953674.3

1000000000 KB (kilobytes)

1000000000 * 1000 B

976,562,500 KiB (KIBIBYTE)

976,562,500 B * 1024

1,000,000,000,000 B (bytes)

–

1,000,000,000,000 B (bytes)

–

Microsoft Windows reports disk capacity both in decimal to an integer 12 digits or more and in binary prefix units to three significant figures.

Capacity a hard disk can be calculated by multiplying the number of cylinders by the number of heads by the number of sectors by the number of bytes / sector (most often 512). Drives with the ATA interface and a capacity of eight gigabytes or more behave as if they were structured in 16,383 cylinders, 16 heads and 63 sectors for compatibility with older operating systems. Unlike in the 1980s, the cylinder, head, sector (C / H / S) figures reported to the CPU by a modern ATA drive are more physical parameters from the actual figures reported are limited by operating system interfaces with a bit historical and registration area the actual number of sectors varies by area. SCSI disks with address interface of each sector with a unique integer, the operating system remains ignorant of their head or number of cylinders.

The old C / H / S system has been replaced by logical block addressing. In some cases, trying to "force-fit the C / H / S system with large disks, the number of heads was given to 64, although no modern reader has anywhere near 32 platters.

General formatted disk

For a formatted disk, the file system of the operating system for internal use is another, although minor reason for the capacity of storage device or a hard drive may show his ability as different from its theoretical capacity. It would including storage, for example, a file allocation table (FAT) or inodes, and other operating data system structures. This file system is at its zenith generally less than 1% on drives larger than 100 MB. For RAID, data integrity and fault tolerance requirements also reduce the capacity achieved. For example, a drive RAID1 will be about half the total capacity to After mirroring data. For disk drives with RAID5 you lose x 1 / x of your space for parity. RAID disks are several readers who seem to be disk to the user, but provides some fault tolerance.

A general rule of thumb to quickly convert the manufacturer's ability Hard disk capacity standard Microsoft Windows-formatted is 0.93 * The capacity of the hard drive manufacturer for the hard drives of a terabyte of and 0.91 * less capacity hard drive manufacturer's hard drives or greater than 1 terabyte.

form factors

5 height 110 MB hard disk

2 (8.5 mm) 6495 MB Hard Drive,

U.S. cents / UK for comparison.

Six hard drives with 8, 5.25, 3.5, 2.5, 1.8, and 1 disks, partially disassembled to show the dishes and read-write heads, with a ruler showing inches.

BCE PCs and small computers, hard drives were very variable dimensions, usually in freestanding cabinets the size of washing machines (DEC RP06 disk) or designed so that the dimensions have allowed the placement in a 19 "(eg, Diablo model 31).

With increasing Sales of small computers with built in floppy disk drives (FDD), hard drives that would fit the media has become desirable FDD, which has led to the evolution market to players with some form factors, first from the size of 8 ", 5.25" and 3.5 "floppy drives. Smaller sizes of 3.5 "have emerged as popular on the market and / or been decided by various industry groups.

8 inches: 9.5 to 4.624 in 14.25 in (241.3 mm 117.5 mm 362 mm)

In 1979, Shugart Associates' SA1000 was the first form factor compatible HDD, having the same dimensions and a compatible interface with the FDD 8.

5.25 inches: 5.75 to 1.63 to 8 in (146.1 mm 41.4 mm 203 mm)

This small form factor, first used in a hard drive from Seagate in 1980, was the same size as the total height of 5 inches in diameter FDD, ie, 3.25 inches high. It is twice as high as "half height" commonly used today, namely, 1.63 in (41.4 mm). Most Desktop scanners models for 120 mm discs (DVD, CD) use half the height dimension 5, but fell into disuse for hard drives. The Quantum Bigfoot HDD was the last to use it in the late 1990s, with ow-profile (25 mm) and ltra-low-profile (20 mm) high versions.

3.5 ": 4 in 1 to 5.75 in (101.6 mm 25.4 mm 146 mm) = 376.77344 cm

This small form factor, first used in a hard disk in Rodime 1984 was the same size as the "half-height" 3 FDD, ie, 1.63 inches high. Today, it has been largely replaced limline high by 1 inch or versions ow-Profile form factor that is used by most desktop hard disks.

