Many PC users know what a hard drive is for, but not many know. From the article you will learn why a hard drive is called a hard drive, how it works, important characteristics, as well as the principle of operation of a hard drive.

A LITTLE HISTORY:
According to a 1973 legend, HDD got its unofficial "nickname" when the first HDD appeared. Its volume was 30Mb + 30Mb in another compartment. The HDD was developed by a team of engineers, for the amount of memory it was given the code name "30-30", this name was very similar to the weapon popular at that time, the cartridge caliber of which was 30-30 Winchester.
Interestingly, in the early 90s in the US, this name went out of the lexicon; in Russia, it is relevant to the present, in addition, the abbreviation "screw" is used.

IMPORTANT FEATURES:
Since the modern market is overwhelmed with various HDDs, SSDs, etc., these characteristics and parameters will help you better understand this issue when buying. hard drive.

1. Connection: basically hard drives connect to motherboard via the SATA interface. But there are exceptions, for example, the eSATA interface, this is not the same thing. In addition, Fire-Wire, IDE are gaining more popularity.
2. Capacity is characterized by a value, an indicator of how much information will fit on the hard drive. Modern computers have 500GB or 1TB hard drives.
3. Physical size: dimensions are also important, they can be used to determine which PC it is intended for. For example, the HDD for a laptop will be 2.5 inches, for a desktop computer, 3.5 inches is required.
4. Turnovers: rotational speed is also an important parameter. The higher the numerical value of the indicator, the higher the speed of the screw will be. The market average is 5400 - 7200 rpm.
5. Intermediate memory: otherwise it is called a buffer. The speed of reading and writing on the hard drive is different, in order to somehow smooth this out, the engineers came up with an intermediate memory, it seems to smooth out the difference in values.

WINCHESTER DEVICE:
Inside the hard drive is:
- electronics board;
- engine;
— magnetic heads;
- magnetic disk;
1. Electronics board - integrated circuits for railway work. Responsible for receiving and processing commands from the PC. The circuit also consists of: ROM, RAM, microcircuits and the main processor.
2. The engine or electric motor is designed to control the controller and speed.
3. Magnetic heads are responsible for writing and reading information on the disk.
4. The magnetic disk is the most important, the operation of the entire hard drive depends on its operation. AT modern types The hard drive has several such magnetic disks installed.

WINCHESTER WORKING PRINCIPLE:
When the computer is connected to the network, the power powers the hard drive, but what happens next, how does everything work? After the HDD is turned on, the main controller starts to work, then the motor rotates. After the speed has reached the desired parameter, the heads that read the signal are connected to work. At startup, data on the state of the disk is read, after which the information saved by the user is connected. Now you know, how does a computer hard drive work how it can differ, what characteristics it has.

How is a hard drive arranged? What are hard drives? What role do they play in a computer? How do they interact with other components? What parameters to consider when choosing and buying a hard drive, you will learn from this article.

HDD- short name for " Hard Disk Drive". You will also meet English HDD- and slang Winchester or abbreviated Screw.

AT computer hard The disk is responsible for storing data. operating room Windows system, programs, movies, photos, documents, all the information that you download to your computer is stored on your hard drive. And the information in the computer is the most valuable thing! If the processor or video card fails, they can be bought and replaced. But lost family photos from last summer's vacation, or a year's worth of accounting data for a small business, are not so easy to recover. Therefore, the reliability of data storage is given special attention.

Why is a rectangular metal box called a disk? To answer this question, we need to look inside and find out how a hard drive works. In the picture below you can see what parts a hard drive consists of and what functions each part performs. Click to enlarge. (Taken from itc.ua)

I also suggest watching an excerpt from the Discovery Channel program about how a hard drive works and works.

Three more facts you need to know about hard drives.

1. The hard drive is the slowest part of a computer. When the computer is frozen, pay attention to the indicator work hard disk. If it blinks frequently or stays on, then the hard drive is executing the commands of one of the programs, while all the others are idle, waiting for their turn. If the operating system does not have enough high-speed RAM to run the program, it uses hard disk space, which greatly slows down the entire computer. Therefore, one way to increase the speed of your computer is to increase the amount of RAM.
2. The hard drive is also the most fragile part of a computer. As you learned from the video, the engine spins the disk up to several thousand revolutions per minute. In this case, the magnetic heads "hover" above the disk in the air flow created by the rotating disk. The distance between the disk and heads in modern devices is about 10 nm. If the disk is subjected to shock or shock at this point, the head may touch the disk and damage the surface with data stored on it. As a result, the so-called bad blocks" - unreadable areas, due to which the computer cannot read any file or boot the system. In the off state, the heads "park" outside the working area and overloads from impact are not so terrible for the hard drive. Please do it backups important data!
3. The capacity of the hard drive is often slightly smaller than what the seller or manufacturer specifies. The reason is that manufacturers indicate the size of the disk based on the fact that there are 1,000,000,000 bytes in one gigabyte, while there are 1,073,741,824 of them.

Buying a hard drive

If you decide to increase the amount of information storage in your computer by connecting an additional hard drive or replacing the old one with a larger one, what do you need to know when buying?

First, look under the lid system block your computer. You need to find out which interface connecting hard disk is supported by the motherboard. By far the most widely used standards SATA and outliving its age IDE. They are easy to distinguish by appearance. The picture on the left shows a fragment of the motherboard, which is equipped with both types of connectors, but yours will most likely be one of them.

