External memory - designed for long-term storage of large amounts of information. it non-volatile memory, since information is stored in it, regardless of whether the computer is connected or not to an electrical power source. Various disks on which information is stored are used as external memory of a computer. They are called carriers of information.

Three types of media are currently in use:

- magnetic disks,

- optical discs,

- magneto-optical disks.

Magnetic disks are disks coated on both sides with a thin film of magnetically sensitive material. The surfaces of the disk on which information is applied are called work surfaces.

Structurally, magnetic disks are of two types:

- hard,

- flexible.

Hard magnetic disks

Rigid the discs are made of a hard but light metal alloy. The hard disks are the external memory of the computer.

It is represented by a device called winchester. The hard drive is located in the system unit of the computer and consists of several hard magnetic disks mounted on a common axis. The whole structure is placed in a box called HDA. Contrary to popular belief, this case is not sealed and communicates with the surrounding air through a special filter.

This is a very important point, since with its complete tightness, any pressure drop, for example, transporting a hard drive in the cargo hold of an aircraft, would lead to deformation of the hard drive case and damage to the precision mechanism. The purpose of this filter is to trap solid particles in the air and prevent them from getting inside the HDA. Another filter, located inside the case, catches particles flying off the surface of the disc.

Information on magnetic disks is placed along concentric circles called paths. Each track is divided into a certain number of sections, called sectors. The sector stores the minimum amount of information available. The amount of information placed in the sector is 512 bytes. One or more sectors arranged in a row form cluster.cluster is the smallest unit of information that can be written to or read from a disk.

The headers of tracks and sectors contain their characteristics (numbers, size, etc.), and after each sector there is a checksum of all its data. Sectors on tracks are not necessarily numbered in sequence. A well-known method is when the sectors alternate on the tracks not sequentially, but in the order 1-4-7-2-5-8-3-6-9. This is done so that the computer has time to receive all the data before the next sector by serial number approaches.

Access to information on a magnetic disk is determined by four coordinates:

- disc side number

- track number,

- sector number,

- byte number.

This access is called physical access. Information is stored on disk in the form files. A file is any information that has a name and is placed on a storage medium. When searching for the necessary information, the user does not indicate its coordinates, but gives its name. By the name of the file, the operating system of the computer looks for its physical location on the disk, which is indicated in special service tables. It should be borne in mind that sectors with the contents of a file are not necessarily located side by side in one place on the disk. When recording, the system actively uses free space. As a result, individual parts of the file can be located in different parts of the disk. The drive controller controls the head movement operation.

The hard drive uses disks of the same diameter and are located one below the other. Tracks of the same diameter on different disks form cylinder. The number of cylinders, the number of tracks on it, as well as the number of sectors on the track determines disk format. The format of the hard drive is set during its design and cannot be changed in any way. Formatting(marking) of the hard drive is always performed at the factory using a high-precision stand. The structure of the disk and the placement of tracks on it is shown in Fig. 2.1

Magnetic

Work surfaces

Fig.2.1 Disk layout

Before writing information to a newly manufactured magnetic disk, it should be format, that is, to mark on tracks and sectors . This is done in order to make the disk surface addressable.

When formatting, the entire disk surface is divided into two areas:

- system area,

- data area.

In the system area are:

- boot record, which hosts system loader and disk parameter block, defining the disk format;

- file allocation table(File Allocation Table - FAT), which is a map of the data area. This map records the state of each cluster and establishes a chain of clusters occupied by a single file. The file occupies an integer number of clusters, while the last cluster may not be fully used. Each FAT element contains either the number of the next cluster belonging to one file, or a special code:

- 0 - the cluster is free,

65521 - the cluster is defective,

65522 - the cluster is the last one in the file.

Due to the special importance FAT is stored on disk in two copies:

- root directory, which stores information about each file (creation time, creation date, size) and a cluster number indicating the physical location of the file or directory in the data area. When a file is deleted, information is not physically erased, but only the first character of the file name is deleted, after which such a file becomes inaccessible to standard operating system commands, and the clusters that the file previously occupied are declared free. Information in these areas of the disk is stored until new information is placed in them.

AT data areas contains all the information that makes up the files.

magnetic

magnetic disk

direction of travel

Rice. 2.2. Scheme of writing and reading information from magnetic disks.

Figure 2.2 shows a diagram that allows you to understand the principle of writing and reading information on magnetic disks. When recording information, a magnetic head is installed above the track, at a distance above the surface of the disk, calculated in microns. The head is a magnetic circuit on which the winding is wound. At a certain point in time, a voltage pulse of one polarity is applied to the winding. This pulse generates a current pulse in the winding, which, in turn, generates a magnetic flux pulse.

The magnetic flux closes along the magnetic circuit of the head, passes through the air gap and through the section of the magnetic surface of the disk, which is at that moment under the magnetic head. This section of the track on the magnetic disk is magnetized with the appropriate polarity. When a pulse of a different polarity is applied to the head, another section of the disk is magnetized with the opposite polarity. A section magnetized with one polarity is perceived as logical unit, and the area magnetized with the opposite polarity is perceived as logical zero. This method records information in an encoded form.

When reading information, all actions occur in the reverse order. The magnetized section of the disk, moving under the magnetic head, induces an emf pulse in its winding. one or the other polarity, which is perceived as a logical unit or logical zero.

The volume of modern hard drives is estimated at tens of GB.

Flexible magnetic disks

Floppy disks are used as portable storage media. diskettes . They are made on a plastic base and have a diameter of 89 mm or 3.5 inches. To protect the working surfaces of the magnetic disk from accidental destruction, the disk is placed in a hard plastic envelope, which almost completely covers the working surfaces of the disk. In the lower corner of the envelope there is a switch to protect the disc from writing. When the switch position in the down position writing new information to a floppy disk, as well as deleting existing information, becomes impossible.

The storage limit for these floppy disks is 1.44 MB. Before putting information on a diskette for the first time, it should be marked, that is, format. Formatting diskettes is carried out using special programs. The Windows operating system that was installed when you sold your computer contains such a program. The principle of marking and applying information to floppy disks is the same as on hard disks, described above.

To work with floppy disks, a computer has a device called disk drive . The drive is located in the system unit, on its front panel there is a slot into which a floppy disk is inserted. When a floppy disk is fully inserted, its movable metal shutter moves away, opening the access slot for magnetic heads to work surfaces for reading or writing information. When performing operations of reading or writing information, the magnetic heads move in the radial direction from the outer border of the floppy disk to its center with the help of a special micromotor and vice versa. In this case, the magnetic disk itself rotates at a speed of about 300 rpm. An arrow is located on its sleeve to orient the correct position of the disc. The correct position of the floppy disk inserted in the drive corresponds to the state when this arrow is on the top surface, in the left corner in front.

The disadvantage of magnetic disks should be considered the loss or distortion of information when these disks enter magnetic fields, which leads to demagnetization of the disk. Such cases are possible if the floppy disk is located near a switched on electric motor or transformer, which create stray magnetic fields.

Magnetic disks computers are used for long-term storage of information (it is not erased when the computer is turned off). At the same time, data can be deleted during operation, while others can be recorded.

Distinguish between hard and floppy disks. However, floppy disks are now very rarely used. Floppy disks were especially popular in the 80s and 90s of the last century.

Floppy disks(floppy disks), sometimes called floppy disks (Floppy Disk), 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, and 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.

3.5" floppy disks have a capacity of 1.44 MB. This type of diskette is the most common at the present time.

Unlike floppy disks HDD allows you to store large amounts of information. The hard drive capacity of 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 was nicknamed "winchester".

A hard drive is a sealed iron box containing one or more magnetic disks, along with a block of read/write heads and an electric motor. When you turn on the computer, 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. Special magnetic heads "hover" above the disk, which write and read information in the same way as on floppy disks. The heads hover above the disk due to its high rotation speed. If the heads touched the disk, then due to the friction force, the disk would quickly fail.

When working with magnetic disks, the following concepts are used.

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

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

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

cluster- the minimum element of the magnetic disk, which operates the operating system when working with disks. Each cluster consists of several sectors.

To store programs and data in personal computers, various types of drives are used, the total capacity of which, as a rule, is hundreds of times greater than the capacity of RAM. In relation to a computer, drives can be external and built-in (internal). External drives have their own case and power supply, which saves space inside the computer case and reduces the load on its power supply. Embedded drives are mounted in special mounting compartments (drive bays), which allows you to create compact systems that combine all the necessary devices in the system unit. The drive itself can be considered as a combination of the carrier and the corresponding drive. There are drives with removable and non-removable media.