2.5 inches: 2.75 to 3.945 0.3740.59 in in (69.85 mm 715 mm 100 mm) = 48.895104.775 cm3

Smaller form factor that was introduced in 1988 by PrairieTek, there is no corresponding FDD. It is now widely used for hard drives in mobile devices (laptops, music players, etc.) and from 2008 the replacement 3.5-inch HDD class enterprise. It is also used in the Xbox 360 and Playstation 3 video game consoles. Today, the dominant height this form factor is 9.5 mm for portable players, but high-capacity drives (750 GB and 1 TB) have a height of 12.5 mm. Enterprise-class players can have a height up to 15 mm. Seagate has released a very thin disk 7mm to laptops, entry-level and high-end netbooks December 2009.

1.8 inches 54 mm 8 mm 71 mm = 30.672 cm

This form factor, originally introduced by Integrated Peripherals in 1993, evolved into the ATA-7 LIF with dimensions as indicated. It is increasingly used in digital audio players and subnotebooks. An original variant exists for the 25 GB hard drive companies that are a direct expansion slot PC Card. They became popular for their use in iPods and other MP3 players with hard disk.

1 inch: 42.8 mm to 36.4 mm 5 mm

This form factor was introduced in 1999 to accommodate IBM Microdrive inside a CF Type II slot. Samsung calls the same form factor "1.3 inch" drive in its documentation.

0.85 inches: 5 mm 24 mm 32 mm

Toshiba announced this form factor in January 2004 for use in mobile phones and similar applications, including the SD / MMC compatible drives optimized for video storage on 4G phones. Toshiba currently sells 4 GB (MK4001MTD) and 8GB (MK8003MTD) version and holds Guinness World Record for the smallest hard drive.

3.5 "and 2.5" hard drives currently dominate the market.

By 2009, all manufacturers had abandoned the development of new products for the 1.3-inch form factors of 1 inch and 0.85 inches due to falling prices of flash memory.

The inch-based nickname of all these form factors are generally not indicate any actual product dimension (which are specified in millimeters to more recent form factors), but only approximately indicate the relative size of disc diameter, in the interest of continuity history.

Other features

Data transfer rate

In 2008, a typical desktop drive has a 7200rpm supported "disk-to-buffer" Data transfer rates of about 70 megabytes per second. This rate depends on the location of the track, it will be higher for data on the outer tracks (where there are areas of data) and lowest to the inner tracks (where there are sectors of data in less), and is generally a little over 10,000 rpm. A current widely used standard for buffer-to-machine "interface is 3.0 Gb / s SATA, which sends about 300 MB / S buffer to the computer, and is still comfortably ahead of today's disk transfer speeds of buffer. transfer rate data (read / write) can be measured by writing a large file on disk using tools generator file, then reading the file. Transfer rate can be influenced by the fragmentation of system files and layout files.

Search time

Search time currently ranges from just under 2 ms for high-end server drives, 15 ms for miniature drives, with the type of office is typically the most common around 9 ms. [Citation needed] There was no significant improvement in this rate in recent years. Some PCs beginning readers used a stepper motor to move the head, and therefore had access time slower than 80,120 ms, but this was quickly improved by Type coil actuation of the late 1980s, reducing access time to about 20 ms.

Consumption

The power consumption has become increasingly important, not only in mobile devices such as laptops but also in the markets for servers and desktops. Increasing density data center machine has led to problems delivering sufficient power to devices (particularly for spin up), and get rid waste heat produced thereafter, and the concerns of environmental costs and power (see green computing). Problems There are similar for large companies with thousands of desktop PCs. Small form factor drives often use less power than larger drives. A interesting development in this area is actively controlling the speed of research so that the head arrives at its destination in time to read the sector rather as to arrive as quickly as possible, then having to wait for the sector to come around (ie the latency of rotation). Many companies Hard disk drives are now producing green that require much less power and cooling. Many of these "green disks spin more slowly (<5400 rpm versus 7200 rpm, 10,000 rpm and 15,000 rpm) and also produce less waste heat.

Also in Server and workstation systems where there may be multiple hard drives, there are several ways to check if the hard drives spin up (pulling power highest).

On the SCSI hard disk drives, the SCSI controller can directly control spin up and spin down drives.

The parallel ATA (PATA aka) and SATA hard disk drives, some support turned on in standby mode or THEN. The hard disk will start only when the controller or system BIOS issues a specific command to do so. That the draw of power limits or consumption on power on.

