Lecture 4

Peripherals

Optical discs: main characteristics and purposes

CD-discs, their types, history of creation

Music optical CDs replaced vinyl CDs in 1982 around the same time the firm's first personal computers appeared.IBM

These devices are the result of a fruitful collaboration between two giants of the electronics industry \u003d a Japanese firmSony and Dutch Philips.

The strictly defined capacity of CDs is associated with such an interesting story.

Executive director of the companySony Akio Morita decided that CDs should only meet the needs of classical music lovers \u003d no more, no less. After a survey was conducted by a development team, it was revealed that the most popular classical piece in Japan at the time was Beethoven's 9th Symphony, which lasted 72-73 minutes. Therefore, it was decided that the CD should be designed specifically for 74 minutes of sound, or rather, for 74 minutes and 33 seconds. This is how the standard known asRed Book (RedBook ). When 74 minutes were converted to megabytes, it turned out to be 640 MB.

Philips specialists defined the minimum requirements for the quality of audio recording and regulated, for example, such characteristics of audio CDs as their size, data encoding method and the use of a single spiral track. In particular, the sampling frequency of stereo signals was determined at the level of 44.1 kHz (22.05 kHz for one channel), and the bit depth of each \u003d 16 bits.

The above two companies also played a leading role in the development of the first specification for digital CDs \u003d the so-calledOf the Yellow Book | (YellowBook), or just CD-ROM. It served as the basis for creating compact discs with a complex presentation of information, that is, capable of storing not only sound, but also text and graphic data (CD- DigitalAudio, CD- DA ). In this case, the drive, reading the disc title, itself determined its type \u003d audio or digital data. In this format, however, the logical and file formats of CDs were not regulated, since the solution of these issues was completely at the mercy of manufacturing firms. This, in particular, meant that a CD that meets the requirements of the Yellow Book could only work on a specific drive model. This state of affairs, especially in connection with the great commercial success of CDs, of course, could not satisfy the manufacturers of such devices. It was in the common interest that a compromise had to be found urgently.

That is why the second de facto standard for digital CDs is the specificationHSG (HighSierraGroup), or simply HighSierra ... This document was, generally speaking, a recommendation and was proposed by the main manufacturers of digital compact discs with the aim of providing at least some compatibility. This specification already defined both logical and file formats for CDs.

The resulting specification turned out to be so attractive that the standardISO -9660 (1988) for digital CDs, in principle, coincided with the guidelinesHSG ... Note that all CDs thatmeeting the requirements of the standard ISO-9660, which defines their logical and file formats, are compatible with each other. In particular, this document defines how to find its contents on a CD. The basic format suggested inHSG -specification, in many ways resembled the floppy disk format. As you know, the system track (track 0) of any floppy disk not only identifies the floppy disk itself (its density, the type of operating system used), but also stores information about how it is organized by directories, files and subdirectories.

Initiating data track on the CD starts with the slug area required for synchronization between the drive and the disc. Next is the system area, which contains information about the structuring of the disk. The system area also contains directories of this volume with pointers or addresses of other areas of the disk. The essential difference between the structure of a CD and, for example, a floppy disk is that theCD the system area contains the direct address of files in subdirectories, which should make them easier to find.

The physical device of the CD.

The CD consists of from several layers connected in a single, round, thin plate. The vast majority of CDs are 120 mm in diameter, which equals five inches. A standard 5-inch disk contains 640-700 MB of information.

CD - ROM , created industrially, consists of three layers (Fig. 3.19,and). The disc base, made of transparent polycarbonate, occupies the bulk of the disc. When the base is made by stamping or injection molding, an information pattern is applied to it, and as a result, a transparent plastic plate is obtained, smooth on one side, and on the other, containing many microscopic depressions (sometimes called pits, fromenglish pit - deepening), the depth of which is measured from the surface (land ). Next, a reflective metal layer is applied to the base (most often aluminum, although other metals or alloys can also be used), and then a protective coating made of a thin film of polycarbonate or special varnish, on which printing is often placed - various drawings and inscriptions

Figure: 3.19. CD structure ("); surface micrographCD ( 6 )

CD-ROM drive ( CD - ROM ). Reading information from a CD in the same way as writing, takes place using a laser beam, but, of course, less power.

The laser emits coherent light, consisting of synchronized waves of the same length (Fig. 3.20,and). The beam, falling on the reflecting surface, is deflected through the splitting prism to the photodetector, which interprets it as "1", and falling into the depression, it is scattered and absorbed - the photodetector fixes "0".

• Unlike hard drives, whose tracks are concentric circles, a CD has one physical track in the form of a continuous spiral, running from the outside to the inside. Nevertheless, one physical track can be split into several logical ones: each of its 360-degree fragments is considered as a separate track by analogy with magnetic disks.

CD - R . One-time write optical disc type ( Write Once / Read Many storage - WORM ) has been known since the late 1980s.

When writing data toWORM physical marks (marks) are made on the surface of the media with a low-power laser and since these marks cannot be erased, the recording is carried out only once.

If ordinaryCD - ROM is made by mechanical stamping of recesses (brands, "pits"), when recordingCD - R a laser is used to "burn out" the marks in an organic dye. When heated to a critical temperature, the "scorched" area becomes opaque (or absorbing) and reflects less light upon reading than adjacent areas that have not been heated by the laser. This technology mimics the way information is read from a conventionalCD when the light is completely reflected from the surface ("land "), But scattered by a deepening ("pit »).

