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Characteristics of optical media. Recovering optical discs What is an optical disc

A variety of data processing and storage facilities have become part of our life. In the distant past, there are printed paper archives. What are modern storage media?

Optical disc: history of creation

The first device for storing audio recordings was produced by Sony back in 1979. It was, as now, a plastic disc with a round hole in the center. Initially, it was used only for recording audio files, and information was applied to it using a special coding method, Pulse Code Modulation. It consists in the fact that text or sound passes through an analog-to-digital converter and turns into a set of bits.

Later, in 1982, mass production of discs began in Germany. They began to be bought for storing various files. Soon they hit the shelves of not only music stores.

How does a CD work? For the manufacture of the base, a 1.2 mm thick polycarbonate plate with a diameter of 120 mm is used, which is first covered with a thin layer of metal (gold, aluminum, silver, etc.), and then varnish. It is on the metal that information is applied in the form of pits (depressions) squeezed out along a spiral path. Files recorded on an optical disc are read using a laser beam with a wavelength of 780 nm. It reflects off the surface of the plate, changes phase and intensity, hitting the pits. It is customary to call a land the intervals between pits. The pitch of one track in the spiral is about 1.6 μm.

Optical disc types

There are several types of Digital Versatile Disc (DVD), Blu-ray Disc (BD). They all have different capacities for recording information. For example, DVDs are produced in capacities ranging from 4.3 to 15.9 GB, and CDs only up to 900 MB.

Also, discs are distinguished by the frequency of recording: single and multiple. In such carriers, the relief structure of pits is formed in different ways. Dubbing is possible thanks to organic material, which darkens under the action of the laser and changes the reflectance. In common parlance, this process is called burning.

Optical media can also differ in shape. Shaped CDs are usually used in show business as custodians of audio and video files. They are of arbitrary shape (square, in the form of an airplane or a heart). We do not recommend using them in CD-ROM drives because they can break at high rotational speeds.

CD-disks and their types

An optical CD-R disc is a read-only media. You can write files to it only once without the right to add and edit. Initially, the capacity of such discs reached only 650 MB or 74 minutes of audio recording. Now devices are produced that can contain up to 900 MB of information. Their advantages are that all standard CDs support reading.

The same amount of memory is possessed by a laser disc CD-RW, only files on it can be written repeatedly (up to 1000 times). For this, standard computer programs are used. The downside is that not all devices are ready to work with this format. CD-RWs are slightly more expensive than CD-Rs.

Audio and video CDs are not protected at all and can be copied and played. But carriers with certain data are protected from copying by StarForce technology.

ROM format discs are recorded at the factory and can only reproduce data. Such media cannot be edited. But optical devices such as RAM can be rewritten up to 10 thousand times and they serve up to 30 years. Such discs are produced in additional cartridges, their reading is not supported by conventional drives.

DVD media and their characteristics

The Digital Versatile Disc is a digital multipurpose storage medium. Its structure is denser and contains a lot of information (up to 15 GB). Such an optical disc resembles two CDs glued together. Storing and reading a large amount of information is possible thanks to the use of a red laser, which is 650 nm, and lenses with a maximum numerical aperture. DVDs have one or two recording sides and one or two scratch layers on each side. These indicators determine their capacity.

As well as are classified into several formats. DVD-R or DVD + R are media that can only be recorded once. The recording standard for such discs was developed by Pioneer in 1997. "Minus" and "plus" devices differ in the material of the reflecting layer and special markings.

Optical discs DVD RW (DVD + RW, DVD-RW) are rewritable. Moreover, the "positive" media allows you to make changes to the necessary places at your discretion. Universal drives help solve the problem of format incompatibility (+ RW and -RW).

What is Blu-ray Disc?

This type of optical disc allows high density digital data to be stored and recorded. To reproduce information (even high definition video), a 405 nm blue laser beam is used, which narrows the spiral path in half. Files that are very close to each other are susceptible to mechanical damage, so special care must be taken for the disc. Recently, carriers have been produced with a special coating that can be wiped off with an ordinary dry cloth.

There are disposable and reusable Blu-ray discs, as well as multilayer (2 to 4 layers). The capacity of the most "layered" media reaches 128 GB. However, it has a standard 12-centimeter diameter. A dual layer standard Blu-ray disc can hold up to 50GB of content. There is a device under development with a capacity of 300-400 GB, which can be read by modern floppy drives. For camcorders, discs of a smaller diameter (80 mm) with a memory capacity of up to 15 GB are used.

