What are hard drives made of? Hard drive: principle of operation and main characteristics

hard drive (hard drive, HDD) - a random access memory (information storage device) based on the principle of magnetic recording. It is the main storage medium in most computers.

Unlike " flexible» disk ( floppy disks), information in HDD recorded on hard (aluminum or glass) plates coated with a layer of ferromagnetic material, most often chromium dioxide - magnetic disks. AT HDD one or more inserts on one axis are used. Reading heads in the operating mode do not touch the surface of the plates due to the layer of air flow formed near the surface during rapid rotation. The distance between the head and the disk is several nanometers, and the absence of mechanical contact ensures a long service life of the device. In the absence of rotation of the disks, the heads are located at the spindle or outside the disk in a safe zone, where their abnormal contact with the surface of the disks is excluded.

First hard drive

AT 1957 year by the firm IBM the very first hard drive was developed, and it was developed even before the creation of a personal computer. For him, he would have to pay a “tidy” sum, although he had only 5 MB. Then a hard disk was developed with a capacity 10 MB specially for personal computer IBM PC XT. Winchester had everything 30 tracks and more on 30 sectors in every track. " Winchesters"- this is how hard drives began to be called, if abbreviated, then" ATintami”, This came from an analogy with the marking of the carbine of the company Winchester - "30/30", which was multi-charged.

For clarity, let's take a look 3.5 inch SATA disk. It will be Seagate ST31000333AS.

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

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

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

Memory Chip is the usual DDR SDRAM memory. The amount of memory determines the size of the hard disk cache. Memory is installed on this circuit board Samsung DDR volume 32 MB, which in theory gives the disk a cache in 32 MB(and this is exactly the amount that is given in the technical characteristics of the hard drive), but this is not entirely true. The fact is that the memory is logically divided into buffer memory (Cache) and firmware memory. The processor needs some memory to load firmware modules. As far as is known, only Hitachi/IBM indicate the actual volume cache in the description of technical characteristics; relative to other disks, about the volume cache one can only guess.

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

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

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

There is another protective device on the board - Transient Voltage Suppression (TVS). It protects the board from power surges. With a power surge TVS burns out, creating a short circuit to ground. This board has two TVS, for 5 and 12 volts.

Consider the hermetic block.

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

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

The lid itself is nothing special. It's just a piece of metal with a rubber seal to keep dust out.

Consider the filling of the containment area.

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

Read-write heads (heads), mounted on the ends of the magnetic head unit brackets, or HSA (Head Stack Assembly, HSA). parking zone- this is the area in which the heads of a healthy disk should be if the spindle is stopped. With this disc, the parking zone is located closer to the spindle, as can be seen in the photo.

On some drives, parking is done in special plastic parking areas located outside the plates.

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

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

Hard drives use very powerful neodymium magnets. These magnets are so powerful that they can lift weight in 1300 times larger than their own. So do not put your finger between the magnet and metal or another magnet - the blow will be very sensitive. This photo shows the restraints. BMG. Their task is to limit the movement of the heads, leaving them on the surface of the plates. BMG limiters different models are arranged differently, but there are always two of them, they are used on all modern hard drives. On our drive, the second limiter is located on the bottom magnet.

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

Now let's remove the block of magnetic heads.

Precision and smooth movement BMG supported by precision bearing. The largest detail BMG, made of aluminum alloy, commonly referred to as bracket or rocker (arm). At the end of the rocker there are heads on a spring suspension (Heads Gimbal Assembly, HGA). Usually the heads and rocker arms are supplied by different manufacturers. Flexible Cable (Flexible Printed Circuit, FPC) goes to the contact pad, docking with the control board.

Consider the components BMG more.

A coil connected to a cable.

Bearing.

The following photo shows BMG contacts.

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

This is a classic rocker design.

The small black pieces at the ends of the spring hangers are called sliders. Many sources indicate that sliders and heads are one and the same. In fact, the slider helps to read and write information by raising the head above the surface of the pancakes. On modern hard drives, the heads move at a distance 5-10 nanometers from the surface of the pancakes. For comparison, a human hair has a diameter of about 25000 nanometers. If any particle gets under the slider, it can lead to overheating of the heads due to friction and their failure, which is why the purity of the air inside the containment is so important. The reading and writing elements themselves are located at the end of the slider. They are so small that they can only be seen with a good microscope.

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

Here is another slider image

Head contacts are clearly visible here.

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

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

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

In this article, we will only talk about hard drives (HDD), that is, about media on magnetic disks. About SSD will be the next article.

What is a hard drive

By tradition, let's look at the definition of a hard drive on Wikipedia:
A hard disk (screw, hard drive, hard disk drive, HDD, HDD, HMDD) is a random access storage device based on the principle of magnetic recording.
They are used in the vast majority of computers, as well as separately connected devices for storing backup copies of data, as file storage, etc.
Let's figure it out a little. I like the term "hard drive". These five words convey the whole point. HDD is a device whose purpose is to store data recorded on it for a long time. HDDs are based on hard (aluminum) disks with a special coating, on which information is recorded using special heads.
I will not consider in detail the recording process itself - in fact, this is the physics of the last grades of the school, and I am sure you have no desire to delve into this, and the article is not about that at all.
Let's also pay attention to the phrase: "random access" which, roughly speaking, means that we (the computer) can read information from any section of the railway at any time.
It is important that the HDD memory is not volatile, that is, it does not matter whether the power is connected or not, the information recorded on the device will not disappear anywhere. This is an important difference between a computer's permanent memory and temporary memory (RAM).
Looking at a computer hard drive in real life, you will not see any disks or heads, since all this is hidden in a sealed enclosure (hermetic zone). Externally, the hard drive looks like this.
I think you understand what HDD is. Move on.

Why does a computer need a hard drive?

