How does a hard drive work? In detail and simply about the hard drive, also known as HDD (hard disk drive)
The purpose of this article is to describe the structure of a modern hard drive, talk about its main components, show what they look like and are called. In addition, we will show the relationship between Russian and English terminologies describing the components of hard drives.
For clarity, let's look at a 3.5-inch SATA drive. This will be a completely new Seagate ST31000333AS terabyte. Let's examine our guinea pig.
The green PCB with copper traces, power and SATA connectors is called an electronics board or control board (Printed Circuit Board, PCB). It is used to control the operation of the hard drive. The black aluminum case and its contents are called a HDA (Head and Disk Assembly, HDA); experts also call it a “can.” The case itself without contents is also called a hermetic block (base).
Now let's remove the printed circuit board and examine the components placed on it.
The first thing that catches your eye is the large chip located in the middle - the microcontroller, or processor (Micro Controller Unit, MCU). On modern hard drives, the microcontroller consists of two parts - the central processor unit (CPU), which performs all calculations, and the read/write channel - a special device that converts the analog signal coming from the heads into digital data during a read operation and encodes digital data into an analog signal during writing. The processor has input/output ports (IO ports) for controlling other components located on the printed circuit board and transmitting data via the SATA interface.
The memory chip is a regular DDR SDRAM memory. The amount of memory determines the size of the hard drive cache. This printed circuit board has 32 MB of Samsung DDR memory installed, which in theory gives the disk a cache of 32 MB (and this is exactly the amount given in the technical 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 requires a certain amount of memory to load firmware modules. To the best of our knowledge, only Hitachi/IBM indicate the actual cache size in the technical specifications; Regarding other disks, one can only guess about the cache size.
The next chip is the engine and head unit control controller, or “twist” (Voice Coil Motor controller, VCM controller). In addition, this chip controls secondary power supplies located on the board, which power the processor and the preamplifier-switch chip (preamplifier, preamp), located in the HDA. This is the main energy consumer 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 temperatures 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 begins executing the code. Without correctly loaded code, the disk will not even want to spin up. If there is no flash chip on the board, it means it is built into the microcontroller.
The vibration sensor (shock sensor) reacts to shaking that is dangerous for the disk and sends a signal about it to the VCM controller. The VCM immediately parks the heads and can stop the disk from spinning. In theory, this mechanism should protect the disc from further damage, but in practice it does not work, so do not drop the discs. On some drives, the vibration sensor is highly sensitive, responding 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 - a transient voltage suppression (TVS). It protects the board from power surges. When there is a power surge, the TVS burns out, creating a short circuit to ground. This board has two TVS, 5 and 12 volts.
Now let's look at the HDA.
Under the board there are contacts for the motor and heads. In addition, there is a small, almost invisible hole on the disk body (breath hole). It serves to equalize pressure. Many people believe that there is a vacuum inside the hard drive. Actually this is not true. This hole allows the disc to equalize the pressure inside and outside the containment area. On the inside, this hole is covered with a breath filter, which traps dust and moisture particles.
Now let's take a look inside the containment zone. Remove the disk cover.
The lid itself is nothing interesting. It's just a piece of metal with a rubber gasket to keep out dust. Finally, let's look at the filling of the containment zone.
Precious information is stored on metal disks, also called platters. In the photo you see the top pancake. The plates are made of polished aluminum or glass and are coated with several layers of different compositions, including a ferromagnetic substance on which the data is actually stored. Between the pancakes, as well as above the top of them, we see special plates called dividers 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 cope more successfully with cooling the air inside the containment zone.
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 should be if the spindle is stopped. For this disk, 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 can form inside the hard drive. To immediately clean the air inside the disc, there is a recirculation filter. This is a high-tech device that constantly collects and traps tiny 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's hidden underneath.
Hard drives use very powerful neodymium magnets. These magnets are so powerful that they can lift up to 1,300 times their own weight. So you should 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 designed 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 lower magnet.
Here's what you can see there.
We also see here a voice coil, which is part of the magnetic head unit. 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. The black plastic part with a complex shape is called an actuator latch. This is a protective mechanism that releases the BMG after the spindle motor reaches a certain number of revolutions. This happens due to the pressure of the air flow. The lock protects the heads from unwanted movements in the parking position.
Now let's remove the magnetic head block.
