What is a computer hard drive? In detail and simply about the hard drive, also known as HDD (hard disk drive)
Greetings to all blog readers. Many people are interested in the question of how a computer hard drive works. Therefore, I decided to devote today’s article to this.
A computer's hard drive (HDD or hard drive) is needed to store information after the computer is turned off, in contrast to RAM () - which stores information until the power supply is cut off (until the computer is turned off).
A hard drive can rightfully be called a real work of art, only an engineering one. Yes Yes exactly. Everything inside is so complicated. At the moment, all over the world, the hard drive is the most popular device for storing information, it is on a par with devices such as flash memory (flash drives), SSD. Many people have heard about the complexity of the hard drive and are perplexed as to how it fits so much information, and therefore would like to know how the computer hard drive is structured or what it consists of. Today there will be such an opportunity).
A hard drive consists of five main parts. And the first of them - integrated circuit, which synchronizes the disk with the computer and manages all processes.
The second part is the electric motor(spindle), causes the disk to rotate at a speed of approximately 7200 rpm, and the integrated circuit maintains the rotation speed constant.
And now the third, probably the most important part is the rocker arm, which can both write and read information. The end of the rocker arm is usually split to allow multiple discs to be operated at once. However, the rocker head never contacts the discs. There is a gap between the surface of the disc and the head, the size of this gap is approximately five thousand times smaller than the thickness of a human hair!
But let's still see what happens if the gap disappears and the rocker head comes into contact with the surface of the rotating disk. We still remember from school that F=m*a (Newton’s second law, in my opinion), from which it follows that an object with a small mass and a huge acceleration becomes incredibly heavy. Considering the enormous rotation speed of the disk itself, the weight of the rocker head becomes very, very noticeable. Naturally, disk damage is inevitable in this case. By the way, this is what happened to the disk in which this gap disappeared for some reason:
The role of friction force is also important, i.e. its almost complete absence, when the rocker begins to read information, while moving up to 60 times per second. But wait, where is the engine that drives the rocker arm, and at such a speed? In fact, it is not visible, because it is an electromagnetic system that works on the interaction of 2 forces of nature: electricity and magnetism. This interaction allows you to accelerate the rocker to the speed of light, in the literal sense.
Fourth part- the hard drive itself is where information is written and read from; by the way, there can be several of them.
Well, the fifth and final part of the hard drive design is, of course, the case into which all other components are installed. The materials used are as follows: almost the entire body is made of plastic, but the top cover is always metal. The assembled housing is often called a “hermetic zone”. There is an opinion that there is no air inside the containment zone, or rather, that there is a vacuum there. This opinion is based on the fact that at such high speeds of rotation of the disk, even a speck of dust that gets inside can do a lot of bad things. And this is almost true, except that there is no vacuum there - but there is purified, dried air or neutral gas - nitrogen, for example. Although, perhaps in earlier versions of hard drives, instead of purifying the air, it was simply pumped out.
We were talking about components, i.e. what does a hard drive consist of?. Now let's talk about data storage.
How and in what form is data stored on a computer’s hard drive?
Data is stored in narrow tracks on the surface of the disk. During production, more than 200 thousand of these tracks are applied to the disc. Each track is divided into sectors.
Maps of tracks and sectors allow you to determine where to write or read information. Again, all information about sectors and tracks is located in the memory of the integrated circuit, which, unlike other components of the hard drive, is located not inside the case, but outside and usually at the bottom.
The surface of the disk itself is smooth and shiny, but this is only at first glance. Upon closer inspection, the surface structure turns out to be more complex. The fact is that the disk is made of a metal alloy coated with a ferromagnetic layer. This layer does all the work. The ferromagnetic layer remembers all the information, how? Very simple. The rocker head magnetizes a microscopic area on the film (ferromagnetic layer), setting the magnetic moment of such a cell to one of the states: o or 1. Each such zero and one are called bits. Thus, any information recorded on a hard drive, in fact, represents a certain sequence and a certain number of zeros and ones. For example, a good quality photograph occupies about 29 million of these cells, and is scattered across 12 different sectors. Yes, it sounds impressive, but in reality, such a huge number of bits takes up a very small area on the surface of the disk. Each square centimeter of a hard drive's surface contains several tens of billions of bits.
How a hard drive works
We have just looked at the hard drive device, each of its components separately. Now I propose to connect everything into a certain system, thanks to which the very principle of operation of the hard drive will be clear.
So, the principle by which a hard drive works next: when the hard drive is put into operation, this means that either writing is being done to it, or information is being read from it, or from it, the electric motor (spindle) begins to gain momentum, and since the hard drives are attached to the spindle itself, accordingly they go with it also begin to rotate. And until the revolutions of the disc(s) have reached a level such that an air cushion is formed between the rocker head and the disc, the rocker arm is located in a special “parking zone” to avoid damage. This is what it looks like.
As soon as the speed reaches the desired level, the servo drive (electromagnetic motor) moves the rocker arm, which is already positioned in the place where information needs to be written or read from. This is precisely facilitated by an integrated circuit that controls all movements of the rocker arm.