Consider what an HDD is in a computer, that is, what role it plays in a PC. It is clear that it stores data, but how and what. Here we highlight the following functions of HDD:
- Storage of OS, user software and their settings;
- Storage of user files: music, video, images, documents, etc.;
- Using part of the hard disk space to store data that does not fit in RAM (paging file) or storing the contents of RAM while using sleep mode;
- As you can see, a computer hard drive is not just a dump of photos, music and videos. It stores the entire operating system, and in addition, the hard drive helps to cope with the workload of RAM, taking on some of its functions.

What is a hard drive made of?

We partially mentioned the components of the hard drive, now we will deal with this in more detail. So, the main components of the HDD:
- Enclosure - protects hard drive mechanisms from dust and moisture. As a rule, it is airtight so that the same moisture and dust do not get inside;
- Discs (pancakes) - plates made of a certain alloy of metals, coated on both sides, on which data is recorded. The number of plates can be different - from one (in budget options) to several;
- Engine - on the spindle of which pancakes are fixed;
- The block of heads - a design from the levers (rocker arms) connected among themselves, and heads. The part of a hard drive that reads and writes information to it. For one pancake, a pair of heads is used, since both the upper and lower parts of it are working;
- Positioning device (actuator) - a mechanism that drives the block of heads. Consists of a pair of permanent neodymium magnets and a coil located at the end of the head unit;
- Controller - an electronic microcircuit that controls the operation of the HDD;
- Parking zone - a place inside the hard drive next to the disks or on their inside, where the heads are lowered (parked) during idle time, so as not to damage the working surface of the pancakes.
Such a simple hard drive device. It was formed many years ago, and no fundamental changes have been made to it for a long time. And we move on.

How a hard drive works

After power is supplied to the HDD, the engine, on the spindle of which the pancakes are fixed, begins to spin up. Having gained a speed at which a constant stream of air is formed near the surface of the discs, the heads begin to move.
This sequence (first the disks spin up, and then the heads start working) is necessary so that the heads hover over the plates due to the resulting air flow. Yes, they never touch the surface of the disks, otherwise the latter would be instantly damaged. However, the distance from the surface of the magnetic platters to the heads is so small (~10 nm) that you cannot see it with the naked eye.
After starting, first of all, service information about the state of the hard disk and other necessary information about it, located on the so-called zero track, is read. Only then does the work with the data begin.
Information on the computer's hard drive is recorded on tracks, which, in turn, are divided into sectors (such a pizza cut into pieces). To write files, several sectors are combined into a cluster, which is the smallest place where a file can be written.
In addition to such a "horizontal" partitioning of the disk, there is also a conditional "vertical" one. Since all heads are combined, they are always positioned over the same track number, each over its own disc. Thus, during the operation of the HDD, the heads, as it were, draw a cylinder.
While the HDD is working, in fact, it performs two commands: reading and writing. When it is necessary to execute a write command, the area on the disk where it will be performed is calculated, then the heads are positioned and, in fact, the command is executed. The result is then checked. In addition to writing data directly to disk, information also ends up in its cache.
If the controller receives a read command, first of all, it checks for the presence of the required information in the cache. If it is not there, the coordinates for positioning the heads are calculated again, then the heads are positioned and read the data.
After completion of the work, when the power supply of the hard drive disappears, the heads are automatically parked in the parking zone.
This is how a computer hard drive works in general terms. In reality, everything is much more complicated, but the average user, most likely, does not need such details, so we will finish this section and move on.

Types of hard drives and their manufacturers

Today, there are actually three main manufacturers of hard drives on the market: Western Digital (WD), Toshiba, Seagate. They fully cover the demand for devices of all types and requirements. The rest of the companies either went bankrupt, or were taken over by someone from the main three, or re-profiled.
If we talk about the types of HDD, they can be divided in this way:

1. For laptops - the main parameter is the device size of 2.5 inches. This allows them to be compactly placed in the laptop case;
2. For PC - in this case, it is also possible to use 2.5″ hard drives, but as a rule, 3.5 inches are used;
3. External hard drives - devices that are separately connected to a PC / laptop, most often acting as a file storage.
There is also a special type of hard drives - for servers. They are identical to conventional PCs, but may differ in interfaces for connection, and greater performance.

All other divisions of HDD into types come from their characteristics, so we will consider them.

Hard drive specifications

So, the main characteristics of a computer hard drive:

Size is a measure of the maximum amount of data that can fit on a disk. The first thing they usually look at when choosing an HDD. This figure can reach 10 TB, although 500 GB - 1 TB is more often chosen for a home PC;
- Form factor - hard drive size. The most common are 3.5 and 2.5 inches. As mentioned above, 2.5″ in most cases are installed in laptops. They are also used in external HDDs. 3.5″ is installed on the PC and on the server. The form factor also affects the volume, as more data can fit on a larger disk;
- Spindle speed - at what speed pancakes rotate. The most common are 4200, 5400, 7200 and 10000 rpm. This characteristic directly affects the performance, as well as the price of the device. The higher the speed, the greater both values;
- Interface - the method (connector type) for connecting the HDD to the computer. The most popular interface for internal hard drives today is SATA (older computers used IDE). External hard drives are usually connected via USB or FireWire. In addition to those listed, there are other interfaces such as SCSI, SAS;
- Buffer size (cache memory) - a type of fast memory (by type of RAM) installed on the HDD controller, designed for temporary storage of data that is most often accessed. The buffer size can be 16, 32 or 64 MB;
- Random access time - the time during which the HDD is guaranteed to write or read from any part of the disk. It fluctuates from 3 to 15 ms;

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

Data transfer rate;
- Number of I/O operations per second;
- Noise level;
- Reliability;
- Resistance to impacts, etc.;
At the expense of the characteristics of the HDD, that's all.

A hard disk drive (HDD) \ HDD (Hard Disk Drive) \ hard drive (carrier) is a material object capable of storing information.

