Optical disc

Optical disk

a data carrier in the form of a plastic disk intended for recording and reproducing sound (CD), images (video disc), alphabetic digital information, (CD-ROM, DVD), etc. using a laser beam. The first optical discs appeared in 1979. Philips created them for recording and playing back sound. An optical disk consists of a hard, optical transparent base, on which a thin working layer and an additional protective layer are applied. Thanks to optical method Optical discs are much more durable than gramophone records. The diameter of a standard CD is 120 mm (4.5 inches), thickness - 1.2 mm, center hole diameter - 15 mm. CDs are made from very durable transparent plastic - polycarbonate or polyvinyl chloride. A label is placed on one side of the disc, and the other side has a mirror surface that shimmers with rainbow colors. This is a recording zone, the spiral track of which consists of pits - recesses of various lengths. The distance between two adjacent spiral tracks is 1.6 microns, i.e. the recording density is 100 times greater compared to a conventional gramophone record. The width of the pits is 0.6–0.8 µm, and their length is variable. It reflects the length of the sequences of "1" 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 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: a very high recording density and the complete absence of mechanical contact between the medium and the reading device during the recording and playback process. Music CDs are recorded at the factory. Like gramophone records, they can only be listened to. Using a laser beam, the signals are recorded digitally on a rotating optical disk. As a result of recording, a spiral track is formed on the disc, consisting of miniature grooves and smooth areas. In playback mode, a laser beam focused on a track moves across the surface of a rotating optical disk and reads the recorded information. In this case, the depressions are read as ones, and the areas that evenly reflect 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 light into electricity. The reading laser beam is focused on a spiral track with pits located deep in the disk. The head never comes into contact with the disk - it is always at a strictly defined distance from it, ensuring that the track of pits is in the focus of the optical system.

Multimedia technology allows you to combine personal computer text and graphics with sound and moving images. As information carriers in such multimedia computers optical compacts are used CD-R discs OM (Compact Disk Read Only Memory - i.e., read-only memory on a CD). Outwardly, they do not differ from 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 written only once in an industrial environment, and on a personal computer it can only be read. A wide 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 allowing you to quickly find the material you need. The memory capacity of two CD-ROMs is enough to accommodate an encyclopedia larger in volume than the Great Soviet Encyclopedia.

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

1 – CD; 2 – translucent coating that protects the information printed on the CD from damage; 3 – reflective coating (the recording medium itself); 4 – protective layer; 5 – focusing; 6 – laser beam; 7 – optical splitter; 8 – photodetector; 9 - ; 10 – electric motor rotating the disk

Replaces existing CDs new standard storage media – DVD (Digital Versatile Disc or general purpose digital disc). They look no different from CDs. Their geometric dimensions are the same. The main difference between a DVD disc is its tens of times higher recording density. This is achieved thanks to a shorter laser wavelength and a smaller spot size of the focused beam, which made it possible to halve the distance between tracks. The DVD standard is defined in such a way that future models of reading devices will be developed taking into account the ability to play all previous generations of compact discs, i.e., in compliance with the principle of “backwards compatibility”. In 1995, Philips developed CD replay technology. The DVD standard allows you to significantly increase the time and improve the quality of video playback compared to existing CD-ROMs. DVD drives are advanced CD-ROM drives.

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

See what an “optical disk” is in other dictionaries:

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

optical disk- A disk containing digital data read using optical technology. [GOST 25868 91] Equipment topics. periphery processing systems information EN optical disk... Technical Translator's Guide

OPTICAL DISK, in computing, a compact storage device consisting of a disk on which information is written 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 optical disc file systems Recording technologies Recording modes Batch recording Types ... ... Wikipedia

Data carrier in the form of a disk made of transparent material (glass, plastic, etc.) with metallization. layer, on which the microscopy method of digital optical recording is used, depressions (pits) are formed, collectively forming spiral or annular... ... Big Encyclopedic Polytechnic Dictionary

A storage medium intended for recording and/or reproducing information using focused laser radiation. It consists of a rigid (usually optically transparent) base, on which a photosensitive or reflective layer is applied and... ... encyclopedic Dictionary

optical disk- 147 optical disc: A disc containing digital data readable using optical technology

Information carriers – material that is intended for recording, storage and subsequent reproduction of information.

Storage medium - a strictly defined part of a specific information system, used for intermediate storage or transmission of information.

Storage medium is the physical environment in which it is recorded.

The media can be paper, photographic film, brain cells, punched cards, punched tapes, magnetic tapes and disks or computer memory cells. Modern technology offers more and more new types of storage media. They use the electrical, magnetic and optical properties of materials to encode information. Media are being developed in which information is recorded even at the level of individual molecules.

All machine media are divided into:

1. Perforated – have a paper basis, information is entered in the form of punches in the corresponding row and column. The volume of information is 800 bits or 100 KB.

2. Magnetic media – they use flexible magnetic disks and cassette magnetic tapes.

3. (compact discs) is a metallized plastic compact disc, 120 mm in diameter and 1.2 mm thick. On one of its sides there is a reflective aluminum layer, which is coated with a protective varnish to prevent damage. Information is recorded and read by a laser beam on a path running in a spiral from the center.