The principle of operation of magnetic storage devices is based on methods of storing information using the magnetic properties of materials. As a rule, magnetic storage devices consist of the actual information reading / writing devices and a magnetic medium, on which the recording is directly carried out and from which information is read. Magnetic storage devices are usually divided into types in connection with the performance, physical and technical characteristics of the information carrier, etc. The most commonly distinguished are: disk drives and tape drives. The general technology of magnetic storage devices is to magnetize sections of the carrier with an alternating magnetic field and read information encoded as regions of variable magnetization. Disk media, as a rule, are magnetized along concentric fields - tracks located along the entire plane of the circular media. Tape media have longitudinally arranged fields - tracks. Recording is usually done in digital code. Magnetization is achieved by creating an alternating magnetic field using the read/write heads. The heads are two or more magnetic controlled circuits with cores, the windings of which are supplied with alternating voltage. A change in the voltage polarity causes a change in the direction of the magnetic induction lines of the magnetic field and, when the carrier is magnetized, means a change in the value of the information bit from 1 to 0 or from 0 to 1.

To record information, as a rule, various coding methods are used, but all of them involve using as an information source not the direction of the magnetic induction lines of an elementary magnetized point of the carrier, but a change in their direction in the process of moving along the carrier along a concentric track over time. This principle requires a tight synchronization of the bit stream, which is achieved by coding methods.

Disk devices are divided into flexible (Floppy Disk) and hard (Hard Disk) drives and media. The main property of disk magnetic devices is the recording of information on a carrier on concentric closed tracks using physical and logical digital encoding of information. The flat disc media rotates during the read/write process, which ensures the maintenance of the entire concentric track, reading and writing is carried out using magnetic read/write heads that are positioned along the radius of the media from one track to another. Disk drives typically use a recording method called the Not Return Zero (NRZ) method. Recording according to the NRZ method is carried out by changing the direction of the bias current in the windings of the read / write heads, causing a reverse change in the polarity of the magnetization of the cores of the magnetic heads and, accordingly, alternate magnetization of the carrier sections along the concentric tracks. When read, these areas of magnetization cause changes in the direction of the magnetic flux in the read / write heads and a change in the polarity of the output voltage, perceived as logical units of data. Absences of such a voltage reversal are treated as logic zeros. In this case, it does not matter at all whether the magnetic flux changes from a positive direction to a negative one or vice versa, only the fact of a change in polarity is important. Data coding methods do not affect changes in the direction of the stream, but only set the sequence of their distribution in time (the method of synchronizing the data stream), so that, when read, this sequence can be converted to the original data.

A floppy disk (English floppy disk), or lisket, is a carrier of a small amount of information, which is a flexible plastic disk in a protective sheath. Used to transfer data from one computer to another and to distribute software.

The method of recording binary information on a magnetic medium is called magnetic coding. It consists in the fact that the magnetic domains in the medium line up along the tracks in the direction of the applied magnetic field with their north and south poles. Usually, a one-to-one correspondence is established between binary information and the orientation of magnetic domains.

Information is recorded in concentric tracks(tracks), which are divided into sectors. The number of tracks and sectors depends on the type and format of the diskette. A sector stores the minimum amount of information that can be written to disk or read. The sector capacity is constant and is 512 bytes.

Figure 2. Magnetic disk surface

At present, the most widespread floppy disks with the following characteristics: diameter 3.5 inches (89 mm), capacity 1.44 MB, number of tracks 80, number of sectors on tracks 18.

The diskette is installed in floppy disk drive(English) floppy disk drive), automatically fixed in it., after which the storage mechanism spins up to a rotational speed of 360 min -1 . The floppy disk itself rotates in the drive, the magnetic heads remain motionless. The floppy disk rotates only when it is accessed. The drive is connected to the processor through floppy disk controller.

Recently, three-inch floppy disks have appeared that can store up to 3 GB information. They are made with new technology. Nano2 and require special hardware to read and write.

If floppy disks are a means of transferring data between computers, then hard drive - information warehouse of a computer.

Hard disk drive (Eng. HDD - Hard Disk Drive) or hard drive- this is the most mass storage device of large capacity, in which the information carriers are round aluminum plates - platters, both surfaces of which are coated with a layer of magnetic material. Used for permanent storage of information - programs and data

Like a floppy disk, the working surfaces of platters are divided into circular concentric tracks, and the tracks are divided into sectors. The read/write heads, along with their supporting structure and disks, are enclosed in a hermetically sealed housing called data module. When a data module is installed on a drive, it automatically connects to a system that pumps purified cooled air. Surface platter has magnetic coating only 1.1 microns thick, and lubricant layer to protect the head from damage when lowering and raising on the go. When the platter rotates above it, a air layer, which provides an air cushion for the head to hang at a height of 0.5 microns above the disk surface.

Winchester drives have a very large capacity: from 1 to 3000 GB. In modern models, the spindle speed (rotating shaft) is usually 7200 rpm, the average data search time is 9 ms, the average data transfer rate is up to 3000 MB / s. Unlike a floppy disk, a hard disk rotates continuously. All modern drives are supplied with built-in cache(usually 64 MB), which significantly improves their performance. The hard drive is connected to the processor through hard disk controller

Task 2

The implementation of this task involves solving examples for translating numbers from one number system to another with the presentation of complete mathematical calculations (the accuracy of the representation of numbers is up to the fifth decimal place) and the representation of numbers in floating and fixed point form.

In the first example, it is necessary to convert numbers from the decimal number system to binary, octal and hexadecimal.

In the second example, it is necessary to convert numbers from the binary number system to decimal, octal and hexadecimal.

In the third example, numbers given in floating point form must be represented in fixed point form.

Task options are determined by the table:

194.741 10 \u003d 11000010.10111102 \u003d 302.57331 8 \u003d C2, VDB22D

194 | 2

194 97 | 2

0 96 48 | 2

1 48 24 | 2

0 24 12 | 2

0
12 6 | 2

0
6 3 | 2

0
2 1

1

0,741 *2 = 1,482

0,482*2 = 0,964

0,964 *2 = 1,928

0,928*2 = 1,856

0,856*2 = 1,712

0,712*2 = 1,424

0,424*2 =0,848

194 | 8

192 24 | 8

2
24
3

0

0,741*8 = 5,928

0,928*8 = 7,424

0,424*8= 3,392

0,392*8 = 3,136

0,136*8 =1,088

194 | 16

192 12

2

0,741*16 = 11,856

0,856*16=13,696

0,696*16=11,136

0,136*16 =2,176

0,176*16=2,818

–729,753 10 = -1011011001.110000001 2 = -1331.60142 (8) = -2D9.C0C49 (16)

729| 2

728 364| 2

1
364 182| 2

0 182 91| 2

0 90 45| 2

1
44 22| 2

0 10 5| 2

1
4 2 | 2

1
2 1

0

0,753 * 2 = 1,506

0,506*2=1,012

0,012*2 = 0,024

0,024*2=0,048

0,048*2=0,096

0,192*2=0,384

0,384*2=0,768

0,768*2=1,536

729 | 8

728 91 | 8

1 88 11 | 8

3 8 1

3

0,753 * 8 = 6,024

0,024*8=0,192

0,192*8 =1,536

0,536*8 =4,288

0,288*8= 2,304

729 | 16

720 45 | 16

9 32 2

13

0,753 * 16 = 12,048

0,048*16 = 0,768

0,768*16 = 12,288

0,288*16 = 4,608

8.182E+03=8182

3.579Е-02=0.03579

2.951E + 04 \u003d - 29510

9.426E-01 = -0.9426.

Task 3

The purpose of this task is to test the student's ability to work with the file system. The task consists of two parts. In the first part, you need to write a template that combines the given files into a group. In the second part of the task, you need to write routes (access paths) to the specified files if the hierarchical tree of folders on the disk looks like this:

Task options table:

D:\Setup\map.doc

D:\Mguk\Work\Terms \literature.doc

2) report?.

*.