Unlike technologyWORM , disksCD - R do not allow erasing previously recorded data, however, they allow you to sequentially add them over several sessions (or sessions) to free areas of the disk. The problem is that such multisession discs may not be completely read on earlier versions of players, computers, or when using outdated operating systems.

CD - R disposable without the ability to add

CD + R disposable with the ability to add

CD - RW - rewritable CD ( rewritable CD ). In mid-1997, the standard was proposedCD - RW (known asOrange book iii ), which allows the user to write over old data or delete individual files. SpecificationsCD - RW guarantee compatibility within the CD-ROM drive family as well as compatibility withCD - ROM .

Recording layer placed between dielectric layers, which remove excess heat from it during recording.

As a recording mediumCD - RW usually uses a transparent compound composed of compounds of silver, indium, antimony and tellurium. In the process of recording, a focused laser beam selectively heats up areas of the material above the melting temperature (500-700 ° C), and after a sufficiently rapid cooling, the substance passes into the so-called amorphous state.

Upon erasure, the layer is heated to a temperature that is below the melting point but higher than the crystallization temperature (200 ° C) for a sufficient time, and the atoms return to an ordered (transparent) state.

To obtain these effects in the recording layer, the laser recording deviceCD - RW uses three power levels:

high, so-called "write power", creates opaque (absorbing) areas in the recording layer;

medium ("erase power"), melts a portion of the recording layer and converts it to a reflective (transparent) state;

low ("read power"), does not change the state of the sensitive layer and can be used to read data.

Transparent areas allow the metallized layer to reflect light, while opaque ones absorb it. The problem is that the disc reflects less light thanCD - ROM orCD - R and therefore disksCD - RW can only be read on devices that support the new specificationMultiread (Multi-reading).

Overcoming buffer deficiency. By the end 1999 g. performance doubled to "8x / 24x", however, a problem arose, known as buffer failure (or write buffer emptying), when the speed of the machine and the drive on the MD began to lag behind the speed of the devicesCD - R (the device is ready to write to the disk, but the information in the write buffer has already been exhausted and there is "nothing to write" - as a result, the disk is damaged). To avoid such effects, firstly, they began to use the cache memory located on the writerCD -player (size from 256 Kbytes to 2 Mbytes), and secondly, devices began to adapt to the speed of information feed, reducing or increasing the write speed.

DVD media

Track widthDVD is 0.8 or 0.74 microns, and the minimum pit length is 0.44 or 0.40 microns. To read data intoDVD - The drives use a red laser with a wavelength of 650 nm and an optical system with a numerical aperture of 0.6. Capacity of standardDVD is 4.7 GB (for 80 mm media - 1.4 GB). Unlike CDs,DVD -carriers can be double-sided or double-sided. Double layer capacityDVD is 8.5 GB, double-sided - 9.4 GB. Double-sided discs are actually two identical media glued to each other (the disc must be turned over to read the other side).

Versatile digital disk (digital versatile disc - DVD) is a type of drive that, unlike CD, has been designed for widespread use since its launch on the market.

There are five physical formats (or books) DVD , which differ little from the various "shades" of the CD:

DVD-ROM is a read-only high-capacity storage medium;

DVD-video - digital storage medium for motion pictures;

DVD audio - for audio storage only; a format similar to audioCO;

DVD-R - write once, read many times; format related to CD-R;

DVD-RAM is a rewritable (erasable) version of DVD that first appeared on the market and subsequently found DVD-RW and DVD + RW as competitors. Same size as standard CDs (120mm diameter, 1.2mm thick), DVD discs provide up to 17GB of memory with faster transfer rates than CD-ROMs, CD-ROM-like access times and four versions :

DVD-5 - 4.7GB single-sided, single-layer disc;

DVD-9 - 8.5 GB single sided, dual layer disc;

DVD-10 - 9.4 GB double sided single layer disc;

DVD-18 - Up to 17GB capacity on double-sided, dual-layer disc.

For the first the look of a DVD disc is no different from a CD: a plastic disc with a diameter of 120 mm and a thickness of 1.2 mm, both use lasers to read data written in the depressions on the spiral track. However, the sevenfold increase in data storage capacity of DVDs over CDs was largely achieved by straining all the tolerances of the predecessor system.

Firstly, the tracks are placed more densely, the DVD track pitch (distance between them) is reduced to 0.74 µm, more than 2 times compared to 1.6 µm for CDs.

Secondly, the DVD specification allows information to be read from more than one layer by changing the focus of the reading laser beam.

Third, DVD allows double sided discs.

The DVD format has been associated with compatibility issues from the beginning. Some of them are now allowed, but others, especially the compatibility of rewritable and video options of the disc, remain. Incompatibility with some CD-R and CD-RW drives has been a longstanding problem. The blanks used in some of these devices cannot properly reflect the laser beam used in DVD-ROM readers, which makes them "unreadable". For CD-RW media, this problem was easily solved by the Multi-Reading standard and by bundling the DVD-ROM device with lasers with two different wavelengths. However, getting DVD-ROM drives to reliably read all CD-R media is a much bigger problem. The laser of a DVD reader has difficulty in reading CD-Rs due to a decrease in surface reflectivity in light at 650 nm, while at 780 nm it is almost the same as for CD-ROMs.

Recordable DVD formats There are five versions of recordable DVDs:

DVD-R normal;

DVD-RAM (rewritable);

DVD-RW;

DVD + RW.