For copy protection, Blu-ray is equipped with ROM-Mark digital watermark and Mandatory Managed Copy technology.

Purpose of MiniDVD Media

Optical media Mini DVD is a reduced copy of a conventional Digital Versatile Disc. It is 8 cm in diameter and is used in photo and video cameras. A single-sided disk holds up to 1.4 GB of information, respectively, a double-sided one - 2.8 GB. In terms of format, they are MiniDVD-R (write once) and MiniDVD-RW (multiple).

The standard 12cm drive is not designed to read Mini DVDs. When using such drives in a laptop, the drive motor spindle should be used. Sometimes there are problems with reading. Usually, in such cases, the computer displays the message "no driver found for the optical disc drive." To solve the problem, you should contact an experienced programmer.

The speed and reliability of modern recorders will be the envy of any Formula 1 car. ComputerBild explains how data gets to CDs, DVDs, and Blu-ray Discs.

Recording music and films on optical media is a familiar process, like using magnetic cassettes twenty years ago, only it is much cheaper. What is the difference between the types of media and how is information recorded on them?

Stamping and Burning

In the industrial production of discs with music, films or games, data is written to a medium by stamping - a process similar to making gramophone records. The information on the discs is stored in tiny indentations. Computer and consumer DVD recorders perform this task differently - they use a laser beam.

The first recordable optical media were write-once CD-Rs. When storing data on such discs, the laser beam heats the working layer of the blank, consisting of dye, to about 250 ° C, which causes a chemical reaction. Dark opaque spots are formed at the place of laser heating. This is where the word "burn" comes from.

Similarly, data is transferred to a write-once DVD. However, no dark specks form on the surface of rewritable CDs, DVDs and Blu-ray discs. The working layer of these accumulators is not a dye, but a special alloy. When heated by a laser to about 600 ° C, it passes from a crystalline state to an amorphous one. The areas exposed to the laser are darker in color and therefore have other reflective properties.

Information carriers

Home discs are the same thickness (1.2 mm) and the same diameter (12 or 8 cm) as industrially recorded discs. Optical media have a multilayer structure.

Substrate. The base for the discs, which is made of polycarbonate, is a transparent, colorless and fairly resistant to external influences polymer material.

Working layer. For recordable CDs and DVDs, it consists of an organic dye, while for rewritable CDs, DVDs (RW, RAM) and Blu-ray discs, it is formed by a special alloy capable of changing the phase state. The working layer is surrounded on both sides by an insulating substance.

Reflective layer. To create a layer that reflects the laser beam, aluminum, silver or gold are used.

Protective layer. Only CD and Blu-ray discs are provided with it. It is a hard varnish coating.

Label.A layer of varnish is applied on top of the disc - the so-called label. This layer is capable of absorbing moisture, so that ink that ends up on the surface of the substrate during printing dries quickly.

Differences between CDs, DVDs and Blu-ray Discs

These media have different characteristics. First of all, different capacities. Blu-ray-disc can store up to 25 GB of data, DVD can store 5 times less information, CD - 35 times less. Blu-ray drives use a blue laser to read and write data. Its wavelength is about 1.5 times shorter than that of the red laser DVD and CD drives. This allows a much larger amount of information to be recorded onto an equal disk surface.

Media formats

The following types of optical media are currently on the market.

CD-R. Recordable CDs can hold up to 700 MB of information. There are also 800 MB discs available, but they are not supported by all recorders and consumer players. The eight-centimeter miniCDs can store 210 MB of data.

CD-RW. Rewritable media has the same storage capacity as CD-R.

DVD-R / DVD + R. Recordable DVDs can hold 4.7GB of information. miniDVD 8 cm diameter - 1.4 GB.

DVD-R DL / DVD + R DL. The DL prefix stands for Dual Layer (DVD-R) or Double Layer (DVD + R), which corresponds to dual layer media. The capacity is 8.5 GB. An eight-centimeter disk can hold up to 2.6 GB.

DVD-RW / DVD + RW. Single layer media of this type are capable of withstanding several hundred write cycles. Like DVDs with write-once, the capacity of rewritable discs is 4.7 GB, and discs with a diameter of 8 cm are about 1.4 GB.

DVD-RAM. These media have the same storage capacity as single layer DVDs. There are also two-layer discs that can hold twice as much information. DVD-RAM can withstand up to 100,000 write cycles, but only a few DVD players work with these discs. Data is written not on a spiral track, but in sectors on circular tracks, as on hard disk platters. The marks defining the boundaries of the sectors are clearly visible on the surface of DVD-RAM - by their presence it is easy to distinguish this type of media from others.