Task 4

To complete the assignment on this issue, it is necessary to develop an advertising sheet on a given topic in the Microsoft Word word processor. The document must contain:

text;


curly text;


picture;


table;


Topics for developing documents are presented in the table:









Your worries about buying/selling a home


We are ready


Take over


Registration of property within 30 days


Type of housing	total area	Living space	Number of rooms	Area	Price
Flat				KSK	100000
Particle				Center	5000
House	1000			Center	1000000
Country house				settlement Znamensky	35000

Task 5


The problem solution should contain the following sections:

Formulation of the problem.


A list of identifiers, including the designation of each identifier, its physical meaning and data type.


Graphic scheme of the algorithm that describes the process of solving the problem (with detailed comments).


The text of the program in a high-level language describing the developed algorithm (with comments).


Calculation of a complex indicator of product quality:



,





Solution


The program should calculate the deposit amount depending on the retention period using the formula:


where S to - the amount of the deposit at the end of the storage period;


S n - the initial amount of the deposit;


P is the interest rate determined depending on the term of deposit T:





Description of variables


To solve the problem, the following variables are needed:


T – deposit storage period, days, data type – integer (integer);


P – interest rate, %, data type – real number (real);


S1 – initial deposit amount, data type – real number (real);


S2 – deposit amount at the end of the storage period, data type – real number (real).


Graphic scheme of the algorithm (Figure 1)


In the first step, the user enters the value of T


We compare T with the values ​​15, 30, 60 and 90. If T is not equal to any of the values, then we issue an error message and exit the program.


If T is equal to one of the values, then we set the corresponding value of P.


The user enters the value S1.


We calculate the value of S2 according to the formula, using the values ​​of S1 .


We display the value of S2 on the screen.





Figure 2. Block diagram of the program algorithm


Program text in PASCAL language


programv11;


varT:Integer;


P,S1,S2:real;


begin


write('Enter the term of the deposit in days (15,30,60 or 90):'); (Output prompt for entering T)

1. What is a hard drive?

HDD(often referred to as a winchester) – device for long-term storage of information. Unlike RAM (RAM or RAM ), which loses information when the power is turned off, the hard disk stores information permanently. The hard drive is usually larger than the RAM.

1.1. Main components and working principle of a hard drive

HDD comprises HDA and fees with electronic elements. The board contains all the control electronics, except for the preamplifier located inside the HDA in close proximity to the heads. All mechanical parts are located in the HDA:platters (disks), spindle (axis), magnetic read/write heads, motor.

plates They are disk-shaped and made of metal (aluminum is most commonly used), ceramic or glass. Both sides of each plate are coated with a thin layer of magnetizable material. Recently, chromium oxide has been used for this, which has a greater wear resistance than the iron oxide coating used in early models. The number of platters determines the physical volume of the drive.

The plates are mounted on the central axis or spindle. The spindle rotates all inserts at the same speed.

On the left or right side of the spindle, there is a rotary positioner, somewhat reminiscent in appearance of a tower crane: on one side of the axis are thin, long and light carriers facing the discs magnetic heads, and on the other hand, a short and more massive tail with an electromagnetic drive winding. Each plate has two rocker arms located on different sides. Thus, one read/write head corresponds to each side of each platter.

The smaller the head and the lower it hovers above the surface of the disk, the smaller the magnetic areas it can write to, and therefore the more data can be written to the disk. The read/write head resembles a horseshoe magnet as it is formed by opposite magnet poles facing each other across a narrow gap. This gap is made extremely narrow so that only very small areas of the disk surface are affected by the field at any given moment of rotation, which leads to an increase in recording density.

When turning the rocker of the positioner, the heads move in an arc between the center and the periphery of the plates. Such a movement, together with the rotation of the plate, allows the heads to gain access to the entire surface of the plate. The angle between the axes of the positioner and the spindle and the distance from the axis of the positioner to the heads are chosen so that the axis of the head deviates as little as possible from the tangent to the track when turning.

In earlier models, the rocker arm was fixed on the axis of the stepper motor, and the distance between the tracks was determined by the step size. In modern models, solenoid positioners are used with a linear motor that does not have any discreteness, and installation on the track is carried out according to the signals recorded on the plates, which gives a significant increase in drive accuracy and disk density.

The winding of the positioner is surrounded by a stator, which is a permanent magnet. When a current of a certain magnitude and polarity is applied to the winding, the rocker begins to turn in the corresponding direction with the corresponding acceleration. By dynamically changing the current in the winding, you can set the positioner to any position. Such a drive system was called VoiceCoil (voice coil) - by analogy with a loudspeaker cone. When a stepper motor positioner moves the heads a long distance, it advances them in steps from track to track. On the contrary, it is enough for solenoid systems to change the value of the magnetic field once, and the heads move directly to their destination. This property allows solenoid systems to operate much faster than stepper motor systems.

The so-called magnetic latch is usually located on the shank - a small permanent magnet, which, at the extreme internal position of the heads (landing zone-landing zone), is attracted to the stator surface and fixes the rocker arm in this position. This is the so-called parking position of the heads, which at the same time lie on the disk surface, in contact with it. In some models, a special electromagnet is provided for fixing the positioner, the armature of which, in a free position, blocks the movement of the rocker arm. Information is not recorded in the landing zone of disks.

Engine, which rotates the disks, is located under the disks or is built into the spindle. When the power is turned on, the hard disk processor performs a test of the electronics, after which it issues a command to turn on the spindle motor. When a certain critical disk rotation speed is reached, the density of the air entrained by the disk surfaces becomes sufficient to overcome the force of pressing the heads to the surface and raise them to a height from fractions to a few microns above the surfaces of the plates - the heads “float”. From this moment until the speed drops below the critical head, they stay on an air cushion without touching the surfaces of the disks.

After the disks reach the rotation speed close to the nominal one, the heads are removed from the parking area, and the search for servo marks begins to accurately stabilize the rotation speed. Then, information is read from the service area (in particular, the table of reassignment of defective sections). At the end of the initialization, the positioner is tested by iterating over the specified sequence of tracks. If the test is successful, the processor sets the interface ready flag and switches to the interface mode.

During operation, the system for tracking the position of the head on the disk is constantly working: an error signal is emitted from the continuously read signal, which is fed into the feedback circuit that controls the current of the positioner winding.

When the power is turned off, the processor, using the energy remaining in the capacitors of the board, or extracting energy from the motor windings, which at the same time works as a generator, issues a command to set the positioner to the parking position. In some hard drives, this is facilitated by a spring-loaded rocker placed between the discs, constantly experiencing air pressure. When the air flow weakens, the rocker additionally pushes the positioner into the parking position, where it is fixed with a latch.

HDAfilled with ordinary dust-free air under atmospheric pressure. When the discs rotate, a strong air flow is created, which circulates around the HDA perimeter and is constantly cleaned by a filter installed on one of its sides. In the HDA covers of some hard drives, small holes are specially made, sealed with a thin film, which serve to equalize the pressure inside and out. In some models, the window is closed with an air-permeable filter.

Inside the hermetic unit is also placed preamplifier signal taken from the heads, and their switch. The positioner is connected to the preamplifier board with a flexible ribbon cable, however, in some hard drives (in particular, some Maxtor AV models), the winding is powered by separate single-core wires, which tend to break during active operation.

In some models of the hard drive, the spindle and the positioner are fixed only in one place - on the hard drive case, in others they are additionally fixed with screws to the HDA cover. The second models are more sensitive to microdeformation during fastening - a strong tightening of the fastening screws is enough to cause unacceptable distortions. In some cases, such a bias can become difficult to reverse or completely irreversible.

Electronics board - removable, connected to the HDA via one or two connectors of various designs. The board contains the main processor of the hard drive, ROM (read only memory) with the program, working RAM, which is usually used as a disk buffer (the buffer is needed to match the speeds of data streams at the read / write level and the external interface, it is often mistakenly called a cache) , digital signal processor (DSP) for preparation of recorded and read signals, and interface logic. On some hard drives, the processor program is completely stored in ROM, on others, a certain part of it is recorded in the service area of ​​\u200b\u200bthe disk. The drive parameters (model, serial number, configuration sectors, defect tables, etc.) can also be recorded on the disk. Some hard drives store this information in electrically programmable ROM (EEPROM).

Many hard drives have a special technological interface with a connector on the electronics board, through which, using bench equipment, you can perform various service operations with the drive - testing, formatting, reassigning defective areas, etc.

The hard drive is connected via a cable (40 or 80 wires) to the motherboard or a separate controller.