All recordable DVD formats include a set of specifications that define the physical characteristics of the recording media. This level of performance is the “physical layer of the medium,” and the ability to read a disc on a particular player or disk drive depends on its ability to support the appropriate physical layer regardless of what data is recorded.

CD-ROM drives allow you to work only with media belonging to the groupCD. DVD drives allow you to work with bothDVD and CD media. The optical disc classification is shown below:

Each of the media groups can be divided into three main types of disks:

1. read-only disks (CD-ROM, DVD-ROM);

2. write-once discs (CD-R, DVD-R, DVD + R, DVD-RDL, DVD + RDL);

3. rewritable discs (CD-RW, DVD-RW, DVD + RW, DVD-RAM).

Differences between formats

DVD + R / RW Devices in no way inferior to drivesDVD-R / RW , and thanks to some improvements, they can surpass their competitors in speed and reliability. For example, the write speed of drivesDVD + RW higher than most devicesDVD-RW ... Some discsDVD-R are recorded at a speed close to the speedsDVD + R , and with the appearance of modelsDVD-RW the performance gap has narrowed even more.
Another difference between the "-" and "+" technologies is the way the disks are rotated in the drives. Storage devicesCD, DVD-ROM and DVD-RW are constant line rate devices that provide a constant transfer rate when reading discs. In these drives, disks spin slower when reading information from longer external tracks.

Varieties of optical drives

Depending on the functions available, optical drives can be divided into several main types.

1. CD- ROM - drives that allow reading information from media belonging to the CD group.

2. DVD- ROM - drives that allow reading information from different typesCD and DVD media.

3. CD- RW - drives that allow reading information from optical discs belonging to a group of compact discs, as well as recording toCD-R and CD-RW.

4. DVD- ROM/ CD- RW - the so-called combined drives, which allow reading information from different typesCD and DVD - carriers, as well as record onCD-R and CD-RW.

5. DVD- RW, DVD+ RW, DVD± RW - universal recording drives that allow reading information from different typesCD and DVD carriers, as well as record onCD-R, CD-RW writable and rewritableDVD (set of supportedDVD - carriers depends on the specific model).

To measure the speed characteristics of optical drives, conventional units are used, and they differ forCD and DVD formats. As the reference point (1x) for the media of the CD group, a read speed of 150 KB / s was chosen. Therefore, 8x forCD the drive corresponds to a baud rate of 1200 Kb / s, 12x - 1800 Kb / s, etc.

In case of DVD devices, the single speed is already equal to 1350 KB / s. So 4x forDVD media corresponds to a speed of 5400 KB / s - which is equivalent to 36x on a scaleCD .

In the characteristics of drives that support reading and / or writing different types of optical drives, usually the maximum speed for each of them is indicated. Short designationthe speed characteristics of the media are called the speed formula. For example, in the case of a driveDVD - ROM speed formula 8/52 means maximum read speed equivalent to 52x forCD and 8x forDVD ... For driveCD - RW speed formula 32/24/48 means the maximum write speed onCD - R andCD - RW respectively 32x and 24x and maximum speed reading 48x.

TechnologyLightScribe

One of the most interesting technological innovations of 2005 in the field of recordable optical discs was the technologyLightScribe ... It allows you to apply high quality monochrome images to the decorative surface of discs directly in the recorder.

The principle behind the technologyLightScribe is pretty simple. As you know, under the influence of a laser beam, the active layer of recordable discs loses its transparency. By illuminating some parts of the working layer with a laser and leaving others untouched, a monochrome image can be formed using a recording drive.

At the beginning of 2004 the companyHP announced the creation of an improved direct disc labeling system (DirectDiscLabelingSystem ), which later received the commercial nameLightScribe ... This technology was developed by specialistsMitsubishiKagakuMedia (MKM) and HP ... Unlike other technology -[email protected], LightScribe provides for the application of images not on the working layer of the disc, but on the reverse side - where the label is usually located (of course, recordable discs must be equipped with an additional photosensitive layer for this).

To take advantage of technologyLightScribe , you need to have three components:LightScribe -compatible recording drive, media with an additional photosensitive layer and special software. In this case, after the end of recording information, the user can turn the disc over and use the recording drive to apply an image to its decorative surface.

Of course, the implementation of additional features will entail a slight increase in the prices of recording drives and blank media. True, according toHP , implementation of supportLightScribe will increase the cost of the recording drive by about $ 10. As for the carriersLightScribe , their production is understandably more expensive compared to conventional recordable discs, but the price difference will also be negligible.

In 2005 HP signed agreements to license the use of this technology to some of the major recorder manufacturers (in particular,LG, Toshiba, Philips and Lite-On (Sony)).

High density optical media

Improving the capabilities of media systems and, as a result, the need for high quality data (video and audio) led to the fact that this kind of information has become cramped on the standardDVD ... New formats have been and are being developed by various companies, but two standards have matured for commercial use.

1. Blu- rayDisc (from English blueray - "blue ray", abbreviatedBD ) is a new generation of high-density optical drives, developed by a consortium of companies led bySony ... This standard has no roots in common withDVD ... The recording density per layer is 25 GB.

Note

When choosing a name for the new standard, the developers had to distort the word blueas, if spelled correctly, it could not be used to register a trademark.

2. HDDVD ( High- DefinitionDVD) is a new generation format developed byToshiba and NEC versus Blu-ray. HDDVD recognized as an evolutionary development of the standardDVD ... The recording density of discs of this format is 15 GB per layer.