Of the newest SATA hard drive He is staggered Spin Up feature. The hard drive will not turn up the SATA Phy is ready (communication with the host controller begins). [Citation necessary]

To better control or reduce the power extraction and consumption, the hard disk can be turned down to reduce energy consumption.

Audible noise

Measured in dBA, audible noise is important for certain applications such as PVR, recording digital audio and computers calm. low noise drives typically use fluid bearings, slower rotational speeds (typically 5,400 rpm) and reduce the seek speed under load (AAM) to reduce audible clicks and sounds of crunching. Discs into smaller form factors (for example 2.5 inches) are often quieter than larger drives.

Shock resistance

Shock resistance is especially important for mobile devices. Some laptops are now active hard disk protection that parks the disk heads if the machine is dropped, we hope before impact, to provide the best possible opportunity to survive in such an event. shock tolerance up to date is 350 Gs for the operation and 1000 G for non-exploitation.

Access and interfaces

This section needs additional citations for verification.

Please help improve this article by adding reliable references. You can share your challenged and removed. (July 2009)

Hard drives are available on one of the many types of buses, including parallel ATA (PATA, also called IDE or EIDE), Serial ATA (SATA), SCSI, Serial Attached SCSI (SAS) and Fibre Channel. Bridge circuitry is sometimes used to connect hard disk drives to buses that they can not communicate with natively, as IEEE 1394, USB and SCSI.

For the ST-506 interface, the system of encoding data as written to the disk surface is also important. Early ST-506 disks used Modified Frequency Modulation (MFM) encoding, and transferred data at a rate of 5 megabits per second. Later on, controllers using 2.7 RLL (or just "RLL) encoding because data show 50% more under the heads relative to a rotating disc MFM, increased data storage and data transfer rates of 50% to 7.5 megabits per second.

Many disk drives ST-506 interface have been recommended by the manufacturer to operate at 1 / MFM 3rd lower transfer rate Data from RLL, while others drive models (usually more expensive versions of the same unit) were specified run at higher rates of data transfer RLL. In some cases, a reader has a sufficient margin to allow the MFM specified model to run rate denser / faster data transfer RLL (not recommended nor guaranteed by the manufacturers). In addition, any player RLL certified to function on any MFM controller, but with 1 / 3 of data capacity less and less as much as 1/3rd of data transfer rate compared to its specifications RLL.

Enhanced Small Disk Interface (ESDI) also supported multiple data rates (ESDI disks always used 2.7 RLL, but 10, 15 or 20 megabits per second), but this was usually negotiated automatically by the disk drive and controller, most of time, however, 15 or 20 megabit ESDI drives were not downward compatible (ie a 15 or 20 megabit drive would not be executed on a controller 10 megabit). ESDI drives typically also had jumpers to set the number of sectors per track and (in some cases) sector size.

Modern hard drives present a consistent interface to the rest of the computer, no matter what system of data coding is used internally. Typically, a DSP in the electronics inside the hard drive is the first analog voltages from the read head and uses PRML and correction Error Reedolomon to decode the sector boundaries and sector data, then sends the data to the standard interface. This DSP also watches the rate Error detected by detecting and correcting errors, and performs bad sector remapping, data collection for the Self-Monitoring, Analysis, and Reporting Technology, and other internal tasks.

SCSI was originally a frequency of 5 MHz signal to a data rate maximum of 5 megabytes per second over 8 parallel conductors, but later this was increased dramatically. The SCSI bus speed had no impact on the internal speed of the disc due to buffer between the SCSI bus and the disk drive's internal data bus, but many early disk drives had buffers very low, and therefore had to be reformatted to a different interleave (like ST-506 disks) when used on slow computers, such as early Commodore Amiga, IBM PC compatible and Apple Macintosh.

ATA drives have typically had no problems with the rate or data interleaving, due to their controller design, but many early models were incompatible with each other and could not operate with two devices on the same physical cable in a master / slave. This was mostly remedied by the mid-1990s, when the specification ATA has been normalized and the details began to be cleaned, but still poses a problem from time to time (especially with CD-ROM and DVD-ROM, and then mixture of Ultra DMA and non-UDMA devices).

Serial ATA eliminates master / slave configurations entirely, placing each disk on its own channel (With its own set of I / O ports) instead.