Optical storage media– (compact discs) is a metallized plastic disc with a diameter of 120 mm. And 1.2mm thick. On one of its sides there is a reflective aluminum layer, which is coated with a protective varnish to prevent damage. Information is recorded and read by a laser beam on a path running in a spiral from the center.

Types of optical disks:

1. CD-ROM (Compact Disk Read Only Memory) – a compact disc without the ability to record information.

2. CD-R (Compact Disk Recordable) – a CD with the ability to record information once.

3. CD-RW (Compact Disk Rewritable) – a CD with the ability to record information multiple times.

4. DVD (Digital Versatile Disk) – a digital multilayer disk for recording large amounts of information (up to 18 GB).

ADVANTAGES: Reliability. Ability to record large amounts of information. Wear-free.

Compact Disk (CD) is a disc with a diameter of 120 mm (4.75 inches) or 80 mm (3.1 inches) and a thickness of 1.2 mm. The depth of the stroke is 0.12 µm, the width is 0.6 µm. The strokes are arranged in a spiral, from the center to the periphery. The stroke length is 0.9–3.3 µm, the distance between the tracks is 1.6 µm. Compact discs are made up of three to six layers. A standard five-inch disc can contain 650–700 MB of information, 74–80 minutes of high-quality stereo sound with a sampling frequency of 44.1 kHz and a digitization depth of 16 bits or great amount audio in MP3 format. Three-inch disks hold about 180 MB of information. Sometimes there are disks called “business cards”. By appearance and they resemble a business card in size, but are actually three-inch disks, cut on both sides. Such a CD can store from 10 to 80 MB.

In the late 1970s, Sony and Philips began joint development unified standard for optical storage media. Philips created the laser player, and Sony developed the technology for recording on optical media. At the corporation's suggestion Sony size the disk was equal to 12 cm, because this volume made it possible to record Beethoven’s Ninth Symphony in its entirety. In 1982, in a document called the Red Book, a standard for processing, recording and storing information on laser disks was published, as well as the physical parameters of the disk, i.e.: 1. Physical size of the disk. 2. Disk structure and data organization. 2. Recording data in a single stream from the center to the periphery. 3. Read data at a constant linear velocity (Constant Linear Velocity, CLV).

All data on the disk is divided into frames. Each frame consists of 192 bits for music, 388 bits for modulation and error correction data, and one control bit. 98 frames make up one sector. Sectors are combined into a track. A maximum of 99 tracks can be recorded on a disc.

During recording and reading of information, when the laser beam moves from the center to the periphery, the rotation speed of the disk is ↓. This is necessary to ensure that the same amount of information can be read and written in the same amount of time. Therefore, without the use of CLV technology, when playing, for example, musical works, the performance speed would change.

Due to the relatively small size of laser discs compared to vinyl records, they were called compact discs, or CD (Compact Disk) for short. The first CDs were designed for recording and playing music and could store up to 74 minutes of high-quality stereo sound. The standard for such discs was called CD-DA (Compact Disk Digital Audio).

With the development of the computer industry, a need arose for technology that allows storing on CDs not only digital audio, but also various data. Computer programs could not fit on floppy disks, and the volume of user files became larger and larger.

In 1984, a standard called the Yellow Book was published. Sony and Philips companies reorganized the structure of CDs and began to use new error correction codes - EDC (Error Detection and Correction) and ECC (Error Correction Code). The main unit of data placement was the sector. One sector contains: 12 bytes for synchronization, 4 bytes for headers, 2048 bytes for user data and 288 bytes for error correction. CAV (Constant Angular Velocity) technology was developed to read computer data. CAV technology allows you to read information from a disk faster than CLV technology, since the data flow increases as the laser beam moves from the center to the periphery. Modern CD drives support both technologies. Computer laser disks were called CD-ROM - Compact Disk ReadOnly Memory (literally, “read-only memory on CDs”). In the late 1990s, the CD drive became a standard component of any computer and the vast majority of programs began to be distributed on CDs.

The consumer market was rapidly expanding, production volumes were increasing, and largest producers began developing technology that allows the user to independently record any information on a CD. In 1988, Tajio Yuden released the world's first CD-R (Compact Disk Recordable). The biggest challenge faced by CD recorder designers is finding highly reflective materials. Tajio Yuden successfully completed the task. The gold-cyanine alloy they used to make these drives had a reflectivity of over 70%. The same company developed a method for applying an active organic layer to the surface of a disk, as well as a technology for dividing the disk into tracks.

DVD, DVD-R, DVD-RW, CD, CD-R, and CD-RW discs are manufactured by various companies: AMD, Amedia, Digitex, HP, Imation, MBI, Memorex, Philips, Smartbuy, Sony, TDK, Verbatim.

DVD structure.