The precision and smooth 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 (arm). At the end of the rocker arm there are heads on a spring suspension (Heads Gimbal Assembly, HGA). Usually the heads and rocker arms themselves are supplied by different manufacturers. A flexible cable (Flexible Printed Circuit, FPC) goes to the pad that connects to the control board.
Let's take a closer look at the components of the BMG.
A coil connected to a cable.
Bearing.
The following photo shows the BMG contacts.
The gasket ensures the tightness of the connection. Thus, air can only enter the unit with discs and heads through the pressure equalization hole. This disc has contacts coated with a thin layer of gold to improve conductivity.
This is a classic rocker design.
The small black parts at the ends of the spring hangers are called sliders. Many sources indicate that sliders and heads are the same thing. 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. For comparison, a human hair has a diameter of about 25,000 nanometers. If any particle gets under the slider, this can lead to overheating of the heads due to friction and their failure, which is why cleanliness of the air inside the containment area 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 stabilize the slider's flight altitude. 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's another image of the slider.
The head contacts are clearly visible here.
This is another important part of the BMG that has not yet been discussed. It is called a preamplifier (preamp). A preamplifier is a chip that controls the heads and amplifies the signal coming to or from them.
The preamplifier is placed 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 move the preamplifier outside the hermetic zone, such a weak signal will be greatly attenuated on the way to the control board.
There are more tracks leading from the preamp to the heads (on the right) than to the containment area (on the left). The fact is that a hard drive cannot simultaneously work with more than one head (a pair of writing and reading elements). The hard drive sends signals to the preamplifier, and it selects the head that the hard drive 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-drives, special piezoelectric or magnetic devices that can move or rotate the slider. This helps to more accurately set the position of the heads over the track. The last path leads to the heater. The heater is used to regulate the flight altitude of the heads. The heater transfers heat to the suspension connecting the slider and rocker. The suspension is made of 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 gimbal straightens.
Enough about the heads, let's disassemble the disk further. Remove the upper separator.
This is what he looks like.
In the next photo you see the containment area with the top separator and head block removed.
The lower magnet became visible.
Now the clamping ring (platters clamp).
This ring holds the block of plates together, preventing them from moving relative to each other.
Pancakes are strung on a spindle hub.
Now that nothing is holding the pancakes, remove the top pancake. That's what's underneath.
Now it’s clear how 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 take everything else out of the disk to inspect the bottom of the hermetic block.
This is what the pressure equalization hole looks like. It is located directly under the air filter. Let's take a closer look at the filter.
Since the air coming from outside necessarily contains dust, the filter has several layers. It is much thicker than the circulation filter. Sometimes it contains silica gel particles to combat air humidity.
The connection between Russian and English terminology was clarified by Leonid Vorzhev.
Article copied from
Today it would not be an exaggeration to say that the vast majority of computer users are familiar with the concept of a “computer hard drive.” They know that every computer has a “memory” that stores all the information such as movies, music, photos, games and programs. However, few of the total number of people who like to stare at the monitor have gone further in understanding this mysterious storage device than the knowledge that “this is such a rectangular thing in which all the files are somehow incomprehensibly stored.” And it is precisely for those readers who want to dig deeper and find out how a hard drive works, as well as understand its structure, that this article was written, in which we will simply and in Russian address these issues.
How does a computer hard drive work?
First, let's take a short excursion into history. The first hard drive was created by IBM almost six decades ago, in 1957. Its volume was 5 megabytes - ridiculous figures by today's standards, but at that time it was a real technological breakthrough. After some time, engineers from the same company created a hard drive with a capacity of 30 MB, and an additional 30 MB in a removable bay. Since this disk structure evoked associations with the marking of the cartridge for the popular Winchester carbine in America - “.30-30” - the designers gave this hard disk the code name “Winchester”. An interesting fact is that nowadays in the West almost no one calls hard drives that way, but in the Russian-speaking environment this name has taken root much more firmly, having also given rise to a convenient abbreviated version - “screw”, which is widely used in colloquial speech.
Hard drive design
Now let's move directly to the highlight of the program and start with its internal structure. The hard drive design consists of the following components.
1. A block of magnetic disks or so-called. “pancakes” (from one to three pieces in one block, located one above the other) are essentially the main element of the hard drive. Each magnetic disk is made of aluminum or glass and coated with a ferromagnetic material, often chromium dioxide. Data is written to the magnetic layer using a magnetic head.
2. Magnetic head block - is a rocker arm connected to an amplifier-commutator microcircuit that amplifies the signal received when reading from a disk. At the tips of the rocker plates there are magnetic heads, which interact with the magnetic disk when performing read and write operations.