There are three versions of the interface SATA. They differ in data transfer speed. SATA, SATA II and SATA III at speeds of 1.5, 3 and 6 gigabytes per second, respectively. All interface versions SATA look the same and are compatible with each other. You can connect them in any combination, as a result, the data transfer rate will be limited to the slower version. At the same time, the speed of the hard drive is even slower. Therefore, the potential of fast interfaces can be revealed only with the advent of new high-speed drives.

If you decide to purchase an additional SATA hard drive, check if you have an interface cable as shown in the picture. It is not sold with a CD. (They are usually bundled with the motherboard.) Also, among the power supply connectors, there should be at least one free one for connecting a hard drive, or you may need an adapter from the old standard to the new one.

Now about the hard drive itself: The main parameter is, of course, the capacity. As I mentioned above, please note that it will be slightly less than stated. For operating system and programs require 100 - 200 gigabytes, which is quite a bit by modern standards. How much additional space you may need, you can determine empirically. Large volumes may be required, for example, to record high quality video. Modern films in HD format reach several tens of gigabytes.

In addition, among the main parameters indicate:

1. Form factor- disk size. 1.8" and 2.5" disks are used in . For a desktop computer, you should purchase a 3.5-inch drive. They have the same SATA connectors and a laptop drive can work in a desktop computer. But small drives are made with an emphasis on compactness and low power consumption, and are inferior to larger models in terms of speed. And they cost more.
2. RPM- disk rotation speed. Measured in revolutions per minute ( RPM- short for revolutions per minute). The faster the rotation speed, the faster the disk writes and reads information. But it also consumes more energy. Today, the most common discs with 5400RPM and 7200RPM. Lower RPMs are more common in laptop drives, high capacity drives (greater than two terabytes), and so-called "green" drives, named for their reduced power consumption. There are also hard drives with a rotational speed 10000RPM and 15000RPM. They are designed to work in highly loaded servers and have an increased reliability resource, but they also cost much more than conventional ones.
3. Manufacturer. At the moment, there are several large manufacturers on the storage market. Among them there is quite tough competition, so they are in no way inferior to each other in quality. Therefore, you can choose any of the well-known names: Hitachi, HP, Seagate, Silicon power, Toshiba Transcend, Western Digital.

Hard drives

Is done by a student
groups 40-101B.
Karimov K.R.
Teacher:
Usov P.A.

1. Working principle of a hard drive.. 3

2. Disk device.. 5

3. Hard disk operation.. 10

4. Volume, speed and access time.. 12

5. Hard drive interfaces .. 14

6. External hard drives .. 16

How a hard drive works

The hard disk drive is one of the most advanced and complex devices of modern personal computer. Its disks are capable of holding many megabytes of information transmitted at great speed. While almost all computer components are silent, the hard drive grumbles and creaks, which makes it one of the few computer devices that contain both mechanical and electronic components.

The basic principles of hard disk operation have changed little since its inception. The device of the hard drive is very similar to an ordinary record player. Only under the body there can be several plates mounted on a common axis, and the heads can read information from both sides of each plate at once. The speed of rotation of the plates (for some models it reaches 15,000 rpm) is constant and is one of the main characteristics. The head moves along the plate at some fixed distance from the surface. The smaller this distance, the greater the accuracy of reading information, and the greater the density of information recording can be. Looking at the hard drive, all you see is a solid metal case. It is completely sealed and protects the drive from dust particles, which, if they enter the narrow gap between the head and the disk surface, can damage the sensitive magnetic layer and disable the disk. In addition, the case shields the drive from electromagnetic interference. Inside the case are all the mechanisms and some electronic components. The mechanisms are the disks themselves, on which the information is stored, the heads that write and read information from the disks, as well as the engines that set it all in motion. The disk is a round plate with a very flat surface, often made of aluminum, less often made of ceramic or glass, coated with a thin ferromagnetic layer. Disks are made. Many drives use a layer of iron oxide (which coats conventional magnetic tape), but latest models hard drives work with a layer of cobalt about ten microns thick. Such a coating is more durable and, in addition, can significantly increase the recording density. The technology of its application is close to that used in the production of integrated circuits.

The number of disks can be different - from one to five, the number of working surfaces, respectively, is twice as much (two on each disk). The latter (as well as the material used for the magnetic coating) determines the capacity of the hard drive. Sometimes the outer surfaces of the outer disks (or one of them) are not used, which makes it possible to reduce the height of the drive, but the number of working surfaces is reduced and may turn out to be odd.

Magnetic heads read and write information to discs. The principle of recording is generally similar to that used in a conventional tape recorder. Digital information is converted into variable electricity, arriving at the magnetic head, and then transferred to the magnetic disk, but already in the form of a magnetic field, which the disk can perceive and "remember". The magnetic coating of the disk is a set of tiny areas of spontaneous (spontaneous) magnetization. For clarity, imagine that the disk is covered with a layer of very small compass arrows pointing in different directions. Such arrow particles are called domains. Under the influence of an external magnetic field, the own magnetic fields of the domains are oriented in accordance with its direction. After the termination of the action of the external field, zones of residual magnetization are formed on the surface of the disk. In this way, the information written to the disc is preserved. Areas of residual magnetization, when the disk rotates opposite the gap of the magnetic head, induce an electromotive force in it, which varies depending on the magnitude of the magnetization. The disc pack, mounted on a spindle axle, is driven by a special motor compactly located underneath. The rotation speed of the discs is typically 7200 rpm. In order to reduce the drive's output time to working condition, the engine, when turned on, runs in forced mode for a while. Therefore, the computer power supply must have a margin for peak power. Now about the work of the heads. They move with precision stepper motor and, as it were, "float" at a distance of fractions of a micron from the surface of the disk, without touching it. As a result of recording information, magnetized areas are formed on the surface of disks, in the form of concentric circles. They are called magnetic tracks. Moving, the heads stop over each next track. A set of tracks located one below the other on all surfaces is called a cylinder. All drive heads move simultaneously, accessing cylinders of the same name with the same numbers.