BD-R / BD-R DL... An abbreviation used to refer to recordable Blu-ray discs. BD-R media have one working layer that can hold 25GB of data. BD-R DL are equipped with two working layers, therefore their capacity is 2 times higher.

BD-RE / BD-RE DL. Rewritable Blu-ray discs are rated for 1000 write cycles. They can hold the same amount of data as non-rewritable media.

"Plus and minus"

The presence of "plus" and "minus" media is a consequence of the old format war. Initially, the computer industry relied on the “plus” format, and the consumer electronics industry promoted the “minus” format as the standard for recordable DVDs. Modern recorders and players support both formats.

None of them have clear advantages over the other. Both types of media use the same materials. Therefore, there are no significant differences between "plus" and "minus" disks from one manufacturer.

Recording quality

The recording quality of media of the same format can vary significantly. Much depends on the model of the recorder used. The recording speed also plays an important role: the lower it is, the fewer errors and the higher the quality.

Recorder and media compatibility

Not every recorder is capable of recording to discs of all formats without exception. There are certain restrictions.

CD recorders. Cannot work with DVD and Blu-ray discs.

DVD recorders. Burn CDs and DVDs, but do not support Blu-ray format.

Blu-ray recorders. They record both Blu-ray and any CD and DVD.

Disc signatures

It is better to sign the carrier on which the information is located, so as not to be confused later. This can be done in different ways.

Blanks with the ability to print. The upper side of these discs is varnished. On such a surface, you can print text and images using inkjet printers and MFPs equipped with a special tray. For the price, the discs do not differ from the usual ones.

Signature with a recorder. The recorder's support for LightScribe or Labelflash technology allows you to print monochrome images and text on the surface of specially designed media. However, the process can take up to 30 minutes, and the cost of LightScribe discs is about twice the cost of conventional discs. Labelflash-enabled media will cost even more.

New LabelTag technology. Developed by the manufacturer of the Lite-On recorders and involves the application of text to the working surface of the disc. This eliminates the need to use special media. However, disk space is wasted because the text is applied directly to the track. And the inscription is well read only if the sections with the text contrast brightly with the empty fragments.

Handwritten signature. To do this, you need to purchase special markers with a soft, rounded tip and solvent-free ink. Other markers can erode the surface of the disc and cause scratches.

Use of stickers. You can print labels on any printer. However, it is not recommended to glue them, as this often leads to damage to the disk surface, and hence to data loss. It may happen that the label comes off during disc playback. In this case, damage to the optical drive is likely.

Data storage period

Disk manufacturers often indicate the shelf life of data on media of 30 years or more. However, this duration is only possible under ideal storage conditions - dry, cool and dark. The recording quality should be high.

Frequent use will significantly reduce the lifespan of self-burned discs. During playback, media is exposed to high temperatures and mechanical stress. Data loss can also be caused by scratches or dirt.

Transferring information to disk

All optical media except DVD-RAM have a spiral track that runs from the center of the disc to the outer edge. Information is recorded on this track by a laser beam. When burning, the laser beam forms tiny spots on the reflective layer - pits (from the English pit - pit). Areas that have not been exposed to the laser are called land (from the English land - surface). Translated into the language of the binary data storage system, pita corresponds to 0, and to land - 1.

When a disc is played back, information is read using a laser. Due to the different reflectivity of pits and lands, the drive recognizes dark and light areas of the disc. Thus, a sequence of zeros and ones is read from the media, which make up all physical files without exception.

With the development of technology, the wavelength of the laser beam used in recorders has been gradually decreasing, which has significantly improved focusing accuracy. The track has become narrower, the pits are smaller, and a larger amount of data is placed on an equal disk area. The shorter the wavelength, the smaller the distance between the working layer and the laser.

Media production

Using DVD as an example, ComputerBild explains how optical media are made and how other types of discs are produced.

1. For casting a plastic substrate, polycarbonate heated to 350 ° C is fed into a mold by injection molding. A microscopic spiral path in the form of a groove (Pre-Groove) is created on the surface of the base using a matrix. Not only is data written to this track - it also contains a signal to synchronize the recorder's spindle drive. After cooling the substrate to 60 ° C, a central hole is made, then the temperature is reduced to 25 ° C and further processing begins. DVDs usually consist of two 0.6mm thick polycarbonate layers each. Single-layer recordable DVDs only have one of the layers further processed as described in steps 2-3, while dual-layer DVDs have both. CD and Blu-ray Discs have only one 1.2mm layer.