Information accumulators can be classified according to the following features:

• information storage method: magnetoelectric, optical, magneto-optical;
• type of information carrier: drives on floppy and hard magnetic disks, optical and magneto-optical disks, magnetic tape, solid-state memory elements;
• the method of organizing access to information - drives of direct, sequential and block access;
• type of information storage device - built-in (internal), external, autonomous, mobile (wearable), etc.

A significant part of the information storage media currently used is based on magnetic media.

Hard disk device

The hard drive contains a set of plates, which are most often metal disks coated with a magnetic material - a platter (gamma ferrite oxide, barium ferrite, chromium oxide ...) and interconnected using a spindle (shaft, axis).
The discs themselves (approximately 2 mm thick) are made of aluminium, brass, ceramic or glass. (see pic)

Both surfaces of discs are used for recording. Used 4-9 plates. The shaft rotates at a high constant speed (3600-7200 rpm)
The rotation of the discs and the radical movement of the heads is carried out using 2 electric motors.
Data is written or read using write/read heads one for each surface of the disk. The number of heads is equal to the number of working surfaces of all disks.

Recording information on the disk is carried out in strictly defined places - concentric tracks (tracks) . The tracks are divided into sectors. One sector contains 512 bytes of information.

Data exchange between RAM and NMD is carried out sequentially by an integer (cluster). cluster- chains of consecutive sectors (1,2,3,4,…)

Special engine using a bracket, positions the read/write head over a given track (moves it in the radial direction).
When the disk is rotated, the head is located over the desired sector. It is obvious that all heads move simultaneously and read data heads move simultaneously and read information from the same tracks on different drives from the same tracks on different disks.

Hard drive tracks with the same sequence number on different hard drives are called cylinder .
The read/write heads move along the surface of the platter. The closer the head is to the surface of the disc without touching it, the higher the allowable recording density.

Hard drive device

Magnetic principle of reading and writing information

magnetic recording principle

The physical foundations of the processes of recording and reproducing information on magnetic media were laid down in the works of the physicists M. Faraday (1791 - 1867) and D. K. Maxwell (1831 - 1879).

In magnetic storage media, digital recording is made on a magnetically sensitive material. Such materials include some varieties of iron oxides, nickel, cobalt and its compounds, alloys, as well as magnetoplasts and magnetoelasts with viscous plastics and rubber, micropowder magnetic materials.

The magnetic coating is several micrometers thick. The coating is applied to a non-magnetic base, which is different plastics for magnetic tapes and floppy disks, and aluminum alloys and composite substrate materials for hard disks. The magnetic coating of the disk has a domain structure, i.e. consists of many magnetized tiny particles.

Magnetic domain (from Latin dominium - possession) - this is a microscopic, uniformly magnetized region in ferromagnetic samples, separated from neighboring regions by thin transition layers (domain walls).

Under the influence of an external magnetic field, the intrinsic magnetic fields of the domains are oriented in accordance with the direction of the magnetic field lines. After the action of the external field ceases, zones of residual magnetization form on the domain surface. Due to this property, information is stored on the magnetic carrier, acting in a magnetic field.

When recording information, an external magnetic field is created using a magnetic head. In the process of reading information, the zones of residual magnetization, being opposite the magnetic head, induce an electromotive force (EMF) in it when reading.

The scheme of recording and reading from a magnetic disk is given in Fig. 3.1. A change in the direction of the EMF over a certain period of time is identified with a binary unit, and the absence of this change is identified with zero. This period of time is called bit element.

The surface of a magnetic carrier is considered as a sequence of dotted positions, each of which is associated with a bit of information. Since the location of these positions is not precisely determined, the recording requires pre-applied marks to help locate the required recording positions. To apply such synchronization marks, the disk must be divided into tracks.
and sectors - formatting .

The organization of quick access to information on the disk is an important step in data storage. Online access to any part of the disk surface is provided, firstly, by giving it a fast rotation and, secondly, by moving the magnetic read/write head along the radius of the disk.
A floppy disk rotates at a speed of 300-360 rpm, and a hard disk - 3600-7200 rpm.

Hard drive logical unit

The magnetic disk is not initially ready for operation. To bring it into working condition, it must be formatted, i.e. the disk structure must be created.

The structure (markup) of the disk is created during the formatting process.

Formatting magnetic disks includes 2 stages:

1. physical formatting (low level)
2. logical (high level).

During physical formatting, the working surface of the disk is divided into separate areas called sectors , which are located along concentric circles - paths.

In addition, sectors unsuitable for data recording are determined, they are marked as bad in order to avoid their use. Each sector is the smallest unit of data on a disk and has its own address for direct access to it. The sector address includes the side number of the disc, the track number, and the sector number on the track. The physical parameters of the disk are set.

As a rule, the user does not need to deal with physical formatting, since in most cases hard drives arrive formatted. Generally speaking, this should be done by a specialized service center.

Low Level Formatting must be done in the following cases:

• if there is a failure in the zero track, causing problems when booting from a hard disk, but the disk itself is available when booting from a floppy disk;
• if you return to working condition an old disk, for example, rearranged from a broken computer.
• if the disk turned out to be formatted to work with another operating system;
• if the disk stopped working normally and all recovery methods did not give positive results.

Keep in mind that physical formatting is very powerful operation.- when it is executed, the data stored on the disk will be completely erased and it will be completely impossible to restore them! So don't start low-level formatting unless you're sure you've saved all your important data off the hard drive!

After you perform a low-level format, the next step follows - creating a partition of the hard disk into one or more logical drives - the best way to deal with the confusion of directories and files scattered across the disk.

Without adding any hardware elements to your system, you get the ability to work with multiple parts of a single hard drive, as with multiple drives.
This does not increase the capacity of the disk, but you can greatly improve its organization. In addition, different logical drives can be used for different operating systems.

