Principle of the functioning(working) the hard disk

The Drive on hard disk pertains to the most making and complex device of the modern personal computer. His(its) disks capable to contain many megabytes to information, sent with enormous velocity. In that time, as nearly all computer elements work noiseless, hard disk grumbles and поскрипывает that allows to refer him(it) to that a little computer device, which contains as mechanical, so and electronic components.

The Cardinal principles of the functioning(working) the hard disk little changed since day of his(its) creation. The Device of the winchester much looks like common player phonograph record. Only under body can be several plates, pinned on the general axis, and heads can read information with both sides of each plate immediately. The Velocity of the rotation of the plates (beside some models she gets to 15000 rotations per minute) constant and is one of the main features. The Head moves along plate on a certain fixed distance from surface. Than this distance less, that more accuracy of the sensing to information, and that more can be density record to information. Having Taken a look at drive on hard disk, you see only strong metallic body. He герметичен completely and protects the spindle from small part of dust, which at hit in narrow clearance between head and surface of the disk can damage the sensitive magnetic layer and remove the disk from building. Besides, body shields the drive from electromagnetic hindrances. Inwardly body are found all mechanisms and some electronic components. The Mechanisms - disks themselves, on which is kept information, heads, which write and read information with disk, as well as engines, bring all this in motion. The Disk presents itself become round plate with very even surface from aluminum more often, less - from ceramics or glass, покрытую fine ferromagnetic sloem. In many drive is used layer of the oxides ferric (which is covered usual magtape), but the most latest models hard disk works with слоем the cobalt by thickness of the order ten microns. Such covering more firmly and, besides, allows vastly to enlarge density a record. Technology of his(its) fixing close to that, which is used at production of the integral microcircuits.

The Amount disk can be different - from one before five, amount worker surfaces, accordingly, double more (on two on each disk). The Last (either as material, used for magnetic covering) defines the capacity of the hard disk. Sometimes medicine to be taken externally to surfaces extreme disk (or one of them) are not used that allows to reduce the height of the drive, but at amount worker surfaces decreases and can turn out to be uneven.

The Magnetic heads read and write information on disks. The Principle record in general similar to those, is used in usual tape-recorder. Digital information is converted in variable electric current, incoming on magnetic head, but is then sent on magnetic disk, but in the manner of magnetic field already, which disk can perceive and "remember". Magnetic covering the disk presents itself ensemble of the most small areas spontaneous (spontaneous) намагниченности. For clarity visualize that disk cover слоем very small arrows from compass, made for different sides. Such particles-arrows are identified the доменами. Under influence of the external magnetic field own magnetic fields доменов are orientated in accordance with his(its) direction. After cessation of the action of the external field on surfaces of the disk are formed zones remaining намагниченности. Thereby recorded information is saved on disk. The Area remaining намагниченности, being at rotation of the disk opposite clearance of the magnetic head, direct in her электродвижущую power, changing depending on values намагниченности. The Package disk mounted on axis-spindel, happens to in motion by special engine, portably located under him. The Velocity of the rotation disk, as a rule, forms 7200 ob./min. To shorten time of the leaving the drive in working condition, engine when enabling certain time works in forced mode. So computer power source must have a spare on peak power. Now about functioning(working) the heads. They move by means of прецизионного crossbar engine and as it were "sail" on distance in share of the micron from surface of the disk, not concerning him(it). On surfaces disk as a result record to information are formed magnetized area, in the form of the concentric circumferences. They are identified the magnetic track. Peremeschayasi, heads stop on each following track. The Collection track, located friend under the other on all surface, name the cylinder. All heads of the drive move simultaneously, realizing access to of the same name cylinder with alike number.

