amber heard photos. Amber Heard

HDD, hard drive, hard drive - all these are the names of one well-known data storage device. In this material, we will tell you about the technical basis of such drives, how information can be stored on them, and about other technical nuances and principles of operation.

Based full name of this storage device - a hard disk drive (HDD) - you can effortlessly understand what underlies its work. Due to their low cost and durability, these storage media are installed in various computers: PCs, laptops, servers, tablets, etc. A distinctive feature of the HDD is the ability to store huge amounts of data, while having very small dimensions. Below we will talk about its internal structure, principles of operation and other features. Let's get started!

HDA and electronics board

Green fiberglass and copper tracks on it, along with connectors for connecting the power supply and the SATA socket are called control board(Printed Circuit Board, PCB). This integrated circuit serves to synchronize the operation of the disk with a PC and manage all processes inside the HDD. The black aluminum case and what's inside it is called sealed block(Head and Disk Assembly, HDA).

At the center of an integrated circuit is a large chip. microcontroller(Micro Controller Unit, MCU). In today's HDDs, the microprocessor contains two components: central computing unit(Central Processor Unit, CPU), which handles all calculations, and read and write channel- a special device that converts an analog signal from the head to a discrete one when it is busy reading and vice versa - digital to analog during recording. The microprocessor has I/O ports, with the help of which it controls the rest of the elements located on the board and exchanges information via a SATA connection.

Another chip located on the schematic is DDR SDRAM memory chip. Its quantity predetermines the volume of the hard drive cache. This chip is divided into firmware memory, partly contained in a flash drive, and buffer memory, which is necessary for the processor in order to load firmware modules.

The third chip is called engine and head controller(Voice Coil Motor controller, VCM controller). It controls additional power supplies that are located on the board. They provide power to the microprocessor and preamplifier-switcher(preamplifier) ​​contained in the sealed unit. This controller requires more power than the rest of the components on the board, as it is responsible for the rotation of the spindle and the movement of the heads. The preamplifier-switcher core is able to work when heated up to 100°C! When power is applied to the hard drive, the microcontroller dumps the contents of the flash chip into memory and begins executing the instructions contained in it. If the code fails to load properly, then the HDD won't even be able to start spinning up. Also, flash memory can be built into the microcontroller, and not contained on the board.

located on the diagram vibration sensor(shock sensor) determines the level of shaking. If it considers its intensity dangerous, then a signal will be sent to the motor and heads control controller, after which it immediately parks the heads or stops HDD rotation altogether. In theory, this mechanism is designed to protect the HDD from various mechanical damage, however, in practice, it does not work out very well. Therefore, you should not drop the hard drive, because this can lead to inadequate operation of the vibration sensor, which can cause the device to become completely inoperable. Some hard drives have sensors that are ultra-sensitive to vibration, which react to the slightest vibration. The data that the VCM receives helps in correcting the movement of the heads, so the drives are equipped with at least two such sensors.

Another device designed to protect the HDD is transient voltage limiter(Transient Voltage Suppression, TVS), designed to prevent possible failure in the event of power surges. There can be several such limiters on one circuit.

HDA surface

Under the integrated board are the contacts from the motors and heads. Here you can also see an almost invisible technical hole (breath hole), which equalizes the pressure inside and outside the hermetic zone of the block, destroying the myth that there is a vacuum inside the hard drive. Its inner area is covered with a special filter that does not allow dust and moisture to pass directly into the HDD.

HDA internals

Under the cover of the hermetic unit, which is an ordinary layer of metal and a rubber gasket that protects it from moisture and dust, there are magnetic disks.

They may also be called pancakes or plates(platters). Discs are usually created from glass or aluminum that has been pre-polished. Then they are covered with several layers of various substances, among which there is also a ferromagnet - thanks to it, it is possible to record and store information on a hard disk. Between the plates and above the uppermost pancake are located separators(dampers or separators). They even out airflow and reduce acoustic noise. Usually made of plastic or aluminum.

