Optical discs are a popular storage medium. Most users are only familiar with CD and DVD discs; in fact, there are many more types of discs. The Land of the Soviets will tell you what are types of discs, and will help you understand their diversity.
Types of CDs
CDs, or CDs, were originally intended for recording and playing music, but are now used to store almost any computer information. 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). Exists mini cd 80 mm in diameter, but their capacity is less - 190-200 MB (21 minutes of sound). Mini CDs can be read on any medium except a car radio. There are curly CDs various forms, they are produced mainly for commercial purposes. Such disks are not recommended for use in computer drives, because at high rotation speeds they can burst.
CDs can be split into CD-ROMs, CD-Rs, and CD-RWs. This division is due to the ability to write information to the disc and the purpose of the disc. Information on disk CD-ROM written by the manufacturer, you cannot change or delete it, you can only read the data. 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 deletion and rewriting of information, but such discs will not be read by all drives.
Types of DVD discs
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
Double layer discs contain two information layers on one side, they are marked with the abbreviation DL. A double-sided disc is actually two discs glued together with non-working surfaces. Naturally, the thickness of such a disc is controlled to match the thickness of a conventional single layer DVD.
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-recordable 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 and have a theoretical lifespan of up to 30 years. But they are expensive, come mainly 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.
It is clear that no drive or player fully supports all DVD formats. Most modern drives support both DVD-R (W) and DVD + R (W) formats. But older drives and consumer players made before the DVD + R (W) format will only read DVD-R (W) discs. There are "super multi" drives that support all kinds of discs, including DVD-RAM.
Other types of discs
The so-called Dual Discs... These discs combine CD and DVD formats. On one surface of such a disc, music is recorded in CD format, and on the other - five-channel sound, video, menus, subtitles, images, etc. in DVD format.
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 100 GB four-layer disc has been announced, and a ten-layer disc up to 320 GB is planned to be released.
The confrontation between BD and HD DVD has been called the "format battle". But major movie studios have moved away from HD DVDs in favor of BD discs, so HD DVDs are officially discontinued and supported.
So, there are many types of optical discs. It is worth choosing a disc for recording information based on its capacity, the ability to rewrite information and the model of your drive or consumer player. Knowing the main types of disks, you will never get confused in their rich assortment.
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 sound recording and reproduction. 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 diameter of 15 mm. CDs are made of very durable transparent plastic - polycarbonate or PVC. The label is placed on one side of the disc, and the other side has a mirrored surface that shimmers with the colors of the rainbow. This is a recording area, a spiral track of which consists of pits - grooves of various lengths. The distance between two adjacent tracks of the spiral is 1.6 µm, that is, the recording density is 100 times greater than that of a conventional gramophone record. The pits are 0.6–0.8 µm wide 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, they can only be listened to. Using a laser beam, the signals are digitally coded onto a rotating optical disc. As a result of the recording, a spiral track is formed on the disc, 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 reflect the light exactly 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 reading 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) as storage media. 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 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. You can record on CD-R discs only once, and on CD-RW discs - many times, 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 printed 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; 9 - ; 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 the 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 designed 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. 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 ... Technical translator's guide
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 optical disc file systems Recording technologies Recording modes Batch recording Types ... ... Wikipedia
Data carrier in the form of a disc made of transparent material (glass, plastic, etc.) with metallization. microscopy, pits (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. It 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
Disks. This word means a lot to a person familiar with a computer. Various types of optical discs have occupied pride of place in the shelves and boxes of users for more than one decade. Years pass, new formats are added, but so far nothing has changed dramatically. And although flash media (popularly called "flash drives") have partially squeezed disks, first of all, as a source of transferring information from computer to computer, optical discs have no competitors as a long-term storage of information. So let's take a closer look at them.
The first optical discs were developed by Sony and Phillips in the late 1970s and 1980s. Since then, a lot of water has flowed under the bridge. The technology of creating disks has changed significantly twice in order to increase their capacity, booms and bumps, competition and format war - these three decades have passed under this sign.
