If we consider the hard drive as a whole, then it consists of two main parts: this is the electronics board, on which the “brain” of the hard drive is located, so to speak. The processor is located on it, there is also a control program, random access memory, a write and read amplifier. The mechanical part includes such parts as a block of magnetic heads with the abbreviation BMG, an engine that gives rotation to the plates, and of course the plates themselves. Let's look at each part in more detail.
HDA.
The hermetic block, also known as a hard disk case, is designed to fasten all parts, and also performs the function of protecting against dust particles on the surface of the plates. It should be noted that the HDA can only be opened in a room specially prepared for this, in order to prevent dust and dirt from getting inside the case.
Integrated circuit.
An integrated circuit or electronics board synchronizes the operation of the hard drive with the computer and controls all processes, in particular, it maintains a constant speed of rotation of the spindle and, accordingly, the plate, which is carried out by the engine.
Electric motor.
An electric motor or engine rotates the plates: about 7200 revolutions per second (the average value is taken, there are hard drives on which the speed is higher and reaches 15000 revolutions per second, and there are also at a lower speed of about 5400, the speed of access to the necessary information on hard drive).
Rocker.
The rocker is designed to write and read information from hard disk platters. The end of the rocker is divided and there is a block of magnetic heads on it, this is done in order to be able to write and read information from several plates.
Block of magnetic heads.
The composition of the rocker arm includes a block of magnetic heads, which quite often fails, but this "often" parameter is very conditional. Magnetic heads are located above and below the platters and serve for direct reading of information from the platinum located on the hard disk.
Plates.
Information is stored directly on the plates; they are made of materials such as aluminum, glass and ceramics. Aluminum is the most widespread, but the so-called "elite wheels" are made from the other two materials. The first manufactured plates were coated with iron oxide, but this ferromagnet had a big drawback. Discs coated with such a substance had little wear resistance. At the moment, most hard drive manufacturers cover the plates with chromium cobalt, which has an order of magnitude higher margin of safety than iron oxide. Plates are attached to the spindle at the same distance from each other, such a design is called a "package". Under the discs is an engine or electric motor.
Each side of the plate is divided into tracks, which, in turn, are divided into sectors or blocks in another way, all tracks of the same diameter are a cylinder.
All modern hard drives have a so-called "engineering cylinder", it stores service information, such as the hdd model, serial number, etc. This information is designed to be read by a computer.
How a hard drive works
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 rotation speed of the plates 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 disc 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. Many drives use a layer of iron oxide (which is the coating on conventional magnetic tape), but the latest 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 outermost 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 an alternating electric current supplied to the magnetic head, and then transferred to the magnetic disk, but in the form of a magnetic field that 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 disc 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. In order to reduce the time for the drive to reach the working state, the engine, when turned on, works for some time in the forced mode. Therefore, the computer power supply must have a margin for peak power. Now about the work of the heads. They move with the help of a stepper motor and, as it were, "float" at a distance of a fraction 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.
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In this article, we will only talk about hard drives (HDD), that is, about media on magnetic disks. About SSD will be the next article.
What is a hard drive
By tradition, let's look at the definition of a hard drive on Wikipedia:
A hard disk (screw, hard drive, hard disk drive, HDD, HDD, HMDD) is a random access storage device based on the principle of magnetic recording.
They are used in the vast majority of computers, as well as separately connected devices for storing backup copies of data, as file storage, etc.
Let's figure it out a little. I like the term "hard drive". These five words convey the whole point. HDD is a device whose purpose is to store data recorded on it for a long time. HDDs are based on hard (aluminum) disks with a special coating, on which information is recorded using special heads.
I will not consider in detail the recording process itself - in fact, this is the physics of the last grades of the school, and I am sure you have no desire to delve into this, and the article is not about that at all.
Let's also pay attention to the phrase: "random access" which, roughly speaking, means that we (the computer) can read information from any section of the railway at any time.
It is important that the HDD memory is not volatile, that is, it does not matter whether the power is connected or not, the information recorded on the device will not disappear anywhere. This is an important difference between a computer's permanent memory and temporary memory (RAM).
Looking at a computer hard drive in real life, you will not see any disks or heads, since all this is hidden in a sealed enclosure (hermetic zone). Externally, the hard drive looks like this.
I think you understand what HDD is. Move on.
Why does a computer need a hard drive?
Consider what an HDD is in a computer, that is, what role it plays in a PC. It is clear that it stores data, but how and what. Here we highlight the following functions of HDD:
- Storage of OS, user software and their settings;
- Storage of user files: music, video, images, documents, etc.;
- Using part of the hard disk space to store data that does not fit in RAM (paging file) or storing the contents of RAM while using sleep mode;
- As you can see, a computer hard drive is not just a dump of photos, music and videos. It stores the entire operating system, and in addition, the hard drive helps to cope with the workload of RAM, taking on some of its functions.