Until the end of 2007, it was not clear which standard would dominate the industry. However, the beginning of 2008 has dotted all "i ". Toshiba announced that it was abandoning the project in favor of building factories for the production of flash memory, which it considers more promising.

As for Blu-ray , then it did not become popular and widespread overnight. As it turned out, positionsDVD are still strong, and consumers are in no hurry to switch to the new format. The high cost of the devices themselves also hinders the rapid spread of the "blue ray". In light of the global economic turmoil, it is still unclear how the price dynamics for this type of device will develop in 2010. DiscsBlu-ray retained the same dimensions as their predecessorsCD and DVD : 120 and 80 mm. Due to the technological features of the coating, they were initially very sensitive to various kinds of mechanical stress. The developers of the prototypes even thought about protecting the media with a special cartridge. In the future, such a nuance would clearly not be in favor of the new standard. Therefore, engineering minds were still able to solve this problem. A new polymer coating has been found that can protect data from external influences. According to some sources, new discs may remain functional even when scratched with a screwdriver. It should be noted that these impressive capabilities have resulted in higher production costs for these media.

Blu-ray technology a blue-violet laser with a wavelength of 405 nm is used for reading and writing. Recall that the usualDVD and CD use red and infrared lasers with wavelengths of 650 and 780 nm, respectively. This reduction made it possible to narrow the track in half compared to the usualDVD - up to 0.32 microns - and increase the data recording density.

Base speed 1x forBD is 36 864 kbps, which is 27 times more thanDVD , and is 243 times greater thanCD ... Players with double the data transfer rate are capable of surpassing 73,000 Kbps.

Volume is an important characteristic of new media. Initial compatibilityBD with disks of previous generations, the standard is not provided, but the associationBDA recommends all manufacturers to implement supportDVD for backward compatibility.

Versions of disks with a capacity of 100 GB and higher are under development.

Latest generation of optical discs

Holographic multi-purpose disc (HolographicVersatileDisc) - a promising technology for the production of optical discs, which implies a significant increase in the amount of data stored on the disc compared to and.

She uses a technology known as which uses two : one - red, and the second - green, combined into one parallel beam. laser reads data encoded in a grid with layer close to the disk surface, while the laser is used to read auxiliary signals from a conventional CD layer deep inside the disc. Ancillary information is used to track the reading position like a system in a regular hard drive.On or this information is embedded in the data.

External memory

Optical discs

Optical (laser) discs are currently the most popular storage media. They use the optical principle of recording and reading information using a laser beam.

Information on a laser disc is recorded on one spiral track starting from the center of the disc and containing alternating areas of depressions and protrusions with different reflectivity.

When reading information from optical discs, the laser beam installed in the drive hits the surface of the rotating disc and is reflected. Since the surface of the optical disk has areas with different reflectances, the reflected beam also changes its intensity (logical 0 or 1). The reflected light pulses are then converted by photocells into electrical pulses.

In the process of recording information on optical discs, various technologies are used: from simple stamping to changing the reflectivity of areas of the disc surface using a powerful laser.

There are two types of optical discs:

CD-disks (CD - Compact Disk, compact disk), which can store up to 700 MB of information;

DVD-disks (DVD - Digital Versatile Disk, digital versatile disk), which have a significantly higher information capacity (4.7 GB), since the optical tracks on them are thinner and more densely packed.
DVDs can be dual-layer (8.5 GB), with both layers having a reflective surface that carries information.
In addition, the information capacity of DVDs can be doubled further (up to 17 GB), since information can be recorded on both sides.

Currently (2006), optical discs (HP DVD and Blu-Ray) have entered the market, the information capacity of which is 3-5 times higher than that of DVD discs due to the use of a blue laser with a wavelength of 405 nanometers.

There are three types of optical disk drives:

• Without recording capability - CD-ROM and DVD-ROM
  (ROM - Read Only Memory, read-only memory).
  CD-ROMs and DVD-ROMs contain information that was recorded on them during the manufacturing process. Writing new information to them is impossible.
• Write once and read many times -
  CD-R and DVD ± R (R - recordable).
  Information can be recorded on CD-R and DVD ± R discs, but only once. The data is written to the disc by a high-power laser beam, which destroys the organic dye of the recording layer and changes its reflective properties. By controlling the laser power, an alternation of dark and light spots is obtained on the recording layer, which, when read, are interpreted as logical 0 and 1.
• Rewritable - CD-RW and DVD ± RW
  (RW stands for Rewritable) CD-RW and DVD ± RW discs can be written and erased multiple times.
  The recording layer is made of a special alloy, which can be heated by heating into two different stable states of aggregation, which are characterized by different degrees of transparency. When writing (erasing), the laser beam heats up a section of the track and transfers it to one of these states.
  When reading, the laser beam has a lower power and does not change the state of the recording layer, and alternating sections with different transparency are interpreted as logical 0 and 1.

Key features of optical drives:

disk capacity (CD - up to 700 MB, DVD - up to 17 GB)

the speed of data transfer from the carrier to the RAM - measured in fractions multiples of the speed
150 Kbytes / sec for CD drives (This is the speed of information reading that the first CD drives had) and
1.3 MB / s for DVD drives (This is the speed of reading information that the first DVD drives had)

Currently, 52x-speed CD-drives are widely used - up to 7.8 MB / sec.
CD-RW discs are burned at a lower speed (for example, 32x).
Therefore, CD-drives are marked with three numbers "read speed X write speed CD-R X write speed CD-RW" (for example, "52x52x32").
DVD drives are also labeled with three numbers (for example, "16x8x6"

access time - the time required to search for information on the disc, measured in milliseconds (for CD 80-400ms).

