External storage devices. How is information written and read? The device and principle of operation of the hard disk

Magnetic disks computers are used for long-term storage of information (it is not erased when the computer is turned off). In this case, in the process of work, data can be deleted, while others can be written.

There are hard disks and floppy disks. However, floppy disks are now very rarely used. Floppy disks were especially popular in the 1980s and 1990s.

Floppy disks(floppy disks), sometimes called floppy disks, are magnetic disks enclosed in square plastic cassettes measuring 5.25 inches (133 mm) or 3.5 inches (89 mm). Floppy disks allow you to transfer documents and programs from one computer to another, store information, make archival copies of information contained on a hard disk.

Information on a magnetic disk is written and read by magnetic heads along concentric tracks. When writing or reading information, the magnetic disk rotates around its axis, and the head is brought to the desired track using a special mechanism.

The 3.5-inch floppy disks have a capacity of 1.44 MB. This type of floppy disk is the most common at the present time.

Unlike floppy disks HDD allows you to store large amounts of information. The capacity of hard drives in modern computers can be terabytes.

The first hard drive was created by IBM in 1973. It allowed to store up to 16 MB of information. Since this disk had 30 cylinders divided into 30 sectors, it was designated as 30/30. By analogy with automatic rifles having a caliber of 30/30, this disc has received the nickname "Winchester".

The hard drive is a sealed iron box that houses one or more magnetic disks along with a read / write head assembly and an electric motor. When the computer is turned on, the electric motor spins the magnetic disk to a high speed (several thousand revolutions per minute) and the disk continues to rotate as long as the computer is turned on. Above the disk, special magnetic heads "hover", which write and read information in the same way as on floppy disks. The heads float above the disc due to its high rotational speed. If the heads touched the disc, the friction force would quickly cause the disc to fail.

The following concepts are used when working with magnetic disks.

Track- a concentric circle on a magnetic disk, which is the basis for recording information.

Cylinder Is a set of magnetic tracks located one above the other on all working surfaces of the hard drive disks.

Sector- a section of the magnetic track, which is one of the main units of information recording. Each sector has its own number.

Cluster- the minimum element of a magnetic disk, which is operated by the operating system when working with disks. Each cluster consists of several sectors.

Communication, communications, electronics and digital devices

The domains of magnetic materials used in longitudinal recording are located parallel to the surface of the medium. This effect is used when recording digital data with the magnetic field of the head changing in accordance with the information signal. Attempts to increase the surface recording density by decreasing the particle size will increase the ratio of the size of the zone of uncertainty to the size of the useful zone not in favor of the latter and, in the end, will inevitably lead to the so-called superparamagnetic effect when the particles pass into the single-domain ...

Magnetic disc recording technologies

Longitudinal recording

The first samples of hard drives, which appeared in the 70s of the twentieth century, used the technology of longitudinal information recording. For this, the surface of the disk, as well as the surface of the magnetic tape, was covered with a layer of chromium dioxide CrO 2 or iron oxide, providing longitudinal magnetization of the recording layer. The coercive force of such a carrier H c = 28 kA / m.

The technology for applying the oxide layer is rather complicated. First, a suspension of a mixture of iron oxide powder and molten polymer is sprayed onto the surface of a rapidly rotating aluminum disk. Due to the action of centrifugal forces, it is evenly distributed over the surface of the disc from its center to the outer edge. After the solution has polymerized, the surface is sanded and another layer of pure polymer is applied to it, which has sufficient strength and low coefficient of friction. Then the disc is finally polished. This type of drive is brown or yellow.

As is known, magnetic materials have a domain structure, i.e. consist of separate microscopic areas - domains , inside which the magnetic moments of all atoms are directed in one direction. As a result, each such domain has a sufficiently large total magnetic moment. The domains of magnetic materials used in longitudinal recording are parallel to the surface of the medium. If the magnetic material is not affected by an external magnetic field, the orientation of the magnetic moments of individual domains is chaotic and any direction is equally probable. If such a material is placed in an external magnetic field, then the magnetic moments of the domains will tend to orient themselves in the direction coinciding with the direction of the external magnetic field. This effect is used when recording digital data by the magnetic field of the head, which changes in accordance with the information signal.