Disk device

A typical hard drive consists of a HDA and an electronics board. All mechanical parts are located in the HDA, and all control electronics are on the board, except for the preamplifier located inside the HDA in close proximity to the heads.

Under the disks is the motor - flat, as in floppy drives, or built into the spindle of the disk package. When the disks rotate, a strong air flow is created, which circulates around the HDA perimeter and is constantly cleaned by a filter installed on one of its sides.

Closer to the sockets, on the left or right side of the spindle, there is a rotary positioner, somewhat reminiscent of a tower crane: on one side of the axis, there are thin, long and light bearing magnetic heads facing the disks, and on the other, a short and more massive shank with electromagnetic drive winding. When the rocker of the positioner is turned, the heads move in an arc between the center and the periphery of the disks. The angle between the axes of the positioner and the spindle is selected together with the distance from the axis of the positioner to the heads so that the axis of the head deviates as little as possible from the tangent track when turning.

In more early models the rocker was fixed on the axis of the stepper motor, and the distance between the tracks was determined by the step size. In modern models, the so-called linear motor is used, which does not have any discreteness, and the installation on the track is carried out according to the signals recorded on the disks, which gives a significant increase in the accuracy of the drive and the recording density on the disks.

The winding of the positioner is surrounded by a stator, which is a permanent magnet. When a current of a certain magnitude and polarity is applied to the winding, the rocker begins to turn in the appropriate direction with the corresponding acceleration; By dynamically changing the current in the winding, you can set the positioner to any position. Such a drive system is called Voice Coil (voice coil) - by analogy with the loudspeaker cone.

The so-called magnetic latch is usually located on the shank - a small permanent magnet, which, at the extreme internal position of the heads (landing zone - landing zone), is attracted to the stator surface and fixes the rocker arm in this position. This is the so-called parking position of the heads, which at the same time lie on the surface of the disk, in contact with it. In a number of expensive models (usually SCSI), a special electromagnet is provided to fix the positioner, the armature of which blocks the movement of the rocker in a free position. Information is not recorded in the landing zone of disks.

In the remaining free space there is a preamplifier of the signal taken from the heads and their switch. The positioner is connected to the preamplifier board with a flexible ribbon cable, however, in some hard drives (in particular, some Maxtor AV models), the winding is powered by separate single-core wires, which tend to break during active operation. The HDA is filled with ordinary dust-free air under atmospheric pressure. In the HDA covers of some hard drives, small windows are specially made, sealed with a thin film, which serve to equalize the pressure inside and outside. In some models, the window is closed with an air-permeable filter. In some models of hard drives, the spindle and positioner axes are fixed only in one place - on the hard drive case, in others they are additionally attached with screws to the HDA cover. The second models are more sensitive to microdeformation during fastening - a strong tightening of the fastening screws is enough to cause an unacceptable misalignment of the axes. In some cases, such a bias can become difficult to reverse or completely irreversible. Electronics board - removable, connected to HDA ​​via one or two connectors various designs. The board contains the main processor of the hard drive, ROM with the program, working RAM, which is usually used as a disk buffer, a digital signal processor (DSP) for preparing recorded and processing read signals, and interface logic. On some hard drives, the processor program is completely stored in ROM, on others, a certain part of it is recorded in the service area of ​​\u200b\u200bthe disk. The drive parameters (model, serial number, etc.) can also be recorded on the disk. Some hard drives store this information in electrically reprogrammable ROM (EEPROM).

Many hard drives have a special technological interface with a connector on the electronics board, through which, using bench equipment, you can perform various service operations with the drive - testing, formatting, reassigning defective areas, etc. For modern Conner brand drives, the technological interface is made in the serial interface standard, which allows you to connect it through an adapter to an alphanumeric terminal or a computer COM port. The so-called test-monitor system (TMOS) is recorded in the ROM, which perceives commands given from the terminal, executes them and outputs the results back to the terminal. Early hard drives, like floppy disks, were made with clean magnetic surfaces; the initial marking (formatting) was made by the consumer at his discretion, and could be performed any number of times. For modern models, marking is done during the manufacturing process; at the same time, servo information is written to the disks - special marks necessary for stabilizing the rotation speed, searching for sectors and tracking the position of heads on surfaces. Not so long ago, a separate surface (dedicated) was used to record servo information, according to which the heads of all other surfaces were tuned. Such a system required a high rigidity of the fastening of the heads, so that there would be no discrepancies between them after the initial marking. Now servo information is recorded in the intervals between sectors (embedded), which allows increasing the useful capacity of the packet and removing the restriction on the rigidity of the moving system. Some modern models use a combined tracking system - built-in servo information combined with a dedicated surface; in this case, rough adjustment is performed on the selected surface, and fine adjustment - on the built-in marks.