But we are, first of all, consumers, right? It is important for us to understand all the variety of optical discs that exists on the market, to get acquainted with their varieties, features and reasons for their appearance. Let's get down to business?
CD (Compact disc)
Our first guest is a compact disc (CD) that appeared in 1982. The purpose of its development was to replace vinyl records with a modern, higher-quality carrier of audio information and directly distribute music. As a result, there were discs containing 74 minutes of sound, which was quite enough for recording a standard audio album. At the same time, the high quality of music recorded in the form of digital data was ensured. Initially, the volume of such a disk was about 650 MB. Varieties of CDs:
CD-ROM - This type of CD is manufactured in factories by stamping and is a non-recordable storage medium
CD-R (CD recordable) is a one-time recordable CD. The standard size is 700 MB. Sometimes there are 800 MB disks.
CD-RW (CD rewritable) - rewritable (reusable) CD. The standard size is 700 MB.
Rewritable discs (this also applies to CD-RW and DVD-RW) cannot be used “forever”. They also have their own resource. Usually referred to as 1000 rewrites. In practice, however, drives fail faster. There are many reasons for this, although the most important is probably the treatment of them.
Most often, after a year of constant use, multiple scratches appear on RW discs and, as a result, problems with reading information. By the way, if once, when using a disposable disc (R), it could be written only once, regardless of how much free space was left on it, now, using a multisession when recording, it can be "added", but erase everything the same is impossible. At the same time MirSovetov reminds that multisession discs are not always perceived by DVD-players, especially older models. They can either not see the entire disc, or read only the first session (recording).
In the early 90s, the DDCD format was developed - a double density compact disc, which contained twice as much information as a regular CD. This was achieved by reducing the size of the pit. But these discs did not become widespread due to incompatibility and high production costs.
Another type of media in the form of disks. Developed in 1992 by Sony as a replacement for compact cassettes, it is therefore mainly used as a carrier of audio information, although since 2004, with the advent of the new Hi MD format, it can be used to store any information. MiniDisk was not widely adopted. It is mainly used in players and camcorders by Sony and Sharp. They can also be found as disks with drivers and utilities for computer peripherals, in particular, for USB equipment (for flash drives, Bluetooth and WiFi adapters, etc.) DVD (Digital Versatile Disc)
In 1995, a group of developers (Toshiba, Matsushita, Sony, Philips, Time Warner, Pioneer, JVC, Hitachi and Mitsubishi Electric) signed an agreement on joint cooperation in the development and promotion of a new type of optical disc called Digital Video Disc (DVD) - digital video disk. Later, DVDs will be decrypted as Digital Versatile Disc (digital versatile / multipurpose disc), as over time these discs will be used to store more than video content. The first DVDs appeared in Japan in the fall of 1996.
What types of DVDs are there?
DVD-5 is a Single_sided, Single_layer disc. The volume is 4.7 GB.
DVD-9 is a Single_sided (Double_layer) disc. The volume is 8.5 GB.
DVD-10 is a Double_sided, Single_layer disc. The volume is 9.4 GB.
DVD-14 is a double-sided disc with one information layer on one side and two on the other. The volume is 13.2 GB.
DVD-18 is a Double_sided, Double_layer disc. The volume is 17 GB.
The last two are very rare and are practically not used in everyday life.
Varieties of DVDs:
DVD-R (Recordable) - one-time recordable DVD discs. The volume is 4.7 GB. DVD-RW (ReWritable) - rewritable (reusable) DVD discs. The volume is 4.7 GB.
Due to the high cost of the license for DVD technology, a number of companies that came together under the name “DVD + RW Alliance” developed the DVD + R (W) standard in 2002. Since then, DVDs have been divided into pros and cons. Now there is not much difference between them. Although some people prefer to use the pluses more (when using disks on a computer), for compatibility with the old ones, use the minuses.