At logical formatting the final preparation of the media for data storage takes place through the logical organization of disk space.
The disk is being prepared for writing files to sectors created by low-level formatting.
After creating a disk breakdown table, the next step follows - logical formatting of individual parts of the breakdown, hereinafter referred to as logical disks.

logical drive is a certain area of ​​the hard disk that works in the same way as a separate drive.

Logical formatting is a much simpler process than low-level formatting.
To do this, boot from the floppy disk containing the FORMAT utility.
If you have multiple logical drives, format them one by one.

During the logical formatting process, the disk is allocated system area which consists of 3 parts:

• boot sector and partition table (Boot record)
• file allocation tables (FAT), which record the numbers of tracks and sectors that store files
• root directory (Root Directory).

Recording information is carried out in parts through the cluster. There cannot be 2 different files in the same cluster.
In addition, at this stage, the disk can be given a name.

A hard disk can be divided into several logical disks and vice versa 2 hard disks can be combined into one logical disk.

It is recommended to create at least two partitions (two logical disks) on a hard disk: one of them is reserved for the operating system and software, the second disk is exclusively allocated for user data. Thus, data and system files are stored separately from each other, and in the event of an operating system failure, the probability of saving user data is much greater.

Hard drive characteristics

Hard drives (hard drives) differ from each other in the following characteristics:

1. capacity
2. speed - data access time, speed of reading and writing information.
3. interface (connection method) - the type of controller to which the hard drive should be connected (most often IDE / EIDE and various SCSI options).
4. other features

1. Capacity- the amount of information that fits on the disk (determined by the level of manufacturing technology).
Today, the capacity is 500 -2000 or more GB. There is never enough hard drive space.

2. Speed ​​of work (performance) The disk is characterized by two indicators: disk access time and disk read/write speed.

Access time - the time required to move (position) the read / write heads to the desired track and sector.
The average characteristic access time between two randomly selected tracks is approximately 8-12ms (milliseconds), faster drives have a time of 5-7ms.
The transition time to the adjacent track (adjacent cylinder) is less than 0.5 - 1.5ms. It also takes time to turn to the right sector.
The total disk rotation time for today's hard drives is 8 - 16ms, the average waiting time for a sector is 3-8ms.
The shorter the access time, the faster the drive will run.

Read/write speed(I/O bandwidth) or data rate (transfer)- the transfer time of sequential data depends not only on the disk, but also on its controller, bus types, processor speed. The speed of slow disks is 1.5-3 Mb / s, for fast ones 4-5 Mb / s, for the latest 20 Mb / s.
Hard drives with a SCSI interface support a rotation speed of 10,000 rpm. and average search time 5ms, data transfer rate 40-80 Mb/s.

3.Hard drive interface standard — i.e. type of controller to which the hard drive should be connected. It is located on the motherboard.
There are three main connection interfaces

1. IDE and its various variants

IDE (Integrated Disk Electronics) or (ATA) Advanced Technology Attachment
Advantages - simplicity and low cost

Transfer rate: 8.3, 16.7, 33.3, 66.6, 100 Mbps. As the data develops, the interface supports the expansion of the list of devices: hard disk, super-floppy, magneto-optics,
NML, CD-ROM, CD-R, DVD-ROM, LS-120, ZIP.

Some elements of parallelization are introduced (gneuing and disconnect / reconnect), control over the integrity of data during transmission. The main disadvantage of IDE is a small number of connected devices (no more than 4), which is clearly not enough for a high-end PC.
Today, IDE interfaces have switched to the new Ultra ATA exchange protocols. Significantly increase your throughput
Mode 4 and DMA (Direct Memory Access) Mode 2 allows you to transfer data at a speed of 16.6 Mb / s, however, the actual data transfer rate would be much less.
Ultra DMA/33 and Ultra DMA/66 standards developed in February 98. by Quantum have 3 operating modes 0,1,2 and 4, respectively, in the second mode, the media supports
transfer speed 33Mb/s. (Ultra DMA/33 Mode 2) This high speed can only be achieved by exchanging with the storage buffer. In order to take advantage
Ultra DMA standards must meet 2 conditions:

1. hardware support on the motherboard (chipset) and on the side of the drive itself.

2. to support the Ultra DMA mode, like other DMA (direct memory Acess-direct memory access).

Requires special driver for different chipsets different. As a rule, they are included with the system board, if necessary, it can be "downloaded"
from the Internet from the motherboard manufacturer's website.

The Ultra DMA standard is backwards compatible with previous slower controllers.
Today's version: Ultra DMA/100 (late 2000) and Ultra DMA/133 (2001).

SATA
Replacing IDE (ATA) with another Fireware (IEEE-1394) high speed serial bus. The use of new technology will make it possible to increase the transmission speed to 100Mb/s,
increases the reliability of the system, this will allow you to install devices without including a PC, which is absolutely impossible in the ATA interface.

SCSI (Small Computer System Interface)- devices are 2 times more expensive than usual ones, they require a special controller on the motherboard.
Used for servers, publishing systems, CAD. Provide higher performance (speed up to 160Mb/s), a wide range of connected storage devices.
The SCSI controller must be purchased with the appropriate drive.

SCSI advantage over IDE - flexibility and performance.
Flexibility lies in a large number of connected devices (7-15), and for IDE (4 maximum), a longer cable length.
Performance - High transfer speed and the ability to process multiple transactions at the same time.

1. Ultra SCSI 2/3(Fast-20) up to 40Mb/s

2. Another SCSI interface technology called Fiber Channel Arbitrated Loop (FC-AL) allows you to connect up to 100Mbps, the cable length is up to 30 meters. FC-AL technology allows you to perform "hot" connection, i.e. on the go, has additional lines for error control and correction (the technology is more expensive than conventional SCSI).

4. Other features of modern hard drives

A huge variety of hard drive models makes it difficult to choose the right one.
In addition to the required capacity, performance is also very important, which is determined mainly by its physical characteristics.
Such characteristics are the average search time, rotation speed, internal and external transfer rate, cache memory size.