Subject to the rules of storage (storage in cases in an upright position) and operation (without causing scratches and dirt), optical media can store information for tens of years.

Additional information on disk layout

An industrially produced disc consists of three layers. An information pattern is applied to the base of the disc made of transparent plastic by stamping. For stamping, there is a special matrix prototype of the future disk, which squeezes the tracks onto the surface. Next, a reflective metal layer is sprayed onto the base, and then a protective layer of a thin film or special varnish is also on top. Various drawings and inscriptions are often applied to this layer. Information is read from the working side of the disk through a transparent base.

Recordable and rewritable CDs have an additional layer. In such discs, the base does not have an information pattern, but a recording layer is located between the base and the reflective layer, which can change under the influence of high temperature. During recording, the laser heats up the specified areas of the recording layer, creating an information pattern.

A DVD disc can have two recording layers. If one of them is performed using standard technology, the other is translucent, applied below the first and has a transparency of about 40%. Complex optical heads with variable focal length are used for reading double-layer discs. The laser beam, passing through the semitransparent layer, first focuses on the inner information layer, and upon completion of its reading it refocuses onto the outer layer.

Optical disc recovery

1. Research part

1.1 Some moments of history

All the things we use in our everyday life have their own fascinating history. The optical disc, familiar to us, appeared in 1958. For a long time, defining the development of optical storage media such as CDs, DVDs and more recently and Blu-ray disc format. First, the optical disc was used for video recordings. Over time, a disc was invented, which began to be used as a carrier for music files.

Despite the fact that the first CD format discs went on sale back in 1982, they are still used to record music files. The DVD format is actively used to record movies.

1.2 Types of optical discs

On disks CD-R (they are sometimes also called "blanks") you can write down your information, but it will be impossible to erase or change it. If there is free space on the disk and you enabled the option to add information during recording, you can add files to the disk.

Discs CD-RW support erasing and rewriting information, but such discs will not be read by all drives. Recording and reading of disc information is carried out using a laser. CD thickness - 1.2 mm, diameter - 120 mm, capacity - 650 or 700 MB (corresponds to 74 or 80 minutes of sound).

DVD discs allow you to store more information than CDs, thanks to the use of a laser with a shorter wavelength. The capacity of a standard size DVD (120mm) can range from 4.7GB to 17GB, while a mini DVD (80mm) can range from 1.6GB.

Depending on the capacity of the DVD, the following types of discs are distinguished:

· DVD-5 - single layer single sided disc, capacity - 4.7 GB

· DVD-9 - double layer single sided disc, capacity - 8.5 GB

· DVD-10 - single layer double-sided disc, capacity - 9.4 GB

· DVD-14 - double-sided disc, double layer on one side and single layer on the other, capacity - 13.24 GB

· DVD-18 - double-layer double-sided disc, capacity - 17.1 GB

As far as possible recording, rewriting and erasing information, DVD discs, like CDs, are divided into ROM, R and RW. But in addition, such types of disks are distinguished:

· DVD-R for general, DVD-R (G) - once-writable disc intended for home use.

· DVD-R for authoring, DVD-R (A) - once-recordable disc for professional purposes.

· DVD-RW - rewritable disc. You can overwrite or erase information up to 1000 times. But you cannot erase some of the information, you can only erase the disc completely and completely overwrite it.

· DVD-RAM use phase change technology. They can be rewritten up to 100,000 times, with a theoretical lifespan of up to 30 years. But they are expensive, come mostly in special cartridges, and are not supported by most drives and turntables.

· DVD + RW are based on CD-RW technology and support rewriting information up to 1000 times. This format appeared later than DVD-RW.

DVD + R - once-recordable disc, similar to DVD-R.

HD DVD (High Density DVD) discs can have capacities up to 15 GB, and dual-layer ones up to 30 GB. Their main competitor is BD, Blu-ray Disc holds from 23 to 66 GB depending on the number of layers. A prototype of a four-layer 100 GB disc has been announced, and 10-layer discs up to 320 GB are also planned.

.3 Optical disc structure

By its structure, a CD-R disc resembles a layer cake, the "filling" of which consists of active, reflective and protective layers, which are sequentially applied to a polycarbonate base - a plastic circle with a hole for fixing on the spindle of the reading drive. At the same time, the base of the CD-R disc is no different from that used in the technology of making compact discs by casting: the characteristics of the plastic must be such that the laser beam passing through it is properly focused and does not cause destruction of the disc.

The active (or recording) layer is the layer on which, in fact, the information is recorded, i.e. it is he who is exposed to the laser beam, which "burns" (pits), encoding information (logical zeros and ones). In other words, during recording, the active layer under the influence of a laser beam changes its structure, and the subsequent irreversibility of the change in the active layer is the essence of the reliability of information storage. One of the types of active layers widely used today is cyanine. Cyanine is the original type referenced by the Orange Book standard and is widely used.

1.4 Recordable discs (CD- RW)

The difference between such discs and CD-Rs lies in the structure of the recording layer. The intermediate layer of special organic material can be either amorphous or crystalline. Amorphous substances tend to crystallize over time. No matter how we store the CD-RW, in a few years the recording will be irretrievably lost. In addition, such discs can be easily wiped off by simple heating.

