What parts does a hard drive consist of? Interface connectors and connections. Why is a hard drive called a hard drive?

When the computer starts, a set of firmware stored in the BIOS chip checks the hardware. If everything is fine, it transfers control to the operating system boot loader. Then the OS loads and you start using the computer. At the same time, where was the operating system stored before turning on the computer? How did your essay, which you wrote all night, remain intact after the PC was turned off? Again, where is it stored?

Okay, I probably went too far and you all know very well that computer data is stored on the hard drive. However, not everyone knows what it is and how it works, and since you are here, we conclude that we would like to find out. Well, let's find out!

What is a hard drive

By tradition, let's look at the definition of a hard drive on Wikipedia:

HDD (screw, hard drive, storage device hard magnetic disks, HDD, HDD, HMDD) is a random access storage device based on the principle of magnetic recording.

Used in the vast majority of computers, and also as separately connected storage devices backup copies data as file storage and so on.

Let's figure it out a little. I like the term " hard disk drive ". These five words convey the essence. HDD is a device whose purpose is to store data recorded on it for a long time. The basis of HDDs are hard (aluminum) disks with a special coating, onto which information is recorded using special heads.

I will not consider the recording process itself in detail - essentially this is the physics of the last grades of school, and I’m sure you have no desire to delve into this, and that’s not what the article is about at all.

Let us 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.

An important fact is that the HDD memory is not volatile, that is, no matter whether the power is connected or not, the information recorded on the device will not disappear anywhere. This important difference permanent memory computer, from temporary ().

Looking at HDD computer in real life, you will not see either disks or heads, since all this is hidden in a sealed case (hermetic zone). Externally, the hard drive looks like this:

Why does a computer need a hard drive?

Let's look at what a 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 the HDD:

Storage of OS, user software and their settings;
Storage of user files: music, videos, images, documents, etc.;
Using part of the hard disk space to store data that does not fit in RAM (swap file) or storing content random access memory while using sleep mode;

As you can see, the computer hard drive is not just a dump of photos, music and videos. The entire operating system is stored on it, and in addition, the hard drive helps cope with the load on the RAM, taking on some of its functions.

What does a hard drive consist of?

We partially mentioned the components of a hard drive, now we will look at this in more detail. So, the main components of the HDD:

Frame — protects hard drive mechanisms from dust and moisture. As a rule, it is sealed so that moisture and dust do not get inside;
Discs (pancakes) - plates made of a certain metal alloy, coated on both sides, on which data is recorded. The number of plates can be different - from one (in budget options), up to several;
Engine — on the spindle of which the pancakes are fixed;
Head block - a design of interconnected levers (rocker arms) and heads. The part of the 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 are working;
Positioning device (actuator ) - a mechanism that drives the head block. Consists of a pair of permanent neodymium magnets and a coil located at the end of the head block;
Controller — electronic chip work manager HDD;
Parking zone - a place inside the hard drive next to the disks or on their inner part, where the heads are lowered (parked) during downtime, so as not to damage the working surface of the pancakes.

This is 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 does a hard drive work?

After power is supplied to the HDD, the motor, on the spindle of which the pancakes are attached, begins to spin up. Having reached the speed at which a constant flow of air is formed at the surface of the disks, the heads begin to move.

This sequence (first the disks spin up, and then the heads start working) is necessary so that, due to the resulting air flow, the heads float above the plates. 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 plates to the heads is so small (~10 nm) that you cannot see it with the naked eye.

After startup, first of all, service information about state of rigid disk and others necessary information about him, located on the so-called zero track. Only then does work with the data begin.

Information on a computer's hard drive is recorded on tracks, which, in turn, are divided into sectors (like 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 this “horizontal” disk partition, there is also a conventional “vertical” partition. Since all the heads are combined, they are always positioned above the same track number, each above its own disk. Thus, during HDD operation the heads seem to draw a cylinder:

While the HDD is running, it essentially performs two commands: read and write. 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 the disk, the information also ends up in its cache.

If the controller receives a read command, it first checks whether the required information is in the cache. If it is not there, the coordinates for positioning the heads are calculated again, then the heads are positioned and the data is read.

After completion of work, when the power to the hard drive disappears, the heads are automatically parked in the parking zone.

Like this in general outline and the computer hard drive is working. In reality, everything is much more complicated, but ordinary user, most likely, such details are not needed, so let's finish this section and move on.