1.2. Storing, writing and reading data

The hard disk surface contains magnetized metal particles. Each particle has a north and south pole. The read/write head can apply a magnetic field to a small group of these particles, changing their polarity so that north becomes south and vice versa. The minimum surface area of ​​a disc that can sustain such changes in magnetic flux is called magnetic domain. As the disk rotates under the head, it changes the polarity of the magnetic field all the time, creating a sequence of polarity reversals across the disk.

Data on the hard disk is written as a sequence of binary (binary) bits (a bit is a digit in the binary number system, i.e. “0” or “1”). Each bit is stored as a magnetic charge (positive or negative) on the platter's magnetic layer. When writing information, the data is sent to the hard drive as a sequence of bits. After the disk receives data, the heads are used for magnetic recording. At this moment, the head generates a stream of magnetic pulses that encode data on the surface of the disk. A polarity change corresponds to the value “1”, and the absence of a change corresponds to the value “0”. Information is not necessarily stored sequentially; for example, data from the same file may be written to different locations on different platters.

When the computer requests data stored on the disk, the platters begin to rotate and the heads move until the area with the requested information is found. The head passively "floats" above the surface of the disc, and as the microscopic magnets that form the magnetic domains pass under it, they affect the head's magnetic field. The drive electronics amplifies these weak perturbations many times, turning them into sequences of zeros and ones, which then enter the computer's memory chips.

It would appear that the set of eight "1's" and "0's" that make up one byte of data is simply written as eight consecutive magnetic domains along a track on a disc. This is quite far from the true state of affairs. Too much data is packed into a small area, and if additional information was not added to the data, there would be too much error. The controller electronics must do the hard work. How does the controller know how much of the disc is heading? After all, if it fails at least once the position of one magnetic domain, then this can lead to unpredictable consequences.

The answer is that the controller navigates to the beginning of the sectors by reading the special information written when the disk was formatted. But as the head flies over the sector data, the controller must keep track of thousands of domains until it encounters the format information again. If the magnetic flux changes were regular, the controller could easy to track the position of the read-write head. But the sector can be filled with zeros, with thousands of magnetic domains rushing by without a single change in magnetic flux, and a failure is bound to occur. For this reason, the data must be encoded so that there are not too many zeros in a row (no change in magnetic flux).

In the original frequency modulation (FM) method, every second magnetic domain was assigned to a sync pulse. Half of the disk space was gone. Then the idea arose to encode changes in the magnetic flux with respect to the previous bit. As a result, the modified frequency modulation (MFM) method was obtained. with FM encoding. There is also an encoding with a limited number of repetitions (RLL - run length limited). Repetition-limited coding translates data into special code sequences. These codes are chosen for certain numerical characteristics, in particular for the possible number of consecutive zeros. There is a very complex logic behind this, but the result is very simple: more data can be packed onto disk.

2. What is formatting?

The computer must be able to quickly access the information you need. However, even the smallest discs can store millions and millions of bits. How does the computer know where to look for the necessary data? To solve this problem, the disk is divided into parts, making it easier to find information. The basic form of disk organization is called formatting. Formatting prepares the hard drive for reading and writing data. There are two types of formatting: physical and logical.

2.1. Physical Formatting

A hard drive must be physically formatted before logical formatting. Early models of hard drives, like floppy disks, were manufactured with clean magnetic surfaces; the initial markup (physical or low-level formatting) was done by the consumer at his discretion, and could be performed any number of times. For modern models, marking is done during the manufacturing process; at the same time, servo information- special marks needed to stabilize the rotation speed, search for sectors and track the position of heads on surfaces. Special sensors on the read/write head monitor these marks; when they detect a strong change in the field, the controller knows that the head is moving away from the center of the track and changes the amount of current in the solenoid accordingly.

Previously, a separate servo surface (DSS - dedicated servo surface, dedicated - dedicated) was often used to record servo information, while the entire side of one of the plates was given for servo data. On this surface, the heads of all other surfaces were tuned. Such a system required a high rigidity of the fastening of the heads, so that there would be no discrepancies between them after the initial marking. Now servo information is recorded in the intervals between sectors (embedd ed - built-in), which allows you to remove the restriction on the rigidity of the moving system. Some models use a combined tracking system - built-in servo information in combination with a dedicated surface; in this case, coarse tuning is performed on a dedicated surface, and fine tuning is performed on built-in marks.

Since the servo information is the reference marking of the disk, the hard drive controller is not able to restore it on its own in case of damage. With software formatting of such a hard drive, it is only possible to overwrite the headers and checksums of the data sectors.

During the initial marking and testing of a modern hard drive at the factory, defective sectors are almost always found, which are entered in a special remapping table. During normal operation, the hard disk controller replaces these sectors with reserved sectors, which are specifically left for this purpose on each track, track group, or dedicated disk area. Thanks to this, the new hard drive creates the appearance of a complete absence of surface defects, although in reality they are almost always present.

Physical formatting divides hard disk platters into basic elements: tracks, sectors, and cylinders. These elements determine the addresses at which data is read and written physically.

Each side of the plate is divided into concentric tracks. Tracks are identified by numbers, starting with track zero on the outside of the platter.

The tracks are divided into sectors, used to store a fixed amount of data. Sectors typically contain 528 bytes of information. 16 bytes are reserved for service information (address information and checksum), and the remaining 512 bytes are for data. The number of sectors in a track is not fixed due to different radii and recording methods. Since the physical radius of a track varies from the smallest radius of the inner track to the largest radius of the outer, zero track, the number of sectors in the track gradually increases from smaller, inner tracks to larger, outer tracks. However, this change is not linear.

Tracks at an equal distance from the center on all surfaces of the plates are combined into cylinders. For example, the third tracks of each side of each insert are located at the same distance from the spindle. If we imagine all these tracks connected vertically, then their union will take the form of a cylinder.

Zones– groups of cylinders, each with the same number of tracks, which in turn have the same number of sectors. To minimize losses, the number of zones installed on a disk can be 10 or more.

Thus, to access a specific sector, you need:

1) move the heads to the desired distance from the center, that is, position them on a specific cylinder;

2) start browsing the track on the desired plate by activating the corresponding head;

3) read all the information until a sector header appears, the number of which (the number contained in this header) matches the one needed for the read or write operation.

In accordance with this scheme for finding the necessary information on the hard disk, this addressing method is called CHS addressing (Cylinder-Head-Sector). Sides and heads are numbered from 0. Track numbering also starts from 0. Accordingly, cylinder 0 consists of the outermost tracks of all plates. Oddly enough, the numbering of sectors starts from 1.

Computer hardware and software often work with cylinders. If the data is written to disk in one cylinder, then it can be accessed without moving the read/write heads. And the movement of the heads is slow, in relation to the rotation of the disk and switching between heads. Therefore, storing information on cylinders significantly increases performance.

An important concept is cylinder density. The density of a cylinder indicates the number of sectors contained in a cylinder. It is equal to the number of sectors per track multiplied by the number of sides of the plates. Drives with a high cylinder density are preferred because they can fit a large file on fewer cylinders. In this case, when reading a file, fewer head movements will be required and the drive will work faster. Manufacturers are increasing cylinder density by building drives with more platters or by using coatings and electronics to achieve higher data densities, resulting in more sectors per track.

After physically formatting a hard drive, the magnetic properties of the platter surface may gradually deteriorate. As a result, it becomes more and more difficult to read data from affected areas and write data to affected areas. Sectors that can no longer be used to store information are called faulty (badsectors).

Affected areas can form in other cases. Strong vibrations or mechanical failure can cause the read/write head to hit the oxide coating and leave an indentation on it. The momentum of the rotating plates makes this collision quite energetic. At the site of the head impact, data can no longer be written, and if this site contained data, they are lost. But even worse, the particles of magnetic material are released upon impact and are free to wander inside the drive. These particles can be much larger than the gap between the heads and plate surfaces; hitting such a particle, the head will fly up and, falling back, will destroy a new portion of data. Sometimes particles stick to the head and disturb its magnetic field.

Most modern computers can detect bad sectors. Such sectors are simply marked and are no longer used.

2.2. Boolean formatting

After physical formatting, the hard drive must be formatted logically. A logical format sets up a file system on a disk, allowing operating systems (such as DOS, OS/2, Windows, Linux ) use available disk space for data storage and access. Different operating systems use different file systems, so the type of logical formatting depends on the operating system you plan to install.