4.1 Average search time.

The hard drive spends some time to move the magnetic head of the current position to a new one, required to read the next piece of information.
In each specific situation, this time is different, depending on the distance that the head must move. Typically, specifications only give average values, and the averaging algorithms used by different companies generally differ, so a direct comparison is difficult.

For example, Fujitsu, Western Digital pass through all possible pairs of tracks, Maxtor and Quantum use the random access method. The result obtained can be further adjusted.

The seek time value for writing is often slightly higher than for reading. Some manufacturers give only the lower value (for reading) in their specifications. In any case, in addition to the average values, it is useful to take into account the maximum (through the entire disk),
and the minimum (that is, from track to track) seek time.

4.2 Rotation speed

From the point of view of the speed of access to the desired fragment of the record, the speed of rotation affects the value of the so-called hidden time, which in order for the disk to turn to the magnetic head with the desired sector.

The average value of this time corresponds to half a disk revolution and is 8.33 ms at 3600 rpm, 6.67 ms at 4500 rpm, 5.56 ms at 5400 rpm, 4.17 ms at 7200 rpm.

The hidden time value is comparable to the average lookup time, so in some modes it can have the same, if not more, performance impact.

4.3 Internal baud rate

The rate at which data is written to or read from disk. Due to zone recording, it has a variable value - higher on the outer tracks and lower on the inner ones.
When working with long files, in many cases it is this parameter that limits the transfer rate.

4.4 External baud rate

- speed (peak) with which data is transmitted through the interface.

It depends on the interface type and most often has fixed values: 8.3; 11.1; 16.7Mb/s for Enhanced IDE (PIO Mode2, 3, 4); 33.3 66.6 100 for Ultra DMA; 5, 10, 20, 40, 80, 160 Mb/s for synchronous SCSI, Fast SCSI-2, FastWide SCSI-2 Ultra SCSI (16 bits), respectively.

4.5 The presence of a hard drive of its Cache memory and its size (disk buffer).

The volume and organization of the cache memory (internal buffer) can significantly affect the performance of the hard drive. Just like for regular cache memory,
the increase in productivity after reaching a certain volume slows down sharply.

Large segmented cache is relevant for high performance SCSI drives used in multitasking environments. The more cache, the faster the hard drive (128-256Kb).

The impact of each of the parameters on the overall performance is quite difficult to isolate.

Hard drive requirements

The main requirement for disks is that reliability of operation is guaranteed by a long service life of components of 5-7 years; good statistics, namely:

• mean time between failures is not less than 500 thousand hours (the highest class is 1 million hours or more.)
• built-in system of active monitoring of the state of disk nodes SMART /Self Monitoring Analysis and Report Technology.

Technology S.M.A.R.T. (Self-Monitoring Analysis and Reporting Technology) is an open industry standard developed at one time by Compaq, IBM and a number of other hard drive manufacturers.

The point of this technology lies in the internal self-diagnostics of the hard drive, which allows you to assess its current state and inform about possible future problems that could lead to data loss or drive failure.

The state of all vital elements of the disk is constantly monitored:
heads, working surfaces, an electric motor with a spindle, an electronics unit. For example, if a weakening of the signal is detected, then the information is overwritten and further observation takes place.
If the signal weakens again, then the data is transferred to another location, and this cluster is placed as defective and inaccessible, and another cluster from the disk reserve is made available instead.

When working with a hard drive, you should observe the temperature regime in which the drive operates. Manufacturers guarantee trouble-free operation of the hard drive at their ambient temperature in the range from 0C to 50C, although, in principle, without serious consequences, you can change the boundaries by at least 10 degrees in both directions.
With large temperature deviations, an air gap of the required thickness may not be formed, which will lead to damage to the magnetic layer.

In general, HDD manufacturers pay quite a lot of attention to the reliability of their products.

The main problem is the ingress of foreign particles into the disk.

For comparison: a particle of tobacco smoke is twice the distance between the surface and the head, the thickness of a human hair is 5-10 times greater.
For the head, a meeting with such objects will result in a strong blow and, as a result, partial damage or complete failure.
Outwardly, this is noticeable as the appearance of a large number of regularly arranged unusable clusters.

Dangerous are short-term large accelerations (overloads) that occur during shocks, falls, etc. For example, from a blow, the head sharply hits the magnetic
layer and causes its destruction in the corresponding place. Or, on the contrary, it first moves in the opposite direction, and then, under the action of an elastic force, it hits the surface like a spring.
As a result, magnetic coating particles appear in the case, which again can damage the head.

You should not think that under the action of centrifugal force they will fly away from the disk - the magnetic layer
draws them firmly in. In principle, the consequences are not the impact itself (you can somehow put up with the loss of a certain number of clusters), but the fact that particles are formed in this case, which will certainly cause further damage to the disk.

To prevent such very unpleasant cases, various firms resort to all sorts of tricks. In addition to simply increasing the mechanical strength of the disk components, the intelligent S.M.A.R.T. technology is also used, which monitors the reliability of recording and the safety of data on the media (see above).

In fact, the disk is always not formatted to its full capacity, there is some margin. This is mainly due to the fact that it is practically impossible to manufacture a carrier
on which absolutely the entire surface would be of high quality, there will definitely be bad clusters (faulty ones). When low-level formatting a disk, its electronics are configured so that
so that it bypasses these failed areas, and it is completely invisible to the user that the media has a defect. But if they are visible (for example, after formatting
the utility displays their number other than zero), then this is already very bad.

If the warranty has not expired (and, in my opinion, it is best to buy an HDD with a warranty), then immediately take the drive to the seller and demand a replacement media or a refund.
The seller, of course, will immediately begin to say that a couple of bad sections are not yet a cause for concern, but do not believe him. As already mentioned, this couple, most likely, will cause many more others, and subsequently a complete failure of the hard drive is generally possible.