2. The working layer of recordable CDs and DVDs is created by centrifugation. With the help of a dispenser, the dye is injected onto the surface of the disc rotating at a constant speed in the region of the central hole and is evenly distributed over the surface of the carrier.

3. The reflective layer is applied to the disc by ion-plasma spraying. In a vacuum chamber, an aluminum, silver or gold plate is bombarded with charged ions, which knock out metal atoms from it - it remains on the surface of the working layer of the blank. For rewritable CDs, DVDs and Blu-ray discs, all working and reflective layers are created using ion-plasma sputtering. In four chambers, a first layer of an insulator, a working layer, a second layer of an insulator and a reflective layer are sequentially applied to the disc. For Blu-ray Disc production, these operations are performed in reverse order.

4. Two polycarbonate backings are glued together. CDs and Blu-ray Discs have a lacquer coating instead of a second substrate, which is dried under an ultraviolet lamp. The lacquer coating of Bly-ray discs is particularly durable, while DVDs do not need a protective lacquer layer.

5. At the last stage, the blanks are labeled, and an absorbent varnish layer is applied to the printed discs.

CD(Compact Disc) is an optical storage medium in the form of a plastic disc with a hole in the center, the process of writing / reading information on / c which is carried out using a laser. CDs are becoming faster and more cheap. Information is recorded on a CD by an industrial method. The most widely used are 5-inch CDs with a capacity of 670 MB. In terms of their characteristics, they are completely identical to ordinary music CDs. The data on the disk is written in the form of a spiral (unlike the hard drive, the data on which is located in the form of concentric circles). Physically, a laser beam defines a digital sequence of ones and zeros recorded on a CD in the form of microscopic pits (pit, pit) on its spiral. Today, with a computer with a CD-writer drive, you can make a disc in less than an hour.

DVD(Digital Versatile Disk, formerly Digital Video Disk), that is, a multipurpose digital disk - a type of CD that stores from 4.7 to 17 GB of information, which is quite enough for a full-length film. This capacity can satisfy any manufacturer of computer games and encyclopedias, which usually required several CD-ROMs to produce, causing inconvenience to the user. The DVD-ROM specification considers discs and DVD technology as a storage medium for computer data with enormous storage capacity. The DVD-Video specification, around which so many copies have been breaking down, provides only for the recording of full-length film programs with high image quality, multichannel sound and international settings. The DVD-Audio specification considers the standard for recording only sound, assuming, however, a much higher quality, multichannel and the ability to place more than 74 minutes on the same disc. music, but also a variety of related information. It becomes clear that the rapid decline in prices for DVD-devices may lead to the displacement of CD-drives in the near future, even if old media are used. There are four types of data structure DVDs:

DVD video - contains movies (video and sound);
DVD-Audio - contains high quality audio data (much higher than on audio CDs);
DVD-Data - contain any data;
mixed content.

BD(Blu-ray - English blue ray - blue ray and disc - disc) is an optical media format used for recording and storing digital data, including high-definition video with increased density. The Blu-ray standard was jointly developed by the BDA consortium, and the new technology introduces dramatic changes in the logical structure of the disc, cost and other parameters. The wavelength of the blue laser was shortened to 405 nm, which made it possible to position the beam much more accurately, and, therefore, to place data on the disk with greater density. The shorter wavelength of the blue-violet laser allows more information to be stored on 12cm discs the same size as CD / DVDs. BD is a new generation product that is more advanced and meets the "requirements of our time" than CDs and DVDs.

16. Personal computers. Device. Main characteristics.

Computer Is an electronic device designed to work with information, namely introduction, processing, storage, output and transmission of information. In addition, the PC is a single entity of two entities - hardware and software (which is reflected in the following diagram).

According to the definition of a computer, the components of a computer can be divided into devices that perform certain functions related to information.

Optical disc

data carrier in the form of a plastic disc, designed 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 with mechanical sound recording, it has a number of advantages: a very high recording density and a 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 on the disc, a spiral track is formed, consisting of miniature depressions 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 focus of the optical system.

Multimedia technology allows you to combine text and graphics with sound and motion pictures on a personal computer. Such multimedia computers use optical CD-ROMs (Compact Disk Read Only Memory) 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 - repeatedly, like on a magnetic disc 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 re-recording CD technology. The DVD standard can significantly increase the time and improve the quality of video playback in comparison with existing CD-ROMs. DVD drives are advanced CD-ROM drives.

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

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

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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

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, 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 ...

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