Device of the disk

The Standard winchester consists of гермоблока and charge of the electronics. In гермоблоке размещены all mechanical parts, on charge - whole controlling electronics, with the exclusion of preamplifier, placed inwardly гермоблока in close proximity heads. Under disk is located engine - flat, as in floppy-spindle, or built-in in spindel of the disc package. The strong flow of the air s At rotation disk, which circulates on perimeter гермоблока and is constantly cleaned by filter, installed on one of his(its) sides. Closer to connector, with left or right sides from spindel, is found thumb positioner, several reminiscent on type tower tap: on the one hand axis, are found turned to disk fine, long and light carrying magnetic heads, but with other - short and more massive хвостовик with winding of the electromagnetic drive. Motion make At tumbling of the yoke of the positioner of the head on arc between the centre and periphery disk. The Corner between axises of the positioner and spindel is selected together with distance from axis of the positioner before heads so that axis of the head at tumbling as small as possible was rejected(deviate) from tangent track.

In more early model yoke was bolted on axis of the crossbar engine, and distance between track was defined by value of the step. In modern model is used so-called linear engine, which has not some дискретности, but installation on track is produced on signal, recorded on disk that gives significant increase to accuracy of the drive and density record on disk.
The Winding of the positioner surrounds статор, representing itself constant magnet. When presenting in winding of the current of the certain value and polarities yoke begins to turn round in corresponding to side with corresponding to speedup; dynamically changing current in winding, possible install the positioner in any position. Such system of the drive has got the name Voice Coil (the sound spool) - with diffuser of the loudspeaker in analogy.

On хвостовике is usually located so named magnetic защелка - a small constant magnet, which under extreme internal position of the heads (landing zone - a landing zone) is attracted to surfaces статора and fixes the yoke in this position. This so named парковочное position of the heads, which herewith rest upon surfaces of the disk, touching with her. In row road models (usually SCSI) for фиксации of the positioner is provided special electromagnet, anchor which in free position blocks moving the yoke. In landing zone disk information is not written.

In remained free space размещен preamplifier of the signal, skim with heads, and their commutator. The Positioner united with charge of the preamplifier by flexible band cable, however in separate winchester (in particular - some models Maxtor AV) power supply windings подведено separate одножильными wire, which tend to conk under active work. Germoblok is filled usual обеспыленным by air under atmospheric pressure. In lid гермоблоков some winchester are specially done small window, stuck by fine film, which serves for leveling the pressure inwardly and outside. In row of the models window is closed воздухопроницаемым by filter. Beside one models winchester to axis of the spindel and positioner are bolted only in one place - on body of the winchester, beside other they in addition bear up the screw to lid гермоблока. The Second models more sensitive to микродеформации when fastening - it is enough strong затяжки крепежных screw to appeared the inadmissible slanting of the axises. In row of the events such slanting can become труднообратимым or inconvertible quite. The Charge of the electronics - withdrawable, is connected to гермоблоку through one - two connectors to different design. On board are located main processor of the winchester, ROM with program, worker OZU, which is usually used and as disc buffer, digital signal processor (DSP) for preparing written and processing scanned signal, and interface logic. On one winchester program processor is completely kept in ROM, on other determined her(its) part recorded in official area of the disk. On disk also can be a recorded parameters of the drive (the model, serial number etc.). Some winchesters is kept this information in electrically репрограммируемом ROM (EEPROM).

Many winchesters have on board of the electronics special technological interface with connector, through which with the help of stand equipment possible to execute the different service operations with drive - a testing, formatting, reassigning fault area etc. Beside modern drives of the mark Conner technological interface is executed in standard of the consequent interface that allows to connect him(it) through adapter to alphabetical-digital terminal or COM-port of the computer. In ROM recorded so named test-мониторная system (TMOS), which perceives the commands, given with terminal, executes them and removes the results on terminal back. The Early models winchester, either as flexible disks, were made with чистыми magnetic surface; initial sectoring (formatting) was produced by user on his(its) discretion, and could be executed any amount once. For modern models sectoring is produced in process of the fabrication; herewith on disks is written сервоинформация - a special marks required for stabilization of the velocities of the rotation, searching for sector and spying for position of the heads on surface. Not so long ago for writing сервоинформации was used separate surface (dedicated - chosen), on which tuned in the heads of all rest surfaces. Such system required high acerbity of the fastening the heads to between they did not appear the divergences after initial sectoring. Now сервоинформация is written in gap between sector (embedded - built-in) that allows to enlarge the useful capacity of the package and remove the restriction on acerbity of the rolling system. In some modern model is used multifunction system of the spying - built-in сервоинформация in combination with chosen by surface; herewith rough tuning is executed on chosen to surfaces, but exact - on built-in mark. Since сервоинформация presents itself supporting sectoring the disk, controller of the winchester unable by itself to restore her(it) in the event of damage. Under software formatting of such winchester possible only rerecording headline and control totals sector data.