The disk is especially sensitive to damage in working condition, so you should not place the computer in a place where it can be subject to various shocks, vibrations, and so on.

Preparing the hard drive for work

Let's start from the very beginning. Let's assume that you bought a hard disk drive and a cable to it separately from the computer.
(The fact is that when you buy an assembled computer, you will receive a disk prepared for use).

A few words about handling it. A hard disk drive is a very complex product containing, in addition to electronics, precision mechanics.
Therefore, it requires careful handling - shocks, drops and strong vibration can damage its mechanical part. As a rule, the drive board contains many small-sized elements, and is not closed with strong covers. For this reason, you should take care of its safety.
The first thing to do when you receive a hard drive is to read the documentation that came with it - it will surely contain a lot of useful and interesting information. In doing so, you should pay attention to the following points:

• the presence and options for setting jumpers that determine the setting (installation) of the disk, for example, defining such a parameter as the physical name of the disk (they may be, but they may not be),
• number of heads, cylinders, sectors on disks, precompensation level, as well as disk type. This data must be entered in response to a prompt from the computer setup program (setup).
  All this information will be needed when formatting the disk and preparing the machine to work with it.
• If the PC itself does not determine the parameters of your hard drive, installing a drive for which there is no documentation will become a bigger problem.
  On most hard drives, you can find labels with the name of the manufacturer, the type (brand) of the device, as well as a table of tracks that are not allowed to be used.
  In addition, the drive may contain information on the number of heads, cylinders and sectors and on the level of precompensation.

In fairness, it must be said that often only its name is written on the disc. But even in this case, you can find the required information either in the directory,
or by calling the company representative. It is important to get answers to three questions:

• How should the jumpers be set in order to use the drive as a master/slave?
• how many cylinders, heads, sectors per track, what is the precompensation value?
• Which type of disk from the ROM BIOS is best suited for this drive?

With this information, you can proceed to install the hard drive.

To install a hard drive in your computer, do the following:

1. Disconnect the entire system unit from the power supply, remove the cover.
2. Connect the hard drive cable to the motherboard controller. If you install a second drive, you can use the cable from the first one if it has an additional connector, but you need to remember that the speed of different hard drives will be compared slowly in the direction.
3. If necessary, switch the jumpers according to how the hard disk is used.
4. Install the drive in a free space and connect the cable from the controller on the board to the hard drive connector with a red stripe to the power supply, the power supply cable.
5. Securely fasten the hard drive with four bolts on both sides, arrange the cables neatly / sparingly inside the computer so that when closing the cover, do not cut them,
6. Close the system block.
7. If the PC itself did not detect the hard drive, then change the computer configuration using Setup so that the computer knows that a new device has been added to it.

Hard drive manufacturers

Hard drives of the same capacity (but from different manufacturers) usually have more or less similar characteristics, and the differences are expressed mainly in the case design, form factor (in other words, dimensions) and the warranty period. Moreover, the latter should be specially mentioned: the cost of information on a modern hard drive is often many times higher than its own price.

If your drive is failing, trying to repair it often means only exposing your data to additional risk.
A much more reasonable way is to replace the failed device with a new one.
The lion's share of hard drives in the Russian (and not only) market is made up of products from IBM, Maxtor, Fujitsu, Western Digital (WD), Seagate, Quantum.

the name of the manufacturer that produces this type of drive,

Corporation Quantum (www. quantum. com.), founded in 1980, is one of the veterans in the disk storage market. The company is known for its innovative technical solutions aimed at improving the reliability and performance of hard drives, disk access time and disk read / write speed, the ability to inform about possible future problems that could lead to data loss or drive failure.

- One of Quantum's proprietary technologies is SPS (Shock Protection System), designed to protect the disk from shock.

- a built-in DPS (Data Protection System) program designed to save the most expensive - the data stored on them.

Corporation Western Digital (www.wdс.com.) is also one of the oldest disk drive manufacturing companies, it has known its ups and downs in its history.
The company has recently been able to introduce the latest technologies into its drives. Among them, it is worth noting our own development - Data Lifeguard technology, which is a further development of the S.M.A.R.T. It attempts to logically complete the chain.

According to this technology, the disk surface is regularly scanned during the period when it is not used by the system. It reads the data and checks its integrity. If in the process of accessing a sector problems are noted, then the data is transferred to another sector.
Information about low-quality sectors is recorded in the internal defect list, which makes it possible to avoid writing to bad sectors in the future.

Firm Seagate (www.seagate.com) very famous in our market. By the way, I recommend the hard drives of this particular company, as they are reliable and durable.

In 1998, she made a new comeback with the release of the Medallist Pro disc series.
with a rotation speed of 7200 rpm, using special bearings for this. Previously, this speed was used only in SCSI interface drives, which increased performance. The same series uses SeaShield System technology, designed to improve the protection of the disk and the data stored on it from the effects of electrostatic and shock. At the same time, the effect of electromagnetic radiation is also reduced.

All produced discs support S.M.A.R.T.
Seagate's new drives include an improved version of its SeaShield system with more features.
Significantly, Seagate claimed the industry's highest impact resistance of the updated series - 300G in non-operating condition.

Firm IBM (www.storage.ibm.com) although it was not until recently a major supplier in the Russian hard drive market, it quickly gained a good reputation for its fast and reliable hard drives.

Firm Fujitsu (www.fujitsu.com) is a large and experienced manufacturer of disk drives, not only magnetic, but also optical and magneto-optical.
True, the company is by no means a leader in the market of hard drives with an IDE interface: it controls (according to various studies) about 4% of this market, and its main interests lie in the field of SCSI devices.

Terminological dictionary

Since some elements of the drive that play an important role in its operation are often perceived as abstract concepts, the following is an explanation of the most important terms.