FireWire / IEEE 1394 and USB (1.0/2.0) hard drives are external units containing generally ATA or SCSI disks with ports on the back for easy expansion and efficient mobility. Most FireWire / IEEE 1394 models are able to connect string in order to continue adding peripherals without requiring additional ports on the computer itself. USB is however one point to network and does not allow for chaining. USB hubs are used to increase the number of ports available and are used for devices that require no load since the current provided by hubs is generally lower than what is available from the construction of USB ports.

Disk interface families Personal Computers

Notable families of disk interfaces include:

History bit serial interfaces connect a hard disk drive (HDD) to a hard disk controller (HDC) with two cables, one for control and one for data. (Each player also has a cable additional power, usually connect directly to the PSU). The HDC provided important functions such as conversion serial / parallel data separation and track formatting, and required matching to the drive (after formatting) to ensure reliability. Each control cable could use two or more discs, while a dedicated (and less) data cable provided each player.

ST506 used MFM (Modified Frequency Modulation) method for encoding data.

ST412 was available in MFM or RLL coding variants (Run Length Limited).

Enhanced small disk interface (ESDI) was an interface developed by Maxtor to allow faster communication between the processor and disk MFM or RLL.

Modern bit serial interfaces to connect a hard drive adapter host bus interface (now generally Built in the "south bridge") with a data cable / control. (As for the serial historic little above, each player also has an extra power cable, usually directly to the power supply.)

Fibre Channel (CF) is a successor to parallel SCSI interface on the market for the company. He is a serial protocol. In the discs usually arbitrated loop Fibre Channel (FC-AL) connection topology is used. FC has much broader usage than mere disk interfaces, and is the cornerstone of networks Storage (SAN). Recently, other protocols for this field, like iSCSI and ATA over Ethernet have been developed. Confusion, readers typically use copper wires, twisted pair for Fibre Channel, not the fiber optics. The latter are traditionally reserved for larger devices, such as servers or disk array controllers.

Serial ATA (SATA). The SATA data cable has a pair of differential data transmission data to the device, and a differential pair of receiving the device, just like EIA-422. This requires that data be transmitted serially. Similar differential signaling system is used in RS485, LocalTalk, USB, Firewire, SCSI and differential.

Serial Attached SCSI (SAS). The SAS protocol is a new generation serial communication devices designed to allow a speed much higher data transfer and is compatible with SATA. SAS uses a database mechanically identical and power connector to standard 3.5 "HDD SATA1/SATA2, and many server oriented SAS RAID controllers are also able to handle SATA drives. SAS uses serial communication instead of the parallel method in traditional SCSI devices but still uses SCSI commands.

Word serial interfaces connect a hard drive to a host bus adapter (usually now part of the "south bridge") with a cable for the combined data / control. (As with all serial interfaces little above, each player also has a separate power cord, most often directly to the power supply.) Early versions of these interfaces typically had an 8-bit parallel data transfers to / from the drive, but 16 bit versions became much more frequent, and there are 32-bit versions. modern variants have serial data transfer. The word nature of data transfer makes the design of a host bus adapter significantly simpler than the hard disk controller precursor.

Integrated Drive Electronics (IDE), later renamed ATA with the alias P-ATA (Parallel ATA) retroactively added during the introduction of the new variant Serial ATA. The original name reflected innovative integration of HDD controller with HDD itself, which was not found in earlier disks. Move hard disk controller card to interface the drive helped to standardize interfaces, and reduce the cost and complexity. The 40-pin IDE / ATA connection transfers data 16 bits at a time on the cable data. The data cable was originally 40 conductor, but the requirements of the latest speed data transfer to and from the hard drive led to an "ultra DMA mode, known as UDMA. Gradually faster versions of this standard finally added the requirement of a variant of the same 80-conductor cable, where half of all drivers the grounding needed to provide improved signal quality at high speed by reducing crosstalk. The interface has only 80 drivers 39 pins, the missing pin acting as a key to prevent incorrect insertion of the connector into a power conflict, a common cause of disc damage programmer.

EIDE was an unofficial update (by Western Digital) to the original IDE standard, with the key improvement being the use of direct memory access (DMA) to transfer data between the disk and the computer without the involvement of the CPU, an improvement later adopted by the official ATA standards. Transferring data directly between memory and disk, DMA eliminates the need for the CPU copy byte by byte, thus allowing to process other tasks while the data transfer occurs.