Under initial sectoring and testing the modern winchester at the factory nearly always come to light the fault sector, which are brought in special table of the reassigning. Under usual functioning winchester controller substitutes these sector reserve, which are specially left to this effect on each track, group track or chosen a zone of the disk. Due to this new winchester creates visibility of the full absence defect to surfaces though indeed they there is nearly always.

At power-up processor winchester executes testing the electronics whereupon gives the command of the cut-in шпиндельного engine. At achievement of a certain critical velocity of the rotation density away surface disk an air becomes to be sufficient for преодоления power прижима heads to surfaces and lifting them on height from share before units micron on surface disk - a heads "surface". At this point of time and before reduction of the velocities below critical head "hung" on air pillow and absolutely do not concern the surfaces a disk.

After achievement disk to velocities of the rotation close to nominal (usually - 3600, 4500, 5400 or 7200 about/mines) of the head are removed from zone of the parking and begins searching for сервометок for exact stabilization of the velocities of the rotation. Is it Then executed sensing to information from official zone - in particular, tables of the reassigning fault area. In termination of the initialization is executed testing the positioner by way перебора given sequences track - if it passes successfully, processor exposes on interface sign to readiness and moves over to state of working on interface.

In operation constantly works the system of the spying for position of the head on disk: from continuously read signal stands out the signal of the unbalance, which is given in scheme to feedback, controlling current windings positioner. As a result of deflections of the head from the centre of the track in winding appears the signal, eager to return her(it) on place. For co-ordination of the velocities dataflow - at a rate of sensing/record and external interface - a winchesters have an intermediate buffer, often wrongly named кэшем, volume in several groups of ten usually or сотен kilobytes. In row of the models (for instance, Quantum) buffer takes seats in general worker OZU, where is in the beginning loaded overlay part микропрограммы control, why real volume of the buffer is got smaller, than full volume OZU (80-90 kb under OZU 128 kb beside Quantum). Beside the other models (Conner, Caviar) OZU buffer and processor are made separate.

When unhooking the power supply processor, using energy, remained in capacitor of the board or extracting her(it) from windings of the engine, which herewith works as generator, gives the command on installing the positioner in парковочное position, which haves time to be executed before reduction of the velocities of the rotation below critical. In some winchester (Quantum) this promotes placed between disk подпружиненное yoke, constantly feelling pressure of the air. The positioner in addition pushes At weakening of the airstream yoke in парковочное position, where that is fixed защелкой. Moving the heads aside spindel promotes also centripetal power, appearing because of rotation disk.