Access time is the amount of time it takes for the hard disk drive to search for and transfer data to or from memory.
The performance of hard disk drives is often determined by the access (fetch) time.

Cluster (Сluster)- the smallest unit of space that the OS works with in the file location table. Usually a cluster consists of 2-4-8 or more sectors.
The number of sectors depends on the type of disk. Searching for clusters instead of individual sectors reduces OS overhead over time. Large clusters provide faster performance
drive, since the number of clusters in this case is less, but the space (space) on the disk is used worse, since many files may be smaller than the cluster and the remaining bytes of the cluster are not used.

Controller (CU) (Controller)- circuits, usually located on an expansion board, that control the operation of a hard disk drive, including moving the head and reading and writing data.

Cylinder (Сylinder)- Tracks located opposite each other on all sides of all discs.

Drive head- a mechanism that moves along the surface of the hard disk and provides electromagnetic recording or reading of data.

File Allocation Table (FAT)- a record generated by the OS that keeps track of the location of each file on the disk and which sectors are used and which are free to write new data to them.

Head gap is the distance between the drive head and the disk surface.

Interleave- the relationship between the speed of rotation of the disk and the organization of sectors on the disk. Typically, the disk rotation speed exceeds the computer's ability to receive data from the disk. By the time the controller reads data, the next serial sector has already passed the head. Therefore, data is written to disk through one or two sectors. With the help of special software, when formatting a disk, you can change the striping order.

Logical drive- certain parts of the working surface of the hard disk, which are considered as separate drives.
Some logical drives can be used for other operating systems such as UNIX.

Parking- moving the drive heads to a certain point and fixing them in a stationary state over unused parts of the disk, in order to minimize damage when the drive is shaken when the heads hit the surface of the disk.

Partitioning– the operation of dividing a hard disk into logical disks. All disks are partitioned, although small disks may have only one partition.

Disk (Platter)- the metal disk itself, covered with a magnetic material, on which data is written. A hard drive usually has more than one drive.

RLL (Run-length-limited) An encoding scheme used by some controllers to increase the number of sectors per track to accommodate more data.

Sector- division of disk tracks, which is the main unit of size used by the drive. OS sectors are typically 512 bytes.

Positioning time (Seek time)- the time required for the head to move from the track on which it is installed to some other desired track.

Track (Track)- concentric division of the disc. Tracks are like tracks on a record. Unlike the tracks on a record, which are a continuous spiral, the tracks on a disc are circular. Tracks, in turn, are divided into clusters and sectors.

Track-to-track seek time- the time required for the transition of the drive head to the adjacent track.

Transfer rate- the amount of information transmitted between the disk and the computer per unit of time. It also includes the track search time.

Greetings to all blog readers. Many people are interested in the question - how does a computer hard drive work. Therefore, I decided to dedicate today's article to this.

A computer hard disk (HDD or hard drive) is needed to store information after the computer is turned off, unlike RAM () - which stores information until the power is turned off (until the computer is turned off).

The hard drive, by right, can be called a real work of art, only engineering. Yes Yes exactly. It's so complicated inside everything is arranged. At the moment, the hard drive is the most popular device for storing information all over the world, it is on a par with devices such as: flash memory (flash drives), SSD. Many people have heard about the complexity of the hard disk device and wonder how so much information is placed in it, and therefore would like to know how a computer hard disk is arranged or what it consists of. Today there will be such an opportunity).

A hard drive is made up of five main parts. And the first of them - integrated circuit, which synchronizes the work of 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 keeps the rotation speed constant.

And now the third one the most important part is the rocker, which can both write and read information. The end of the rocker is usually divided so that you can work with several discs at once. However, the rocker head never comes into contact with the discs. There is a gap between the surface of the disk and the head, the size of this gap is about 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 huge acceleration becomes incredibly heavy. Given the huge speed of rotation 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 the friction force is also important, i.e. its almost complete absence, when the rocker begins to read information, while shifting up to 60 times per second. But wait, where is the engine here that drives the rocker, and even 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. Such interaction allows accelerating the rocker to the speed of light, in the literal sense.

Fourth part- the hard drive itself, this is where information is written and read from, by the way, there may be several of them.

Well, the fifth, final part of the hard drive design is, of course, the case in 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 referred to as a "containment zone". There is an opinion that there is no air inside the containment area, or rather, that there is a vacuum there. This opinion is based on the fact that at such high disk rotation speeds, 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 cleaning the air, it was simply pumped out.

We talked about components, i.e. what is a hard drive made of. Now let's talk about data storage.

How and in what form is data stored on a computer hard drive

Data is stored in narrow tracks on the disk surface. During production, more than 200,000 such tracks are applied to the disc. Each of the tracks is divided into sectors.

Track and sector maps allow you to determine where to write or where to read information. Again, all information about sectors and tracks is located in the memory of an integrated circuit, which, unlike other components of a hard drive, is not located inside the case, but outside and usually from below.

The surface of the disc itself is smooth and shiny, but this is only at first glance. On closer examination, 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 disk is, in fact, a certain sequence and a certain number of zeros and ones. For example, a good quality photo 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 hard disk surface contains several tens of billions of bits.

How a hard drive works

We have just examined the hard drive device, each of its components separately. Now I propose to link everything into a certain system, thanks to which the very principle of the hard disk operation will be clear.

So, how a hard drive works next: when the hard drive is put into operation, it means either it is being written to, or information is being read from it, or from it, the electric motor (spindle) starts to gain momentum, and since the hard drives are fixed on the spindle itself, respectively, they are together with it also start to rotate. And until the speed of the disk(s) has reached the level that an air cushion is formed between the rocker head and the disk, the rocker is in a special "parking zone" to avoid damage. Here's what it looks like.

As soon as the speed reaches the desired level, the servo drive (electromagnetic motor) sets in motion the rocker, which is already positioned in the place where you want to write or read information. This is just facilitated by an integrated circuit that controls all movements of the rocker.