Small Computer System Interface (SCSI), originally SASI Shugart Associates appointed to System Interface, was an early competitor of ESDI. SCSI disks were standard on servers, workstations, Commodore Amiga and Apple Macintosh computers through the mid-90s, when most models were switched to IDE (and later, SATA) family. Only in 2005 did the capacity of SCSI disks behind IDE disk technology, but the disks are still the most powerful available in SCSI and Fibre Channel only. The length limitations of the data cable allows external SCSI devices. Originally SCSI data cables used single data transmission complete (common mode), but server class SCSI could use differential transmission, either low voltage differential (LVD) or differential High Voltage (HVD). ("Low" and "High" for SCSI differential voltages are with respect to the SCSI standards and does not meet the meaning of low voltage and high voltage used in the general context of electrical engineering, which applies for example to law electrical codes and two LVD and HVD use signals low voltage (3.3 V and 5 V, respectively) in the general terminology.)

Acronym or abbreviation

Meaning

Description

SASI

Shugart Associates System Interface

historical predecessor of SCSI.

SCSI

Small Computer System Interface

Bus oriented that handles concurrent operations.

SAS

Serial Attached SCSI

Improved SCSI, uses serial communication instead of parallel.

ST-506

Seagate Technology

History Seagate interface.

ST-412

Seagate Technology

History Seagate interface (minor improvement over ST-506).

ESDI

Improved interface small disk

Historical ST-412/506 backwards compatible, but faster and more integrated.

ATA

Fastening technology

Succeeding ST-412/506/ESDI by integrating the disk controller completely onto the device. Incapable of concurrent operations.

SATA

Serial ATA

Modification of ATA, uses serial communication instead of parallel.

Integrity

An IBM HDD head resting on a disc tray. As the reader is not running, the head is simply pressed against the disk by the suspension.

Close-up of a head resting on a hard disk drive tray. A reflection of the head and its suspension is visible on the disk as a mirror.

Due very close spacing between the head and the disk surface, any contamination of the read-write heads or platters can lead to a head crash disk failure in which the head scrapes across the platter surface, often grinding away the thin magnetic layer and causing data loss. Head injuries can be caused by electronic failure, a sudden power failure, physical shock, wear, corrosion, or poorly manufactured platters and heads.

The HDD spindle system relies on air pressure inside the chamber to support the heads at their proper flying height while the disk rotates. The hard drives require a certain range of air pressure to operate properly. The connection to the outside environment and the pressure is through a small hole in the enclosure (about 0.5 mm in diameter), usually with a filter inside (the breather filter). If the air pressure is too low, then there is not enough lift for the flying head, so that the head is too close to the disc, and there is a risk of head crashes and data loss. Specially manufactured sealed and pressurized disks are needed for operation at high reliable altitude, above about 3,000 meters (10,000 feet). Modern disks include temperature sensors and adjust their operation to the environment operating. Breather holes can be seen on all disk drives typically 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 turntables. This air passes through an internal recirculation (or "recirculation") filter to remove any leftover contaminants from manufacturing, chemicals or particles 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 make data unreadable for a short period until the head temperature stabilizes (so called "thermal asperity", a problem that can partly be addressed by proper electronic filtering of the read signal).

The operation of the mobile arm

The electronics of the drive to control the movement of the actuator and the rotation of the disk, and perform reads and writes to the disk controller's request. Comments of the drive electronics is achieved by means of specific segments of the disk dedicated servo feedback. They are either complete concentric circles (in the case of servo technology dedicated), or segments interspersed with data Actual (in the case of servo technology integrated). Comments servo optimizes the signal to noise ratio of GMR sensors by adjusting the coil actuated arm. The rotation 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 who have failed.

landing zones and load / unload technology

A reading / writing from a to-1998 Fujitsu 3.5 "HDD. The area of the photo is about 2.0 mm x 3.0 mm.

Micrograph of a head Legacy Drive and the cursor (1990). The size of the front (which is the "trailing face" of the slider) is about 0.3 mm to 1.0 mm. It is the location of the current "head" (magnetic sensors). The non-visible at the bottom of the slider is about 1.0 mm 1.25 mm (so-called "Nano" size) and faces the platter. It contains the air at the surface micromachined on lithography (ABS) that enables the slider to fly a very controlled way. A functional part of the head is round orange structure visible in the middle – the copper coil defined by lithography writing the transducer. Also note the electric connections by son welded studs gold plated.

Modern hard drives avoid blackouts or Other problems landing the lead in the data area by parking the heads, or in a landing zone or unloading (by example, loading / unloading) heads. Some PC hard drives did not start the park office and leaders on earth they would be given. In some other units at the beginning of the user manually parked the head by running a program to park the heads of hard drives.