DVD + R (Recordable) - one-time recordable DVD discs. Volume - 4.7 GB
DVD + RW (ReWritable) - rewritable (reusable) DVD discs. Volume - 4.7 GB
DVD-RAM (Random Access Memory) - special rewritable disks with random access to memory, which allow you to work with them as floppy disks, that is, freely write, erase data. They are more expensive than regular discs and are less common.
DVD-DL (Double Layer) - double layer recordable DVD discs. The volume is 8.5 GB. These discs are created using sophisticated technologies and are several times more expensive than conventional ones. Therefore, if you do not want to waste money and need to use a dual-layer disc for recording, MirSovetov recommends choosing discs from well-known manufacturers, only they can provide acceptable quality (for example, Verbatim).
In fact, regular DVD discs are not 4.7 GB, but 4.38 GB. This is due to the fact that when displaying the number 4.7, decimal numbers are counted, i.e. 1 KB = 1000 bytes, while in the digital world the binary system is used, in which 1 KB = 1024 bytes
HD DVD & Blu-ray (BD)
The next generation of optical discs are HD DVD and Blu-ray (BD) discs. Until February 2008, they coexisted in the market as competitors, but after the refusal of Toshiba (the main ideologue of HD DVD) to support their product, Blu-ray from Sony became the standard among high-definition video discs. Discs and players of the new generation are still quite expensive. In addition, MirSovetov would like to draw your attention to the fact that viewing high-definition films requires a large TV that would support high screen resolutions. And he, too, is not cheap. Therefore, most are quite satisfied with the quality of films on DVD and the new standard is moving into the market with a scratch. It will take at least several years to supplant DVD.
Blu-ray translates to blue ray. In the word blue, the last letter was deliberately omitted to avoid problems when registering a trademark.Types of HD DVD discs:
HD DVD-R (High Density DVD Recordable) is a one-time recordable disc. The volume of the disk is 15 GB. If the disk is dual-layer - 30 GB. HD DVD-RW (High Density DVD Rewritable) is a rewritable (reusable) disc. The volume of the disk is 15 GB. If the disk is dual-layer - 30 GB.
Varieties of Blu-ray discs
BD-R (Blu-ray Disk Recordable) is a single-use, recordable disc. The volume of such a disk is 25 GB. If the disk is double-layer - 50 GB
BD-RE (Blu-ray Disc Rewritable) is a rewritable (reusable) disc. The volume of such a disk is 25 GB. If the disk is double-layer - 50 GB
For several years now, a fundamentally new format for optical discs HVD (holographic multifunction disc) has been developed. Unlike previous formats, the principle of which has not changed (only the width of the tracks, pits and the laser wavelength changed), this solution is based on holographic technology, that is, data storage in a three-dimensional volume of the carrier (two lasers are used). At the same time, a phenomenal capacity is achieved - TB of information on one disk, and a high data transfer rate. Optical disc manufacturers
If you go to a store specializing in computer technology, you will see many different discs from different manufacturers, both well-known and completely unfamiliar (and sometimes even without identification marks). What can you advise here? It all depends on your needs. The price difference is usually not significant. If you need a disc to record something, without expecting long-term storage, you can use almost any product. If you are looking for long-term storage and are worried about reliability, then I would recommend buying discs from time-tested manufacturers such as Verbatim and TDK. They are a little more expensive, but much more reliable and of better quality. I highly do not recommend buying Digitex discs, especially rewritable (RW) discs, they account for a lot.
With all this, remember that even discs from leading manufacturers are not perfect. And they can sometimes let you down. This does not go anywhere. Besides, apart from discs, a lot depends on the drive and recording software.
About storing and using optical discs
What else would you like to say about optical discs? Many people think that this is a very reliable medium for storing information, but this is not entirely true. Discs can be stored for a long time, however, you need to remember about storage methods. It should be a dry, dark place. It is advisable to store discs in boxes. Handle them with care, as scratches can make it unreadable. Although during writing it is allowed, so to speak, the reserve for reading, but it is far from unlimited. And sometimes after a disk is damaged, it has to be revived ... but that is a topic for another conversation. Do not allow dust to fall on the working area of the disc, in general, this is the most delicate part of the media. Be attentive to her. I had to see people who seem to be experienced, put discs with their working part on the table, a heap of papers, wherever ... and then wondered - why did these discs become poorly readable? Before inserting a disc into the drive tray, carefully inspect its inner ring for cracks. Their appearance can lead to the fact that at the most crucial moment your data carrier will simply fly to pieces right in the drive.