3. Spindle motor is a special electric motor that is used to accelerate magnetic disks. Depending on the hard drive model, this figure can reach 15,000 rpm. The design of the engine is based on the use of bearings (ball and hydrodynamic), which allows it to be silent and not create vibrations.
4. The controller board is an integrated circuit whose function is to control the operation of the hard drive by converting the signals transmitted from the magnetic heads into understandable ones for the computer.
How a hard drive works
Having studied the individual components, we can paint a complete picture of what is happening and describe step by step how a computer hard drive works. So, the hard drive is powered - the electronic controller sends a signal to the spindle motor, which begins to rotate magnetic disks firmly fixed to its axis. After reaching the required rotation speed, at which an air gap appears between the pancake and the head, eliminating the possibility of their contact, the rocker brings the heads to them at a “working” distance, which is about 10 nanometers (a billionth of a meter, imagine!).
The first data received from a switched-on hard drive is always service information or so-called. "zero track". It contains information about the status of the hard drive and its characteristics. If for some reason this information cannot be obtained, the device will not boot and will not work.
If the service data is received successfully and does not contain errors, the phase of working with information directly recorded on the disk begins. Most likely, you are already tormented by the question - “how is it recorded?” We answer: magnetic heads, under the influence of current pulses, are capable of magnetizing sections of the disk, thereby forming bits (logical “zeros” and “ones”, different from each other in the direction of the magnetic moment). In other words, all the information on a computer’s hard drive is its differently magnetized sections, which, after being converted into standardized signals, are recognized by the computer and presented to the user in a form that is understandable to him. It should be noted that these areas are strictly structured - they represent the so-called. "tracks", that is, ring-shaped areas on the surface of a magnetic disk.
It is important to note that the head block is one piece, so all the heads in it move synchronously - therefore, they are always located over the same track of each individual pancake. Based on this, the tracks form a cylinder in the vertical plane. Moreover, each track consists of segments called “sectors”. When writing information to these sectors, magnetic heads change their magnetic field, and when reading information, they simply capture it. Having understood the physical structure of data storage, we can conclude that the volume of a hard drive is equal to the product of the number of cylinders, the number of heads and the number of sectors.
Formatting your hard drive
A story about how a computer hard drive works cannot be called complete if it does not touch on the topic of formatting. Formatting is a special process of marking up the information storage area of a hard drive, the essence of which is to create certain structures for accessing this data, for example a file system, by recording certain service information. In this case, previously stored data is destroyed (however, not always irretrievably). Most often, formatting is performed when installing (or reinstalling) an operating system on a computer, since the best option for this is a “clean”, formatted disk, cleared of data from the previous OS. In order not to lose the necessary information, the “screw”, as a rule, is first logically divided into several partitions - in this case, formatting will only be required for the partition on which the OS will be installed, while the data on the remaining partitions will remain untouched, which is a very user-friendly approach .
Despite the fact that relatively recently the hard drive has a competitor - the SSD - a solid-state information drive, whose performance is several times higher than the speed of the HDD, the use of a hard drive has not lost its relevance. The reason is the low cost of the device.
There are enough problems with HDD, because the device is mechanical. Today, the hard drive is practically the only mechanical device that can be present in a modern computer. Of course, not counting the disk drive. It is for this reason that HDD is quite vulnerable. It should be handled with care. It can suffer from shaking and impacts, and if there is a strong magnet nearby, you can safely spend money on a new storage medium, because the old one will be hopelessly demagnetized.
What does a hard drive consist of?
To become better acquainted with all the misfortunes, as well as the advantages, of a hard drive, it is worth studying its structure in more detail, which is what we will do in this article. How does a hard drive work? In fact, HDD is quite a complex, but at the same time simple and interesting device. It consists of two parts - a mechanical one, which puts it into operation, and an electronic one, which controls and controls its operation. In appearance, the hard drive is similar to an old gramophone with records, and even the principle of its operation is reminiscent of this player.
Information in the HDD is also recorded on round plates. Information is read using special heads (just like in a gramophone). The HDD has several storage plates fixed on the spindle. Disk performance largely depends on this detail. The higher the spindle speed, the faster the drive runs. This is why hard drives have different speeds for writing and reading information. The plates are made of metal, coated with a very thin layer of ferromagnetic alloy, which is the information carrier.