Functioning the drive

Now we shall consider the process of the functioning(working) the drive from start before stop. When presenting supplying voltages begins to work the microprocessor of the controller. In the beginning he, either as computer, executes самотестирование and in the event of his(its) success starts the scheme of control engine rotations of the spindel. The Disks begin be untwisted, leading away for itself adjoining to surface layer air, and at achievement of a certain velocities pressure running up on heads of the flow of the air overcomes power of the springs, pressing them to disk, and heads "surface", rising on disk on share of the micron. At this point of time, up to stop disk, heads do not concern the disk and "steam" on surface so neither disks, nor heads themselves practically do not abrade. In the interim, engine of the spindel continues to untwist to surfaces. His(its) velocity gradually approaches to nominal (the thousand rotation per minute). In this time drive comsumes the maximum supplying voltages and creates the limiting load on power supply unit of the computer on voltage 12 Volts. Since in any zone disk is present серворазметка, that сервоимпульсы begin to enter with heads immediately after begin rotations, and upon their frequency контроллерсудит about velocities of the rotation disk. The System to stabilizations of the rotation keeps a check on flow сервоимпульсов, and at achievement of the nominal velocity occurs so-called "seizure", under which any deflection to velocities of the rotation immediately is the current corrected by change in winding of the engine. After achievement by spindel to nominal velocity of the rotation is freed fixative of the positioner of the heads of the reading/record, and system of his(its) control checks the ability to turn round and remain on chosen track by way of the selective free positioning. Herewith series quick tumbling is done in different sides that on rumour looks as typical "тарахтение", heard through several seconds after start. During moving the positioner of the heads occurs spying for enterring with heads servo-pulse, and managerial system always "knows", on how much track passed the heads. Similarly occurs and deduction of the heads on chosen by track - at detour from the centre of the track changes at time value and form servo-pulse. The Managerial system can liquidate the deflection, changing current in winding of the engine of the positioner of the heads. During testing the drive of the heads is at the same time done and his(its) calibration - a selection parameter controlling signal for the most quick and exact moving the positioner under minimum amount "miss". Here, it is necessary to say that микрокомпьютер ZHD, either as computer, has ROM, in which recorded BIOS drive - a set of the programs for initial start and control in operation, and OZU, in which after раскрутки of the mechanical system are loaded remaining portions controlling programs. Except whole other, in OZU is loaded so named a card of the reassigning fault sector, in which noted fault sectors, revealled under factory sectoring the disk. These sectors are excluded from work and are sometimes substituted reserve, which there are on each track and in special reserve zone of each disk. Thereby even though disks and have a defects (but under modern density record and mass productions of the surfaces of the carriers they have their always), impression "clean" disk s for user, free sector from сбойных. Moreover there is certain spare reserve sector on each disk of the drive, which possible substitute and appearing subsequently defects. For one drives this, possible, do under governing the special programs, for other - automatically in process of the functioning. Keeping to similar page footing on disk, except obvious advantage, has and their own defect - under her(its) damage микрокомпьютер will not be able it is correct be started, and, even if all information sectors are not damaged, restore their possible will only be on special factory stand.

After initial adjusting the electronics and mechanical engineers микрокомпьютер ZHD moves over to mode of the waiting the commands of the controller, located on system charge or interface card, which is in turn programmed procedure own BIOS or BIOS computer under control OS. The Got command, he позиционирует on necessary cylinder, on сервоимпульсам finds the necessary track, дожидается while before head will reach the necessary sector, and executes sensing or record to information. If controller has required reading/record not one sector, but several - a drive can work in block mode, using OZU as buffer and combining reading/record several sectors with transmission of information to controller or from it.

The Modern drives (as ATA, so and SCSI) support the developed command system of device control, amongst which there are and such, which allow to stop the rotation of the spindel and translate the drive in waiting mode. The Givenned mode is used ON OS and BIOS ов PC for ensuring standard conservations to energy and functioning(working) the procedures of the system of the conservation to energy, unplugging drive in a certain time after waiting of his(its) use. Necessary to note that does not follow to abuse the frequent stop and enabling the drive since exactly during runaway drive works in forced mode and abrades the сильнее, than under normal usage in completely worker active condition. Use the possibility of the conservation to energy of the procedures BIOS and OS follows only on machine-server, working night and day, disc operations, on which can be not executed on few hours while, the whole system must be able full readiness.

At de-energization engine spindel works in mode of the generator, providing meals charges of the electronics for time, necessities for correct close-down. First of all, is blocked presenting the current record in magnetic heads that they have not spoilt information on surface, but the remainder to energy is given in windings of the drive of the heads, pushing them to the centre disk (in this motion head helps and natural rolling down power, appearing at rotation disk). As a rule that запарковать heads it is enough one rolling down power. Getting to landing zone, drive of the heads is snapped magnetic or mechanical fixative before that else, as heads will have time to to concern the surfaces as a result of falls to velocities of the rotation disk. In this and consists the essence "автопарковки" - any fault-free drive always запаркует the heads, as it were suddenly was not switched off power supply, however if in this moment occurred record to information then for user of the consequence can be more sad because of недописанных or необновленных, both areas data, and controlling structures of the file system PC, regardless of type and type installed OS.