In December 1995, 10 companies united in the DVD Consortium officially announced the creation of a single unified standard - DVD. The abbreviation DVD first stood for Digital Video Disc, but later its meaning was changed to Digital Versatile Disc. The disc was fully compatible with the Red Book and Yellow Book standards. DVD is identical in appearance to CD, but allows you to record information that is 24 times larger in volume, that is, up to 17 GB. This became possible thanks to changes in the physical characteristics of the disk and the use of new technologies. The distance between the tracks was reduced to 0.74 μm, and the geometric dimensions of the pits were reduced to 0.4 μm for a single-layer disk and 0.44 μm for a double-layer disk. The data area has increased, the physical sizes of sectors have decreased. A more efficient error correction code, RSPC (Reed Solomon Product Code), was used, and more efficient bit modulation became possible. DVD technology provides a huge number of formats and four types of designs in two sizes. A disc of this standard can be either single-sided or double-sided. There can be one or two working layers on each side.

Burning single-layer DVDs is similar to burning CDs, but burning dual-layer discs is significantly different from the process described earlier.

Double-layer discs of types DVD-2 and DVD-9 have two working layers for recording information. These layers are separated using a special translucent material. To perform its function, such a material must have mutually exclusive properties: reflect the laser beam well when reading the outer layer and at the same time be as transparent as possible when reading the inner layer. At the request of Philips and Sony corporations, 3M created a material that meets the following requirements: having a reflectivity of 40% and the necessary transparency. DVDs are 0.6mm thick. For physical compatibility with CDs, a 0.6 mm thick polycarbonate backing was additionally glued onto the DVD.

The CD specification does not provide any copy protection mechanism - discs can be freely copied and played. However, starting in 2002, various Western record companies began attempting to create copy-protected CDs. The essence of almost all methods comes down to deliberately introducing errors into the data written to the disk, so that on a household CD player or music center The disc played, but not on the computer. The result is a game of cat and mouse: such discs are not readable on all household players, but on some computers they are readable, it turns out software, allowing you to copy even protected discs, etc. The recording industry, however, does not give up hope and continues to test more and more new methods.

There are also magneto-optical disks : FLOPTICAL = FLOPPY (floppy disk) + OPTICAL.

The surface of the magneto-optical disk is covered with a special material, the properties of which change under the influence of temperature and magnetic fields. All these disks differ from each other in diameter and number of working surfaces. The volume of information is up to 10 GB.

The speed and reliability of modern recorders will be the envy of any Formula 1 car. ComputerBild explains how data ends up on CDs, DVDs and Blu-ray discs.

Recording music and films on optical media is a familiar process, like using magnetic cassettes twenty years ago, but it is much cheaper. How do the types of media differ and how is information recorded on them?

Stamping and burning

In the industrial production of discs with music, films or games, data is recorded onto the media by stamping - a process reminiscent of the production of gramophone records. Information on disks is stored in the form of tiny indentations. Computer and consumer DVD recorders perform this task differently - they use a laser beam.

The first recordable optical media was CD-R with write-once capability. When storing data on such disks, the laser beam heats the working layer of the disc, which consists of a dye, to approximately 250 ° C, which causes a chemical reaction. Dark, opaque spots form where the laser is heated. This is where the word “burn” comes from.

In a similar way, data is transferred to DVD with the ability to write once. But no dark spots form on the surface of rewritable CDs, DVDs and Blu-ray discs. The working layer of these drives is not a dye, but a special alloy. When heated by a laser to approximately 600 °C, it transforms from a crystalline state to an amorphous one. The areas exposed to the laser are darker in color and therefore have different reflective properties.

Information carriers

Discs intended for recording at home have the same thickness (1.2 mm) and the same diameter (12 or 8 cm) as discs on which data is recorded industrially. 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, and for rewritable CDs, DVDs (RW, RAM) and Blu-ray discs, it is formed by a special alloy that can change the phase state. The working layer is surrounded on both sides by an insulating substance.

Reflective layer. Aluminum, silver or gold are used to create the layer from which the laser beam is reflected.

Protective layer. Only CDs and Blu-ray discs are equipped 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 able to absorb moisture, so that the ink that appears on the surface of the media during printing dries quickly.

Differences between CDs, DVDs and Blu-ray Discs

These media have different characteristics. First of all, different capacities. A Blu-ray disc can hold up to 25 GB of data, a DVD can store 5 times less information, and a CD can store 35 times less. Blu-ray drives use a blue laser to read and write data. Its wavelength is approximately 1.5 times shorter than that of red laser DVD and CD drives. This allows you to record a significantly larger amount of information on an equal disk surface area.

Media formats

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

CD-R. Recordable CDs can hold up to 700 MB of information. There are also disks with a capacity of 800 MB, but they are not supported by all recorders and home players. Eight-centimeter miniCDs can record 210 MB of data.

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

DVD-R/DVD+R. Recordable DVDs hold 4.7 GB of information. miniDVD with a diameter of 8 cm – 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 two-layer media. Capacity – 8.5 GB. An eight-centimeter disk can hold up to 2.6 GB.

DVD-RW/DVD+RW. Single-layer media of this type can withstand several hundred write cycles. Like write-once DVDs, rewritable discs have a capacity of 4.7 GB, while 8 cm discs have a capacity of about 1.4 GB.