Types of hard drives and their manufacturers

Today, there are actually three main ones on the market manufacturer of hard drives: Western Digital (WD), Toshiba, Seagate. They fully cover the demand for devices of all types and requirements. The remaining companies either went bankrupt, were absorbed by one of the main three, or were repurposed.

If speak about types of HDD, they can be divided this way:

For laptops, the main parameter is the device size of 2.5 inches. This allows them to be compactly placed in the laptop case;
For PC - in this case it is also possible to use 2.5″ hard drives, but as a rule, 3.5 inches are used;
External hard disks are devices that are separately connected to a PC/laptop, most often serving as file storage.

There is also a special type of hard drive - for servers. They are identical to regular PC ones, but may differ in connection interfaces and greater performance.

All other divisions of HDD into types come from their characteristics, so let’s consider them.

Hard drive specifications

So, the main characteristics of a computer hard drive:

Volume — an indicator of the maximum possible amount of data that can be stored on the disk. The first thing they usually look at when choosing HDD. This indicator can reach 10 TB, although for a home PC they often choose 500 GB - 1 TB;
Form factor — size of the hard drive. 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 in PCs and servers. The form factor also affects the volume, since a larger disk can fit more data;
Spindle speed — at what speed do the 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 - method (connector type) HDD connections to the computer. The most popular interface for internal hard drives today is SATA (older computers used IDE). External hard disks are usually connected via USB or FireWire. In addition to those listed, there are also such interfaces as SCSI, SAS;
Buffer volume (cache memory) - type fast memory(type of RAM) hard drive installed on the 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. Ranges from 3 to 15 ms;

In addition to the above characteristics, you can also find such indicators as:

Greetings, friends!

Today we will talk about such a thing as a hard drive. Rarely a computer user has not heard of it!

A hard drive, also known as HDD (Hard Disk Drive), is a device for storing information.

The HDD got its slang name from the famous rifle with which white men conquered America. One of the first models of hard drives was designated "30/30", which coincided with the caliber of this firearm.

Below we will talk about computer hard drives.

How does a computer hard drive work?

We will look at how a traditional (electromechanical) hard drive used in personal computers. It is based on one or more information disks. The first hard drive models used aluminum disks.

But those first models had big size and low capacity.

Floppy and hard drives

Those "screws" (another slang name) had physical dimensions and a capacity approximately equal to a 5.25-inch floppy drive. At the dawn of the computer industry, data was stored on 5.25 and 3.5 inch floppy disks.

The drive for reading and writing such disks was called FDD (Floppy Disk Drive).

These discs were made from a round piece of plastic with a ferromagnetic coating applied to both sides. They were thin and flexible, which is why the drive got its name. To protect them from external influences, these discs were placed in a square plastic case.

Disks in HDDs have a similar structure, but they are thicker and do not bend, which is reflected in the name. A thin ferromagnetic layer of metal oxides is applied to such a disk using a centrifuge. Data is written and read using magnetic heads.

When recording, an information signal is sent to the magnetic head, which changes the orientation of domains (ferromagnetic particles) in the ferromagnetic layer.

When reading, the magnetized areas induce current in the head, which is then processed by the control circuit (controller). Requirements for speed and data volumes are constantly growing. The best minds in the world were sent to this area. And hard drives, like the rest of computer hardware, were continuously improved.

Disks began to be made from glass and glass ceramics. This made it possible to reduce their weight, thickness and increase rotation speed.

The disk rotation speed increased from 3600 rpm to 5400, 7200, and then to 10,000 and even 15,000 rpm! For comparison, let's say that the disk rotation speed in FDD was 360 rpm.

The higher the rotation speed, the faster the data is read.

Ferromagnetic layer

A ferromagnetic layer can be applied to the surface of disks in two ways - galvanic deposition and vacuum deposition. In the first case, the disk is immersed in a solution of metal salts, and a thin film of metal (cobalt) is deposited on it.

In vacuum deposition, the disk is placed in a sealed chamber, the air is pumped out of it, and metal particles are deposited using an electric discharge.

A protective carbon coating is applied on top of the magnetic layer. It protects the thin magnetic layer from destruction (and loss of information) in case of possible contact with the head.

A hard drive can have one physical disk or several. In the latter case, the disks are assembled into a single structure and rotate synchronously. Each disk has two sides with a ferromagnetic layer, the data is read by two different heads (located on the top and bottom).

The heads are also assembled into a single structure and move synchronously.