There is a widespread opinion, a kind of myth, that at times when the disk is “idle”, i.e. No read/write operations are temporarily performed with it, and the hard drives inside stop rotating. This is truly a myth, because in fact, the hard drives inside the case rotate constantly, even when the hard drive is in power-saving mode and nothing is written to it.
Well, we have looked at the device of a computer hard drive in detail. Of course, within the framework of one article, it is impossible to talk about everything related to hard drives. For example, this article did not talk about - this is a big topic, I decided to write a separate article about it.
I found an interesting video about how a hard drive works in different modes
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Hard disks
Is done by a student
groups 40-101B.
Karimov K.R.
Teacher:
Usov P.A.
1. The principle of operation 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
A hard disk drive is one of the most advanced and complex devices of a modern personal computer. Its disks are capable of storing many megabytes of information transmitted at enormous speed. While most computer components operate silently, the hard drive grunts and creaks, making it one of the few computer devices that contains both mechanical and electronic components.
The basic operating principles of a hard drive have changed little since its inception. The device of a 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 (for some models it reaches 15,000 rpm) is constant and is one of the main characteristics. The head moves along the plate at a certain fixed distance from the surface. The smaller this distance, the greater the accuracy of information reading, and the greater the information recording density can be. When you look at the hard drive, all you see is a durable metal casing. It is completely sealed and protects the drive from dust particles, which, if they get into the narrow gap between the head and the surface of the disk, can damage the sensitive magnetic layer and damage 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 information is stored, the heads that write and read information from the disks, and the motors that set it all in motion. The disk is a round plate with a very smooth surface, usually made of aluminum, less often of ceramics or glass, coated with a thin ferromagnetic layer. The disks are made. Many drives use an iron oxide layer (which coats regular magnetic tape), but the latest hard drives use a cobalt layer about ten microns thick. This coating is more durable and, in addition, allows you to 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 is correspondingly twice as large (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 at the same time the number of working surfaces is reduced and may turn out to be odd.
Magnetic heads read and write information to disks. The recording principle 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 transmitted to the magnetic disk, but in the form of a magnetic field, which the disk can perceive and “remember”. The magnetic coating of the disk consists of many tiny areas of spontaneous magnetization. To illustrate, 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 domains' own magnetic fields are oriented in accordance with its direction. After the termination of the external field, zones of residual magnetization are formed on the surface of the disk. In this way, the information recorded on the disk is saved. 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 magnetization. The disk package, mounted on the spindle axis, is driven by a special motor compactly located underneath it. The rotation speed of the disks is usually 7200 rpm. In order to reduce the time it takes for the drive to become operational, the engine runs in forced mode for some time when turned on. Therefore, the computer's power supply must have a reserve of peak power. Now about the operation of the heads. They move with the help of a precision stepper motor and seem to “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. These 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; all control electronics are on the board, with the exception of the preamplifier, which is located inside the HDA in close proximity to the heads.
Under the disks there is a 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 perimeter of the HDA and is constantly cleaned by a filter installed on one of its sides.
Closer to the connectors, on the left or right side of the spindle, there is a rotary positioner, somewhat reminiscent in appearance of a tower crane: on one side of the axis, there are thin, long and light carriers of magnetic heads facing the disks, and on the other, a short and more massive shank with electromagnetic drive winding. When the positioner rocker arm turns, the heads move in an arc between the center and periphery of the disks. The angle between the axes of the positioner and the spindle is selected along with the distance from the positioner axis to the heads so that the axis of the head deviates as little as possible from the tangent track when turning.
In earlier models, the rocker arm was mounted on the axis of the stepper motor, and the distance between the tracks was determined by the step size. Modern models use a so-called linear motor, which does not have any discreteness, and installation on the track is carried out according to signals recorded on the disks, which significantly increases the accuracy of the drive and the recording density on the disks.
The positioner winding is surrounded by a stator, which is a permanent magnet. When a current of a certain magnitude and polarity is supplied to the winding, the rocker begins to rotate in the appropriate direction with corresponding acceleration; By dynamically changing the current in the winding, you can set the positioner to any position. This drive system is called Voice Coil, by analogy with a loudspeaker cone.
On the shank there is usually a so-called magnetic latch - a small permanent magnet, which, when the heads are in the extreme internal position (landing zone), is attracted to the surface of the stator and fixes the rocker in this position. This is the so-called parking position of the heads, which 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, in a free position, blocks the movement of the rocker arm. No information is recorded in the disk landing zone.