DVD-RAM. These media have the same storage capacity as single-layer DVDs. There are also double-layer discs that hold twice as much information. DVD-RAM can withstand up to 100 thousand write cycles, but only a few DVD players work with these discs. Data is written not on a spiral track, but in sectors on ring tracks, like on plates hard drive. Marks defining sector boundaries 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 has one working layer that can hold 25 GB of data. BD-R DL are equipped with two working layers, so their capacity is 2 times higher.

BD-RE/BD-RE DL. Rewritable Blu-ray discs are rated for 1,000 write cycles. They can store as much data as non-writable media.

"Plus and minus"

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

Neither of them has 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 the same manufacturer.

Recording quality

The recording quality of media of the same format can vary significantly. Much depends on the recorder model used. The recording speed also plays an important role: the lower it is, the lower the number of 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 DVDs and Blu-ray discs.

DVD recorders. Writes CDs and DVDs, but does not support Blu-ray format.

Blu-ray recorders. They record to Blu-ray as well as any CD and DVD.

Signatures on discs

It is better to sign the media on which the information is located immediately, so as not to confuse it later. This can be done in different ways.

Printable blanks. The top 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. The price of the discs is no different from regular ones.

Signature using a recorder. The recorder's support for LightScribe or Labelflash technology allows you to print single-color images and text on the surface of media specially designed for this purpose. True, the process can take up to 30 minutes, and the cost of LightScribe discs is approximately twice the cost of conventional discs. Media with Labelflash support will cost even more.

New LabelTag technology. Developed by the recorder manufacturer Lite-On and involves applying text to the working surface of the disc. This eliminates the need to use special media. However, disc space is wasted because the text is written directly onto the track. And the inscription is readable only if the areas with text contrast brightly with the empty fragments.

Signature made by hand. To do this, you need to purchase special markers with a soft, rounded tip and solvent-free ink. Other markers may corrode the disc surface and cause scratches.

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

Data storage period

Disc manufacturers often specify a storage life of 30 years or more for data on media. However, such a duration is only possible under ideal storage conditions - in a dry, cool and dark place. The recording quality must be high.

If used frequently, the service life of self-burned discs will be significantly reduced. During playback, media is exposed to high temperatures and mechanical stress. Data loss can also be caused by scratches or contamination.

Transferring information to disk

All optical media, with the exception of DVD-RAM, have a spiral-shaped track that runs from the center of the disk to the outer edge. Information is recorded onto this track using a laser beam. When burning, the laser beam forms tiny spots on the reflective layer - pits (from the English pit - hole). The areas that were not exposed to the laser are called lands (from the English land - surface). Translated into the language of the binary storage system, pita corresponds to 0, and land corresponds to 1.

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

With the development of technology, there was a gradual reduction in the wavelength of the laser beam used in recorders, which made it possible to significantly improve focusing accuracy. The track has become narrower, the pits have become smaller, and a larger amount of data can be placed on an equal area of ​​the disk. The shorter the wavelength, the shorter the distance between the working layer and the laser.

Media production

Using DVD as an example, ComputerBild explains how optical media is produced and how the production of other types of discs differs.

1. To cast a plastic substrate, polycarbonate, heated to 350 °C, is fed into a mold using injection molding. A microscopic spiral track in the form of a groove (Pre-Groove) is created on the surface of the base using a matrix. This track not only records data, it also contains a signal to synchronize the recorder 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 typically consist of two polycarbonate layers, each 0.6mm thick. For single-layer recordable DVDs, only one of the layers undergoes further processing, as described in steps 2–3, while for dual-layer DVDs, both layers are processed further. CDs and Blu-ray discs have only one layer 1.2 mm thick.

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

3. The reflective layer is applied to the disk using ion-plasma sputtering. 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, the first insulator layer, the working layer, the second insulator layer and the reflective layer are sequentially applied to the disk. When producing Blu-ray discs, these operations are performed in reverse order.

4. Two polycarbonate bases are glued together. For CDs and Blu-ray discs, instead of a second base, a varnish coating is applied, which is dried under an ultraviolet lamp. The varnish coating of Bly-ray discs is particularly durable, while DVDs do not need a protective layer of varnish.

5. At the last stage, the blanks receive a label, and an absorbent layer of varnish is applied to the printable discs.

Recording and reading of information in optical storage devices is carried out contactlessly using a laser beam. Such devices include, first of all, CD-ROM, CD-R, CD-RW and DVD drives (ROM, R and RW).

CD-ROM devices. In CD-ROM devices (Compact Disk Read-Only Memory - read-only CD), the information carrier is an optical disk (CD), manufactured in line production using stamping machines and intended for read-only.

The CD is a transparent polymer disk with a diameter of 12 cm and a thickness of 1.2 mm, on one side of which a reflective layer of aluminum is sprayed, protected from damage by a layer of transparent varnish. The coating thickness is several ten thousandths of a millimeter.

Information on the disk is represented as a sequence of depressions and protrusions (their level corresponds to the surface of the disk), located on a spiral track emerging from an area near the axis of the disk (there are only a few hundred tracks per inch radius on the surface of the hard disk). The capacity of such a CD reaches 780 MB, which makes it possible to create on its basis help systems and educational complexes with a large illustrative database. One CD has the same information capacity as almost 500 floppy disks. Reading information from a CD-ROM occurs at a fairly high speed, although noticeably lower than the speed of hard disk drives.

