See also: Disc

The hard drive or Hard Disk Drive is a magnetic Mass memory . It effectively replaced the drum S (today obsolete) and the bands, which are used nowadays only for the filing and the Sauvegarde.

The hard drives were developed at the origin for the computers. First of all in local attachment, they can be today organized in networks (NAS and SAN) of capacity and increasing Fiabilité. The hard drives are the subject of multiple uses beyond the computers, one can find them in particular in Caméscope S, read/write drives of DVD of living room, video game consoles, personal digital assistants and mobile phones.

Summary of the history of the hard drive

Invented in 1956 by IBM, the capacity of the hard drive since strongly increased while its obstruction was also strongly reduced. The abbreviation HDD means Hard Disk Drive : reader of hard drive.

The first hard drive, the IBM 350 (which belonged to the computer RAMAC 305), had a capacity of five megabyte S; it was composed of 50 plates 24 inches in diameter (61 centimetres). In 1998, year when the centenary of the tape recording was commemorated (invented by the Dane Valdemar Poulsen), IBM marketed the first hard drive of 25 gigaoctet S (Deskstar 25 GP), capacity presented at the time by the press like disproportionate compared to the real needs of the private individuals. Five years later, one regarded 80 Go as a hardly sufficient size. In 50 years, the capacity of the hard drives was multiplied by a factor: 500,000 since a current disc (2007) can reach 1 To (under an incomparably less volume).

More than 3,5 million terabytes are stored each year on peripherals of storage of mass of the type magnetic hard drives . The surface occupied by a bit of information on the disc was seen reduced of a factor 100.000 in thirty years of research and innovations, basically improving storage capacities, the access times, the obstruction and the storage cost.

Principle of operation

In an hard drive, one finds plates rigid in rotation. Each plate consists of a disc generally made out of aluminum, which has the advantages of being light, easily usinable and nonmagnetic. More recent technologies use glass or the ceramics, which allow surface qualities still better than those of aluminum. The faces of these plates are covered with a magnetic layer, on which the data are stored. These data are written in code Binaire on the disc thanks to a read/write head, small antenna very close to magnetic material. According to the electric flux which crosses this head, it modifies the local magnetic field to write either one 1, or one 0, on the surface of the disc. For reading, it is the same principle which is used, but in the other direction: the local magnetic field generates an electric flux within the head which depends on the value previously written, one can thus read one 1 or one 0.

A typical hard drive contains a central axis around whose the plates turn at a number of constant revolutions. The read/write heads are connected to the same reinforcement which moves on the surface of the plates, with a head by plate. The reinforcement radially moves the heads through the plates while they turn, thus making it possible to reach the totality of their surface.

The electronic associated controls the movement of the reinforcement as well as the rotation of the plates, and carries out the readings and the writings according to the requests emitted by the controller of the disc. The Firmware S of the recent hard drives are able to organize the requests so as to minimize the access time to the data, and thus to maximize the performances of the disc.

Mechanics

Plates

The plates are interdependent of an axis on rolls of the dice or with oil. This axis is maintained moving by an electrical motor. The number of revolutions currently (2007) lies between: 3,600 and: 15,000 turns/minute (the typical scale speeds is: 3,600: 4,200: 5,400: 7,200: 10,000 and: 15,000 turns/minute). The number of revolutions is preserved constant.

The plates are composed of zinc or aluminum a substrate, (), more and more often out of glass, are formerly treated by various layers including one ferromagnetic covered with a layer of protection. The surface quality must be the best possible one.

Read/write head

Fixed at the end of an arm, they are interdependent of a second axis which makes it possible to make them swivel in arc of circle on the surface of the plates. All the heads thus swivel at the same time. There is a head by surface. Their geometry enables them to fly above the surface of the plate without the touch: they rest on an air cushion created by the rotation of the plates. In 1997, the heads flew to 25 nanometers of the surface of the plates, today (2006) this value is of approximately 10 nanometers.

The engine which involves them must be able to provide very important accelerations and decelerations. One of the algorithms of control of the movements of the arm carry-head is to accelerate to the maximum then to slow down to the maximum so that the head positions on the good cylinder. A short moment will have then to be waited so that the vibrations generated by braking grow blurred.