The minimum element (cell) of the memory of the magnetic recording layer capable of storing one bit of information is not a separate domain, but a particle (area) consisting of several tens of domains (70-100). If the direction of the total magnetic moment of such a particle coincides with the direction of motion of the magnetic head, then such a state of it can be associated with the logical "0" of the data, if the directions are opposite, - with the logical "1".

However, if neighboring regions have the opposite direction of the magnetic moments, then the domains located on the border between them and touching the poles of the same name will repel each other and eventually change the directions of their magnetic moments in some unpredictable way in order to take an energetically more stable position. ... As a result, on the border of the two regions, an uncertainty zone is formed, which reduces the size of the region storing the bit of recorded information and, accordingly, the level of the useful signal during reading (Fig. 5.6). In this case, the noise level, of course, increases.

Attempts to increase the surface recording density by reducing the particle size will increase the ratio of the size of the zone of uncertainty to the size of the useful zone not in favor of the latter and, in the end, will inevitably lead to the so-calledsuperparamagnetic effectwhen the particles go tosingle-domain stateand will no longer be able to fix the recorded information, since neighboring domains with oppositely directed magnetic moments will change their orientation immediately after the magnetic field of the recording head is removed. The material of the recording layer will become uniformly magnetized throughout the entire volume.

Thus, due to the presence of superparamagnetism, the longitudinal recording technology, having reached by the middle of the first decade XXI centuries of the value of the recording density of 120 Gbit per inch 2 , has practically exhausted its capabilities and is no longer able to provide a significant increase in the capacity of hard drives. This forced the developers to turn to other technologies free of this flaw.

Perpendicular recording

The possibility of perpendicular writing is based on the fact that in thin films containing cobalt, platinum and some other substances, the atoms of these substances tend to be oriented in such a way that their magnetic axes are perpendicular to the surface of the carrier. Domains formed from such atoms are also located perpendicular to the carrier surface.

The signal in the readout magnetic head is generated only when it crosses the lines of force of the magnetic field of the domain, i.e. in the place where these lines of force are perpendicular to the surface of the carrier. For a domain located parallel to the surface of the carrier, the lines of force of the magnetic field are perpendicular to the surface only at its ends, where they come out to the surface (Fig. 5.7, a). When the head moves parallel to the domain and, therefore, parallel to its lines of force, there is no signal in it. Reducing the length of the domain, seeking to increase the recording density, is possible only up to certain limits - until the superparamagnetic effect begins to show itself. If the domains are located perpendicular to the surface of the carrier, then the lines of force of their magnetic fields will always be perpendicular to the surface and will contain information (Fig. 5.7, b). There will be no “idle” runs due to the length of the domain. As there will be no superparamagnetism, since domains with opposite magnetization will not repel each other. It is obvious that the recording density on a medium with perpendicular magnetization can be obtained higher.

A disc designed for perpendicular recording requires a special manufacturing technology. The base of the plate is carefully polished, and then a leveling layer of nickel phosphate is applied to its surface by vacuum deposition NiP with a thickness of about 10 microns, which, firstly, reduces the surface roughness, and secondly, increases adhesion to subsequent layers (Fig.5.8).

Next, a layer of soft magnetic material is applied, which makes it possible to read data from the recording layer, and the recording layer itself is made of material with the perpendicular orientation of the magnetic domains. Cobalt (Co), platinum ( Pt), palladium (Pd ), their alloys with each other and with chromium ( Cr ), as well as multilayer structures consisting of thin films of these metals several atoms thick.

A protective glass-ceramic film with a thickness of the order of hundredths of a micron is applied over the recording layer.

The recording of information on the recording layer with perpendicular magnetization has its own peculiarities. In order to ensure an acceptable signal level and ensure a good signal-to-noise ratio, the lines of force of the magnetic field generated by the recording head must, passing through the recording layer, again close to the head core. For this, the soft magnetic sublayer, located below the registering one, serves (Fig. 5.9).

According to preliminary forecasts of specialists, the perpendicular recording technology will allow realizing a recording density of up to 500 Gbit / inch. 2 ... In this case, the capacity of a 3.5-inch drive will be 2 TB, 2.5-inch - 640 GB, 1-inch - 50 GB. However, these are only preliminary forecasts. It is possible that the upper limit will be 1 Tbit / inch 2 and even more. Future will tell.