Since the servo information is a reference marking of the disk, the hard drive controller is not able to restore it on its own in case of damage. With software formatting of such a hard drive, it is only possible to overwrite the headers and checksums of the data sectors.

During the initial marking and testing of a modern hard drive at the factory, defective sectors are almost always found, which are entered in a special remapping table. During normal operation, the hard drive controller replaces these sectors with spare ones, which are specially left for this purpose on each track, group of tracks or dedicated area of ​​the disk. Thanks to this, the new hard drive creates the appearance total absence surface defects, although in fact they are almost always present.

When the power is turned on, the hard drive processor tests the electronics, after which it issues a command to turn on the spindle motor. When a certain critical speed of rotation is reached, the density of the air entrained by the surfaces of the disks becomes sufficient to overcome the force of pressing the heads to the surface and raise them to a height from fractions to a few microns above the surfaces of the disks - the heads "float". From this moment until the speed drops below the critical head, they "hang" on an air cushion and do not touch the surfaces of the disks at all.

After the discs reach a rotation speed close to the nominal one (usually 3600, 4500, 5400 or 7200 rpm), the heads are removed from the parking zone and the search for servo marks begins to accurately stabilize the rotation speed. Then, information is read from the service area - in particular, the table of reassignment of defective sections.

At the end of the initialization, the positioner is tested by iterating over the specified sequence of tracks - if it is successful, the processor sets the readiness flag on the interface and switches to the interface operation mode.

During operation, the system for tracking the position of the head on the disk is constantly working: an error signal is extracted from the continuously read signal, which is fed into the circuit feedback, which controls the current of the positioner winding. As a result of the deviation of the head from the center of the track, a signal arises in the winding, seeking to return it to its place.

To match the speeds of data streams - at the read / write level and the external interface - hard drives have an intermediate buffer, often erroneously called a cache, usually several tens or hundreds of kilobytes in size. In a number of models (for example, Quantum), the buffer is located in the general working RAM, where the overlay part of the control firmware is loaded first, which is why the actual buffer size is less than the full amount of RAM (80-90 kb with 128 kb RAM for Quantum). Other models (Conner, Caviar) have separate buffer and processor RAM.

When the power is turned off, the processor, using the energy left in the capacitors of the board or extracting it from the motor windings, which at the same time works as a generator, issues a command to set the positioner to the parking position, which has time to be executed before the rotation speed drops below the critical one. In some hard drives (Quantum), this is facilitated by a spring-loaded rocker placed between the disks, constantly experiencing air pressure. When the air flow weakens, the rocker additionally pushes the positioner into the parking position, where it is fixed with a latch. The movement of the heads towards the spindle is also facilitated by the centripetal force arising from the rotation of the disks.

Hard disk operation

Now - actually about the process of the hard drive. After initial setting electronics and mechanics, the microcomputer of the hard drive goes into the mode of waiting for commands from the controller located on system board or interface card. Having received a command, it turns on the desired head, searches for the desired track by servo pulses, waits until the desired sector "reaches" the head, and reads or writes information. If the controller requested to read/write not just one sector, but several, the hard drive can operate in the so-called block mode, using RAM as a buffer and combining reading/writing with transferring information to or from the controller.

For optimal use The surface of the disks uses the so-called zone recording (Zoned Bit Recording - ZBR), the principle of which is that on external tracks that are longer (and therefore information capacity), information is recorded with a higher density than on internal ones. Up to a dozen or more such zones with a constant recording density are formed within the entire surface; accordingly, the speed of reading and writing on the outer zones is higher than on the inner ones. Thanks to this, files located closer to the "beginning" of the hard drive will generally be processed faster than files located closer to its "end".

Now about where the incredibly large numbers of heads indicated in the parameters of hard drives come from. Once upon a time, these numbers - the number of cylinders, heads and sectors on the road - really meant the real physical parameters (geometry) of the hard drive. However, when using ZBR, the number of sectors varies from track to track, and for each hard drive these numbers are different - therefore, the so-called logical geometry began to be used, when the hard drive tells the controller some conditional parameters, and when receiving commands, it itself converts logical addresses into physical ones. At the same time, in a hard drive with a logical geometry, for example, 520 cylinders, 128 heads and 63 sectors (total volume - 2 GB), there are most likely two disks - and four read / write heads.

The latest generation of hard drives use PRML (Partial Response, Maximum Likelihood) and S.M.A.R.T. (Self Monitoring Analysis and Report Technology - technology for self-monitoring analysis and reporting). The first was developed due to the fact that at the existing recording densities it is no longer possible to clearly and unambiguously read the signal from the disk surface - the level of interference and distortion is very high. Instead of directly converting the signal, it is compared with a set of samples, and based on the maximum similarity, a conclusion is made about the reception of one or another code word - approximately the same way we read words in which letters are missing or distorted.

The hard drive, which implements the S.M.A.R.T. technology, keeps statistics of its operating parameters (the number of starts/stops and hours worked, the spindle acceleration time, detected/corrected errors, etc.), which is regularly stored in the flash ROM or in the service areas of the disk. This information is accumulated throughout the life of the hard drive and can be requested by analysis programs at any time; it can be used to judge the state of mechanics, operating conditions or the approximate probability of failure.

Similar information.