How information is read
Information from the disk is reproduced by several read heads, combined into one block, moving freely in any area of the media plates. In a modern HDD, the reels rotate quickly - 7200 rpm. Of course, there are faster devices, but their cost is always significantly higher than average. The standard speed of 7200 rpm is quite acceptable even for a home PC. When reading information, the head does not touch the magnetic surface of the plate, but operates directly above it at an incredibly close distance - 10 nm. This is 10 times less than the thickness of a human hair. With this operating principle, wear from mechanical friction is completely eliminated. What makes the head float in the air? The air flow that occurs when the spindle rotates. It is unacceptable for dust particles to get between the head and the surface of the disk - this will lead to instant damage to the surface of the platter and loss of recorded information.
When the disk is put into operation, the read heads also do not touch its magnetic surface, being in a safe position until the speed reaches the desired limit. The heads do not enter the working area when the HDD is started; they are held in place by a special device, which prevents wear of the disk elements. When the rotating motor stops, a protective device automatically turns on, removing the heads from the reading area.
There is no need to fear that there will be dust or debris inside the electrical-mechanical part of the disk - the device is reliably protected from this by a sealed box. Only the electronic part of the HDD remains outside, which controls its operation. Essentially, this is an electronic board, the location of which is the lower part of the drive. This part of the device is not protected, therefore, if handled carelessly (unprofessional installation) or inappropriately stored, it is easily vulnerable.
When working with a hard drive, pay attention to the following points:
- The device must be protected from mechanical shocks;
- Do not disconnect or connect the internal hard drive without turning off the computer;
- Do not let the device overheat. There are special programs for monitoring HDD temperature.
- To avoid complications due to unexpected power outages, try to use an uninterruptible power supply when working on a desktop PC.
That's all. This information is enough for an inexperienced user to understand how a hard drive works, and also to know how to avoid breakdowns. Despite the rapidly growing popularity and gradually improving technical characteristics of SSDs, our native HDDs have not yet reached the shelf of history, like floppy disks or audio cassettes. We will be using hard drives for many more years, so we hope that the information about its design will be useful and interesting to you.
As most personal computer users are well aware, all data in a PC is stored on a hard drive - a random access information storage device that operates on the principle of magnetic recording. Modern hard drives are capable of storing information with a total volume of up to 6 terabytes (the capacity of the most capacious disk currently released by HGST), which seemed impossible ten years ago. In addition to the fact that the computer hard drive has enormous capacity, thanks to the sophisticated modern technologies used in its operation, it also allows you to get almost instant access to the information stored on it, without which productive PC operation would be impossible. How does this miracle of modern technology work, and how does it work?
Hard drive device
If you remove the top cover of the hard drive, you will only see the electronics board and another cover, under which there is a sealed area. It is in this hermetic zone that the main elements of the HDD are located. Despite the widespread belief that the hermetic zone of a hard drive contains a vacuum, this is not at all the case - inside the hermetic zone is filled with dry, dust-free air, and the lid usually has a small hole with a cleaning filter designed to equalize the air pressure inside the hermetic zone.
In general, a hard drive consists of the following main components:
How a hard drive works
What happens when power is supplied to the computer's hard drive and it starts working? Following the command of the electronic controller, the hard drive motor begins to rotate, thereby setting in motion the magnetic disks that are rigidly attached to its axis. As soon as the spindle rotation speed reaches a value sufficient to create a constant flow of air over the surface of the disk, which will prevent the read head from falling onto the surface of the drive, the rocker mechanism begins to move the read heads, and they hover above the surface of the disk. At the same time, the distance from the read head to the magnetic layer of the drive is only about 10 nanometers, which is equal to one billionth of a meter.
The first step when turning on the hard drive is to read service information from the drive (also called the “zero track”), which contains information about the disk and its state. If sectors with service information are damaged, the hard drive will not work.
Then work begins directly with the data located on the disk. Particles of ferromagnetic material that cover the surface of the disk, under the influence of the magnetic head, conditionally form bits - units of digital information storage. The data on a hard drive is distributed across tracks, which are a circular area on the surface of a single magnetic disk. The track, in turn, is divided into equal segments called sectors. Thus, hovering above the working surface of the disk, the magnetic head can, by changing the magnetic field, write data strictly to a specific location on the drive, and by capturing the magnetic flux, information can be read by sector.
Formatting your hard drive
In order for data to be stored on the hard drive, it is first subjected to a formatting process. Also, formatting is sometimes required when reinstalling the operating system, although in the second case it is not the entire disk that is formatted, but only one of its logical partitions.