3. Floppy disk

Floppy disks work on the same principle as hard disks, but their design is somewhat different. The read-write heads are slightly pressed against the surface of the disk when the drive door is closed. The disc coating is made thick to resist friction between the heads and the protective sleeve. Since floppy disks are flexible, they are subject to deformation; disk dimensions are constantly changing with temperature and humidity. And since floppy disks are mounted on a thin hub in the drive, they lose their precise alignment. For these reasons, the track positions are not determined with the same accuracy as on a hard disk. Floppy disk drives use stepper motor head positioners that do not track the position of the tracks, but simply move the head to the intended track location.

Why don't floppy disks have head crashes? In fact, floppy disks are, as it were, in a permanently emergency state, since the heads are always on the surface when they rotate. The diskette rotates slowly, the heads are large, and the diskette itself is flexible. When impacted on the drive, the force transmitted to the head is not increased by the rotation of the floppy disk; it falls on a large area, and the floppy disk itself is fed under the blow of the head. The result is virtually no damage. Although floppy disks do not crash, they are still subject to wear and tear from head friction and the protective sleeve in which the floppy disk is located. This is why flexible disks are constantly in a state of rotation.

Like hard drives, floppy disks get their main capacity gain not from packing more data per track, but from packing more tracks per floppy disk. Paradoxically, the smaller the floppy disk, the higher the track density. Reducing the diameter means reducing the deformation of the floppy disk. A sleeve in a hard plastic sleeve can center the floppy disk more accurately. The sleeve itself flattens the floppy disk as it spins, so that it doesn't deviate too much from the heads.

Summing up, we can say that hard drives remain the basis of secondary memory. They are getting faster and faster, and they hold more and more data. And they have many features that increase their reliability and performance. Unfortunately, they still pose a threat to data integrity. Since hard drives will be with us for a long time to come, you'd better understand them well.

Section 3. Accumulators of information.

Information storage- a device for recording, reproducing and storing information, and information carrier- this is an object on which information is recorded (disk, tape, solid state media).

Information accumulators can be classified according to the following criteria:

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;

Method of organizing access to information - drives
direct, sequential and block access;

The type of information storage device - embedded (internal), external, stand-alone, mobile (wearable), etc.

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

The physical foundations of the processes of recording and reproducing information on magnetic media are laid down in the works of physicists M. Faraday () and (). In magnetic storage media, digital recording is made on a magnetically sensitive material. Such materials include some types of iron oxides, nickel, cobalt and its compounds, alloys, as well as magnetoplasts and magnetoelasts with a binder of 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 various plastics, and for hard disks - aluminum alloys and composite materials of the substrate. The magnetic coating of the disk has a domain structure, that is, it consists of many magnetized tiny particles. Magnetic domain (from lat. dominium- possession) is a microscopic, uniformly magnetized region in ferromagnetic samples, separated from neighboring regions by thin transition layers (domain walls). Under the influence of an external magnetic field, the intrinsic magnetic fields of the domains are oriented in accordance with the direction of the magnetic field lines. After the action of the external field ceases, zones of residual magnetization form on the domain surface. Due to this property, information about the acting magnetic field is stored on the magnetic carrier. 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 writing 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. The specified period of time is called a bit element.

Rice. 3.1. Writing and reading data from a magnetic disk

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.

Topic 3.1. Magnetic disk drives.

Plan:

Floppy disk drives. Hard disk drives

2.1 Design and principle of operation.

2.2 Hard drive interfaces.

2.3 Main characteristics.

1. Floppy disk drives.

Floppy disk drives are long-term storage devices. The first flexible magnetic disk (FMD) was created in 1971 in the laboratory of IBM, headed by A. Shugart, and had a diameter of 8". disks with a diameter of 3.5 ". In 1986, IBM began producing floppy magnetic disks (GMD or floppy disks) 3.5" with a capacity of 720 KB, and in 1987, many manufacturing companies began producing GMD 3.5 "with a capacity of 1, 44 MB Toshiba introduced new 2.88 MB disks in 1989. Currently, 3.5" disks are the most widely used.

To write and read information from the GMD, PC peripheral devices are used - drives (Floppy Dick Drive - FDD).

Structurally, the drive consists of mechanical and electronic components: a working motor, a working head, a stepper motor and control electronics.

working engine turns on when a floppy disk is inserted into the drive. The engine provides a constant diskette rotation speed: for a 3.5" disk drive - 300 rpm. The engine start time is about 400 ms.

Working heads serve to read and write information and are located above the working surface of the floppy disk. Since floppy disks are usually double-sided, that is, they have two working surfaces, one head is for the top and the other for the bottom surface of the floppy disk.

Stepper motors provide positioning and movement of working heads. It is they who make a characteristic sound already when the PC is turned on, moving the heads to check the drive's performance.

Control electronics the drive is most often placed on its lower side. They perform the functions of transmitting signals to the controller, i.e., they are responsible for converting information that is read or written by the heads.

For 3.5" floppy disks with a capacity of 2.88 MB, called ED floppy disks (Extra high Density), a special floppy disk standard has been developed, since ordinary disk drives cannot work with such floppy disks. In addition, special drives are available for installation in small cases ( slim line drives 3.5"), which have a reduced height (19.5mm) compared to conventional 3.5" FDD (25.4mm).

The controller acts as an intermediary between the drive and the PC. In modern PCs, the controller is already installed on motherboards. It is integrated into one of the Chipset chips, and the motherboard has a special connector for connecting cables. Modern controllers support two FDDs, provide data transfer rates up to 62 Kb / s for standard 3.5" disk drives.

floppy disks (floppe disk driver, abbreviated Floppy) 3.5" format are modern storage media for FDD drives.

On fig. 3.2 shows the device of a 3.5" floppy disk.
Rice. 3.2. 3.5" floppy disk design

Inside the case (case) there is a plastic disk with a magnetic layer applied on it - a magnetic disk. All cases have a cutout protected by an easily moved shutter to protect the disc from mechanical damage. After inserting a floppy disk into the drive, the shutter automatically moves to allow access to the disk for the read/write heads. Since the disk itself is constantly rotating inside the case, the heads "look through" the entire area of ​​\u200b\u200bthe diskette, while being in constant contact with its surface. The floppy disk has a hole with a sliding plastic latch. If the latch does not cover the hole, then the diskette is write-protected. Most computers use 3.5" floppy disk drives with a capacity of 1.44 MB - HD standard (high Density), while older PCs use 720 KB disks - DD standard (Double Density). The capacity of the newest 3.5" discs reaches 2.88 MB - the ED standard with ultra-high recording density.

Magnetic disks are called direct-access storage media, since due to the rotation of the disk at high speed, it is possible to move any part of it under the read / write heads. Thus, any part of the recorded data can be directly accessed. This is facilitated by a special organization of disk memory, in accordance with which the information space of the disk is formatted, that is, it is divided into certain sections: tracks and sectors.

Recording track (Track) each of the concentric rings of the disk on which the data is recorded is called. The disk surface is divided into tracks starting from the outer edge, the number of tracks depends on the type of disk.

In 3.5" floppy disks with a capacity of 1.44 MB, the number of tracks is 80. Tracks, regardless of the number, are identified by a number (the outer track has a zero number). The number of tracks on a standard disk is determined by the recording density, i.e., the amount of information that can be securely placed on a unit area of ​​the media surface. For magnetic disks, two types of recording density are defined - radial (transverse) and linear (longitudinal). which can be written on a track of unit length.

Each ring of the track is divided into sections called sectors. For example, a 3.5" floppy disk may have 18 sectors per track (disk capacity 1.44 MB) or 36 sectors (disk capacity 2.88 MB).

Rice. 3.3. Partitioning a magnetic disk into tracks and sectors. when formatting

The sector size of various disks can be from 128 to 1024 bytes, but the sector size of 512 bytes is accepted as a standard. On fig. 3.3 shows the partitioning of magnetic disks into tracks and sectors. Sectors on a track are assigned numbers starting from zero. The zero-numbered sector on each track is reserved for recording information identification, but not for data storage.

The capacity of a floppy disk is calculated using the following formula:

floppy disk capacity = number of sides X number of tracks per side X number of sectors per track X the number of bytes in the sector.

2. Hard disk drives

First hard drive ( Hard disk Drive - HDD) was created in 1973 using IBM technology and had the code designation "30/30" (a double-sided disk with a capacity of 30 + 30 MB), which coincided with the name of the famous Winchester hunting rifle used in the conquest of the Wild West. For this reason, hard disk drives are called "hard drives". In 1979, F. Konner and A. Shugart organized the production of the first five-inch hard drives with a capacity of 6 MB.