DVD disc structure

The principle of recording a DVD is not very different from the principle of recording a CD. The basis for recording and storing data on DVD-RAM and DVD-RW disks is the technology of changing the phase state of matter. The layered structure of one half of the disc is shown in the figure.

How to burn a DVD

The recording of amorphous areas is shown in this graph. A short, high power laser pulse melts the recording material. This is followed by cooling below the crystallization temperature. The result of cooling is to prevent the formation of crystallization centers. Thus, the growth of the crystalline phase does not occur, and the substance remains in an amorphous state.

.5 Erase fromDVD-disk

To erase, it is necessary to return the substance to the crystalline state. Again, with the help of a laser, the amorphous substance is heated to a temperature T. Heating (more precisely, annealing) continues for a time sufficient to restore the crystalline state of the substance. This time must be longer than the so-called crystallization time.

.6 Advantages of Optical Discs

The advantages of optical discs include: relatively large volume, ease of use, prevalence, low cost, resistance to magnetic influences.

1.7 Disadvantages of optical discs

The disadvantages, perhaps, can be attributed - not resistance to mechanical damage (scratches, ultraviolet light, temperature ...).

1.8 Difficulties in device design

The main device problems that need to be addressed are:

Select suitable power motors

When rubbing, the plastic clogs the pores of the sponge; to avoid this, you need to moisten the sponge with water.

1.9 Alternative

The Sanwa Supply company will offer a very peculiar functionality innovation called CD-RE1AT.

This miracle of technology restores damaged optical discs, as it is able to apply a special protective layer on their surface that fills in scratches. Externally, the product is similar in weight to a conventional portable CD / DVD player with a hinged top cover, under which there are two slots for accommodating the supplied two recovery and two cleaning heads. The cost of this disc reducer in Japan is about 50 euros. Nothing is known about the sale of such devices in Kazakhstan.

2. Experimental part

.1 Calculations for the demo model

The principle of operation of the device is to smooth out scratches and clean an optical disc. I used two electric motors, one rotating disc, the second rubbing, a sponge, parts from the DVD, lower pulley, rubber cambric, goy paste, an empty can of discs, rubber glue, solvent, a power supply from the phone.

Carved a sponge in the form of a cylinder

Goi paste dissolved in a solvent

The resulting dried cylinder from a sponge soaked in a solution of goy's paste I glued to the lower pulley for mounting the disc.

I cut out the disc cover in the form of a disc, cutting out the upper part.

I screwed the electric motor from the edge by 3 centimeters and put a pulley with a sponge on the rotor of the electric motor.

To the bottom of the box, I screwed a second motor onto the rotor, which was put on a thick rubber cambric so that the disc on the finger rotated.

Since this is just a demo model, I used two 12 volt motors from the DVD, one spinning disc, the second grinding, motor rpm (250 rpm) and power (0.1A).

I connected two electric motors in parallel to the power supply from the phone.

3. Diagram-drawing of a working device for disk recovery

.1 Manufacturing and assembly of a disc cleaner

I took a 15x15 corner on the frame of the device

To rotate the disc

1. I took the electric motor from the breeze of the heater 220 (v) 0.7 (w)

2. Two pulleys from the tape recorder

Hub with bearings from the radio

Belt from the tape recorder.

Details from DVD for disk mounting.

To clean the disc

6. I took the second electric motor from the 12 (v) 2 (a) screwdriver.

7. The pulley from the tape recorder is small.

Paste GOI

Rubber glue,

Solvent

Power supply unit from a tape recorder.

.2 Practical work on making a model

1) First, the corners were cut by 15x15x300

2) An electric motor was welded onto the corners to rotate the disk, a pulley from a tape recorder was put on the rotor of the electric motor.

A pulley from a tape recorder was glued to the hub with bearings from the radio, and parts from the DVD were glued to the pulley to mount the disk.

Holes were drilled into the metal plate to hold the sleeve.

The plate was welded to the frame by welding, so that the belt was taut.

Checking in the case, mounting the disc and what speed the disc is gaining.

Holes were drilled in the plate for attaching the second electric motor to 12 (v) 2 (a), a small pulley from the tape recorder was put on the rotor of the electric motor and a sponge in the form of a cylinder was glued with a mixture of goy paste.

Angles 15x15x150 2 pieces were welded to the frame by welding vertically.

A plate was welded to the corners by welding horizontally, two holes were drilled for mounting the motor.

In the plate on which the electric motor is screwed, oval holes were cut to adjust on the surface of the dick, and to remove the electric motor to replace the sponge with a mixture of goy paste.

To give a look, they were sheathed with plywood and painted around the frame.

9. The power supply was made of plywood, a 12 volt transformer with a diode bridge is screwed into the box inside. From the outside, two sockets are screwed on one 12 volts goes out to the second 220 volts and a common switch for turning off - turning on the power.

Conclusion

Recovering data from an optical disc is a reality thanks to special programs. The fact is that the operating system, if it cannot correctly read information from some part of the disk, immediately interrupts copying and completely deletes the already copied part of the data. Special programs that use mechanisms for reading disks and make it possible to copy the necessary files help to bypass this function (they do not guarantee 100% recovery of all information from a damaged disk).

These programs read information from damaged disks by directly accessing them. At the same time, bypassing standard Windows OS tools. The utilities repeatedly try to read the damaged sector of the disk, and at the same time, if read errors occur, they can continue copying (or reading) information, which makes it possible to "pull" lost files from the disks in their original form. If some sectors are unreadable, some programs simply replace them with zeros, which in turn leads to a defect in the file.