There is a widespread opinion, a kind of myth, that at times when the disk is "idle", i.e. no read / write operations are performed with it temporarily, the hard drives inside stop spinning. This is really a myth, because in fact, hard drives inside the case are constantly spinning, even when the hard drive is in power-saving mode and nothing is being written to it.

Well, here we have examined with you the device of the computer hard disk in all details. Of course, within the framework of one article, it is impossible to tell about everything related to hard drives. For example, in this article it was not said 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

Thank you all for your attention, if you have not yet subscribed to updates of this site - I highly recommend doing this so as not to miss interesting and useful materials. See you on the blog pages!

If we consider the hard drive as a whole, then it consists of two main parts: this is the electronics board, on which the “brain” of the hard drive is located, so to speak. The processor is located on it, there is also a control program, random access memory, a write and read amplifier. The mechanical part includes such parts as a block of magnetic heads with the abbreviation BMG, an engine that gives rotation to the plates, and of course the plates themselves. Let's look at each part in more detail.

HDA.

The hermetic block, also known as a hard disk case, is designed to fasten all parts, and also performs the function of protecting against dust particles on the surface of the plates. It should be noted that the HDA can only be opened in a specially prepared room to prevent dust and dirt from getting inside the case.

Integrated circuit.

An integrated circuit or electronics board synchronizes the operation of the hard drive with the computer and controls all processes, in particular, it maintains a constant speed of rotation of the spindle and, accordingly, the plate, which is carried out by the engine.

Electric motor.

An electric motor or engine rotates the plates: about 7200 revolutions per second (the average value is taken, there are hard drives on which the speed is higher and reaches 15000 revolutions per second, and there are also at a lower speed of about 5400, the speed of access to the necessary information on hard drive).

Rocker.

The rocker is designed to write and read information from hard disk platters. The end of the rocker is divided and there is a block of magnetic heads on it, this is done in order to be able to write and read information from several plates.

Block of magnetic heads.

The composition of the rocker arm includes a block of magnetic heads, which quite often fails, but this "often" parameter is very conditional. Magnetic heads are located above and below the platters and serve for direct reading of information from the platinum located on the hard disk.

Plates.

Information is stored directly on the plates; they are made of materials such as aluminum, glass and ceramics. Aluminum is the most widespread, but the so-called "elite wheels" are made from the other two materials. The first manufactured plates were coated with iron oxide, but this ferromagnet had a big drawback. Discs coated with such a substance had little wear resistance. At the moment, most hard drive manufacturers cover the plates with chromium cobalt, which has an order of magnitude higher margin of safety than iron oxide. Plates are attached to the spindle at the same distance from each other, such a design is called a "package". Under the discs is an engine or electric motor.

Each side of the plate is divided into tracks, they, in turn, are divided into sectors or blocks in another way, all tracks of the same diameter are a cylinder.

All modern hard drives have a so-called "engineering cylinder", it stores service information, such as the hdd model, serial number, etc. This information is designed to be read by a computer.

How a hard drive works

The basic principles of hard disk operation have changed little since its inception. The device of the hard drive is very similar to an ordinary record player. Only under the body there can be several plates mounted on a common axis, and the heads can read information from both sides of each plate at once. The rotation speed of the plates is constant and is one of the main characteristics. The head moves along the plate at some fixed distance from the surface. The smaller this distance, the greater the accuracy of reading information, and the greater the density of information recording can be.

Looking at the hard drive, all you see is a solid metal case. It is completely sealed and protects the drive from dust particles, which, if they enter the narrow gap between the head and the disk surface, can damage the sensitive magnetic layer and disable the disk. In addition, the case shields the drive from electromagnetic interference. Inside the case are all the mechanisms and some electronic components. The mechanisms are the disks themselves, on which the information is stored, the heads that write and read information from the disks, as well as the engines that set it all in motion.

The disc is a round plate with a very flat surface, often made of aluminum, less often made of ceramic or glass, coated with a thin ferromagnetic layer. Many drives use a layer of iron oxide (which is the coating on regular magnetic tape), but the latest hard drives work with a layer of cobalt about ten microns thick. Such a coating is more durable and, in addition, can significantly increase the recording density. The technology of its application is close to that used in the production of integrated circuits.

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

Magnetic heads read and write information to discs. The principle of recording is generally similar to that used in a conventional tape recorder. Digital information is converted into an alternating electric current supplied to the magnetic head, and then transferred to the magnetic disk, but already in the form of a magnetic field that the disk can perceive and "remember".

The magnetic coating of the disk is a set of tiny areas of spontaneous (spontaneous) magnetization. For clarity, imagine that the disk is covered with a layer of very small compass arrows pointing in different directions. Such arrow particles are called domains. Under the influence of an external magnetic field, the own magnetic fields of the domains are oriented in accordance with its direction. After the termination of the action of the external field, zones of residual magnetization are formed on the surface of the disk. In this way, the information written to the disc is preserved. Areas of residual magnetization, when the disk rotates opposite the gap of the magnetic head, induce an electromotive force in it, which varies depending on the magnitude of the magnetization.

The disc pack, mounted on a spindle axle, is driven by a special motor compactly located underneath. In order to reduce the time it takes for the drive to enter the operating state, the engine operates in the forced mode for some time when it is turned on. Therefore, the computer power supply must have a margin for peak power. Now about the work of the heads. They move with the help of a stepper motor and, as it were, "float" at a distance of a fraction of a micron from the surface of the disk, without touching it. As a result of recording information, magnetized areas are formed on the surface of disks, in the form of concentric circles.

They are called magnetic tracks. Moving, the heads stop over each next track. A set of tracks located one below the other on all surfaces is called a cylinder. All drive heads move simultaneously, accessing cylinders of the same name with the same numbers.