Hard disk device

Artyom Rubtsov,R.LAB Clarification of the connection between Russian and English terminology was made by Leonid Vorzhev.

The purpose of this article is to describe the structure of a modern hard drive, talk about its main components, show how they look and are called. In addition, we will show the relationship between Russian and English terminologies describing hard drive components.

For clarity, let's take a look at a 3.5-inch SATA drive. It will be a brand new terabyte Seagate ST31000333AS. Let's examine our guinea pig.

A green textolite with copper tracks, power connectors and SATA is called an electronics board or a control board (Printed Circuit Board, PCB). It is used to manage the operation of the hard drive. The black aluminum case and its contents are called HDA (Head and Disk Assembly, HDA), experts also call it a "can". The body without contents is also called the HDA (base).

Now let's remove the printed circuit board and examine the components placed on it.

The first thing that catches your eye is a large chip located in the middle - a microcontroller, or processor (Micro Controller Unit, MCU). On modern hard drives, the microcontroller consists of two parts - the Central Processor Unit (CPU) itself, which performs all calculations, and the read / write channel - a special device that converts the incoming from the heads analog signal into digital data during a read operation and encodes the digital data into an analog signal during a write operation. The processor has input-output ports (IO ports) to control other components located on printed circuit board, and data transfer via SATA interface.

The memory chip is a conventional DDR SDRAM memory. The amount of memory determines the size of the hard disk cache. This circuit board has 32 MB Samsung DDR memory, which in theory gives the drive a 32 MB cache (and this is exactly the amount given in the specifications of the hard drive), but this is not entirely true. The fact is that the memory is logically divided into buffer memory (cache) and firmware memory. The processor needs some memory to load firmware modules. To the best of our knowledge, only Hitachi/IBM list the actual amount of cache in the specification sheet; As for the rest of the drives, we can only guess about the amount of cache.

The next chip is the engine and head unit control controller, or “twist” (Voice Coil Motor controller, VCM controller). In addition, this chip controls the secondary power sources located on the board, from which the processor and the preamplifier-switching chip (preamplifier, preamp) located in the HDA are powered. This is the main consumer of energy on the printed circuit board. It controls the rotation of the spindle and the movement of the heads. The VCM controller core can operate even at 100°C.

Part of the drive's firmware is stored in flash memory. When power is applied to the disk, the microcontroller loads the contents of the flash chip into memory and starts executing the code. Without a correctly loaded code, the disk will not even want to spin up. If there is no flash chip on the board, then it is built into the microcontroller.

The vibration sensor (shock sensor) reacts to shaking dangerous for the disk and sends a signal about this to the VCM controller. The VCM immediately parks the heads and can stop the disk from spinning. Theoretically, this mechanism should protect the drive from additional damage, but it doesn't work in practice, so don't drop the discs. On some discs, the vibration sensor is highly sensitive, reacting to the slightest vibration. The data received from the sensor allows the VCM controller to correct the movement of the heads. At least two vibration sensors are installed on such disks.

The board has another protective device - the transient voltage suppression (TVS). It protects the board from power surges. During a power surge, the TVS burns out, creating a short circuit to ground. This board has two TVS, 5 and 12 volts.

Now consider the HDA.

Under the board are the contacts of the motor and heads. In addition, there is a small, almost imperceptible hole (breath hole) on the disk case. It serves to equalize pressure. Many people think that there is a vacuum inside the hard drive. Actually it is not. This hole allows the disk to equalize the pressure inside and outside the containment. On the inside, this hole is covered with a breath filter, which traps dust and moisture particles.

Now let's look inside the containment area. Remove the disc cover.

The lid itself is nothing special. It's just a piece of metal with a rubber seal to keep dust out. Finally, consider the filling of the containment area.

Precious information is stored on metal discs, also called pancakes or plates (platters). In the photo you see the top plate. The plates are made of polished aluminum or glass and are covered with several layers of various compositions, including a ferromagnetic substance, on which, in fact, the data is stored. Between the pancakes, as well as above the top of them, we see special plates called separators or separators (dampers or separators). They are needed to equalize air flows and reduce acoustic noise. As a rule, they are made of aluminum or plastic. Aluminum separators are more successful in cooling the air inside the containment area.

Side view of pancakes and separators.

Read-write heads (heads) are installed at the ends of the brackets of the magnetic head unit, or HSA (Head Stack Assembly, HSA). The parking zone is the area where the heads of a healthy disk must be when the spindle is stopped. With this disc, the parking zone is located closer to the spindle, as can be seen in the photo.

On some drives, parking is carried out on special plastic parking areas located outside the plates.

The hard drive is a precision positioning mechanism and requires very clean air to function properly. During use, microscopic particles of metal and grease may form inside the hard drive. For immediate cleaning of the air inside the disk there is a recirculation filter. This is a high-tech device that constantly collects and traps the smallest particles. The filter is located in the path of air flows created by the rotation of the plates.

Now let's remove the top magnet and see what is hidden under it.

Hard drives use very powerful neodymium magnets. These magnets are so powerful that they can lift 1,300 times their own weight. So do not put your finger between the magnet and metal or another magnet - the blow will be very sensitive. This photo shows the BMG limiters. Their task is to limit the movement of the heads, leaving them on the surface of the plates. BMG limiters of different models are arranged differently, but there are always two of them, they are used on all modern hard drives. On our drive, the second limiter is located on the bottom magnet.