Advanced magnetic recording technologies

The technology of perpendicular recording is currently in the stage of active development and it is still far from the limit values ​​of the recording density. However, this moment will come someday. Maybe even earlier than it seems now. Therefore, research in the direction of finding new highly efficient magnetic recording technologies is already underway.

One of these technologies is thermomagnetic recordingHAMR (Heat Assisted Magnetic Recording), i.e. recording with preheating the media. This method provides for a short-term (1 picosecond) heating of the area of ​​the recording medium, on which the recording is made, by a focused laser beam - just like in magneto-optical recording.The difference between the technologies is manifested in the way information is read from the disk. In magneto-optical drives, information is read by a laser beam operating at a lower power than during recording, and during thermomagnetic recording, information is read by a magnetic head in the same way as from a conventional hard disk.And the recording density here is planned to be much higher than in magneto-optical formats. MD, CD - MO or DVD - MO - up to 10 Tbps 2 ... Therefore, other materials are needed here as a recording medium. Now, as such materials, various compounds of platinum, cobalt, neodymium, samarium and some other elements are considered: Fe 14 Nd 2 B, CoPt, FePt, Co 5 Sm, etc. Such materials are very expensive - both because of the high cost of the rare earth elements included in their composition, and because of the complexity and high cost of the technological process for their production and application to the surface of the base of the intended carrier. The design of the read / write head in technology HAMR it is also assumed to be quite different than in magneto-optical recording: the laser should be located on the same side as the magnetic head, and not on the opposite, as in magneto-optical recorders (Fig. 5.10). Heating is supposed to be done up to a temperature of the order of 100 degrees Celsius, and not 180.

Another promising direction in the development of magnetic recording is the use of materials as a recording layer in which particles are arranged in a clearly structured domain array ( Bit patterned media ). With this structure, each bit of information will be stored in just one cell-domain, and not in an array of 70-100 domains (Fig. 5.11).

Such a material can either be created artificially using photolithography (Fig. 5.12), or an alloy with a suitable self-organizing structure can be found.

The first method is unlikely to be developed, since to obtain material that allows a recording density of at least 1 Tbit / inch 2 , the size of one particle should be 12.5 nm maximum. Neither the existing lithography technology, nor the lithography technology planned for the next 10 years, provides this. Although there are some pretty clever solutions to avoid dismissing this approach.

Search for self-organizing magnetic materials (SOMA - Self-Ordered Magnetic Array) Is a very promising direction. For several years now, Seagate has been pointing out the features of a FePt alloy evaporated in a hexane solvent. The resulting material has a perfectly smooth cellular structure. The size of one cell is 2.4 nm. Considering that each domain has high stability, we can talk about the allowable recording density at the level of 40-50 Tbit / inch. 2 ! It looks like this is the ultimate limit for recording on magnetic media.

S

Uncertainty zones

Rice. 5.6. Uncertainty zones arising from longitudinal recording

There is a signal

No signal

Rice. 5.7. Parallel (a) media

and perpendicular (b) magnetization

Sublayer made of soft magnetic material

Disc base (Al)

Leveling layer ( NiP)

Recording layer with perpendicular magnetization

Protective layer

Rice. 5.8. Hard disk structure with perpendicular

magnetization

Hard magnetic recording layer

Magnetically soft underlayer

Rice. 5.9. Recording on material with a perpendicular

magnetization

Recording pole

Return pole pole

Rice. 5.10. Magneto-optical head HARM

Rice. 5.11. Microstructure of BPM: 1 - area corresponding to one bit of information during normal recording; 2 - array, the boundaries of which coincide with the boundaries of domains; 3 - a domain that is capable of storing one bit of data

Rice. 5.12. Recording layer obtained by photolithography

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Magnetic disks computers are used for long-term storage of information (it is not erased when the computer is turned off). In this case, in the process of work, data can be deleted, while others can be written.

There are hard disks and floppy disks. However, floppy disks are now very rarely used. Floppy disks were especially popular in the 1980s and 1990s.