Functioning the hard disk

After initial adjusting the electronics and mechanical engineers микрокомпьютер winchester moves over to mode of the waiting the commands from controller, located on system charge or interface card. The Got command, he includes the necessary head, on сервоимпульсам finds the necessary track, дожидается while before head "доедет" necessary sector, and executes sensing or record to information. If controller has required reading/record not one sector, but several - a winchester can work in so named block mode, using OZU as buffer and combining reading/record with transmission of information to controller or from it. For optimum use the surfaces disk is used so named зоновая record (Zoned Bit Recording - ZBR), which principle consists in that that on external track, having greater length (but consequently - and information capacity), information is written with greater density, than on internal. Such zones with constant density record within the whole surface is formed before group of ten and more; accordingly, velocity of the reading and record on external zone above, than on internal. Due to this files, located to "beginning of" winchester closer, will as a whole be processed quicker files, located closer to his(its) "end".

Now about that, whence r improbable greater amount of the heads, specified in parameter winchester. At one time these numbers - a number cylinder, heads and sector on cherish - really marked the real physical parameters (the geometry) of the winchester. However when use ZBR amount sector is changed from track to track, and for each winchester of these number different - so became be used so named logical geometry, when winchester reports the controller certain conditional parameters, but at reception of the commands itself will convert the logical address in physical. Herewith in winchester with logical geometry, for instance, in 520 cylinders, 128 heads and 63 sectors (the general volume - 2 Gb) is found, sooner whole, two disks - and four heads of the reading/record.

In winchester of the last generation are used technologies PRML (Partial Response, Maximum Likelihood - a maximum plausibility under incomplete response) and S.M.A.R.T. (Self Monitoring Analysis and Report Technology - technology independent watching analysis and reporting). The First is designed because of what under existing density record already impossible clearly and uniquely read the signal with surfaces of the disk - a level of the hindrances and distortion very great. His(its) comparison is used Instead of direct transformation of the signal with set sample, and on the grounds of maximum похожести is done conclusion about acceptance that or other code word - approximately in the same way if we read the word, in which are missed or garbled letters.

The Winchester, in which marketed technology S.M.A.R.T., leads the statistics their own worker parameter (the amount start/foot and produced hours, acceleration time of the spindel, discovered/amendable errors etc.), which is regularly saved in reprogrammable ROM or in official zone of the disk. This information is accumulated during the whole life of the winchester and can be is any time required program of the analysis; on her possible to judge about condition mechanical engineers, condition to usages or approximite probability mortality

Volume, velocity and time of the access

The Primary tasks of the producers always was an increase the volume keeping on disk of information and velocities of the work with this information. What enlarge the volume of the disk? The most obvious decision is an increase amount plates housed hard disk. Such a image usually differ the models within one model row. This way is most simple and allows on one and same element base to get the disks to different capacity. But beside this way exist the natural restrictions: amount disk can not be endless. Increases the load on motor, grow worse warm-up and noise features of the disk, probability of the marriage grows pro rata amount of the plates, but signifies, harder provide reliability. Amongst industrial produced disk by most amount of the plates possesses SCSI disk Seagate Barracuda 180 - beside this winchester 12 plates! There is and world record holders in the field of simplifications device disk -, for instance, Maxtor 513DX and 541DX, beside which one disk, used only on the one hand.

Technologically more complex (and more perspective) method increase the volume - an increase to density record to information. Here appears variety of technological problems. The Modern plates are made from aluminum or even from flow (some models IBM). Magnetic covering has a complex laminated structure and is coated overhand special defensive слоем. The Sizes of the particles of the magnetic covering decrease, but sensitivity their increases. Aside from improvement parameter plates themselves, essential improvements must be subjected to the system of the sensing to information. Necessary to reduce the clearance between head and surface of the plate, raise sensitivity of the head. But also here laws physicists superimpose their own natural restrictions on limit of the using like technology. After all sizes of the magnetic particles can not decrease infinitely.