What is a hard drive made of?
We partially mentioned the components of the hard drive, now we will deal with this in more detail. So, the main components of the HDD:
- Enclosure - protects hard drive mechanisms from dust and moisture. As a rule, it is airtight so that the same moisture and dust do not get inside;
- Discs (pancakes) - plates made of a certain alloy of metals, coated on both sides, on which data is recorded. The number of plates can be different - from one (in budget options) to several;
- Engine - on the spindle of which pancakes are fixed;
- The block of heads - a design from the levers (rocker arms) connected among themselves, and heads. The part of a hard drive that reads and writes information to it. For one pancake, a pair of heads is used, since both the upper and lower parts of it are working;
- Positioning device (actuator) - a mechanism that drives the block of heads. Consists of a pair of permanent neodymium magnets and a coil located at the end of the head unit;
- Controller - an electronic microcircuit that controls the operation of the HDD;
- Parking zone - a place inside the hard drive next to the disks or on their inside, where the heads are lowered (parked) during idle time, so as not to damage the working surface of the pancakes.
Such a simple hard drive device. It was formed many years ago, and no fundamental changes have been made to it for a long time. And we move on.
How a hard drive works
After power is supplied to the HDD, the engine, on the spindle of which the pancakes are fixed, begins to spin up. Having gained a speed at which a constant stream of air is formed near the surface of the discs, the heads begin to move.
This sequence (first the discs spin up, and then the heads start working) is necessary so that the heads hover over the plates due to the resulting air flow. Yes, they never touch the surface of the disks, otherwise the latter would be instantly damaged. However, the distance from the surface of the magnetic platters to the heads is so small (~10 nm) that you cannot see it with the naked eye.
After starting, first of all, service information about the state of the hard disk and other necessary information about it, located on the so-called zero track, is read. Only then does the work with the data begin.
Information on the computer's hard drive is recorded on tracks, which, in turn, are divided into sectors (such a pizza cut into pieces). To write files, several sectors are combined into a cluster, which is the smallest place where a file can be written.
In addition to such a "horizontal" partitioning of the disk, there is also a conditional "vertical" one. Since all heads are combined, they are always positioned over the same track number, each over its own disc. Thus, during the operation of the HDD, the heads, as it were, draw a cylinder.
While the HDD is working, in fact, it performs two commands: reading and writing. When it is necessary to execute a write command, the area on the disk where it will be performed is calculated, then the heads are positioned and, in fact, the command is executed. The result is then checked. In addition to writing data directly to disk, information also ends up in its cache.
If the controller receives a read command, first of all, it checks for the presence of the required information in the cache. If it is not there, the coordinates for positioning the heads are calculated again, then the heads are positioned and read the data.
After completion of the work, when the power supply of the hard drive disappears, the heads are automatically parked in the parking zone.
This is how a computer hard drive works in general terms. In reality, everything is much more complicated, but the average user, most likely, does not need such details, so we will finish this section and move on.
Types of hard drives and their manufacturers
Today, there are actually three main manufacturers of hard drives on the market: Western Digital (WD), Toshiba, Seagate. They fully cover the demand for devices of all types and requirements. The rest of the companies either went bankrupt, or were taken over by someone from the main three, or re-profiled.
If we talk about the types of HDD, they can be divided in this way:
1. For laptops - the main parameter is the device size of 2.5 inches. This allows them to be compactly placed in the laptop case;
2. For PC - in this case, it is also possible to use 2.5″ hard drives, but as a rule, 3.5 inches are used;
3. External hard drives - devices that are separately connected to a PC / laptop, most often acting as a file storage.
There is also a special type of hard drives - for servers. They are identical to conventional PCs, but may differ in interfaces for connection, and greater performance.
All other divisions of HDD into types come from their characteristics, so we will consider them.