Floppy disks(floppy disks), sometimes called floppy disks, are magnetic disks enclosed in square plastic cassettes measuring 5.25 inches (133 mm) or 3.5 inches (89 mm). Floppy disks allow you to transfer documents and programs from one computer to another, store information, make archival copies of information contained on a hard disk.

Information on a magnetic disk is written and read by magnetic heads along concentric tracks. When writing or reading information, the magnetic disk rotates around its axis, and the head is brought to the desired track using a special mechanism.

The 3.5-inch floppy disks have a capacity of 1.44 MB. This type of floppy disk is the most common at the present time.

Unlike floppy disks HDD allows you to store large amounts of information. The capacity of hard drives in modern computers can be terabytes.

The first hard drive was created by IBM in 1973. It allowed to store up to 16 MB of information. Since this disk had 30 cylinders divided into 30 sectors, it was designated as 30/30. By analogy with automatic rifles having a caliber of 30/30, this disc has received the nickname "Winchester".

The hard drive is a sealed iron box that houses one or more magnetic disks along with a read / write head assembly and an electric motor. When the computer is turned on, the electric motor spins the magnetic disk to a high speed (several thousand revolutions per minute) and the disk continues to rotate as long as the computer is turned on. Above the disk, special magnetic heads "hover", which write and read information in the same way as on floppy disks. The heads float above the disc due to its high rotational speed. If the heads touched the disc, the friction force would quickly cause the disc to fail.

The following concepts are used when working with magnetic disks.

Track- a concentric circle on a magnetic disk, which is the basis for recording information.

Cylinder Is a set of magnetic tracks located one above the other on all working surfaces of the hard drive disks.

Sector- a section of the magnetic track, which is one of the main units of information recording. Each sector has its own number.

Cluster- the minimum element of a magnetic disk, which is operated by the operating system when working with disks. Each cluster consists of several sectors.

Any magnetic disk has a logical structure that includes the following elements:

• boot sector;
• file allocation tables;
• data area.

Boot sector(Boot Record) occupies sector number 0. It contains a small program IPL2 (Initial Program Loading 2), with which the computer determines the ability to boot the operating system from this disk.

A feature of the hard drive is the presence, in addition to the boot sector, of one more area - master boot sector(Master Boot Record). The point is that a single hard drive can be split into several logical drives. The physical sector 1 is always allocated for the master boot sector on the hard disk. This sector contains the IPL1 (Initial Program Loading 1) program, which, when executed, determines the boot disk.

File Allocation Table used to store information about the location of files on the disk. For magnetic disks, two copies of tables are usually used, which follow one after the other, and their contents completely match. This is done in case any failures occurred on the disk, then the disk can always be "repaired" using a second copy of the table. If both copies are damaged, then all information on the disk will be lost.

Data area(Data Area) takes up the bulk of the disk space and serves directly for storing data.

In HDD, two main recording methods are used: the frequency modulation (FM) method (Fig. 13.2) and the modified FM method. In the controller (adapter) of the floppy disk drive, the data is processed in binary code and transmitted to the floppy disk drive in sequential code.

Frequency method modulation is dual frequency. When recording at the beginning of the clock interval, the current is switched to the MG and the direction of the surface magnetization changes. The switching of the write current marks the beginning of the write cycles and is used during the read to generate synchronization signals. Thus, this method has the property self-sync... Writing "1" and "0" is performed in the middle of the clock interval, and when writing "1" in the middle of the clock interval, the current is inverted, and when writing "0" - not. When reading at the moments of the middle of the clock interval, the presence of a signal of arbitrary polarity is determined. The presence of a signal at this moment corresponds to "1", and the absence - to "0".

3. Format for recording information on a floppy disk

The organization of placing information on a floppy disk assumes the location of user data along with service information necessary for numbering individual areas, separating them from each other, for information control, etc.

V HDDs use standard information formats for unification (generalization) of HDDs and their adapters. Each track on a floppy disk is divided into sectors. The sector size is the main characteristic of the format and determines the smallest amount of data that can be written in a single I / O operation. The formats used in the floppy disk drive differ in the number of sectors per track and the volume of one sector. The maximum number of sectors per track is determined by the operating system. The sectors are separated from each other by intervals in which information is not recorded. The product of the number of tracks by the number of sectors and the number of sides of a floppy disk determines its information capacity.