CD-R (CD-Recordable) drives. They allow, along with reading regular CDs, to write information once onto special optical CD-R discs. The information volume of such disks is 700 MB.

Recording on such discs is carried out due to the presence on them of a special light-sensitive layer of organic material that darkens when heated. During the recording process, the laser beam heats selected points on the layer, which darken and stop transmitting light to the reflective layer, forming areas similar to depressions.

Burning information onto CD-R discs is a cheap and fast way to store large amounts of data.

CD-RW (CD-ReWritable) drives. Allows you to write to disk multiple times. The information volume of such disks is 700 MB.

CD-R drive OM – allows you to only read information from any CD. Accordingly, such devices will differ in read speed and cache memory. The CD-R drive is read and write, and the CD-RW drive not only reads, but also rewrites (erases information and writes new information over it). Such drives differ in read/write/rewrite speed (the latter only for CD-RW) and cache size.

DVD drives (Digital Versatile Disc, general purpose digital disc). The first DVDs appeared on the market around 96–97 of the last century. DVD is an excellent storage medium for any type of data and is used as a common computer storage medium.

From the outside, the DVD looks like a regular CD, and even upon closer inspection it's hard to tell the difference. However, DVD has much more possibilities. DVDs can store 26 times more data than CD-ROMs.

DVD technology was a huge leap forward in the field of storage media. A standard single-sided, single-layer disk can store 4.7 GB of data. But DVDs can be produced using a two-layer standard, which allows you to increase the amount of data stored on one side to 8.5 Gb.

In addition, DVD discs are double-sided, which increases the disc capacity to 17 Gb. True, to read a DVD, you need a new device (DVD-ROM), but DVD technology is compatible with CD technology, and the DVD-ROM drive also reads CDs, and in different formats.

There are various combination optical drives available on the market. For example, DVD-CD R/RW allows you to read DVDs and CDs and write/rewrite onto CDs. Another option is DVD-RW - CD-RW. Allows you to read, write and rewrite DVDs and CDs.

DVD Directory

DVD

DVD is a family of optical discs that are the same size as compact discs (CDs) but have significantly greater storage capacity achieved by increasing recording density.

The advent of DVD. DVD forum

At the heart of the appearance DVD discs The idea was to develop a storage medium that could be equally successfully used in sound and video equipment, computer equipment, and game consoles. This would bring the different areas of electronics closer together.

The name DVD originally meant Digital Video Disc (Digital Video Disc). Later, in connection with the decision to expand the functions of DVD, the abbreviation began to be read differently - Digital Versatile Disk.

The development of the DVD format was officially announced in September 1995 by a group of 10 companies: Hitachi, JVC, Matsushita, Mitsubishi, Philips, Pioneer, Sony, Thomson, Time Warner and Toshiba. In May 1997, on the basis of this consortium, the DVD Forum was created - an organization open to membership, which today has more than 200 members.

The main tasks of this organization are the development and promotion of the DVD format, the development of agreed specifications, as well as licensing the activities of enterprises in the field of DVD technology. Within the framework of the forum there are special working groups on various aspects of DVD technology. International standards have been adopted for a number of specifications.

The most important advantages of DVD technology

Today DVD is already a widespread, time-tested and at the same time dynamically developing technology with enormous potential.

• recording and playback of high-quality video and audio in real time, effective work with computer multimedia information, as well as providing efficient random access to data stored in the form of many small files;
• disk capacity up to 4.7 GB (about 2 hours MPEG-2) per side for single-layer recording and 8.5 GB per side for dual-layer recording;
• the ability to record information in two layers on each side;
• unified UDF file system;
• the ability to record and rewrite DVDs multiple times;
• backward compatibility with existing CD disks - the geometric dimensions of DVD and CD disks are identical, all DVD equipment is capable of reading CD-Audio and CD-ROM disks (MultyRead specification).

First DVD formats

DVD technology initially relied on 3 main formats, the availability of which was determined by the specific requirements for various DVD applications:

• DVD-ROM is used to record data, including multimedia, used in computer technology;
• DVD-Video is used when recording video materials for later viewing on video equipment or using a DVD-ROM drive connected to a computer. The format provides protection against illegal copying of information;
• DVD-Audio is used to record high-quality multi-channel audio. Additionally, the DVD Forum recommends additional support for video, graphics, and other information.

These formats described read-only disks. Information is placed on such disks once - during their production. With the development of DVD technology, disc specifications have emerged that allow disc users to record and rewrite information. However, the main forum participants were unable to agree on a single specification for such disks due to the desire to maintain independent control over their proprietary technical developments. As a result, several competing specifications emerged (DVD-RAM, DVD-RW, DVD+RW formats). Let's look at the list of DVD disc formats being developed today.