Recovering data from an optical disc is not an easy and time-consuming process, often taking a long time. In practice, not all files recovered in this way will be usable. For example, if a couple of paragraphs disappear in a text document, then this is much better than all the text that you wrote for a whole month disappears.

With music and video, everything can also be quite decent - it is unpleasant, of course, if at some point while listening to your favorite song or watching a video plot you see incomprehensible squares on the screen, or you hear some kind of incomprehensible sound, but again, this much better than losing your favorite materials altogether.

To restore the physical part of the plane of the disc, our optical disc cleaner will help.

List of references

optical disc laser recovery

1.http: //strana-sovetov.com/computers - types of disks.

2.http: //ergosolo.ru/reviews/gadgets/ - smart gadgets.

Http://www.datars.ru/recovery/optics-disc/ - disk recovery

It's no secret that the story began with gramophone records... Storing information at home is problematic, and only sound was stored on it. The principle of operation is not a secret, so vinyl record was popular for over a hundred years, and collectors and DJs still use and store them. It was fun to watch how the needle, while scrolling the disc, walked around like a perfectly flat spiral. On this, the principle of obtaining sound was built. With a change in the depth and width of the groove, the sound wave changed and was further strengthened by a pipe (gramophones, gramophones). With the development of electronics, the principle of information retrieval was made on a piezoelectric needle and received a modern, until recently, turntable.

The 70s have come. And there was a jump in storage media (we will skip magnetic tapes). They invented a disc made of transparent polycarbonate with an aluminum coating. Polycarbonate served as a base and protected the spraying from external influences, and depressions were burned in the spraying in a spiral. The principle of removing and recording information is based on this, as you can see, not far from the gramophone record. A thin beam was reflected from the deposition surface and came to the light detector, which in turn determined the changes and, relative to the information received, ones and zeros were created. And then, according to the principle of the alphabet Morse information is converted into music, movies, photos, files, etc.

Now let's understand the notation for CDs:

But with DVD disks, everything turned out much more complicated. This disk was created to store information in a large volume and a large number of companies were engaged in the development (DVD-R and DVD-RW)... Different spraying had different characteristics and household players, of different companies, began to conflict with discs, hence the universality was lost. Therefore, having united, they invented a new type of disk, called DVD + R and DVD + RW, they cost, oddly enough, cheaper. Now it makes no difference which disc to use, as home turntables have been adapted. The only difference is in rewritable discs, DVD-RW must be completely erased before recording, and DVD + R it is enough to erase the "header" and overlay the recording on top.

As the saying goes, don't give us much, but it's not enough for us. Therefore, progress did not stop there, double-sided and two-layer and two in one discs. Well with bilateral, everything is simple, the spraying was applied on both sides, and like an audio cassette you need to turn the disc over. Double layer - this is one of the layers closest to the laser, made translucent, and you do not need to get up from the sofa to turn the disc. Well, with the last option, take two two-layer and glue together.

So we have reached the peak of the development of the modern world of the optical disc, this is - HD-DVD and Blu-ray.
HD-DVD - this is a disc that was made on the basis of our laborer described above, but using a blue laser.
Blu-ray - a completely different development, a blue laser is used.

If we recall the spectrum (rainbow), it will be seen that from the blue ray, you can get a much thinner ray, so these disks are much more voluminous. But this will be discussed in the next topic.

It seems, for today, everything. It remains only to tell a little about storage and use of the disk. A disc is not tasty, you don't need to gnaw it, well, if only someone has a lack of plastic in the body. And also this is not a tool for playing on the nerves, so you do not need to drive your claws on it. It is advisable not to bend, although it is difficult to break, but the fragments can go where they should not, and this will affect your body. Also, the constant bend breaks the deposition inside, it cracks and the zeros of one will no longer match for you. Do not fry him in the sun, he has an element D is not needed at all, but turn into a sic-like product and you will not shove it anywhere. Do not insert a disc with a crack into the drive, otherwise you will have to spend either on repairs or on buying a new one.

I hope YOU literate and you do not need to list everything point by point, things need to be treated with care and they YOU they will be thanked for this.

Optical disc

Optical disc

a data carrier in the form of a plastic disc, intended for recording and reproducing sound (CD-ROM), images (video disc), alphanumeric information (CD-ROM, DVD), etc. using a laser beam. The first optical discs appeared in 1979. Philips created them for recording and reproducing sound. An optical disc consists of a rigid, optically transparent base, on which a thin working layer and an additional protective layer are applied. Thanks to the optical reading method, optical discs are much more durable than phonograph records. A standard CD has a diameter of 120 mm (4.5 inches), a thickness of 1.2 mm, and a center hole of 15 mm. CD-disks are made of very durable transparent plastic - polycarbonate or polyvinyl chloride. The label is placed on one side of the disc and the other side has a rainbow-colored mirror surface. This is the recording area, the spiral track of which consists of pits - grooves of various lengths. The distance between two adjacent tracks of the spiral is 1.6 microns, that is, the recording density is 100 times greater than that of a conventional gramophone record. The pits are 0.6–0.8 µm in width and variable in length. It reflects the length of sequences “1” of the recorded digital signal and can vary from 0.9 to 3.3 µm. Information in the form of pits is protected from mechanical damage on one side by a transparent disc material, and on the other - by a layer of plastic and a label. Compared to mechanical sound recording, it has a number of advantages: very high recording density and complete absence of mechanical contact between the medium and the reader during recording and playback. Music CDs are recorded at the factory. Like gramophone records, you can only listen to them. Using a laser beam, the signals are digitally coded onto a rotating optical disc. As a result of recording, a spiral track is formed on the disc, consisting of miniature pits and smooth sections. In the reproduction mode, a laser beam focused on a track moves over the surface of the rotating optical disc and reads the recorded information. In this case, the valleys are read as ones, and the areas that are evenly reflecting light are read as zeros.