The separator plates, which were made of aluminum, do a better job of lowering the air temperature inside the sealed area.

Block of magnetic heads

At the ends of the brackets located in block of magnetic heads(Head Stack Assembly, HSA), read / write heads are located. When the spindle is stopped, they should be in the preparation area - this is the place where the heads of a healthy hard disk are located at a time when the shaft is not working. In some HDDs, parking takes place on plastic preparation areas that are located outside the plates.

For the normal operation of the hard drive, the air that is as clean as possible, containing a minimum of third-party particles, is required. Over time, grease and metal microparticles form in the accumulator. To output them, HDDs are equipped circulation filters(recirculation filter), which constantly collect and retain very small particles of substances. They are installed in the path of air flows, which are formed due to the rotation of the plates.

Neodymium magnets are installed in the HDD, capable of attracting and holding weight, which can be 1300 times more than its own. The purpose of these magnets in HDDs is to limit the movement of the heads by holding them over plastic or aluminum pancakes.

Another part of the block of magnetic heads is coil(voice coil). Together with magnets, it forms BMG drive, which together with BMG is positioner(actuator) - a device that moves the heads. The protective mechanism for this device is called fixative(actuator latch). It releases the BMG as soon as the spindle picks up a sufficient number of revolutions. The release process involves the pressure of the air flow. The retainer prevents any movement of the heads in the preparation state.

Under the BMG there will be a precision bearing. It maintains the smoothness and accuracy of the given block. There is also a part made of aluminum alloy, which is called yoke(arm). At its end, on a spring suspension, heads are located. From the rocker goes flexible cable(Flexible Printed Circuit, FPC) leading to a pad that connects to the electronics board.

This is what the coil looks like, which is connected to the cable:

Here you can see the bearing:

Here are the BMG contacts:

pad(gasket) helps ensure the tightness of the clutch. Due to this, air enters the block with disks and heads only through a hole that equalizes the pressure. The contacts of this disk are covered with the finest gold plating, which improves conductivity.

Typical bracket assembly:

At the ends of the spring hangers are small parts - sliders(sliders). They help read and write data by raising the head above the platters. In modern drives, the heads operate at a distance of 5-10 nm from the surface of metal pancakes. Elements for reading and writing information are located at the very ends of the sliders. They are so small that they can only be seen with a microscope.

These parts are not completely flat, as they have aerodynamic grooves on them that serve to stabilize the flight height of the slider. The air underneath creates pillow(Air Bearing Surface, ABS), which maintains a flight parallel to the surface of the plate.

preamplifier- a chip responsible for controlling the heads and amplifying the signal to or from them. It is located directly in the BMG, because the signal that the heads produce is not powerful enough (about 1 GHz). Without the amplifier in the sealed area, it would simply dissipate on its way to the integrated circuit.

There are more tracks from this device towards the heads than to the sealed zone. This is explained by the fact that the hard drive can interact with only one of them at a certain point in time. The microprocessor sends requests to the preamplifier so that it selects the head it needs. From the disk to each of them there are several tracks. They are responsible for grounding, reading and writing, controlling miniature drives, working with special magnetic equipment that can control the slider, which allows you to increase the accuracy of head positioning. One of them should lead to a heater, which regulates the height of their flight. This design works like this: heat is transferred from the heater to the suspension that connects the slider and rocker. The suspension is created from alloys that have different expansion parameters from the incoming heat. When the temperature rises, it bends towards the plate, thereby reducing the distance from it to the head. With a decrease in the amount of heat, the opposite effect occurs - the head moves away from the pancake.