Evolving DVD formats

Only for reading

• DVD-ROM
• DVD-Video
• DVD-Audio

For multiple rewrites

• DVD-RAM
• DVD+RW (not supported by DVD forum)
• DVD-RW

For one-time recording

• DVD-R (G)
• DVD-R(A)

For video recording

• DVD-VR

Compatibility

The developers were unable to achieve a unified approach when developing the format of recordable discs. Competition has predetermined the lack of support for several recording formats by one device. Therefore, discs written in one of the formats, as a rule, are not readable on drives of other recordable formats. An attempt to overcome the disunity of recording formats was made by Panasonic, which in April 2001 introduced a device that works with DVD-RAM and DVD-R(G) formats.

Some devices may not understand DVD disc formats that were introduced after their release. Naturally, consumer electronics can be targeted at a very specific segment of the consumer market (DVD-Audio, DVD-Video, both formats), and does not necessarily have to be capable of reading computer discs, as defined by the DVD forum. At the same time, computer drives work equally well with video, audio, multimedia and other computer discs.

UDF file system

A major achievement in ensuring compatibility in DVD technology was the unified file system MicroUDF, adopted in 2000. The MicroUDF file system is a version of the UDF (Universal Disk Format) file system adapted for use in DVDs, which, in turn, is based on international standard ISO-13346. This file system is gradually replacing the outdated ISO9660, which was created at one time for use in CDs. For a transition period (until they go out of circulation computer devices and disks running in the ISO9660 format) the UDF Bridge file system will be used, which is some combination of MicroUDF and ISO9660. Only MicroUDF can be used to burn Audio/Video DVD discs.

The capabilities of the MicroUDF file system are as follows:

• independence from the hardware and software platform used (in this sense, UDF is optimal choice in archival systems);
• large capacity. The entire disk can be represented as a single volume;
• optimal transfer speed. The speed of reading and writing data in UDF format can be higher than the performance of many “native” ones file systems when large files are transferred (for example, in multimedia systems)
• maximum possible file sizes;
• use of the UNICODE font format, which provides effective international support;
• support for extended file attributes, which is used in some “native” operating systems;
• Support for long file names with extension of operating system restrictions. The maximum file name length is 255 characters;
• interchangeability of DVD discs in consumer electronics and computer systems.

Using MicroUDF, you can simultaneously store videos, audio recordings, digitized photos, and computer files on a single DVD disc. This ensures cross-platform compatibility, i.e. the DVD becomes a single medium for Macintosh, DOS/Windows, OS/2, UNIX.

Perspectives DVD

The presence of different standards and specifications does not mean that DVD technology stands still. The efforts of various companies today are aimed at introducing “blue laser” technology - with a shorter wavelength. This will increase the recording density on disks with the resulting improvement in other characteristics.
Calimetrics Inc has proposed ML (multilevel) technology, which can triple the capacity of a standard DVD/CD. In this case, there is no need to make any modifications to the mechanism and optics of existing drives. To implement new technology, it is enough to use a chipset developed by this company. The essence of the technology is the ability to use information characteristics pit depth (up to 8 levels) when working with discs. Note that a similar technology, but for CD discs, is being developed by TDK in collaboration with other companies.

Read-only DVD formats

DVD-ROM(Digital Versatile Disc Read Only Memory)

DVD-ROM discs are intended for use in computer technology. Information is written to the disk only once - during its production.

The progress of DVD devices largely follows the path traveled by CDs, and is mainly aimed at improving speed characteristics and introducing a recording function. First-generation DVD-ROM devices used CLV mode and read from the disc at a speed of 1.38 MB/s (in traditional DVD notation this is 1x). Second generation devices could read DVDs at twice the speed - 2x (2.8 MB/s). Modern DVD-ROMs - third-generation devices - use rotation control mode (CAV) with a maximum reading speed of 4x-6x (5.5 - 8.3 MB/s) or more. Modern DVD-ROM drives (disk drives) support reading almost all formats, including CDs.

DVD-Video

The DVD-Video format is designed for storing and playing video. Like DVD-ROM, this specification defines the ability to read-only information - playback of recordings using video players (video recorders). The specification is based on the DVD-ROM format, but provides a special way of placing data that prevents the possibility of bit-by-bit copying of discs. Video materials in encoded form are placed on the disk during the production process. Playing DVD-video is only possible on household video players (video recorders) or DVD drives connected to a computer. When using computer equipment, information decoding is carried out either in hardware or software. The modern specification provides recording of high-quality video on disc (up to 2 hours in MPEG-2 compression format), as well as multi-channel audio in 8 languages, selectable screen format, captions in 32 languages, interactive control via on-screen menu, up to 9 angular directions viewing, protection against illegal copying, differentiation of viewing video products by region, managing children’s access to video materials.

DVD-Audio

A new generation of music format after CD. The format specification defines high-quality multi-channel audio, support for a wide range of audio quality (quantization 16, 20, 24 bits at a frequency of 44.1 to 192 kHz), playback DVD players CD discs, support for additional information (including video, text, menus, screensavers, convenient navigation system), connection with websites providing information support, expanding opportunities when new technologies emerge.

There are two versions of the DVD-Audio format: simply DVD-Audio - for audio content only, and DVD-AudioV - for audio with additional information.