Each sector (Fig. 13.3) includes two areas: an overhead field and a data field. Service information composes a sector identifier to distinguish it from others.

Address marker is a special code that differs from data and indicates the beginning of a sector or data field. Head number indicates one of the two MGs located on the corresponding sides of the floppy disk. Sector number is a logical sector code that may not match its physical number. Sector length indicates the size of the data field. Control bytes are designed to control read errors.

Average access time to disk in milliseconds is estimated by the following expression:

t cf = (N-1) t 1/3 + t 2, (17.1)

where N is the number of tracks on the working surface of the GMD; t 1 - time of movement of MG from track to track; t 2 is the settling time of the positioning system.

4. Adapters for floppy disk drives

The floppy disk drive adapter translates the commands coming from the BIOS ROM into electrical signals that control the floppy disk drive, and also converts the stream of pulses read from the MG diskette into information perceived by the PC. Structurally, the electronic equipment of the adapter can be placed on the PC motherboard or combined with the equipment of other adapters on a separate board of expansion modules. It is possible to program the length of the data record, the speed of the transition from track to track, the time of loading and unloading the MG, as well as data transmission in the DMA or interrupt mode.

One of the options for constructing a structural diagram of the floppy disk drive adapter is shown in Fig. 13.4.

The address decoder recognizes the base addresses of the adapter's software-accessible registers. For the CPU, the HDD adapter is available programmatically through the control register and two ports of the HDD controller - the status register and the data register. The values ​​of the individual bits of the control register determine the choice of the floppy disk drive, the controller reset, the engine start, the interrupt enable and the RAP.

O The main functional block of the floppy disk drive adapter is the floppy disk drive controller, which is usually structurally implemented in the form of an LSI (integrated circuits 8272 Intel, 765 NEC, etc.). This controller provides control over the operations of the floppy disk drive and determines the conditions of exchange with the central processor. Functionally, the controller is subordinate to the CPU and is programmed by it. The controller has a status register and a data register in which data, commands and parameters about the state of the floppy disk drive are stored. When writing, the data register is used as a buffer into which data from the processor is fed byte by byte. The controller receives data from the register and converts it into a serial code used in the frequency recording method.

The floppy disk drive controller performs the following command set: positioning, formatting, reading, writing, checking the status of the floppy disk drive, etc. Each command is executed in three phases: preparatory, execution and final. V preparatory phase The CPU sends control bytes to the controller, which include the opcode and parameters required to execute the opcode. Based on this information in execution phase the controller performs the actions specified by the command. In the final phase, the contents of the status registers are read through the data register, which store information about the result of command execution and the state of the floppy disk drive. The conditions for completing the operation are passed to the CPU.

Table 13.1

The purpose of the signals of the interface of the floppy disk drive

Signal designation	Signal assignment	Direction
	Index / Sector
	Drive selection 0
	Drive Selection 1
	Motor turn on
	Step direction
	Recording data
	Recording Resolution
	Track 00
	Data reproduced
	Surface selection
	Drive ready

The recording signal generation circuit operates under the control of the controller and is designed to prevent information distortion during recording. A phase detector, a voltage-controlled oscillator (VCO), a low-pass filter (LPF) and a synchronization unit form a circuit for separating sync pulses - separator... When reading, data from the floppy disk drive is fed to the separator circuit, and is received by the controller, which decodes it and converts it byte by byte into a parallel code. Bytes are buffered in the data register and transferred to the PC's RAM.

The exchange control between the CPU and the floppy disk drive adapter is carried out by the interface circuit with the system bus. The bi-directional data generator matches the electrical parameters of the data bus of the system and internal bus of the adapter. The exchange of information between the adapter and the CPU takes place in two modes: RAP and interrupts. Software support for the adapter is provided by the driver included in the OS.

The interface between the floppy disk drive and the floppy disk drive adapter is coupled with a flexible cable. All signals of the HDD interface have a standard TTL level (Table 13.1).