Hard drive specifications
So, the main characteristics of a computer hard drive:
Size is a measure of the maximum amount of data that can fit on a disk. The first thing they usually look at when choosing an HDD. This figure can reach 10 TB, although 500 GB - 1 TB is more often chosen for a home PC;
- Form factor - hard disk size. The most common are 3.5 and 2.5 inches. As mentioned above, 2.5″ in most cases are installed in laptops. They are also used in external HDDs. 3.5″ is installed on the PC and on the server. The form factor also affects the volume, as more data can fit on a larger disk;
- Spindle speed - at what speed pancakes rotate. The most common are 4200, 5400, 7200 and 10000 rpm. This characteristic directly affects the performance, as well as the price of the device. The higher the speed, the greater both values;
- Interface - the method (connector type) for connecting the HDD to the computer. The most popular interface for internal hard drives today is SATA (older computers used IDE). External hard drives are usually connected via USB or FireWire. In addition to those listed, there are other interfaces such as SCSI, SAS;
- Buffer size (cache memory) - a type of fast memory (by type of RAM) installed on the HDD controller, designed for temporary storage of data that is most often accessed. The buffer size can be 16, 32 or 64 MB;
- Random access time - the time during which the HDD is guaranteed to write or read from any part of the disk. It fluctuates from 3 to 15 ms;
In addition to the above characteristics, you can also find indicators such as:
Data transfer rate;
- Number of I/O operations per second;
- Noise level;
- Reliability;
- Resistance to impacts, etc.;
At the expense of the characteristics of the HDD, that's all.
hard drive (hard drive, HDD) - a random access memory (information storage device) based on the principle of magnetic recording. It is the main storage medium in most computers.
Unlike " flexible» disk ( floppy disks), information in HDD recorded on hard (aluminum or glass) plates coated with a layer of ferromagnetic material, most often chromium dioxide - magnetic disks. AT HDD one or more inserts on one axis are used. The reading heads in the operating mode do not touch the surface of the plates due to the layer of the oncoming air flow formed near the surface during rapid rotation. The distance between the head and the disk is several nanometers, and the absence of mechanical contact ensures a long service life of the device. In the absence of rotation of the disks, the heads are located at the spindle or outside the disk in a safe zone, where their abnormal contact with the surface of the disks is excluded.
First hard drive
AT 1957 year by the firm IBM the very first hard drive was developed, and it was developed even before the creation of a personal computer. For him, he would have to pay a “tidy” sum, although he had only 5 MB. Then a hard disk was developed with a capacity 10 MB specially for personal computer IBM PC XT. Winchester had everything 30 tracks and more on 30 sectors in every track. " Winchesters"- this is how hard drives began to be called, if abbreviated, then" ATintami”, This came from an analogy with the marking of the carbine of the company Winchester - "30/30", which was multi-charged.
For clarity, let's take a look 3.5 inch SATA disk. It will be Seagate ST31000333AS.
Green textolite with copper tracks, power connectors and SATA called the electronics board or control board (P rinted 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 " jar". The body without contents is also called 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 - actually CPU(Central Processor Unit, CPU), which does all the calculations, and the channel read/write (read/write channel)- a special device that converts the analog signal coming from the heads into digital data during the read operation and encodes the digital data into an analog signal during the write operation. The processor has ports input-output (IO ports) to control the rest of the components located on the printed circuit board and transmit data via SATA interface.
Memory Chip is the usual DDR SDRAM memory. The amount of memory determines the size of the hard disk cache. Memory is installed on this circuit board Samsung DDR volume 32 MB, which in theory gives the disk a cache in 32 MB(and this is exactly the amount that is given in the technical characteristics 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. As far as is known, only Hitachi/IBM indicate the actual volume cache in the description of technical characteristics; relative to other disks, about the volume cache one can only guess.
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 supplies located on the board, from which the processor is powered and preamplifier-switcher chip (preamplifier, preamp) located in the HDA. 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. Nucleus VCM controller can work even at a temperature of 100°C.
Part of the disk 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 the code loaded correctly, the disk won't even want to spin up. If there is no flash chip on the board, then it is built into the microcontroller.
Vibration sensor (shock sensor) reacts to shaking dangerous for the disk and sends a signal about it to the controller VCM. VCM controller 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 controller VCM correct head movement. At least two vibration sensors are installed on such disks.
There is another protective device on the board - Transient Voltage Suppression (TVS). It protects the board from power surges. With a power surge TVS burns out, creating a short circuit to ground. This board has two TVS, for 5 and 12 volts.
Consider the hermetic block.
Under the board are the contacts of the motor and heads. In addition, there is a small, almost imperceptible hole on the disk body (breath hole). 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 is a hole covered by 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.
Consider the filling of the containment area.
Precious information is stored on metal discs, also called pancakes or Pfins (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.
Read-write heads (heads), mounted on the ends of the magnetic head unit brackets, or HSA (Head Stack Assembly, HSA). parking zone- this is the area in which the heads of a healthy disk should be if 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 done in special plastic parking areas located outside the plates.
HDD is a precise positioning mechanism and requires very clean air to function properly. During use, microscopic particles of metal and grease may form inside the hard drive. To immediately clean the air inside the disc, there is 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.