Compared to floppy disks, HDDs have the following advantages: a significantly larger capacity (one HDD or about 290 3.5" HD diskettes is required to store 420 MB of data) and access time for NDD. It is an order of magnitude faster than for floppy disk drives.

2.1. Design and principle of operation

Despite the wide variety of hard drive models, the principle of their operation and the main structural elements are the same. On fig. 3.4 shows the main elements of the design of the hard drive:

Magnetic disks;

Read/write heads;

Head drive mechanism;

Disc drive motor;

CD-ROM drives can work with either a standard IDE (E-IDE) interface or a high-speed SCSI interface.

The most popular CD-ROM drives in Russia are Panasonic, Craetive, Samsung, Pioneer, Hitachi, Teac, LG.

2. Write-once drivesCD- WORM / CD- Rand repeated recording of informationCD- RW

Drives CD- WORM (Write once read Many) or CD-R (CD- recordable) provide a single record of information on a disc and subsequent repeated reading of this information, while CD-RW drives (CD- Re Writable- rewritable) allow multiple recording on optical discs.

Rice. 3.9. Structure of CD-ROMs and CD-Rs/CD-WRs

For write-once disks are used, which are an ordinary compact disk, the reflective layer of which is usually made of gold or silver film. Between it and the polycarbonate base is a recording layer (Fig. 3.9), made of an organic material that darkens when heated. During the recording process, the laser beam, the wavelength of which, as in reading, is 780 nm, and the intensity is more than 10 times higher, heats individual areas of the recording layer, which darken and scatter light, forming areas similar to pits. However, the reflectivity of the mirror layer and the clarity of the pits of CD-R discs are lower than those of commercially produced CD-ROMs.

AT rewritable discs The CD-RW recording layer is made of organic compounds known as cyanine (Cyanine) and phthalocyanine (Phtalocyanin), which tend to change their phase state from amorphous to crystalline and back under the influence of a laser beam. Such a change in the phase state is accompanied by a change in the transparency of the layer. When heated by a laser beam above a certain critical temperature, the material of the recording layer passes into an amorphous state and remains in it after cooling, and when heated to a temperature significantly below the critical temperature, it restores its original (crystalline) state. In rewritable discs, the recording layer is usually made of gold, silver, sometimes aluminum and its alloys.

Existing rewritable CD-RW discs can withstand from several thousand to tens of thousands of rewriting cycles. However, their reflectivity is much lower than that of pressed CD-ROMs and CD-Rs. In this regard, to read CD-RW, as a rule, a special drive with automatic gain control of the photodetector is used. However, there are models of CD-ROM drives labeled Multiread that can read CD-RW discs.

The advantage of CD-R/RW discs is that they fade and wear out more slowly than conventional discs because the gold and silver reflective layer is less prone to oxidation than the aluminum in most pressed CD-ROM discs. Disadvantages of CD-R/RW discs - the material of the recording layer of CD-R/RW discs is more sensitive to light and is also subject to oxidation and decomposition. In addition, the recording film is in a semi-liquid state and is therefore very sensitive to impacts and disk deformations.

Information on a CD-R can be written in several ways. The most common way to write a disc for one pass (disk- at- once) , when a file from the hard disk is written directly in one session and adding information to the disk is not possible. In contrast to this, the method multi-session records (track- at- once) allows you to record individual sections (tracks) and gradually increase the amount of information on the disk.

Like any drives, CD-R and CD-RW are available in two versions: with a standard interface for connecting to a IDE (E- IDE) and with high speed interface SCSI. External CD-RW drives are available with SCSI and USB interfaces.

The size of the built-in cache memory is important for recording devices, since it is in it that the data coming from the hard disk is accumulated. The average size of the cache memory is 2 - 4 MB.

The most popular in the Russian market are drives with trademarks Panasonic, Sony, Ricoh, Teac, Yamaha. The highest quality and most expensive models are produced by firms Plextor and Hewlett- Packard. Among inexpensive IDE drives, models are popular Mitsumi.

Thanks to the further development of CD-technologies, there appeared:

· Modified CD-R discs with a capacity of up to 870 MB - 1 GB, released by Traxdata, Philips and Sony;

· Double Density CD standard proposed by Sony for discs of all modifications (CD, CD-R, CD-RW), which allows to increase the speed of traditional CDs up to 1.3 GB, or 150 minutes of audio information;

· FMD-ROM disk containing up to 100 working layers, the total capacity of which is not less than 140 GB. Each layer of such a disk contains a luminescent substance that emits light under the action of a readout beam. Each layer glows differently, but at the same time it is perfectly transparent to laser beams, which makes it possible to read information simultaneously from several layers.

3. DrivesDVD

The solution to the problem of increasing the capacity of optical information carriers based on the improvement of the production technology of CDs and drives, as well as the available scientific and technical solutions in the field of high-quality digital video, has led to the creation of high-capacity CDs. In 1995, CD manufacturers proposed their own CD standards with increased capacity. One of these standards was the SD format ( Super Density). To avoid diversity and incompatibility of standards, in September 1995, Sony, in alliance with eight other companies, proposed a new universal format for recording data on CD-DVD ( Digital Versatile disk). This format, which satisfies the requirements for video playback and data storage, has received strong support from leading CD manufacturers.

The quality of the image stored in the DVD format is commensurate with the quality of professional studio video recordings, and the sound quality is also not inferior to the studio. Reading audio information in DVD format is performed at a speed of 384 Kb / s, which allows you to organize multi-channel audio.

Such features of DVD discs are due to the improved parameters of the working surface of the discs. On fig. 3.10 shows the parameters of the elements of the working surface of discs recorded in CD and DVD formats. Just like a CD, a DVD disc has a diameter of 120 mm. The DVD drive uses a semiconductor laser with a visible wavelength of 0.63 - 0.65 µm. Such a reduction in the wavelength (compared to 0.78 microns for a conventional CD drive) made it possible to reduce the size of recording strokes (pit) by almost two times, and the distance between recording tracks from 1.6 to 0.74 microns. The pits are arranged in a spiral, like on vinyl LPs.

Rice. 3.10. Elements of the working surface of CD and DVD discs

DVD-disks are structurally made single-sided and double-sided, single-layer and multi-layer, as shown in Fig. 3.11. A single-sided single-layer DVD has a capacity of 4.7 GB, while a double-layer DVD has a capacity of 8.5 GB. A double-sided DVD consists of two 0.6 mm thick discs tightly bonded to each other. A full-length video (up to 135 minutes long) with three channels of high-quality sound and four channels of subtitles can be placed on a DVD disc using MPEG-2 compression.

Rice. 3.11. DVD options

DVD-standard drives use a narrower laser beam than CD-ROM drives, which made it possible to reduce the thickness of the protective layer of the disc by half: from 1.2 mm to 0.6 mm. Since the overall thickness of the disk had to remain the same (1.2 mm), a reinforcing layer was placed under the protective layer.

The reinforcing layer also began to record information, which led to the emergence of dual-layer DVDs. Sequential reading of information from each layer is provided by changing the position of the focus. When the information recorded on the first layer located in the depth of the disc is read by a focused laser beam, the beam passes unhindered through the translucent film that forms the second layer. Upon completion of reading information from the first layer, the focusing of the laser beam changes at the command of the controller. The beam is focused in the plane of the second (outer) translucent layer, and data reading continues. The dual-layer, single-sided disc design provides a capacity of 8.5 GB.

The next step in the development of DVD technology was the creation of double-sided discs, both single-layer and double-layer, while the capacity of the discs was 9.4 and 17 GB with the playback time of the information recorded on them, respectively, 4.5 and 8 hours.

To avoid the need to manually flip a double-sided disc to access data on the second side, DVD drives equipped with two independent reading systems have become the most popular.

DVD-ROM drives come with both a hardware MPEG-2 decoder in the form of an expansion card for the PCI bus, and a software decoder. DVD-R writers and DVD-RW rewritable drives are capable of handling single-layer, single-sided discs with a capacity of up to 4.7 - 5.2 GB at a write speed of about 1 MB / s.

4. Drives on magneto-optical disks

A magneto-optical (MO) drive is an information storage device based on a magnetic carrier with optical (laser) control.