Here's what you can see there.

We also see here the coil (voice coil), which is part of the block of magnetic heads. The coil and magnets form the VCM drive (Voice Coil Motor, VCM). The drive and the block of magnetic heads form a positioner (actuator) - a device that moves the heads. A black plastic piece of complex shape is called a latch (actuator latch). This is a safety mechanism that releases the HMG after the spindle motor has reached a certain number of revolutions. This happens due to the pressure of the air flow. The latch protects the heads from unwanted movements in the parking position.

Now let's remove the block of magnetic heads.

Accuracy and smoothness of movement of the BMG is supported by a precision bearing. The largest part of the BMG, made of aluminum alloy, is usually called a bracket or rocker (arm). At the end of the rocker are heads on a spring suspension (Heads Gimbal Assembly, HGA). Usually the heads and rocker arms are supplied by different manufacturers. A flexible cable (Flexible Printed Circuit, FPC) goes to the pad that mates with the control board.

Consider the components of the BMG in more detail.

A coil connected to a cable.

Bearing.

The following photo shows the BMG contacts.

The gasket (gasket) ensures the tightness of the connection. Thus, air can enter the inside of the disk and head unit only through the pressure equalization hole. The contacts on this disc are coated with a thin layer of gold to improve conductivity.

This is a classic rocker design.

The little black pieces at the ends of the spring hangers are called sliders. Many sources indicate that sliders and heads are one and the same. In fact, the slider helps to read and write information by raising the head above the surface of the pancakes. On modern hard drives, the heads move at a distance of 5-10 nanometers from the surface of the pancakes. By comparison, a human hair is about 25,000 nanometers in diameter. If any particle gets under the slider, it can lead to overheating of the heads due to friction and failure, which is why the purity of the air inside the containment is so important. The reading and writing elements themselves are located at the end of the slider. They are so small that they can only be seen with a good microscope.

As you can see, the surface of the slider is not flat, it has aerodynamic grooves. They help to stabilize the flight altitude of the slider. The air under the slider forms an air cushion (Air Bearing Surface, ABS). The air cushion maintains the flight of the slider almost parallel to the surface of the pancake.

Here is another slider image.

Head contacts are clearly visible here.

This is another important part of the BMG, which has not yet been discussed. It is called a preamplifier (preamplifier, preamp). A preamplifier is a chip that controls the heads and amplifies the signal coming to or from them.

The preamplifier is located directly in the BMG for a very simple reason - the signal coming from the heads is very weak. On modern drives, it has a frequency of about 1 GHz. If you take the preamp out of the containment area, such weak signal will strongly fade on the way to the control board.

More tracks lead from the preamp to the heads (right) than to the containment area (left). The fact is that a hard disk cannot simultaneously work with more than one head (a pair of writing and reading elements). The hard disk sends signals to the preamplifier, and it selects the head that the hard disk is currently accessing. This hard drive has six tracks leading to each head. Why so many? One track is ground, two more are for read and write elements. The next two tracks are for controlling mini-actuators, special piezoelectric or magnetic devices capable of moving or turning the slider. This helps to more precisely set the position of the heads above the track. The last path leads to the heater. The heater is used to control the flight height of the heads. The heater transfers heat to the suspension connecting the slider and rocker. The hanger is made from two alloys with different thermal expansion characteristics. When heated, the suspension bends towards the surface of the pancake, thus reducing the flight height of the head. When cooled, the suspension straightens.

Enough about the heads, let's disassemble the disk further. Remove the top separator.

Here's what it looks like.

In the next photo, you can see the containment area with the top separator and head assembly removed.

The lower magnet became visible.

Now the clamping ring (platters clamp).

This ring holds the stack of plates together, preventing them from moving relative to each other.

Pancakes are strung on a spindle (spindle hub).

Now that nothing is holding the pancakes, let's remove the top pancake. Here's what's underneath.

Now it’s clear how the space for the heads is created - there are spacer rings between the pancakes. The photo shows the second pancake and the second separator.

The spacer ring is a high precision part made of non-magnetic alloy or polymers. Let's take it off.

Let's pull everything else out of the disk to inspect the bottom of the HDA.

This is what the pressure equalization hole looks like. It is located directly below the air filter. Let's take a closer look at the filter.

Since the outside air necessarily contains dust, the filter has several layers. It is much thicker than the circulation filter. Sometimes it contains particles of silica gel to combat air humidity.

Hard drives, or, as they are also called, hard drives, are one of the most important components computer system. Everyone knows about it. But far from every modern user even in principle guesses how a hard drive functions. The principle of operation, in general, is quite simple for a basic understanding, but there are some nuances, which will be discussed further.

Questions about the purpose and classification of hard drives?

The question of purpose is, of course, rhetorical. Any user, even the most entry level, will immediately answer that the hard drive (aka hard drive, aka Hard Drive or HDD) will immediately answer that it is used to store information.

In general, it is true. Do not forget that on the hard disk, in addition to the operating system and user files, there are boot sectors created by the OS, thanks to which it starts, as well as some marks by which you can quickly find necessary information.

Modern models are quite diverse: ordinary HDDs, external rigid disks, high-speed SSDs, although they are exactly hard drives attributed and not accepted. Further, it is proposed to consider the device and the principle of operation of the hard drive, if not in full, then at least in such a way that it is enough to understand the basic terms and processes.