Zone Landing is a shelf area usually near its inner diameter (ID), where data are stored. This area is called First Contact / Stop (CSS) zone. The discs are designed so that either a spring or, more recently, rotational inertia in the platters is used for the park's head in the event of unexpected power loss. In this case, the spindle motor temporarily acts as a generator to provide power the actuator.

Spring tension mounting head constantly pushes the heads towards the plateau. While the drive is spinning, the heads are made supported by a cushion of air and experience no physical contact or wear. CSS drives the sliders carrying the head sensors (often just called heads) are designed to withstand a certain number of landings and takeoffs from the carrier surface, though wear these microscopic components eventually takes its toll. Most manufacturers design the sliders to survive 50,000 contact cycles before the risk of damage increases Started more than 50%. However, the rate of decrease is not linear: when a disk is younger and had fewer cycles on and off, it has better chance of surviving the next startup of an old record higher mileage (as head literally drags along the disk surface to that the air cushion is established). For example, the Seagate Barracuda 7200.10 series of desktop hard drives are rated at 50,000 cycles on and off in other words no failures attributed to the head-plate interface were seen before at least 50,000 start-stop cycles during testing.

Around 1995, IBM developed a technology where a landing zone on the disk is manufactured by a precision laser process (Laser Zone Texture = LZT) producing an array of smooth nanometer scale "bumps" in a landing zone, which greatly improves stiction and wear performance. This technology is still widely used today (2008), mainly in desktop and enterprise (3.5 inch) drives. In general, CSS can be prone to increased stiction (the tendency for leaders to stick to the surface Shelf), for example due to increased humidity. Excessive stiction can cause physical damage to the plate and slider or spindle motor.

Load / Unload technology relies on the head lifted off the trays in a safe place, eliminating the risk of wear and stiction at all done. The first HDD RAMAC and disk drives used complex mechanisms earlier to load and unload the heads. Modern hard drives use the loading ramp, the first time by Memorex in 1967, to load / unload onto plastic "ramps" near the outer edge of the disc.

All day hard drives still use one of these two technologies listed above. Everyone has a list of advantages and disadvantages in terms of loss of storage space on disk, the relative difficulty of mechanical tolerance control, non-operating shock robustness, cost of implementation, etc.

Speaking shock robustness, IBM also created a technology for their line of ThinkPad notebooks called the Active Protection System. Suddenly, the sudden movement is detected by the accelerometer in the Thinkpad, internal hard disk heads automatically unload themselves to reduce the potential loss of data or zero defects. Apple later also utilized this technology in their PowerBook, iBook, MacBook Pro, MacBook and line, known as the Sudden Motion Sensor. Sony, HP 3D DriveGuard with their HP and Toshiba have released similar technology in their laptops.

This sensor based shock accelerometer was also used to build inexpensive sensor networks earthquake.

failures disc and their indicators

Wikipedia has a book on the topic of

Minimizing hard disk failure and data loss

Most leading suppliers of hard disk and motherboard now supports SMART (Self-Monitoring, Analysis, and Reporting Technology), which measures transmission characteristics such the operating temperature, spin-up rates, data error, etc. Some trends and sudden changes of these parameters are assumed to be associated with an increased likelihood of disk failure and data loss.

However, all failures are predictable. Normal use may eventually lead to a breakdown in the fragile nature of the device, making it essential for the user to backup data regularly a separate storage device. Failure to do so lead to data loss. While it is sometimes possible to retrieve information lost, there is normally an extremely costly procedure, and it is not possible to guarantee success. A 2007 study published by Google is very little correlation between failure rates and either high temperature or activity level, but the correlation between the manufacturer and model and the failure rate is relatively high. Statistics on this matter is kept secret by most entities. Google does not publish the names of the manufacturer and their respective failure rates, but they have since revealed that they use Hitachi Deskstar in some of their servers. Although several parameters SMART affect the probability of failure, a large fraction of failed drives do not produce predictive SMART parameters. parameters SMART can not only be useful for predicting individual drive failures.

A common misconception is that the hard drive will last longer than a cold HDD warmer. The Google study seems to imply the opposite "lower temperatures are associated with higher failure rates "The hard disks. SMART-recorded average temperatures below 27 C (80.6 F) had a higher failure rate than hard drives with the highest average reported temperature of 50 ° C (122 F), the failure rate at least twice higher than the optimal range SMART-reported temperature of 36 C (96.8 F) to 47 C (116.6 ° F).