Magneto-optical technology was developed by IBM in the early 1970s. The first prototypes of magneto-optical storage devices were introduced in the early 1980s. Sony firm. The first magneto-optical drives were initially not in demand due to their high cost and complexity, but as technology developed and prices fell, they began to take their place in the market of technical means of informatization. On fig. 3.12 shows the device of a typical magneto-optical disk having one working surface. Magneto-optical discs are also available with two working surfaces in two main sizes - 3.5" and 5.25". A single-sided magneto-optical disk is a sequence of layers: protective, dielectric, magneto-optical, dielectric, reflective and substrate.

The manufacturing technology of the magneto-optical disk is as follows. An aluminum (or gold) coating is applied to the fiberglass substrate, which provides reflection of the laser beam. The dielectric layers surrounding the magneto-optical layer on both sides are made of a transparent polymer and protect the disk from overheating, increase the sensitivity when recording and the reflectivity when reading information. The magneto-optical layer is created on the basis of a powder from an alloy of cobalt, iron and terbium. The properties of such a coating change both under the influence of temperature and under the action of a magnetic field. If the disk is heated above a certain temperature, it is possible to change the magnetic polarization by means of a small magnetic field. The upper protective layer of transparent polymer, made by UV curing, protects the work surface from mechanical damage. Thanks to this technology and being placed in a special plastic envelope - a cartridge, magneto-optical disks have increased reliability and are not afraid of adverse environmental conditions.

Rice. 3.12. The structure of a magneto-optical disk

Data is written to the MO disk using laser technology. A laser beam focused on the surface of the magneto-optical layer into a spot with a diameter of about 1 μm is directed to the magneto-optical layer and heats it at the focusing point to the Curie point temperature (about 200 ° C) (Fig. 3.13, a). At this temperature, the magnetic permeability drops sharply, and the change in the magnetic state of the particles is carried out by a relatively small magnetic field of the magnetic head. After cooling the material, the magnetic orientation of the domains at a given point is preserved. Depending on the magnetic orientation of a piece of magnetic material, it is interpreted as a logical zero or a logical one. Data is written in blocks of 512 bytes.

To change part of the information in the block, it is necessary to overwrite it completely, therefore, during the first pass, the entire block is initialized (warmed up), and when the sector approaches the magnetic head, new data is written.

Data is read from the disk by a polarized laser beam of reduced power, which is not enough to heat the working layer: the laser power during reading is 25% of the laser power during writing. The impact of the beam on the ordering of the magnetic particles of the disk oriented during data recording leads to the fact that their magnetic field slightly changes the polarization of the beam, i.e., the Kerr effect is observed. On fig. 3.13, b arc arrows conventionally show different polarizations of the reflected light.

Rice. 3.13. Schemes for writing and reading information in a magneto-optical drive

The reflected light hits a photosensitive receiver, which determines the change in the state of its polarization. Depending on this, the photosensitive element sends a binary one or a binary zero to the magneto-optical drive controller.

Unlike a compact disc, data can theoretically be written to an MO disc indefinitely, since no irreversible processes occur in the carrier material. If you need to delete old data, it is enough to heat the corresponding tracks (sectors) with a laser beam and demagnetize them with an external magnetic field.

Standard capacities of MO disks: 3.5" single-sided discs - 128, 230 and 640 MB, double-sided - 600 and 650 MB. 5.25" discs are available in capacities from 1.7 to 4.6 GB.

Maxell produces 12" write-once disks with a capacity of 3.5 GB (single-sided) and 7 GB (double-sided). Drives for these giant disks used in archiving systems are manufactured by Hitachi.

Performance of MO drives lower than drives with removable magnetic media, although the speed of new models is steadily increasing. One reason for the comparatively slow performance of MO drives is that the drive spins at only 2000 RPM. In addition, MO drives use a fairly massive read/write head that combines optical and magnetic assemblies in one device.

The average data access time in MO-drives is about 30 ms, and the warranty period (mean time between failures) is 1 hour.

The technology of magneto-optical recording is constantly being improved. Several firms produce MO drives with 3600 rpm MO drives, but their cost is quite high. The market leaders in MO drives are companies Sony, FujitsuandHewlett- Packard.

Magneto-optical disks and drives from most manufacturers comply with the requirements of international standards, are available both as built-in devices and in external stand-alone versions with IDE and SCSI interfaces.

In addition to conventional disk drives, so-called optical libraries with automatic disk change have become widespread, the capacity of which reaches hundreds of gigabytes and even several terabytes. The time for automatic disk change is a few seconds, and the access time and data transfer speed are the same as for conventional disk drives.

Test questions.

1. List the main steps in the CD manufacturing process.

2. What structural parts does a CD ROM drive consist of? Their purpose.

3. How is data organized on a CD-ROM? Main CD formats

4. Give the main characteristics of rewritable discs.

5. How is information recorded on CD-WORM, CD-R and CD-RW discs?

6. What is the main advantage of DVD drives? How is information read from a dual layer DVD?

7. How are information recorded and read from magneto-optical disks? Their characteristics.

Topic 3.3. Other types of storage.

Plan:

Magnetic tape drives.

External storage devices.

Flash is storage.

1. Tape drives

Tape drives are used in backup systems. Data backup is necessary if the capacity of the hard disk drive used is small and there are many programs stored on it; the results of the work are represented by large data arrays; there is no free space on the hard disk.

At first, reel-to-reel drives, similar to household reel-to-reel tape recorders, were first used as devices for recording data on magnetic tape (streamers). In 1972, 3M developed the first 15x10x1.6 cm cassette for storing data. Inside the cassette there were two reels, on which the tape was wound by a tape drive mechanism during the reading / writing process. In 1983 the first standard QIC (quarter- Inch- Catridge - tape drive), the capacity of which was 60 MB. Data was recorded on nine tracks, and the magnetic tape had a length of about 90 m. Subsequently, a standard was developed for mini-cassettes (MS format). The dimensions of the mini-cassette, according to this standard, are 8.25 x 6.35 x 1.5 cm. The basis of the magnetic layer of QIC tapes is iron oxide.

The most widely used magnetic tape drives QIC-40 and QIC-80 format MS, the capacity of which is respectively 40 and 80 MB. Information is recorded on a QIC-40 cassette on 20 tracks, the data recording density is bits / inch.

The advantages of these drives are that the unit cost of storing data on tape (in terms of 1 MB) is significantly lower than using floppy disk drives, and in addition, tape drives are easy to use and reliable.

The disadvantages of QIC-40 and QIC-80 cassette drives include their slow performance, as they connect to an interface designed for floppy drives. In this case, data is recorded at a speed of 250 - 500 Kbps, formatting a cassette before recording data also requires a lot of time (for example, it takes about an hour and a half to format a cassette with a capacity of 60 MB of the QIC-40 standard).

Further development of magnetic tape drives followed the path of increasing the capacity of cassettes and increasing the density of data recording. Standards have been developed for backup systems with tape capacities ranging from 86 MB to 13 GB. In such devices, the data density on the tape is over bits per inch. The recording is made on 144 tracks. The compatibility of cartridges of different types is an extremely important factor to consider when choosing a backup device for information on a magnetic tape, since tapes are not always compatible in their magnetic properties.

Along with the currently common devices and backup formats QIC, other devices for copying on magnetic tape are becoming popular, in particular, in computer networks that manipulate large amounts of data.

The following standards exist for recording data on magnetic tapes.

Sony has mastered the production of devices that use 4 mm wide magnetic tapes for digital sound recording DAT (Digital Audio Tape) and tapes 8 mm wide for video recording. In addition, a standard has been developed for storing data in digital form. DDS (Digital Data Storage). When writing data to a magnetic tape, a slanted line technology is used, as a result of which almost the entire surface of the tape is used (unlike other methods in which the tracks are separated by gaps).

In the mid 1990s. there is a new technology that allows for higher capacity, data transfer speed and reliability of backup - technology DLT (Digital Linear Tape), considered one of the most popular. DLT drives can store 20 - 40 GB of data and provide data transfer rates of 1.5 - 3.0 MB/s. In DLT drives, during reading / writing, a magnetic tape divided into parallel horizontal tracks passes through a fixed magnetoresistive head at a speed of 2.5 - 3.7 m / s, thereby increasing the reliability of the head and ensuring low wear of the magnetic layer of the tape . The estimated service life of the tape is 500,000 rewinds. DLT drives are designed for use in network servers as automated data backup systems on magnetic tapes.