The remaining free space contains a preamplifier for the signal removed 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 hermetic block is filled with ordinary dust-free air under atmospheric pressure. In the lids of the hermetic blocks 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 a breathable filter. For some hard drive models, the spindle and positioner axes are fixed in only one place - on the hard drive body; for others, they are additionally secured with screws to the HDA cover. The second models are more sensitive to microdeformation during fastening - tightening the fastening screws sufficiently to cause unacceptable misalignment of the axes. In some cases, such a distortion may become difficult to reverse or completely irreversible. The electronics board is removable and connects to the HDA via one or two connectors of various designs. The board contains the main hard drive processor, ROM with a 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 the disk. The disk can also contain drive parameters (model, serial number, etc.). Some hard drives store this information in an electrically programmable 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. Modern Conner brand drives have a technological interface made in the serial interface standard, which allows you to connect it via an adapter to an alphanumeric terminal or a computer COM port. The ROM contains the so-called test-monitor system (TMOS), which receives commands sent from the terminal, executes them and outputs the results back to the terminal. Early hard drives, like floppy disks, were manufactured with clean magnetic surfaces; the initial markup (formatting) was done by the consumer at his discretion, and could be done any number of times. For modern models, markings are made during the manufacturing process; At the same time, servo information is recorded on the disks - special marks necessary to stabilize the rotation speed, search for sectors and monitor the position of heads on surfaces. Not long ago, a separate surface (dedicated) was used to record servo information, along which the heads of all other surfaces were adjusted. Such a system required high rigidity of fastening the heads so that there would be no discrepancies between them after the initial marking. Nowadays, servo information is recorded in the spaces between sectors (embedded), which makes it possible to increase the useful capacity of the package and remove restrictions on the rigidity of the moving system. Some modern models use a combined tracking system - built-in servo information in combination with a dedicated surface; in this case, coarse adjustment is performed on the selected surface, and fine adjustment is performed on the built-in marks.
Since servo information represents the reference layout of the disk, the hard drive controller is not able to independently restore it in the event of damage. When formatting such a hard drive with software, it is only possible to rewrite the headers and checksums of data sectors.
During the initial marking and testing of a modern hard drive at the factory, defective sectors are almost always detected, which are entered into a special reassignment table. During normal operation, the hard drive controller replaces these sectors with reserve 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 of a complete absence of surface defects, although in fact they are almost always present.
When the power is turned on, the hard drive processor performs electronics testing, after which it issues a command to turn on the spindle motor. When a certain critical rotation speed is reached, the density of the air entrained by the surfaces of the disks becomes sufficient to overcome the pressing force of the heads to the surface and raise them to a height of fractions to several microns above the surfaces of the disks - the heads “float”. From this moment until the speed decreases below the critical level, the heads “hang” on a cushion of air and do not touch the surfaces of the disks at all.
After the disks 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 for reassigning defective areas.
At the end of initialization, the positioner is tested by enumerating a given sequence of tracks - if it is successful, the processor sets a readiness sign on the interface and switches to operating mode via the interface.
During operation, the system for monitoring the position of the head on the disk is constantly working: an error signal is extracted from the continuously read signal, which is fed to the feedback circuit that controls the current of the positioner winding. As a result of the deviation of the head from the center of the track, a signal appears in the winding, tending to return it to its place.
To coordinate the speeds of data flows - at the read/write level and the external interface - hard drives have an intermediate buffer, often mistakenly called a cache, usually several tens or hundreds of kilobytes in size. In a number of models (for example, Quantum), the buffer is placed in the common working RAM, where the overlay part of the control microprogram is first loaded, making the actual volume of the buffer less than the full amount of RAM (80-90 kB with 128 kB RAM for Quantum). For other models (Conner, Caviar), the buffer and processor RAM are made separate.
When the power is turned off, the processor, using the energy remaining in the capacitors of the board or extracting it from the windings of the motor, which at the same time operates as a generator, issues a command to set the positioner to the parking position, which manages to be completed before the rotation speed drops below critical. 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 secured 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 drive operation
Now - about the process of the hard drive itself. After the initial setup of electronics and mechanics, the hard drive microcomputer goes into the mode of waiting for commands from the controller located on the system board or interface card. Having received the command, it turns on the desired head, uses servo pulses to find the desired track, waits until the desired sector “reaches” the head, and reads or writes information. If the controller has 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 information transfer to or from the controller.
For optimal use of the disk surface, so-called zoned bit recording (ZBR) is used, the principle of which is that on external tracks that are longer (and therefore information capacity), information is recorded with greater 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 read and write speed on external zones is higher than on internal 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 let’s talk about where the incredibly large numbers of heads specified in the hard drive parameters come from. Once upon a time, these numbers - the number of cylinders, heads and sectors at a higher price - actually indicated the real physical parameters (geometry) of the hard drive. However, when using ZBR, the number of sectors changes 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 certain conditional parameters, and when receiving commands it itself converts logical addresses into physical ones. At the same time, a hard drive with logical geometry, for example, 520 cylinders, 128 heads and 63 sectors (total volume - 2 GB), most likely contains two disks - and four read/write heads.
The latest generation hard drives use PRML (Partial Response, Maximum Likelihood) and S.M.A.R.T technologies. (Self Monitoring Analysis and Report Technology - technology for self-monitoring analysis and reporting). The first was developed due to the fact that with 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 maximum similarity, a conclusion is made about the acceptance of a particular code word - in much the same way we read words in which letters are missing or distorted.
The hard drive, which implements S.M.A.R.T. technology, keeps statistics of its operating parameters (number of starts/stops and hours worked, spindle acceleration time, detected/corrected errors, etc.), which are regularly stored in reprogrammable ROM or in service areas of the disk. This information accumulates 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 the mechanics, operating conditions or the approximate probability of failure.
Related information.
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 .
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.
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