SCSI, SAS and FC drives are typically more expensive and are traditionally used in servers and disk arrays, while inexpensive ATA and SATA drives evolved in the market for home computers and has been collected as being less reliable. This distinction is becoming blurred.

The mean time between failure (MTBF) of SATA drives is usually about 600,000 hours (Some drives such as Western Digital Raptor have rated 1.2 million hours MTBF), while SCSI drives are rated at more than 1.5 million hours. [Citation needed] However, independent research indicates that MTBF is not a reliable estimate of the longevity of a player. The MTBF is conducted in laboratory environments in test chambers and is an important metric to determine the quality of a disc before it enters the high volume production. Once the drive product is in production, the more valid metric is annualized failure rate (AFR). [Citation needed] AFR is the percentage of drive failures in the real world after shipping.

SAS drives are similar to hard SCSI, with an MTBF and reliability. [Citation needed]

S-ATA company designed and produced for enterprise markets, unlike to S-ATA standard, a reliability comparable to other enterprise class drives.

Typically enterprise drives (all companies drives, including SCSI, SAS, SATA and FC business) experience between 0.70% -0.78% annual failure rate of the total installed drives. [Citation needed]

Finally, all mechanical hard drives fail. And so the strategy to mitigate data loss is to have redundancy in some form, such as RAID and backup. RAID should never be used as a backup, as RAID controllers also fail, which makes inaccessible disks. Following a backup strategy, for example, the differential daily and weekly full backups is the only sure way prevent loss of data.

Manufacturers

A Western Digital 3.5 inch 250 GB SATA HDD. This model features two SATA and entries Molex power.

Seagate hard drives being manufactured in a factory in Wuxi, China

See also List of defunct manufacturers Hard Drives

Resources and technological know-how required for modern drive development and production means that by 2010, almost all hard drives in the world are manufactured by five major companies: Seagate, Western Digital, Hitachi, Samsung and Toshiba.

Dozens of manufacturers old hard drives have failed, merged or closed their HDD divisions; that capacity and demand for products increased, profits became difficult to find, and the market has experienced significant consolidation in the late 1980s and late 1990s. The first notable victim of the company in the PC era was Memories Inc. or CMI; after an incident with faulty 20 MB disc in 1985, the CMI's reputation never given, and they exited the HDD business in 1987. Another notable failure was MiniScribe, which went bankrupt in 1990 after he was found that they had engaged in accounting fraud and inflated sales figures for several years. Many other companies smaller (as Kalok, Microscience, Lapine, Areal, Priam and PrairieTek) also did not survive the debacle, and had disappeared in 1993, Micropolis was able to keep until 1997, and JTS, a relative latecomer to the scene, lasted only a few years and disappeared in 1999 after attempting of manufacturing hard drives in India. Their claim to fame was to create a new form factor drive 3 for use in laptops. Quantum and Integral also invested in the form factor of 3, but eventually ceased to argue that this form factor has not become widespread. Rodime also been a leading manufacturer in the 1980s, but stopped making records in the early 1990s amid the debacle and is now focusing about licensing the technology that they hold a number of patents relating to hard drives 3.5-inch form factor.

The following is the genealogy of the current Companies HDD

1967: Hitachi enters the market the hard drive.

1967: Toshiba enters the market the hard drive.

1979: Seagate Technology is founded by a group of former IBM and those ex-Memorex.

1988: Western Digital (WDC), then a controller designer well known from the hard drive activity through the acquisition of Tandon Corporation of the disk manufacturing division.

1989: Seagate Technology Company Procurement of Control Data hard drive.

1990: Maxtor MiniScribe purchases of bankruptcy, making it the heart of its low-end drives.

1994: Division Quantum storage purchases in December, giving it a broad high-end disk to go with its more consumer oriented ProDrive range.

1996: Seagate acquired Conner Peripherals a merger.

2000: Acquires Maxtor Quantum HDD, Quantum is in the business strip.

2003: Hitachi acquires majority IBMs disk division, who renamed it Hitachi Global Storage Technologies (HGST).

2006: Seagate acquires Maxtor.

2009: Toshiba Acquires Division Fujitsu HDD

Sales

In 2007 516200000 years hard drives have been sold.

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