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 weight in 1300 times larger than their own. So do not put your finger between the magnet and metal or another magnet - the blow will be very sensitive. This photo shows the restraints. BMG. Their task is to limit the movement of the heads, leaving them on the surface of the plates. BMG limiters 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 we see here coil (voice coil), which is part of the head unit. Coil and magnets form BMG drive (Voice Coil Motor, VCM). The drive and the block of magnetic heads, form positioner- a device that moves heads. A black plastic piece of complex shape is called latch (actuator latch). It is a defense mechanism that releases BMG 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.
Precision and smooth movement BMG supported by precision bearing. The largest detail BMG, made of aluminum alloy, commonly referred to as bracket or rocker (arm). At the end of the rocker there are heads on a spring suspension (Heads Gimbal Assembly, HGA). Usually the heads and rocker arms are supplied by different manufacturers. Flexible Cable (Flexible Printed Circuit, FPC) goes to the contact pad, docking with the control board.
Consider the components BMG more.
A coil connected to a cable.
Bearing.
The following photo shows BMG contacts.
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 small 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 5-10
nanometers from the surface of the pancakes. For comparison, a human hair has a diameter of about 25000 nanometers. If any particle gets under the slider, it can lead to overheating of the heads due to friction and their 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 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. BMG, which has not yet been discussed. It's called p preamplifier (preamplifier, preamp). preamplifier- this is a chip that controls the heads and amplifies the signal coming to or from them.
preamplifier located right in 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 a weak signal will be strongly attenuated 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.
HDD ("winchester", hdd, hard disc drive - eng.) - an information storage device based on magnetic plates and the effect of magnetism.
Applies everywhere in personal computers, laptops, servers and so on.
Hard disk device. How a hard drive works.
In the floor sealed the block contains double-sided plates, with applied on them magnetic layer planted on motor shaft and rotating at a speed of 5400 revolutions per minute. The block is not completely sealed, but most importantly, it does not let through small particles and does not allow humidity fluctuations. All this adversely affects the life and quality of the hard drive.
In modern hard drives, the shaft is used. This gives less noise during operation, significantly increases durability and reduces the chance of jamming the shaft due to collapsed.
Reading and writing is done with head block.
In working order, heads soar above the disk surface at a distance ~10nm. They are aerodynamic and rise above the disk surface due to updraft from the rotating plate. Magnetic heads can be located on both sides plates, if magnetic layers are deposited on each side of the magnetic disk.
The connected head unit has fixed position, that is, the heads move all together.
All heads are controlled by a special drive unit based on electromagnetism.
Neodymium magnet creates a magnetic field, in which the head unit can move with a high reaction speed under the influence of current. This is the best and fastest way to move the block of heads, and after all, once the block of heads was moved mechanically, with the help of gears.
When the disc is turned off, to prevent the heads from sinking onto the disc and damaged him, they clean up in head parking area(parking zone, parking zone).
It also allows you to transport offline hard drives without any special restrictions. In the off state, the disk can withstand heavy loads and not be damaged. In the on state, even a small push at a certain angle can destroy the magnetic layer of the plate or damage the heads when touching the disk.
In addition to the sealed part, modern hard drives have an outer control board. Once upon a time, all control boards were inserted into the computer motherboard in expansion slots. It was not convenient in terms of versatility and capabilities. With hard drives these days, all the drive electronics and interfaces are located on a small circuit board at the bottom of the hard drive. Thanks to this, it is possible to configure each disk for certain parameters that are beneficial from the point of view of its structure, giving it a gain in speed, or quieter operation, for example.
To connect the interface and power, standard common connectors are used / and Molex/Power SATA.
Peculiarities.
Hard drives are the most capacious custodians of information and regarding reliable. The volume of disks is constantly growing, but recently this is due to some complexities and for further expansion of the volume, new technologies are required. We can say that hard drives have practically gone straight in achieving maximum capabilities. The spread of hard drives was mainly facilitated by the ratio pricevolume. In most cases, a gigabyte of disk space costs less than 2.5 rubles.
Pros and cons of hard drives vs.
Before the advent of solid state SSD(solid state drive) - drives, hard drives had no competitors. Now hard drives have a direction to aim for.
Cons of hard drives(hard drive)(ssd) drives:
- low sequential read speed
- low access speed
- slow reading speed
- slightly slower write speed
- vibrations and slight noise during operation
Although on the other hand, hard drives have other more weighty the benefits to which SSD accumulators strive and strive.
pros hard drives (hard drive) compared to solid state (ssd) drives:
- significantly better volume price
- the best indicator of reliability
- higher maximum volume
- in case of failure, many times more chance to recover data
- the best option for use in media centers, due to its compactness and large capacity 2.5 drives
About what worth paying attention when choosing a hard drive, you can see in our article "". If you need hard drive repair or data recovery, you can refer to.