Please note that there is also a special classification of modern HDDs according to some basic criteria, among which the following can be distinguished:

• method of storing information;
• media type;
• way of organizing access to information.

Why is a hard drive called a hard drive?

Today, many users are thinking about why they call hard drives related to small arms. It would seem that what can be common between these two devices?

The term itself appeared back in 1973, when the world's first HDD appeared on the market, the design of which consisted of two separate compartments in one sealed container. The capacity of each compartment was 30 MB, which is why the engineers gave the disk the code name "30-30", which was fully consonant with the brand of the popular at that time gun "30-30 Winchester". True, in the early 90s in America and Europe this name practically fell into disuse, but it still remains popular in the post-Soviet space.

The device and principle of operation of the hard drive

But we digress. The principle of operation of a hard disk can be briefly described as the processes of reading or writing information. But how does it happen? In order to understand the principle of operation of a magnetic hard drive, it is first necessary to study how it works.

The hard drive itself is a set of platters, the number of which can vary from four to nine, interconnected by a shaft (axis) called a spindle. The plates are placed one above the other. Most often, the material for their manufacture is aluminum, brass, ceramics, glass, etc. The plates themselves have a special magnetic coating in the form of a material called platter, based on gamma ferrite oxide, chromium oxide, barium ferrite, etc. Each such plate is about 2 mm thick.

Radial heads are responsible for writing and reading information (one for each plate), and both surfaces are used in the plates. For which it can range from 3600 to 7200 rpm, and two electric motors are responsible for moving the heads.

At the same time, the basic principle of the computer hard drive is that information is recorded not anywhere, but in strictly defined locations, called sectors, which are located on concentric tracks or tracks. To avoid confusion, uniform rules apply. This means that the principles of operation of hard disk drives, from the point of view of their logical structure, are universal. So, for example, the size of one sector, adopted as a single standard throughout the world, is 512 bytes. In turn, sectors are divided into clusters, which are sequences of adjacent sectors. And the features of the principle of operation of a hard disk in this regard are that the exchange of information is carried out by whole clusters (an integer number of chains of sectors).

But how is information read? Principles of hard drive operation magnetic disks look like this: using a special bracket, the reading head moves in the radial (spiral) direction to the desired track and, when rotated, is positioned above the specified sector, and all heads can move simultaneously, reading the same information not only from different tracks, but also from different disks ( plates). All tracks with the same serial numbers are called cylinders.

At the same time, one more principle of hard disk operation can be distinguished: the closer the read head is to the magnetic surface (but does not touch it), the higher the recording density.

How is information written and read?

Hard drives, or hard drives, were called magnetic because they use the laws of physics of magnetism, formulated by Faraday and Maxwell.

As already mentioned, plates made of non-magnetically sensitive material are coated with a magnetic coating, the thickness of which is only a few micrometers. In the process of work, a magnetic field arises, which has the so-called domain structure.

The magnetic domain is a magnetized region of a ferroalloy strictly limited by boundaries. Further, the principle of operation of a hard disk can be briefly described as follows: when an external magnetic field is applied, the disk's own field begins to orient itself strictly along the magnetic lines, and when the impact stops, zones of residual magnetization appear on the disks, in which the information that was previously contained in the main field is stored. .

The reading head is responsible for creating an external field during recording, and when reading, the residual magnetization zone, being opposite the head, creates an electromotive force or EMF. Further, everything is simple: the change in the EMF corresponds to unity in binary code, and its absence or termination is zero. The time of change of the EMF is usually called a bit element.

In addition, the magnetic surface, purely for computer science reasons, can be associated as a certain dotted sequence of bits of information. But, since the location of such points is absolutely impossible to calculate exactly, you need to install some pre-provided marks on the disk that helped determine the desired location. The creation of such marks is called formatting (roughly speaking, breaking the disk into tracks and sectors combined into clusters).

The logical structure and principle of operation of the hard disk in terms of formatting

As for the logical organization of the HDD, formatting comes first here, in which two main types are distinguished: low-level (physical) and high-level (logical). Without these steps, there is no need to talk about bringing the hard drive into working condition. How to initialize a new hard drive will be discussed separately.

Low-level formatting involves a physical impact on the surface of the HDD, which creates sectors located along the tracks. It is curious that the principle of operation of a hard disk is such that each created sector has its own unique address, which includes the number of the sector itself, the number of the track on which it is located, and the number of the side of the plate. Thus, when organizing direct access, the same RAM addresses directly to a given address, and does not search for the necessary information over the entire surface, due to which speed is achieved (although this is not the most important thing). Please note that when performing low-level formatting, absolutely all information is erased, and in most cases it cannot be restored.

Another thing is logical formatting (in Windows systems, this is quick formatting or Quick format). In addition, these processes are applicable to the creation of logical partitions, which are some area of ​​the main hard drive that works according to the same principles.

Logical formatting primarily affects the system area, which consists of boot sector and partition tables (Boot record), file allocation tables (FAT, NTFS, etc.) and the root directory (Root Directory).

Information is written to sectors through the cluster in several parts, and one cluster cannot contain two identical objects (files). Actually, the creation of a logical partition, as it were, separates it from the main system partition, as a result of which the information stored on it, when errors and failures occur, is not subject to change or deletion.

HDD Main Features

It seems that in general terms the principle of the hard drive is a little clear. Now let's move on to the main characteristics, which give a complete picture of all the possibilities (or disadvantages) of modern hard drives.