Special measures have been developed to protect disks from pirated copying.

Rewritable DVD formats

Multiple write

All known specifications of rewritable DVD discs use multiple recording technology based on the physical principle of changing the phase state (crystalline/amorphous) of the information layer under the influence of a laser with a wavelength of 650 (635) nm (phase-change recording). Reading information is carried out by determining the optical characteristics of the information layer in its various phase states upon reflection of laser beams (the same as during recording).

Re-recordable material

The working material used is AVIST, created by TDK in 1995. The characteristics of this material almost perfectly meet the requirements of DVD rewriting technology:

• high reflectivity - up to 25-35%, which is quite enough for compatibility of DVDs during playback;
• ease of changing the phase state at both high and low write speeds, which is especially important when working with various applications. Applications that work with rewritable CDs (such as CD-E) write at speeds less than 3 m/s. Working with data in the DVD-RAM format requires a higher recording speed from the working layer - from 3 to 6 m/s. When working with compressed video information, the recording speed must exceed 6 m/s;
• excellent signal-to-noise ratio and phase change characteristics allowed TDK to achieve ultra-small marker sizes (less than 0.66 mm);
• AVIST can withstand at least 1000 rewrite cycles even at speeds less than 3 m/s. With more high speeds recording, the number of rewrite cycles increases.

Each of the formats has its own advantages and disadvantages, which determined their areas of application. The most common format today is the DVD-RAM format due to the lower cost of drives and disks that work with it.

DVD-RAM(Digital Versatile Disc Random Access Memory)

Rewritable format developed by Panasonic, Hitachi, Toshiba.

The format was approved by the DVD forum in July 1997. Equipment and discs of this format were tested for 3 months in more than 20 computer manufacturing companies around the world. Over 160 forum participants voted to accept the specification. Today it is the most common DVD format in the computer industry.

DVD-RAM drives read DVD-ROM discs. In turn, DVD-RAM discs can only be read by so-called third generation DVD-ROM drives produced since mid-1999.

The first generation of DVD-RAM discs held 2.6 GB per side. Modern - second - generation disks carry 4.7 GB on the side or 9.4 GB for a two-sided modification.

Two types of single-sided DVD-RAM discs are available: in a cartridge and without a cartridge. Discs in a cartridge are mainly intended for household video equipment, where it is necessary to exclude the influence of external factors during intensive manual use. Cartridges, in turn, can be of two types - openable and solid.

The most important advantages of DVD-RAM format discs are the ability to be rewritten up to 100,000 times and the presence of a recording error correction mechanism.

The largest number of rewrite cycles among all DVDs, an error correction mechanism and random access to the disk both when writing and reading predetermined the maximum efficiency of this format in secondary storage devices. The vast majority of mass storage devices - robotic DVD libraries - use this technology.

DVD-RAM discs can be used to record and play streaming video on equipment that supports the DVD-VR specification (see below).

DVD+RW(Digital Versatile Disc ReWritable)

The DVD+RW format is promoted only by its developers - Hewlett-Packard, Mitsubishi Chemical, Philips, Ricoh, Sony and Yamaha (not supported by the DVD forum).

DVD+RW discs can record streaming video or audio, as well as computer data. DVD+RW discs can be rewritten approximately 1000 times.

Based on DVD+RW, a streaming video recording format has been created - DVD+RW Video Format. Devices and discs operating in this format are positioned on the market as fully compatible with equipment operating in DVD-Video formats. This means that DVD+RW discs containing video content can be played on older consumer DVD equipment.

Philips announced the launch of its DVD video recorder in September 2001. DVD+RW discs recorded on this device can also be read by conventional DVD-Video players. This solution was proposed as a response to the DVD-VR specification adopted by the DVD forum (see below).

DVD-RW(Digital Versatile Disc ReRecordable)

There are other names for this format: DVD-R/W and less commonly DVD-ER.

DVD-RW is a rewritable format developed by Pioneer. DVD-RW format discs hold 4.7 GB per side, are available in single-sided and double-sided versions and can be used to store video, audio and other data.

DVD-RW discs can be rewritten up to 1000 times. Unlike DVD+RW and DVD-RAM formats, DVD-RW discs can be read on first-generation DVD-ROM drives.

TDK claims that its DVD-RW discs have a lifespan of approximately 100 years.

Write-once DVD formats

DVD-R(Digital Versatile Disc Recordable)
DVD-R is a write-once format developed by Pioneer. Devices based on this format were the first to record DVDs. The recording technology is similar to that used in CD-R and is based on an irreversible change under the influence of a laser of the spectral characteristics of the information layer coated with a special organic composition.

DVD-R discs can record computer data, multimedia programs, and video/audio information. Depending on the type of information recorded, discs can be read on other types of devices compatible with the recorded format, including DVD-Video video players and most DVD-ROM drives. Single-sided DVD-R discs hold 4.7 or 3.95 GB per side. Double-sided discs are only available in 9.4 GB total capacity (4.7 GB per side). Currently, the format does not support dual-layer recording technology.

The durability of DVD-R discs is estimated at over 100 years.