The Simplest way to enlarge the reading rate - enlarge the velocity of the rotation of the plates. On this way and will go the constructors. If plates revolve with greater velocity, that per unit time under reading head passes more to information. On increase reading rate affects as well as considered above increase to density record to information. Exactly for this reason SCSI disks, as a rule, possess the greater velocity of the rotation. However on such velocities сложнее exactly to position the head of the sensing so density record there less, than on some IDE disk, but cost(stand) such disks more.

Since head at information retrieval moves across disk only, she have to "wait" while disk to turn and sector with required data will turn out to be available to reading. This time depends from velocity of the rotation of the disk only and is identified rotational latency to information (latency). But necessary to understand that general time of the access to information is defined by time of searching for of the necessary track on disk and time of the positioning inwardly this tracks. Increase to velocities of the rotation of the disk reduces only last importance. For reduction of time of searching for of the necessary track improve the drive reading heads and reduce the diameter of the plates of the disk. Nearly all modern winchesters are released with plate by diameter 2,5 inches.

Positioning the head in general is separate very нетривиальной by problem. It is Enough to say that under modern density record happens to to take into account even heat expansion! Thereby, increase to velocities of the rotation of the disk greatly obstructs exact positioning the head. And in attempt to enlarge the speed of the disk sometimes happens to to donate the volume, using plates with smaller density record. Not surprising that the most expensive and quick winchesters, differring more high velocity of the rotation, do not use maximum technologically available on given moment to density record. For velocity it happens to to pay.

So what disk to show a preference? The models deserve Under alike volume greater attention with greater density record, in contrast with model with big amount disk if for no reason than beside them above linear velocity of the reading/record (the greater files are read quicker). The Velocity of the access to information stright depends on velocities of the rotation of the plates (quicker work with big amount of the small files). But increase to velocities brings about удорожанию product, but sometimes happens to to donate and density record.

Interfaces hard disk

The Development interface winchester went two parallel fetters: cheap and expensive. The Expensive decision was concluded in creation on charge most winchester of the separate intellectual controller, which undertook the much of the work on interaction with winchester. The Result of this approach was an interface SCSI, which has quickly conquered popularity on the market server. One of the advantage of this approach was shown possibility of the connection to computer significant therefor time amount device, requiring for its functioning(working) the broad channel data communication.

The Idle time and cheap decision - replace the much an operation on entering-conclusion on central processor. Beside this decisions wholly obvious defect: reduction to general computing power of the system, particularly observable under multitasking work. А in that timeses, when processors were not such powerful, this powerfully limited the possibility, in particular, file server. The Result of the entailment in life of this approach was a widespread interface IDE.

This interface was relatively дешев and though was not the most production, has completely displaced other interfaces with the market cheap and inexpensive systems. He gradually developed, and standards UDMA appeared since time, greatly accelerating functioning winchester, interfaces IDE became more knowledge-based. But since power processor grew quicker power a winchester, that restrictions of the interface IDE played all smaller role.

Hereunder on today we have two types winchester: large powered SCSI and "mass consumption" - IDE. The Principle difference in device winchester SCSI themselves and IDE no, but historically formed that SCSI is calculated on segment road server decisions so at the average they quicker and, as effect, greatly cherish. The Admission velocity SCSI well above IDE, integer 160 Mb/with. But IDE works at the speed of 33,66 and 100 Mb/with. The Corresponding to standards are identified ATA/33, ATA/66 and ATA/100.

External hard disks

The Dialect about interface for connection winchester, cost(stand)s to recall and about portable winchester. At present exists several decisions for connection external device. First, there is winchesters, being connected to USB-port. They are used basically for changing given with digital camera and other mobile device. On the strength of low reception capacity of this bus similar disks, certainly, will not be able be compared in capacity with internal device.

All greater spreading gets the new interface IEEE1394, which can be used not only for connection hard disk, but also the other device, working with greater array data, for instance, video cameras. The Controllers of this interface sometimes are even built in in maternal charge. His(its) capacity is enough, for instance, for проигрывания video high quality - declared reception capacity of the interface reaches 50 Mb/with. We shall Remind that else vapour(pair) of the years back such velocity could not boast the interface IDE.

Author: А. V. Savin It Is Added: 03.05.2007