The TRAVAN cassette standard was developed by 3M. TRAVAN drives are housed in a 3.5" drive bay. They can work with both original TRAVAN mini-cassettes and QIC-standard cassettes. A TRAVAN cassette (or cartridge) contains 225 meters of 8 mm wide magnetic tape. Today there are four TRAVAN cassettes and drives (TR-1, -2, -3, -4) Travan mini cassettes (according to type 1, 2, 3 or 4) have capacities of 400, 800, 1000 and 4000 MB respectively. TRAVAN drives provide 2:1 hardware data compression, doubling the capacity of the cassettes, i.e. the TR-4 drive can store up to 8 GB of information.TR-1, -2, -3 drives are usually connected to the system through the drive controller on floppy disks or a parallel port, and the TR-4 uses a SCSI-2 interface.

The current level of development of computer technology is characterized by a steady increase in the volume of data stored on servers. Backup technologies are coming to the fore, as the costs of recovering lost data are too high.

Many new possibilities are expected from the development of technical means. The DAT DDS-3 format is considered the most promising - for small organizations with a total amount of data up to 10 GB and the DLT standard - for large volume magnetic tape drives. The DLT standard is currently developing in two directions: the creation DLT 4000 (interfaceSCSI-2 Fast) - for a data volume of 20 GB and DLT7000 (SCSI-2 interfaceFast/ Wide) - for a data volume of 35 GB. Data transfer rate for DLT 7000 5-10 MB/s. The American company ADIC announced the release in the near future of drives for data backup on magnetic tapes with a capacity of 11 to 55 TB. Guaranteed storage period of information is 30 years.

To ensure the guaranteed storage of critical data in original drives, a new magnetic head and MLR-RWR recording technology are used ( Multi- channel Linear Recording- read While Write), which consists in the fact that simultaneously with the recording of information through several channels, it is read and compared with the original, and, if necessary, correction.

2. External storage devices

With modern volumes of software and file sizes, a floppy disk storage medium with a capacity of only 1.44 MB is not able to provide data exchange between PCs and, moreover, cannot be used to store backups and archives.

The solution to this problem is associated with the creation of such drives as LS-120, SyQuest, Zip, jazz, MO,ORB and others. The most important parameter for evaluating these devices is FDD compatibility, i.e., the ability of the device to read and write data to a 3.5" floppy disk with a capacity of 1.44 MB. All of these devices are incompatible with FDD, since they work only with their own disks. The exception is the LS-120 drive, which is able to read, in addition to its 120 MB floppy disks, standard 1.44 MB floppy disks.

LS-120 drives are produced by firms as external devices with an LPT interface or internal with an IDE interface. The undoubted advantage of the LS-120 drive is the high capacity of the floppy disk (120 MB) at a fairly low price of a drive with an IDE interface. At the same time, the read / write speed is several times higher than that of FDD (80-100 KB / s in DOS and 200 - 300 KB / s in Windows compared to 60 KB / s for FDD). LS-120 drives are magnetic storage media and have the same drawbacks as all magnetic storage media: sensitivity to magnetic fields, dust and mechanical deformations.

Replaceable hard drives are used when it is necessary to place large amounts of data on small-sized media. For a removable hard drive, not only the storage medium is portable, but also the entire drive, which is removed from its guides in the PC case. Most often, these are IDE drives that are installed in the computer case. To remove the drive on the front panel there is a special handle. On the back of it is an adapter, which usually provides power supply and communication for receiving / transmitting data. The use of a removable hard drive of this kind for frequent exchange of information between remote PCs does not give the desired results due to insufficient protection from external influences that occur during their transportation. It is recommended to use removable hard drives primarily for data archiving purposes.

Consider individual models of drives on removable hard drives.

SyQuest- This is a removable disk drive with a capacity of more than 2 GB. Such drives are manufactured only with SCSI interface. The device uses magnetic media technology with built-in heads, i.e. the read heads are in the cartridge. The peak transfer rate is over 10.6 MB/s and the access time is about 12 ms. SyQuest drives are designed for use in corporate networks and professional video studios.

Storage device SyJet contains 1.5 GB hard drive cartridges. The cartridge has two disks, four surfaces, and the reading heads are outside, i.e., in the drive. The use of such cartridges made it possible to achieve high performance of the drive: the peak data exchange rate is more than 10 MB / s, the average transfer rate is 7 MB / s, and the data access time is 11 ms.

SparQ - 3.5" drive with replaceable cartridges with a capacity of 1 GB. Available with LPT, EIDE and USB interfaces. Provides access time of 12 ms. Average data transfer rate is 3.7 - 6.9 MB/s.

EZ Flyer - 3.5" drive with 30 MB cartridge. Based on hard disk technology. Available in SCSI (both internal and external), LPT, and EIDE interfaces. 3600 rpm disk rotation speed and 13.5 ms average access time provides data transfer rates up to 16.6 MB/s.

Drives jazz and Zip iOmega's developments outperform existing removable media drives on the market due to their good price/performance ratio. These devices use traditional magnetic media technology, but with improved read/write head positioning and robust drive mechanics. The Jaz drive uses a hard disk platter as the medium, while the Zip uses a floppy disk, similar to conventional floppy disk platters. The capacity of the Zip 250 model cartridge is 250 MB, the Jaz cartridges are 540 and 1070 MB, and the Jaz 2 model cartridge is 2 GB.

Jaz drives and Zi p drives come in two types - internal and external. The internal drive is installed in one of the drive bays. This device comes with a SCSI adapter. An external Zip drive connects directly to the PC's parallel port. The Jaz drive is a SCSI device that comes with a SCSI adapter.

The Zip drive can be effectively used as a floppy disk drive of the multimedia age: it can be used to transfer files of quite a large size, since the Zip drive weighs only 450 g, and the overall dimensions are 3.7 x 13.6 x 18.0 cm. Can also be used for storing backup copies of files written to the hard drive. Zip can be effectively used when working with classified information, since the device itself provides a password entry function.

ORB is a removable disk drive designed with advanced MR technology ( Magneto Resistive) firm Intel. The storage medium is a 3.5" removable hard disk encapsulated in a cartridge. Through the use of MR technology (magnetoresistive heads and a special magnetic material) and a digital signal processor, it was possible to create a removable disk drive with a capacity of 2.2 GB (more than the Jaz 2 drive), with a rotation speed of 5400 rpm and a maximum data transfer rate of 12.2 MB/s. With an optimal ratio of quality / price, the ORB drive successfully competes with devices of a similar purpose.

3. Flash drive.

Flash-card- a portable storage medium with a USB interface. One of the first on the domestic market appeared MAXIMUS Flash USB Drive (Korean company Jung MyungTelecom). Strictly speaking, the word Drive in the name of a Korean flash drive is a marketing exaggeration - there is no drive there, just as there are no moving parts. In fact, the developers simply reflected in the name the procedure for working with MAXIMUS Flash USB Drive, as with any external drive (CD-RW, Zip, hard drive). In fact, the "pseudo-disk" consists of a flash ROM chip, a special controller and a USB interface.

This type of memory has many advantages:

Fast access time

high reliability (due to the absence of moving parts);

· compactness;

durability.

Devices are supported by Windows 2000 and XP operating systems without the need to install any special drivers.

When a device is plugged into the slot, it is automatically recognized by the system and registered. At the end of the work, it is necessary to turn off the device, after which it will be removed from the system and can be removed.

Figure 6.11. USB Flash Drive.

Until recently, Flash-memory cards were mainly used only in PDAs and digital cameras. And here we have a combination of two progressive technologies: USB bus and Flash memory - USB Drive from J. M. Tek (Fig. 6.11). The device is small in size (the size of a lighter), the USB connector is closed with a protective plug with a latch to secure it in your pocket. At the end there is a microswitch to protect the disc from accidental writing and a control indicator of the operating mode. In write mode, it glows yellow, in read mode - green.

Device specifications: disk capacity - 32 MB; interface - USB 1.1; reading speed - 800 KB / s; write speed - 500 KB / s; operating temperature -0...+45 0С; humidity - 5-95%; service life - 10 years; dimensions - 54 x 20 x 10 mm; weight - 15 g.

test questions

1. List the applications, advantages and disadvantages of magnetic tape drives.

2. What external storage devices are available? Their characteristics.

3. What are the design features and characteristics of a flash drive?