Hard disk drives combine a medium (s), a reader / writer, and an interface called a hard disk controller in a single enclosure. A typical design of a hard disk is execution in the form of one device - a camera, inside of which there is one or more disk media mounted on one spindle and a block of read / write heads with their common driving mechanism (Figure 1). Next to the media and heads camera are the head and disk control circuits and the interface part. The interface card of the device contains the interface of the disk device, and the controller with its interface is located on the device itself. The drive circuits are connected to the interface adapter using a set of loops.

Figure 1. Hard Drive Arrangement

Information is recorded on concentric tracks, evenly distributed throughout the medium. In the case of more than one disc, the number of media, all the tracks below one another is called a cylinder. Read / write operations are performed in succession over all tracks of the cylinder, after which the heads move to a new position.

The sealed chamber protects media not only from the penetration of mechanical dust particles, but also from the effects of electromagnetic fields. The chamber is not completely sealed as connects to the surrounding atmosphere using a special filter that equalizes the pressure inside and outside the chamber. The air inside the chamber is as free of dust as possible. even the smallest particles can damage the magnetic coating of the discs and lead to loss of data and device functionality.

Disks spin continuously at media speeds between 4500 and 10,000 rpm for high read / write speeds. By the size of the media diameter, 5.25,3.14,2.3 inch disks are most often produced.

Currently, the most commonly used are stepper and linear motors of positioning mechanisms and mechanisms for moving heads in general.

In systems with a stepper mechanism and a motor, the heads move a certain amount corresponding to the distance between the tracks. The discreteness of the steps depends either on the characteristics of the stepper motor, or is set by servo-marks on the disk, which can be of a magnetic or optical nature.

In systems with a linear drive, the heads are moved by an electromagnet, and to determine the required position, special service signals are used, recorded on the medium during its production and read out during the positioning of the heads. Many devices use a whole surface and a dedicated head or optical sensor for servo signals.

Linear drives move heads much faster than stepper drives, and they also allow small radial movements "inside" the track, making it possible to track the center of the servo track's circumference. This achieves the best position of the head for reading from each track, which significantly increases the reliability of the read data and eliminates the need for time-consuming correction procedures. Typically, all linear drive devices have an automatic read / write head parking mechanism when the device is powered off.

Principles of Magnetic Hard Disk Recording

The principle of magnetic recording of electrical signals on a moving magnetic medium is based on the phenomenon of remanent magnetization of magnetic materials. Recording and storage of information on a magnetic medium is carried out by converting electrical signals into the corresponding changes in the magnetic field, affecting it on the magnetic medium and preserving traces of these effects in the magnetic material for a long time, due to the phenomenon of residual magnetism. Reproduction of electrical signals is performed by reverse conversion. The magnetic recording system consists of a recording medium and magnetic heads interacting with it (Figure 2).

Figure 2. The principle of recording and reading information from a magnetic medium

With digital magnetic recording, a current is supplied to the magnetic head, at which the recording field changes its direction to the opposite at regular intervals. As a result, under the action of the stray field of the magnetic head, magnetization or magnetization reversal of individual sections of the moving magnetic carrier occurs.

With a periodic change in the direction of the recording field in the working layer of the carrier, a chain of sections with the opposite direction of magnetization arises, which are in contact with each other with the same poles. The considered type of recording, when sections of the working layer of the carrier are remagnetized along its movement, is called longitudinal recording (Figure 3).

Alternating areas with different directions of magnetization, which have arisen in the magnetic coating, are magnetic domains (bit cells). The smaller the cell size, the higher the information recording density. However, with a decrease in the cell size, the mutual influence of their demagnetizing fields, directed in the direction opposite to the magnetization in the cells, increases, which, when the bit cell decreases below the critical value, leads to spontaneous demagnetization.

Figure 3. Sequence of sections with opposite direction of magnetization

For magnetic recording, media in the form of magnetic plates (disks) are used. The wafers are made by sputtering multiple metal films and a protective coating layer onto a very flat, defect-free glass or aluminum substrate. Information is arranged in concentric circles called tracks (Figure 4). In modern hard disk drives, the track density reaches 4.3 * 104 tracks per centimeter of the radius of the plate.

Figure 4. Placing tracks on the surface of the disc