With the stop, the heads must be parked, either on a special zone (nearest to the center, it then does not have there data at this place), or apart from the plates.

If one or more heads come into contact with the surface of the plates, that is called a landing and generally causes the destruction of the information located at this place. An imperfection on surface such as a dust will have the same effect. The mechanics of the hard drives is thus assembled in Clean room and all the precautions (joined, etc) are taken so that no impurity can penetrate inside the case (called “HDA” for “Head Disk Assembly” in English).

Technologies for the design of the heads are (in 2006):

Electronics

It is made up of a part dedicated to control of the engines and another to the exploitation of electric information resulting from the electromagnetic interaction between the play-back heads and surfaces of the plates. A data-processing part will make the interface with the outside and the translation of the absolute address of a block in coordinates with 3 dimensions (head, cylinder, block).

Electronics also makes it possible to correct the errors.

Types of interface of the hard drives

The interfaces of the hard drives largely evolved/moved with time in a preoccupation of simplicity and an increase in the performances. Here some possible interfaces:

  • Storage Modulates Device (SMD), very much used in the Années 1980, it was mainly reserved for the mass storage units installed on waiters.

  • ST506 , very much used at the beginning of microprocessing in the years 1980.
  • ESDI (Enhanced Small Device Interfaces), succeeded ST 506, qu ' it improves.
  • the interface the IDE (or PATA in opposition to SATA , to see further), most current in the personal machines until recently (2005), also called ATA (AT ATACHMENT), not to confuse with S-ATA, the latter having replaced it.
  • SCSI (Small Computer System Interfaces), more expensive, but offering higher performances. Always used and improved (passage from 8 to 16 bits in particular, and increase in the speed of transfer, standards SCSI-1, SCSI-2, SCSI-3).
  • SAS (Serial Attached SCSI), combines the advantages of SCSI with those of the Serial ATA (it is compatible with the latter).
  • Serial ATA (or S-ATA), is an interface series, inexpensive and more rapid that ATA (standards SATA and SATA II), it is most current from now on (2005).
  • Fiber-Chanel (FC-AL), is a successor of the SCSI. The connection is series and can use a connector industry fiberoptic or copper. Mainly used on the waiters.

Power supply

  • It is carried out in general by a connector Molex. It should be noted that many Serial ATA hard drives do not use a connector molex to be fed but a long catch and punt characteristic of this standard of transfer.

Geometry

Each plate (2 surfaces) is composed of concentric tracks. The tracks located at the same ray form a cylindre.
Here 3 plates; 6 play-back heads because 6 surfaces with reading.

The track is delimited in sectors (also called blocks) containing the data.

One thus needs three coordinates to reach a block (or sector):

  1. the number of the play-back head (choice of surface)
  2. the number of the track (the displacement of the head determines)
  3. the number of the block (or sector) on this track (determines from when it is necessary to start to read the data).

This conversion is made by the controller of the disc starting from the absolute address of the block (a number ranging between 0 and the full number of blocks (less 1) contained on the disc).

It will be noted that the external and interior sectors do not have the same physical size.

On the first discs, a surface was formatted in factory and contained information making it possible the system to synchronize itself (knowledge which was the position of the heads constantly). This surface was called “servo”. Thereafter, these zones of synchronization were mixed between the storage blocks, but they are always formatted in factory. Typically thus, one will find on a track a succession of:

  1. a small “white” or “space” (“English gap”),
  2. a servo zone,
  3. a heading with container the number of the block which will follow,
  4. data,
  5. a sum of control allowing to correct errors.

To measure the capacity

The capacity of an hard drive can be calculated as follows: many cylinders * many heads * many sectors * many bytes/sector (generally 512) However, the values of cylinder, head, & of sector are not exact for the discs using the " zone bit recording" (recording of zonal piece Laughing), or translation of addresses. On discs ATA of size higher than 8 Go, the values are fixed at: 16383 cylinders, 16 heads, 63 sectors for compatibility with the older operating systems.

Example with an hard drive S-ATA Hitachi of at the end of 2005:

63 sectors * 255 heads *: 10,011 cylinders * 512 bytes/sector =: 82343278080 bytes is 76,688 Gio (or 82,343 Go).