The principle of operation of the hard drive and the main characteristics can be completely different. To understand what we are talking about, let's highlight the most basic parameters that characterize all information storage devices known today:

• capacity (volume);
• speed (data access speed, reading and writing information);
• interface (connection method, controller type).

Capacity is the total amount of information that can be written and stored on a hard drive. The HDD industry is developing so fast that today hard drives with volumes of the order of 2 TB and above have already come into use. And, as it is believed, this is not the limit.

The interface is the most significant feature. It determines exactly how the device is connected to the motherboard, which controller is used, how reading and writing is performed, etc. The main and most common interfaces are IDE, SATA and SCSI.

Drives with an IDE interface are not expensive, but among the main disadvantages are limited quantity simultaneously connected devices (maximum four) and a low data transfer rate (even if Ultra DMA direct memory access or Ultra ATA protocols (Mode 2 and Mode 4) are supported. Although, as it is believed, their use allows you to increase the read / write speed up to 16 Mb/s, but in reality the speed is much lower.In addition, to use the UDMA mode, you need to install a special driver, which, in theory, should be supplied with motherboard.

Speaking about what is the principle of operation of a hard drive and characteristics, one cannot ignore and which is the successor to the IDE ATA version. The advantage of this technology is that the read/write speed can be increased up to 100 Mb/s by using the high-speed Fireware IEEE-1394 bus.

Finally, the SCSI interface is the most flexible and fastest compared to the previous two (write/read speed reaches 160 Mb/s and more). But these hard drives are almost twice as expensive. But the number of simultaneously connected storage devices is from seven to fifteen, the connection can be made without de-energizing the computer, and the cable length can be about 15-30 meters. Actually, this type of HDD is mostly used not in user PCs, but on servers.

Speed, which characterizes the speed of transmission and throughput I/O, usually expressed in terms of transfer time and amount of sequential data transferred, and is expressed in Mbps.

Some additional options

Speaking about what is the principle of operation of a hard disk and what parameters affect its functioning, one cannot ignore some additional characteristics, which may affect the performance or even the life of the device.

Here in the first place is the rotation speed, which directly affects the search and initialization (recognition) time of the desired sector. This is the so-called hidden seek time - the interval during which the desired sector turns to the read head. Today, several standards have been adopted for spindle speed expressed in revolutions per minute with dwell times in milliseconds:

• 3600 - 8,33;
• 4500 - 6,67;
• 5400 - 5,56;
• 7200 - 4,17.

It is easy to see that the higher the speed, the less time is spent on searching for sectors, and in physical terms - on disk rotation until the required platter positioning point is set for the head.

Another parameter is the internal transfer rate. On the outer tracks, it is minimal, but increases with a gradual transition to the inner tracks. Thus, the same defragmentation process, which is moving frequently used data to the fastest areas of the disk, is nothing more than moving it to an internal track with a faster read speed. The external speed has fixed values ​​and directly depends on the interface used.

Finally, one of important points associated with the presence of a hard drive its own cache or buffer. In fact, the principle of the hard disk in terms of buffer use is somewhat similar to the operational or virtual memory. The larger the amount of cache memory (128-256 KB), the faster the hard drive will work.

Main requirements for HDD

There are not so many basic requirements that in most cases apply to hard drives. The main thing is long service life and reliability.

The main standard for most HDDs is considered to be a service life of about 5-7 years with an operating time of at least five hundred thousand hours, but for high-end hard drives this figure is at least a million hours.

As for reliability, the S.M.A.R.T. self-test function is responsible for this, which monitors the status of individual elements of the hard drive, carrying out continuous monitoring. Based on the collected data, even a certain forecast of the appearance of possible faults further.

It goes without saying that the user should not be left out. So, for example, when working with a HDD, it is extremely important to observe the optimal temperature regime (0 - 50 ± 10 degrees Celsius), avoid shocks, bumps and falls of the hard drive, dust or other small particles getting into it, etc. By the way, many will it is interesting to know that the same particles of tobacco smoke are approximately twice the distance between the reading head and the magnetic surface of the hard drive, and a human hair - 5-10 times.

Initialization issues in the system when replacing a hard drive

Now a few words about what actions should be taken if, for some reason, the user changed the hard drive or installed an additional one.

We will not fully describe this process, but will dwell only on the main stages. First, the hard drive must be connected and looked in BIOS settings, whether new hardware has been determined, in the disk administration section, initialize and create a boot record, create a simple volume, assign an identifier (letter) to it and perform formatting with a choice file system. Only after that the new "screw" will be completely ready for work.

Conclusion

That, in fact, is all that briefly concerns the basics of the functioning and characteristics of modern hard drives. Principle of operation external hard disk was not considered fundamentally here, since it practically does not differ in any way from what is used for stationary HDDs. The only difference is only in the method of connecting an additional drive to a computer or laptop. The most common is the connection via a USB interface, which is directly connected to the motherboard. In this case, if you want to ensure maximum performance, it is better to use USB standard 3.0 (the port inside is colored blue), of course, provided that the external HDD supports him.

For the rest, it seems that many have at least a little understood how a hard drive of any type functions. Perhaps, too many topics were given above, even from a school physics course, however, without this, it will not be possible to fully understand all the basic principles and methods inherent in the production and application of HDDs.