To protect against illegal copying, two specifications have been developed: DVD-R(A) and DVD-R(G). These two versions of the same specification use different laser wavelengths when recording information. Thus, discs can only be written on equipment that meets their specifications. Disc playback can be performed equally successfully on any equipment that supports the DVD-R format.

DVD-R(A) (DVD-R for Authoring) is used in professional applications. In particular, support for a special format (Cutting Master Format) allows you to use these discs to record the original replica of information (pre-mastering) instead of the usual use of DLT tapes for these purposes.

DVD-R(G) (DVD-R for General) is intended for wider use. Disks of this format are protected from the possibility of bit-by-bit copying of information onto them from other disks. The format is supported in mass storage devices (for example, in robotic DVD libraries offered by Pioneer itself).

The DVD-VR specification is based on DVD-RAM and is supported by the DVD Forum. The DVD-VR format allows you to record up to 2 hours of high-quality MPEG-2 video in real time on a single-sided 4.7 GB DVD-RAM disc and provides capabilities such as editing of already recorded video footage, recording various types static images. Electronics based on this format are produced, for example, by Panasonic, Toshiba, Samsung, Hitachi.

Lookup tables

Table 1. DVD disc capacities

Format	Specification	Number of sides	Number of layers per side	Capacity, GB*
DVD-Video and DVD-ROM	DVD-5	1	1	4.7, or more than 2 hours of video
	DVD-9	1	2	8.5, or more than 4 hours of video
	DVD-10	2	1	9.4, or more than 4.5 hours of video
	DVD-14	2	1+2	13.2, or more than 6.5 hours of video
	DVD-18	2	2	17.1, or more than 8 hours of video
DVD-RAM (DVD-VR)	DVD-RAM 1.0	1	1	2.6
		2	1	5.2
	DVD-RAM 2.0	1	1	4.7
		2	1	9.4
DVD-R	DVD-R 1.0	1	1	3.9
	DVD-R 2.0	1	1	4.7
		2	1	9.4
DVD-RW	DVD-RW 2.0	1	1	4.7
		2	1	9.4

* 1GB – 1 billion bytes

Table 2. Basic parameters of DVD discs of the latest modifications

Parameter	Disk type
	DVD-ROM	DVD-RAM	DVD-RW	DVD+ RW	DVD-R
One side capacity	4.7 GB	4.7 GB	4.7 GB	4.7 GB	4.7 GB
Laser wavelength	650	650	650	650	650 (G) 635(A)
Reflectivity	18-30% (two-layer)	15-25% (2,6)		18-30%
Recording method	Impression from the matrix during production	Phase change	Phase change	Phase change	Changing dye color
Entry form	Not applicable	Wobbled Land& Groove	Wobbled groove	Wobbled groove	Wobble pre-groove
Inter-track distance	0.74 µm	0.615 µm		0.74 µm	0.74 µm
Minimum pit length	0,40	0,28			0,40
Number of zones	Not applicable	35	Not applicable	Not applicable	Not applicable
Rotation control method*	CAV	ZCLV CAV within zone	CLV	CLV (for video) or CAV (for data)	CLV
Data writing speed	up to 8.31 MB/s (read)	2.77 MB/s		11-26 Mbit/s,	2.77 MB/s
File system	Micro UDF and/or ISO9660	UDF/UDF Bridge	UDF/UDF Bridge	UDF/UDF Bridge	Type1 UDF Bridge Type2 UDF
Cost of a single-sided disk (drive)		$20-30($500)			$10-15 ($1000)

* CLV - (Constant Linear Velocity) constant linear speed

CAV - (Constant Angular Velocity) constant angular velocity

ZCLV - (Zone Constant Linear Velocity) zone constant linear velocity

DVD formats	Types of DVD drives
	DVD-RAM		DVD-RW		DVD-R(G)		DVD-R(A)		DVD+ RW		DVD-Video		DVD-Audio		DVD-player (universal)
	H	Z	H	Z	H	Z	H	Z	H	Z	H	Z	H	Z	H	Z
DVD-ROM	+	−	+	−	+	−	+	−	+	−	+	−	−	−	+	−
DVD-R(G)	+	−	+	+	+	+	+	−	+	?	+	−	+	−	+	−
DVD-R(A)	+	−	+	−	+	−	+	+	+	−	−	−	+	−	+	−
DVD-RAM	+	+	−	−	−	−	−	−	−	−	−	−	+	−	+	−
DVD-RW	+	−	+	+	+	+	+	−	+	−	+	−	+	−	+	−
DVD+RW	−	−	+	−	+	+	+	−	+	+	+	−	+	−	+	−
DVD-Video	+	−	+	−	+	−	+	−	+	−	+	−	−	−	+	−
DVD-Audio	+	−	+	−	+	−	+	−	+	−	−	−	+	−	+	−
DVD-AudioV	+	−	+	−	+	−	+	−	+	−	+	−	−	−	+	−

Note - in some cases, "+" means that reading or writing does not conflict with the DVD forum specifications, however such devices may not yet be on the market.
"-" means that there is no specific requirement for reading or writing, but there may be devices on the market that provide this capability