Performances

The access time and the flow of an hard drive make it possible to measure the performances of them. The principal factors to take into account are:

  1. latency time , factor number of revolutions of the plates. The latency time (in second) equal to 60 is divided by the number of revolutions into turn per minute. The average latency time is equal to the latency time divided by 2 (because it is estimated that statistically the data are with a half-turn close to the heads). In the first hard drives, until 1970, the latency time was of a turn: one was indeed to wait until the home address is presented, ray origin (1/2 turn) in front of the heads, then one sought the sectors concerned starting from this home address (1/2 turn). IBM provides with discs 3033 of a whole fixed track intended for the addressing, and which eliminated the need for home address .

  2. the time search , or seek time in English, is time that the head puts to move to the selected cylinder. It is an average between time tracks with track, and longest possible ( full-stroke ).
  3. time the transfer is the time which the data will spend with being transferred between the hard drive and the computer by the means of its interface.

To consider the transfer time total, these three times are added. One will be able to add the response time of the controller, etc It is often necessary to pay attention to the specifications of the manufacturers, those will tend to communicate the peak values instead of the constant values (for example for the flows).

Here two compared discs. The first, DEC RP07 equipped the computers DEC with the Années 1970 - 80, while Maxtor is a recent disc of 3,5 inches (2004). They can both be regarded as top-of-the-range discs at the time of their marketing.

The addition of Random access memory on the controller of the disc makes it possible to increase the performances. This memory will be filled by the following blocks the required block, by hoping that the access to the data will be sequential. In writing, the disc can inform the host who initiated the transfer that this one is finished whereas the data are not written yet on the media itself. Like any system of mask, that poses a problem of coherence of the data.

Storage capacity

The current capacities (2007) spread out between 74 Mo and 8 To (terabytes) reached thanks to the use of several hard drives at the same time. The hard drive solo with the most important capacity is Hitachi Deskstar T7K1000, which has 1 To (terabytes) (2007). The capacity of the hard drives increased much more quickly than their speed, limited by mechanics.

Formats

Dimensions of the hard drives are standardized:

  • 19 inches for the old discs (with interface SMD).

  • 8 inches: following generation, allowing to put two discs over a bay width.
  • 5 inches 1/4: format appeared in the Years 1980, one also finds it in half-height.
  • 3 inches ½ is the standard size to date.
  • 2 inches ½ for the portable Computers at the origin and installed on the waiters since 2006.
  • 1 inch 1/8 for the walkmen, the computers ultraportables, certain external hard drives.

The smallest discs are included in the category of the microdrives , with a size of 1 inch.

Microdrives

The microdrives were created by IBM. The beginning of their development dates of more than 10 years but they were marketed only very recently, to meet the needs for the walkmen and especially for the Numeric photography.

The discs microdrive are with the format of the memory cards CompactFlash (standard CF 2) and are used same manner. Their capacity varies from 384 Mo with 8 Go.

They are nevertheless more expensive (precision mechanics with systems antichocs), more fragile however, and consume more because of their micro engine.

They are mainly used in the professional cameras and certain readers MP3 because of their important capacities. This success made their prices more accessible.

Manufacturers

The number of manufacturers of hard drives is limited enough nowadays, because of various repurchases or industrials merger of undertakings, even the abandonment by certain companies of this activity.

Historical manufacturers:

  • peripheral Bulls

  • CDC (Imprimis)
  • Conner Peripherals
  • Hewlett-Packard
  • IBM
  • Maxtor
  • Micropolis
  • NEC
  • Quantum
  • Storage Technology
  • Tandem
  • Univac

Emulation

Sometimes it is necessary to have a peripheral in any point similar to an hard drive, but with access times much faster, with the detriment of the capacity. There are two ways of achieving this goal: either by the use of a disc SSD , or by the creation of a virtual disk, as described below.

Virtual disks

Sometimes also called RAM Disc S . It is an artifice which makes it possible to emulate an hard drive starting from a space allocated in main memory. Its creation, its obliteration and its access are done by the means of calls systems (the core can contain pilot adequate). The access times are extremely fast; on the other hand, by construction, their capacity cannot exceed the central memory size.