During formatting, service information is applied to the disk, as well as data about the location of sectors and tracks on the surface of the disk. This is necessary for precise positioning of the magnetic heads when working with a hard drive.
Hard drive specifications
The modern hard drive market offers a wide variety of hard drive models to choose from, differing in various technical parameters. Here are the main characteristics by which hard drives differ:
- Connection interface. Most modern hard drives are connected to the motherboard via the SATA interface, but there are also models with other types of connections: eSATA, FireWire, Thunderbolt and IDE.
- Capacity. A value characterizing the amount of information that can fit on a hard drive. At the moment, the most popular drives are 500 GB and 1 TB.
- Form factor. Modern hard drives come in two physical sizes: 2.5 inches and 3.5 inches. The former are intended for use in laptops and compact versions of PCs, the latter are used in regular desktop computers.
- Spindle rotation speed. The higher the spindle speed of the hard drive, the faster it works. The bulk of hard drives on the market have a rotation speed of 5400 or 7200 rpm, but there are also disks with a spindle speed of 10,000 rpm.
- Buffer volume. To smooth out the difference in read/write speed and transfer speed through the interface, hard drives use intermediate memory called a buffer. The buffer size ranges from 8 to 128 megabytes.
- Random access time. This is the time required to perform the operation of positioning the magnetic head on an arbitrary area of the hard disk surface. Can range from 2.5 to 16 milliseconds.
Why is a hard drive called a hard drive?
According to one version, the hard drive received its unofficial nickname “Winchester” in 1973, when the world’s first HDD was released, in which aerodynamic readout heads were placed in one sealed box with magnetic plates. This drive had a capacity of 30 MB plus 30 MB in a removable compartment, which is why the engineers who worked on its development gave it the code name 30-30, which was consonant with the designation of a popular shotgun using the .30-30 Winchester cartridge. In the early nineties, the name “Winchester” fell out of use in Europe and the USA, but is still popular in Russian-speaking countries. You can also often hear a more abbreviated slang version of the name hard drive - “screw”, used mainly by computer specialists.
The computer is an indispensable component of human society. It processes pictures, sounds, numbers, words. Fortunately, all information can be saved so as not to be lost when the computer turns off.
The job of a hard drive inside a computer is to store and retrieve information very quickly. The hard drive is a very amazing invention of the computer industry. It can store an astronomical amount of information. This miniature device records a virtually unlimited amount of information using the laws of physics.
If you accidentally format your hard drive, it will be possible to recover data from it, but it will be time-consuming and expensive.
How does a hard drive work?
To understand, you need to break it. A hard drive consists of five main parts:
It is necessary to protect the disk if we want to use this device for years. What kind of damage could there be? Disc damage is not a metaphor. In such thin layers, the weight of the head is equivalent to the weight of a 747 aircraft, and the weight of a 747 aircraft is comparable to the weight of one hundred thousand passengers flying at a speed of 100 kilometers per hour. Deviation of a fraction of a millimeter and that’s it...
What an important role does friction play when the rocker begins to read information, moving up to 60 times per second. The rocker motor is invisible because this electromagnetic system works on the interaction of two forces of nature - electricity and magnetism. This interaction accelerates the rocker to the speed of light.
Before this we were talking about components, now let's talk about data storage. Data is stored in narrow tracks on the surface of the disk. During production, more than two hundred thousand of these tracks are created on a disc. Each track is divided into sectors. The map of tracks and sectors allows the head to determine where to write or read information. The surface of the disk is smooth and shiny, but upon closer inspection the structure turns out to be more complex. The ferrimagnetic film on the surface remembers all recorded information. The head magnetizes a microscopic area on the film, setting the magnetic moment of such a cell to one of the states “0” or “1”, each such zero and one are called bits. The bit value corresponds to the orientation of the magnetic field, plus or minus, and there is no need to worry about the safety of the data, because a good quality photograph occupies about 29 million such cells and is scattered over 12 different sectors. This sounds impressive, but in reality this incredible number of bits takes up a very small area of the disk's surface. Each square centimeter of surface contains 31 billion bits. This is what I understand memory to be.
The hard drive records and outputs information at speeds that are hard to imagine. Using the laws of magnetism, thin film can remember many different encyclopedias or hundreds of thousands of photographs easily. The hard drive is actually an amazingly miniature device that records any information in small bits. This masterpiece of engineering pushes the boundaries of reasonable physics bit by bit.