The mechanism for moving the heads contains a coil of wire and a fixed permanent magnet. When current is applied to the coil, a magnetic field is generated in it, interacting with the magnet. The resulting force moves the coil with the entire moving part of the mechanism (and the heads too).

The mechanism contains a spring, which, in the absence of power, moves the heads to their original position (parking area). This protects the heads and disks from damage.

Note that small neodymium magnets that create a constant magnetic field are very strong!

In operating condition, the disks rotate at a constant speed, the heads “hover” above the disk. During rotation, an aerodynamic flow occurs, lifting the heads. As technology improves, the distance between the heads and the disk decreases.

To date, it has been brought to several tens of nanometers!

Reducing the distance allows you to increase the density of information recording. This way, more information can be squeezed into the same amount of space.

Read and write heads

Modern hard drives use magnetoresistive heads.

The magnetoresistor crystal can change its resistance depending on the magnitude and direction magnetic field. As the head passes over areas with different magnetization, its resistance changes, which is detected by the control circuit.

The hard drive head contains, in fact, two heads - reading and writing. The recording head works on the same principle as the head in older tape recorders, which used magnetic tape cassettes.

It contains an open core, in the gap of which a magnetic field is created, which changes the orientation of magnetic domains on the surface of the disk. The “winding” of the head is printed using photolithography.

Spindle and HDA

The main drive motor (spindle), which rotates the disk, contains hydrodynamic bearing. It differs from a ball bearing in that it has much less radial runout.

In modern hard drives, the recording density of information is very high, the tracks are located very close to each other.

A large radial runout would not allow an increase in recording density, or (with a decrease in the distance between tracks) the head would “jump” along adjacent tracks during one revolution. A hydrodynamic bearing contains a thin layer of lubricant between the moving and stationary parts.

In conclusion, we say that the spindle, disks, head with drive are placed in a separate compartment. The first models of hard drives contained leaky compartments equipped with a filter with very small cells to equalize pressure.

Then sealed compartments appeared, which had a hole in them closed with a flexible membrane. The membrane can bend in both directions, compensating for the difference in air pressure inside and outside the compartment with the heads.

In the next part of the article we will continue our acquaintance with how the hard drive is designed and works.

Victor Geronda was with you. See you on the blog!

The purpose of this article is to describe the structure of 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 the 3.5-inch SATA drive. This will be a completely new Seagate ST31000333AS terabyte. Let's examine our guinea pig.

Green textolite with copper tracks, 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. Black aluminium case and its contents are called 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 data coming from the heads analog signal into digital data during a read operation and encoding the digital data into an analog signal during a write operation. 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 PCB has Samsung memory DDR with a capacity of 32 MB, 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 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.

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. During a power surge, the TVS burns out, creating short circuit to the 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. WITH 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 can 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 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. Black plastic part complex shape 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 one an important part BMG, which 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 to which to this moment the hard drive is 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.

Clarifying the connection between Russian-speaking and English terminology made by Leonid Vorzhev.

Article copied from

Storing information on hard drives

Part 1

1. Introduction

Most users, when asked what is in their system unit, among other things, they mention a hard drive. The hard drive is the device on which your data is most often stored. There is a legend explaining why hard drives there was such a fancy name. The first hard drive, released in America in the early 70s, had a capacity of 30 MB of information on each working surface. At the same time, O. F. Winchester's repeating rifle, widely known in America, had a caliber of 0.30; Maybe the first hard drive rumbled like a machine gun during its operation, or it smelled of gunpowder - I don’t know, but from then on they began to call hard drives hard drives.

During the operation of the computer, malfunctions occur. Viruses, power outages, software errors - all this can cause damage to information stored on your hard drive. Damage to information does not always mean its loss, so it is useful to know how it is stored on the hard drive, because then it can be restored. Then, for example, if the boot area is damaged by a virus, it is not at all necessary to format the entire disk (!), but, having restored the damaged area, continue normal operation while preserving all your invaluable data.

On the one hand, in the process of writing this article, I set myself the task of telling you:

about the principles of recording information on a hard drive;
about the placement and loading of the operating system;
about how to wisely divide your new hard drive into sections in order to use several operating systems.

On the other hand, I want to prepare the reader for the second article, in which I will talk about programs called boot managers. In order to understand how these programs work, you need to have basic knowledge about things like MBR, Partitions, etc.

Enough common words- let's get started.