This is how the top separator looks like:

This photo shows the sealed area without the head assembly and top separator. You can also notice the bottom magnet and pressure ring(platters clamp):

This ring holds the blocks of pancakes together, preventing any movement relative to each other:

The plates themselves are strung on shaft(spindle hub):

And here is what is under the top plate:

As you can understand, a place for heads is created using special spacer rings(spacer rings). These are high-precision parts that are made from non-magnetic alloys or polymers:

At the bottom of the HDA is a pressure equalization space located directly below the air filter. The air that is outside the sealed unit certainly contains dust particles. To solve this problem, a multilayer filter is installed, which is much thicker than the same circular one. Sometimes you can find traces of silica gel on it, which should absorb all the moisture into itself:

Conclusion

This article has been given detailed description internals of the HDD. We hope this material was interesting for you and helped you learn a lot of new things from the field of computer equipment.

Each of us daily encounters various computer terms, knowledge of which is superficial, and some terms are completely unfamiliar to us. And why should we know something about something that does not concern us or does not bother us. Is not it? Known truth: while any equipment (including HDD) functions normally and without problems, then no one will ever fill his head with the intricacies of his work, and this is useless.

But, at the moments when failures begin during the operation of any device of the system unit, or you just suddenly need help with a computer, many users immediately take a screwdriver and the book “the basics of computer literacy, or how to reanimate a computer at home”. And they try to solve the problem on their own, without resorting to the help of a specialist. And most often it ends very badly for their computer.

• The concepts of "hard drive" or "hard drive" and their occurrence

Definition and emergence of the concept of "hard drive"

So, the topic of our next article this time will be such a spare part of the system unit as a hard drive. We will consider in detail the very meaning of this concept, briefly recall the history of its development, and dwell in more detail on the internal structure, analyze its main types, interfaces and details of its connection. In addition, let's take a look into the future, or maybe even almost into the present, and tell you what is gradually replacing the good old screws. Looking ahead, let's say that these are solid-state drives that work on the principle of USB flash drives - SSD devices.

The very first hard drive in the world, of the type we are accustomed to seeing and using, was invented by IBM employee Kenneth Haughton in 1973. This model was called a mysterious combination of numbers: 30-30, just like the caliber for everyone famous rifle Winchester, It is not difficult to guess that one of the names came from here - the hard drive, which is still popular among IT people. And, perhaps, someone now read it in general for the first time.

Let's move on to the definition: a hard drive (and, if it's convenient for you, then a hard drive, HDD or screw) is a computer (or laptop) storage device, on which information is written, stored and deleted using special read / write heads, as needed .

"But how does this all differ from simple floppy disks or CD-DVDs?" you ask. And the thing is that, unlike flexible or optical media, here the data is recorded on rigid (hence the name, although someone may have already guessed it himself) aluminum or glass plates, on which a thin layer of ferromagnetic material is applied, most often for these purposes, chromium dioxide is used.

The entire surface of such rotating magnetic plates is divided into tracks and sectors of 512 bytes each. Some drives have only one such drive. Others contain eleven or more plates, and information is recorded on both sides of each of them.

Internal structure

The very design of the hard disk consists not only of direct storage of information, but also of a mechanism that reads all this data. All together, this is the main difference between hard drives and floppy disks and optical drives. And unlike random access memory(RAM), which needs constant power, the hard drive is a non-volatile device. You can safely unplug it and take it with you wherever you go. The data is stored on it. This becomes especially important when you need to recover information.

Now let's talk a little directly about the internal structure of the hard drive. The hard drive itself consists of a sealed block filled with ordinary dust-free air under atmospheric pressure. We do not recommend opening it at home, because. this may damage the device itself. No matter how clean you are, there is always dust in the room and it can get inside the case. In professional services that specialize in data recovery, there is a specially equipped "clean room" inside which the hard drive is opened.

The device also includes a board with an electronic control circuit. Inside the block are the mechanical parts of the drive. One or more magnetic plates are fixed on the spindle of the disk rotation drive motor.