Contactless reading of information from a CD is carried out using an optical head or laser pickup. The optical head consists of a semiconductor laser, an optical system and a photodetector that converts the light into an electrical one. The readout laser beam is focused on a spiral track with pits deep in the disc. The head never touches the disc - it is always at a strictly defined distance from it, ensuring that the track of the pits is in the focus of the optical system.

Multimedia technology allows you to combine text and graphics with sound and motion pictures on a personal computer. These multimedia computers use optical CD-ROMs (Compact Disk Read Only Memory - that is, read-only CD-ROM) as storage media. Outwardly, they do not differ from the audio CDs used in players and music centers.

The capacity of one CD-ROM reaches 650 MB, in terms of capacity it occupies an intermediate position between floppy disks and a hard magnetic disk (hard drive). A CD drive is used to read CDs. Information on a CD is recorded only once in an industrial environment, and on a personal computer it can only be read. A variety of games, encyclopedias, art albums, maps, atlases, dictionaries and reference books are published on CD-ROM. All of them are equipped with convenient search engines that allow you to quickly find the material you need. The memory capacity of two CD-ROMs is enough to accommodate an encyclopedia larger than the Great Soviet Encyclopedia.

Informational optical CD-disks are intended for one-time (so-called CD-R) and multiple (so-called CD-RW) recording of information on a personal computer equipped with a special drive. This makes it possible, like a tape recorder, to record on them at home. On CD-R discs, you can record only once, and on CD-RW discs - repeatedly, like on a magnetic disk or tape, you can erase the previous record and make a new one in its place.

1 - CD_disk; 2 - a translucent coating that protects the information on the CD from damage; 3 - reflective coating (the actual recording medium); 4 - protective layer; 5 - focusing; 6 - laser beam; 7 - optical splitter; 8 - photodetector; nine - ; 10 - electric motor rotating the disk

The existing compact discs are being replaced by a new media standard - DVD (Digital Versatilе Disc or general purpose digital disc). They look no different from CDs. Their geometrical dimensions are the same. The main difference between a DVD is that it is dozens of times higher data recording density. This is achieved due to the shorter laser wavelength and smaller spot size of the focused beam, which made it possible to halve the distance between the tracks. The DVD standard is defined in such a way that future models of readers will be developed taking into account the playability of all previous generations of CDs, that is, observing the principle of "backward compatibility". In 1995 Philips developed a re-recording CD technology. The DVD standard can significantly increase the time and improve the quality of video playback compared to existing CD-ROMs. DVD drives are advanced CD-ROM drives.

Encyclopedia "Technics". - M .: Rosman. 2006 .

See what an "optical disc" is in other dictionaries:

A data carrier in the form of a plastic or aluminum disk intended for recording and / or reproducing sound (compact disc), image (video disc), alphanumeric information, etc. using a laser beam. Recording density of St. 108 ... ... Big Encyclopedic Dictionary

optical disc - A disc containing digital data readable using optical technology. [GOST 25868 91] Equipment topics periphery. processing systems information EN optical disk ...

OPTICAL DISC, in computing, a compact storage device consisting of a disk on which information is recorded and read using a laser. The most common type is CD ROM. Audio CDs also represent ... ... Scientific and technical encyclopedic dictionary

Working with optical discs Optical disc Optical disc image, ISO image Optical drive emulator Software for working with file systems of optical discs Recording technologies Recording modes Batch recording Types ... ... Wikipedia

Data carrier in the form of a disc made of transparent material (glass, plastic, etc.) with metallisers. microscopy, depressions (pits), which together form spiral or circular ... ... Big Encyclopedic Polytechnic Dictionary

A data carrier intended for recording and / or reproducing information using focused laser radiation. Consists of a rigid (usually optically transparent) base on which a light-sensitive or reflective layer is applied and ... ... encyclopedic Dictionary

optical disc - 147 optical disc: A disc containing digital data readable using optical technology Source: GOST 25868 91: Peripheral equipment for information processing systems. Terms and Definitions … Dictionary-reference book of terms of normative and technical documentation

OPTICAL DISC - according to GOST 25868-91, “Peripheral equipment for information processing systems. Terms and definitions ", - a disc containing digital data readable using optical technology ... Records management and archiving in terms and definitions

A data carrier intended for recording and / or reproducing information using focused laser radiation. It consists of a rigid (usually optically transparent) base, a photosensitive or reflective layer is applied to it and ... ... Natural science. encyclopedic Dictionary

blue laser optical disc - Blu Ray Discs (BDs) are the next generation storage media for storing high definition video (HDTV) and high density data. The Blu Ray standard was jointly developed by a group of consumer electronics and computer companies. Technical translator's guide

Books

• Methods for the development of social, emotional and practical intelligence of a young athlete + CD, Kuzmenko Galina. The textbook presents the content side of the manifestation of the psychological and pedagogical skill of the trainer in the development of social and emotional intelligence in the system of significant qualities ...