2. Hard drive device

A hard drive (HDD - Hard Disk Drive) is designed as follows: on a spindle connected to an electric motor, there is a block of several disks (pancakes), above the surface of which there are heads for reading / writing information. The heads are shaped like a wing and are attached to a crescent-shaped leash. During operation, they “fly” over the surface of the disks in the air flow that is created when the same disks rotate. Obviously, the lifting force depends on the air pressure on the heads. It, in turn, depends on external atmospheric pressure. Therefore, some manufacturers indicate a maximum operating ceiling (for example, 3000 m) in the specifications for their devices. Why not a plane? The disk is divided into tracks (or tracks), which in turn are divided into sectors. Two paths equidistant from the center, but located along different sides disk are called cylinders.

3. Information storage

A hard drive, like any other block device, stores information in fixed portions called blocks. A block is the smallest piece of data that has a unique address on the hard drive. To read or write necessary information to the right place, you need to provide the block address as a parameter of the command issued to the hard disk controller. The block size has long been standard for all hard drives - 512 bytes.

Unfortunately, quite often there is confusion between such concepts as “sector”, “cluster” and “block”. In fact, there is no difference between a “block” and a “sector”. True, one concept is logical, and the second is topological. A “cluster” is several sectors considered by the operating system as one whole. Why didn't you abandon simple work with sectors? I will answer. The move to clusters occurred because the size of the FAT table was limited and the disk size was increasing. In the case of FAT16, for a 512 MB disk, the cluster will be 8 KB, up to 1 GB - 16 KB, up to 2 GB - 32 KB, and so on.

In order to uniquely address a data block, you must specify all three numbers (cylinder number, sector number on the track, head number). This method of disk addressing was widespread and was subsequently designated by the abbreviation CHS (cylinder, head, sector). It was this method that was originally implemented in the BIOS, so limitations associated with it subsequently arose. The fact is that the BIOS has defined a bit address grid of 63 sectors, 1024 cylinders and 255 heads. However, the development of hard drives at that time was limited to the use of only 16 heads due to the complexity of manufacturing. This is where the first limitation on the maximum permissible hard disk capacity for addressing appeared: 1024 × 16 × 63 × 512 = 504 MB.

Over time, manufacturers began to make HDDs bigger size. Accordingly, the number of cylinders on them exceeded 1024, the maximum valid number cylinders (from the point of view old BIOS). However, the addressable portion of the disk continued to be 504 MB, provided that the disk was accessed using BIOS. This limitation was eventually removed by the introduction of the so-called address translation mechanism, which is discussed below.

Problems that arose with the limitations of the BIOS in terms of the physical geometry of the disks eventually led to the emergence of a new way to address blocks on the disk. This method is quite simple. Blocks on a disk are described by one parameter - the linear address of the block. Disk addressing linearly received the abbreviation LBA (logical block addressing). The linear address of a block is uniquely associated with its CHS address:

lba = (cyl*HEADS + head)*SECTORS + (sector-1);

The introduction of support for linear addressing in hard drive controllers made it possible for BIOSes to engage in address translation. The essence of this method is that if you increase the HEADS parameter in the above formula, then fewer cylinders will be required to address the same number of disk blocks. But then more heads will be required. However, only 16 of 255 heads were used. Therefore, BIOSes began to transfer excess cylinders to heads, reducing the number of some and increasing the number of others. This allowed them to use the entire discharge grid of heads. This moved the boundary of what is addressed by the BIOS disk space up to 8 GB.

It is impossible not to say a few words about Large Mode. This operating mode is designed to operate hard drives up to 1 GB. In Large Mode, the number of logical heads increases to 32, and the number of logical cylinders is halved. In this case, accesses to logical heads 0..F are translated to even physical cylinders, and accesses to heads 10..1F are translated to odd ones. A hard drive partitioned in LBA mode is incompatible with Large mode, and vice versa.

Further increase in addressable disk volumes using previous BIOS services has become fundamentally impossible. Indeed, all parameters are used at the maximum “bar” (63 sectors, 1024 cylinders and 255 heads). Then a new extended BIOS interface was developed, taking into account the possibility of very large block addresses. However, this interface is no longer compatible with the previous one, as a result of which older operating systems, such as DOS, which use older BIOS interfaces, could not and will not be able to cross the boundaries of 8GB. Almost everything modern systems no longer use the BIOS, but use their own drivers to work with disks. Therefore this limitation does not apply to them. But you should understand that before the system can use its own driver, it must at least load it. Therefore, at the stage bootstrap any system is forced to use the BIOS. This causes restrictions on placing many systems outside 8GB; they cannot boot from there, but they can read and write information (for example, DOS which works with the disk through the BIOS).