The data being lost if the memory is not fed any more electrically, one in general uses them for files in reading alone , copies of data on disc, or for intermediate files whose loss imports little.

  • arrangement of data very often consulted (for examples files .h in Language C)

  • arrangement of intermediate files of compilation (under Linux, files .o )

The competitor of the HDD: the Solid State Drive

A disc SSD (for Solid State Drive , called usually, wrongly Disk , whereas no part is mobile) has outside the appearance of a traditional hard drive, including the interface, but technically, it does not contain any machine element, the data being stored in Mémoire flash.

So the access times are very fast and the very important flows, but during their introduction, their capacity was still limited to 512 Mo. In 2007, one finds models of higher capacity (1 to 8 Go at more or less accessible prices according to the desired capacity), even much more (60 Go). and more still, but at prohibitive prices at present.

This technology is used mainly under environments or conditions of use not adapted to the traditional hard drives (abrupt movements, important accelerations, extreme temperatures, shocks and important vibrations, etc).

Because of their still crippling price, these memory supports for the moment are still reserved for rare scopes of application of the professional world. The M-system company develops for example such products bound for the forces Armée S.

Hybrid hard drives

Halfway between the hard drive and SSD (Solid State Drive - entirely composed of memory Flash), the hybrid hard drives are traditional magnetic disks accompanied by a small module of Flash memory.

Developed in priority for the portables, the advantage of these discs is to reduce the consumption of energy, to increase the speed of starting and to increase the life of the hard drive.

When a laptop equipped with a hybrid disc needs to store data, in fact, it temporarily arranges them in the memory flash what avoids with the machine elements getting under way.

The core use Flash should make it possible to improve of 20% the loadings and the time of starting of the PC. The portable PC should them benefit from an increase in autonomy from 5 to 15%, which could result in a 30 minutes profit on the last generations of portable PC.

History

The engineers of IBM were not satisfied of the magnetic storage systems on drum S: the volumetric effectiveness was very low, the drums occupied much space for little capacity. In 1953, an engineer recently engaged had the idea to superimpose plates along an axis and to associate there a mobile read/write head, located on an axis parallel with that of the plates. This head came to fit between the plates to read information, but was to be withdrawn completely to pass from a plate to another. A prototype was built with a number of revolutions of approximately: 1,000 turns/minute. At this speed it was complicated to maintain the heads above the surface of the plates. The idea was then to inject air uplift through the play-back head, which maintained it above the plate. The distance head-plate was of 20 μm.

In 1955, the first system of this type was revealed with the public by IBM, it was baptized RAMAC (Random Access Method off Accounting and Control), model 305, and the commercial production began in June 1957. Up to 1961 more than one thousand of units were sold. Its price: : 10,000 dollars (of the time) by megabyte.

The RAMAC 305 consisted of 50 discs of 24 inches of diameter, two read/write heads which could move of a plate to another in less than one second. Full capacity was of five million characters.

To note that the RAMAC had already a competitor: the Univac File Computer , composed of 10 magnetic drums each one of a capacity of 180.000 characters. Although the latter had an high speed, in fact the RAMAC could store three times more information, which had the cost ratio/performance most interesting for the greatest number of applications.

In June 1954 J.J. Hagopian, engineer IBM, with the idea to make “steal” the read/write heads to the top of the surface of the plates, on an air cushion. He proposes the design of the shape of these heads. In September 1954 it draws the equivalent of the current hard drives: superimposed plates and an axis on which the read/write heads are fixed. That will become a commercial product in 1961 pennies the denomination “IBM 1301 Disk Storage”.

End 1969, three engineers think of what could be for them the system ideal disc. They fall from agreement on a model made up of two discs of 30 Mo each one, one removable, the other fixes. “30 - 30” thus, which is also a model of Winchester rifle. The name remained, and still today a disc Winchester indicates a nonremovable hard drive (either almost all discs produced today).

References

See too

  • Clusters - NAS - RAID - SAN - SSD

External bonds

  • 100 years of tape recording
  • Operation of an hard drive (video with the format mp4 of 85 Mo - is read very well with VLC media player of the project VideoLAN)
  • Article on the hard drives, summary of the principal concepts,
  • the first hard drive.

Simple: Hardware disk

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