The case also houses a preamplifier-switch of magnetic heads. The magnetic head itself reads or writes information from the surface of one of the sides of the magnetic disk. The rotation speed of which reaches 15 thousand revolutions per minute - this is what concerns modern models.

At power up, the hard disk processor starts by testing the electronics. If everything is in order, the spindle motor is turned on. After a certain critical speed of rotation is reached, the density of the air layer that flows between the surface of the disk and the head becomes sufficient to overcome the force of pressing the head to the surface.

As a result, the read/write head "hangs" above the wafer at a tiny distance of only 5-10 nm. The operation of the read / write head is similar to the principle of operation of the needle in the gramophone, with only one difference - it does not have physical contact with the plate, while in the gramophone the needle head is in contact with the record.

At the moments when the computer's power is turned off and the disks stop, the head falls on the non-working zone of the platter surface, the so-called parking zone. Therefore, it is not recommended to shut down the computer in an emergency - simply by pressing the shutdown button or pulling the power cord from the outlet. This can lead to failure of the entire HDD. Early models had special software that initiated the head parking operation.

In modern HDDs, the head is brought to the parking zone automatically when the rotation speed drops below the nominal value or when a command is given to turn off the power. The heads are brought back into the working area only when the rated speed of the engine is reached.

Surely in your inquisitive mind the question has already matured - how tight is the disk block itself and what is the likelihood that dust or other small particles can seep there? As we wrote above, they can lead to a failure of the hard drive or even to its breakdown and loss of important information.

But don't worry. Manufacturers have foreseen everything for a long time. The disc block with the motor and the heads are located in a special hermetically sealed housing - a HDA (chamber). However, its contents are not completely isolated from environment, it is necessary to move air from the chamber to the outside and vice versa.

This is necessary to equalize the pressure inside the block with the external one in order to prevent deformation of the body. This balance is achieved using a special device called a barometric filter. It is located inside the HDA.

The filter is able to capture the smallest particles, the size of which exceeds the distance between the read / write head and the ferromagnetic surface of the disk. In addition to the above mentioned filter, there is another one - the recirculation filter. It captures particles that are present in the airflow within the block itself. They can appear there from the shedding of magnetic pollination of disks (for sure you have ever heard the phrase that “hard fell down”). In addition, this filter captures those particles that its barometric "colleague" "missed".

HDD connection interfaces

Today, to connect a hard drive to a computer, you can use one of three interfaces: IDE, SCSI, and SATA.

Initially, in 1986, the IDE interface was developed only for connecting an HDD. Then it was modified to an extended ATA interface. As a result, not only hard drives, but also CD / DVD drives can be connected to it.

The SATA interface is faster, more modern and more productive than ATA.

In turn, SCSI is a high-performance interface that can connect various kinds of devices. This includes not only storage media, but also various peripherals. For example, faster SCSI scanners. However, when the USB bus appeared, the need to connect peripherals via SCSI disappeared. So, if you are lucky enough to see him somewhere, then consider yourself lucky.

Now let's talk a little about connecting to the IDE interface. The system can have two controllers (primary and secondary), each of which can connect two devices. Accordingly, we get a maximum of 4: primary master, primary slave and secondary master, secondary slave.

After connecting the device to the controller, you should select the mode of its operation. It is selected by installing a special jumper (called a jumper) in a certain place in the connector (next to the connector for connecting the IDE cable).

It should be remembered that the faster equipment is connected to the controller first and is called master. The second is called slave (slave). The last manipulation will be to connect the power, for this we need to select one of the power supply cables. This information will come in handy if you have a very, very old computer. Since in modern times the need for such manipulations has disappeared.

Connecting via SATA is much easier. The cable for it has the same connectors at both ends. The SATA drive has no jumpers, so you don't have to select the operating mode of the devices - even a child can handle it. Power is connected using a special cable (3.3 V). However, it is possible to connect through an adapter to a conventional power cable.