4. Sections, or Partitions

Let us now turn to placing operating systems on hard drives. To organize systems, the disk address space of blocks is divided into parts called partitions. Partitions are exactly like a whole disk in that they are made up of contiguous blocks. Thanks to this organization, to describe a section, it is enough to indicate the beginning of the section and its length in blocks. A hard drive can contain four primary partitions.

When the computer boots, the BIOS loads the first sector of the head partition (boot sector) at address 0000h:7C00h and transfers control to it. At the beginning of this sector there is a bootloader (boot code) that reads the partition table and determines the bootable partition (active). And then everything repeats itself. That is, it loads the boot sector of this partition to the same address and transfers control to it again.

Sections are containers for all of their content. This content is typically a file system. From a disk point of view, a file system refers to a system for marking blocks for storing files. Once a file system has been created on the partition and the operating system files are located on it, the partition can become bootable. The loading section has in its first block small program, which loads the operating system. However, to download a certain system you need to explicitly launch its boot program from the first block. How this happens will be discussed below.

Partitions with file systems should not overlap. This is because two different file systems each have their own idea of where files are placed, but when that placement falls on the same physical disk space, a conflict occurs between the file systems. This conflict does not arise immediately, but only as files begin to be located in the place on the disk where the partitions intersect. Therefore, you should be careful about dividing the disk into partitions.

The intersection of sections in itself is not dangerous. It is dangerous to place multiple file systems on overlapping partitions. Partitioning a disk does not mean creating file systems. However, the very attempt to create is empty file system(that is, formatting) on one of the overlapping partitions can cause errors in the file system of the other partition. All of the above applies equally to all operating systems, and not just the most popular ones.

The disk is partitioned programmatically. That is, you can create an arbitrary partition configuration. Information about disk partitioning is stored in the very first hard block disk called the Master Boot Record (MBR).

5.MBR

MBR is the primary hard disk boot facility supported by the BIOS. For clarity, let’s present the contents of the boot area in the form of a diagram:

Everything that is located at offset 01BEh-01FDh is called a partition table. You can see that it has four sections. Only one of the four partitions has the right to be marked as active, which will mean that the boot program must load the first sector of that particular partition into memory and transfer control there. The last two bytes of the MBR must contain the number 0xAA55. Based on the presence of this signature, the BIOS verifies that the first block was loaded successfully. This signature was not chosen by chance. A successful test of this will establish that all data lines can carry both zeros and ones.

The boot program looks through the partition table, selects the active one, loads the first block of this partition and transfers control there.

Let's see how the section descriptor works:

* 0001h-0003h start of section
** 0005h-0007h end of section

From the point of view of disk partitions, the most popular until recently was and remains MS-DOS. It takes over two of the four partitions: Primary DOS partition, Extended DOS partition. The first of them, (primary) is a regular DOS drive C:. The second is a container of logical drives. They all hang out there in the form of a chain of subsections, which are called: D:, E:, ... Logical drives may also have foreign file systems other than the DOS file system. However, as a rule, the foreignness of the file system is due to the presence of another operating system, which, generally speaking, should be placed in its own partition (not extended DOS), but the partition table is often too small for such tricks.

Let us note one more important circumstance. When on pure hard The disk is installed with DOS, then when loading there are no alternatives in choosing operating systems. Therefore, the bootloader looks very primitive; it does not need to ask the user what system he wants to boot. With the desire to have several systems at once, there is a need to create a program that allows you to select a system to boot.

6. Conclusion

I hope that I was able to provide you with sufficiently clear and detailed basic information about the hard disk device, MBR and PT. In my opinion, such a set of knowledge is quite enough for minor “repairs” of the information storage. In the next article I will tell you about programs called Boot Manager and the principles of their operation.

Thank you very much for your help to Vladimir Dashevsky

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 terminology 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 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.

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 preparation zone is the area where the heads of a working disk should be if the spindle is stopped. With this disc, the preparation zone is located closer to the spindle, as can be seen in the photograph.

On some drives, parking is done on special plastic preparation areas located outside 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 retainer protects the heads from unwanted movements in the preparation position.

Now let's remove the magnetic head block.

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.

This is a classic rocker design.

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.

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 a 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.