Let's give one helpful advice: if friends often come to you with their hard drives to rewrite new films or music (yes, your friends are so harsh that they carry not an external HDD, but an ordinary internal one), and you are already tired of spinning up the system unit all the time, we recommend purchase a special hard drive pocket (it's called a Mobile Rack). They are available with both IDE and SATA interfaces. To connect another additional hard drive to your computer, simply insert it into such a pocket and you're done.

SSD drives - a new stage in development

Already today (or maybe even yesterday) the next stage in the development of information storage devices has begun. Hard drives are being replaced by a new type - SSD. Next, we will tell about it in more detail.

So, SSD (Solid State Disk) is a solid state drive that works on the principle of USB flash memory. One of his most important distinguishing features from conventional hard drives and optical drives - its device does not include any moving parts and mechanical components.

Drives of this type, as often happens, were originally developed exclusively for military purposes, as well as for high-speed servers, since the good old hard drives for such needs were no longer fast and reliable enough.

We list the most important advantages of SSD:

• Firstly, writing information to an SSD and reading from it is much faster (tens of times) than from an HDD. The work of a conventional hard drive is very much slowed down by the movement of the read / write head. And since If the SSD doesn't have it, then there's no problem.
• Secondly, due to the simultaneous use of all memory modules installed in the SSD drive, the data transfer speed is much higher.
• Thirdly, they are not so susceptible to blows. While hard drives can lose some data on impact or even fail, which happens most often - be careful!
• Fourthly, they consume less energy, which makes them convenient to use in devices powered by batteries - laptops, netbooks, ultrabooks.
• Fifthly, this type of drive practically does not produce any noise during operation, while during operation of hard drives we hear the rotation of the disks and the movement of the head. And, when they fail, there is generally a strong crack or knock of the heads.

But let's not hide: perhaps there are two drawbacks of SSD - 1) you will pay much more for its certain capacity than for a hard drive of the same amount of memory (the difference will be several times, although every year it becomes less and less); 2) SSDs have a relatively small limited number of read/write cycles (i.e. inherently limited lifespan).

So, we got acquainted with the concept of "hard drive", examined its structure, principle of operation and features of various connection interfaces. We hope that the information provided was easy to understand, and most importantly, useful.

If you have any difficulties with the choice, if you cannot determine what type of hard drives your motherboard supports, which interface is suitable or which HDD capacity will best suit your needs, then you can always contact Compolife computer service for help throughout our territory. service.

Our experts will help you with the choice and replacement of the hard drive. In addition, you can order the installation of a new device in your system unit or laptop from us.

call the master

During computer startup, a set of firmware stored in the BIOS chip checks the hardware. If everything is in order, it transfers control to the operating system 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 that you wrote all night stay intact after turning off the power of the PC? Again, where is it kept?

Okay, maybe I've gone too far and you all know very well that computer data is stored on a hard drive. Nevertheless, not everyone knows what it is and how it works, and since you are here, we conclude that we would like to know. 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, 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 disk 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.

Also note the phrase: random access ” which, roughly speaking, means that we (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 ().

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:

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:

• Frame 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;
• Disks (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) to several;
• Engine - on the spindle of which pancakes are fixed;
• Head block - a design of interconnected levers (rocker arms), 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 downtime, 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 are devices that are separately connected to a PC / laptop, most often acting as 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:

• Volume - an indicator of the maximum possible amount of data that can be accommodated on the 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 - the 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 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 - How fast do 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) of 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 volume (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.

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 used for magnetic tapes and floppy disks using a different plastic, and for hard disks - aluminum alloys and composite substrate materials. 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, their own magnetic fields 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 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. Main disadvantage IDE - 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. Application new technology will allow you to bring the transfer rate equal to 100 Mb / 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 is necessary 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 disk, please observe 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 turn into with 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 about the number of heads, cylinders and sectors and the level of pre-compensation.

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.
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, place 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 allows you 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 a special software You can change the stripe order when formatting a disk.

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.