By the way, what if the disc drive won't open? If the standard opening methods did not help, MirSovetov advises using a mechanical one (do not worry, you will not have to disassemble the drive for this). First, take a regular paper clip and straighten it. Then look at the drive bezel. Most of them have a small (1 mm) hole. Turn off the computer and insert a straightened paper clip into the hole. Press and the disc tray should open slightly. We grab it with our hand and open it completely. We take out the disk. This method can also be used if you turned off your computer, accidentally forgetting the disk that you need in the middle.
It should also be remembered that even without damage, the disks, after lying for a year or two, may become unreadable. Therefore, if you have very important information, it is better to re-save it periodically.
And finally, a banal warning. Do not forget that you can write on the disc only with a special marker. And only on the upper, non-working surface.
Of course, other factors also affect the safety of your information. For example, which drive do you use, which ones do you use. And just how you write them. But this is a topic for a separate conversation. And we will talk about this next time.
CDs, DVDs, and Blu-ray Discs are optical storage media that can electronically store movies, music, or other digital data. They operate primarily with a digital code. On the one hand, these storage media are digital information and communication technology, on the other hand, they are technical tools for any kind of digitization, calculations, recording, archiving, processing, transmission and presentation of digital content.
CD and DVD are acronyms, but Blu-ray disc has a slightly different nature.
CD stands for Compact Disc.
DVD is short for Digital Video Disc. A little later, the name "Digital Versatile Disc" appeared, since DVD can be used not only for video recording.
The Blu-ray Disc gets its name from the blue laser (as opposed to the white laser), which reads information from the disc and also writes information.
Compact disc (CD-ROM) has long been the main medium for transferring information between computers. Now he has practically ceded this role to more promising solid-state media, which work much faster and take up less space.
Story
For the first time, the idea of optical recording appeared in 1965, at the American Battelle Memorial Institute, Ohio. This technology was still extremely primitive at that time - with a photographic method, dark dots and lines were applied to the disc. To read the information, the disc was shone through with a special lamp. The technology was pioneered by the American physicist James Russell. But as is usually the case, he did not earn a dime from his invention. The scientist patented his technology in 1970. He also owns the idea of using a laser as a light source.
The CD was developed in 1979 by Sony. Sony used its own PCM signal coding method, Pulse Code Modulation, which was previously used in digital professional tape recorders. In 1982, the mass production of CDs began, at the plant in Langenhagen near Hanover, Germany. The first commercial music CD was announced on June 20, 1982.
According to Philips, more than 200 billion CDs have been sold worldwide in 25 years. Despite the fact that more and more people prefer to purchase music files over the Internet, according to IFPI, CD sales still account for about 70% of all music sales.
Microsoft and Apple Computer have made significant contributions to popularizing CDs. John Scully, then CEO of Apple Computer, said in 1987 that CDs would revolutionize the world of personal computers. One of the first mainstream multimedia computers / entertainment centers to use CDs was the Amiga CDTV (Commodore Dynamic Total Vision), later CDs were used in the Panasonic 3DO and Amiga CD32 game consoles. First standard
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In 1979, Philips and Sony entered into an agreement to jointly develop a new media. A year later, the companies introduced a new standard called CD-DA (Compact Disk Digital Audio). It was a disc with a diameter of 12 centimeters and a playing time of just over an hour. The format turned out to be surprisingly successful and convenient. It quickly won the hearts of both manufacturers and buyers.
The CD format has unconditionally ruled the market for 15 years. During this time, it ceased to be just a music disc, turning into a universal storage medium. However, by the middle of the 90s of the last century, the amount of information that one CD could contain was sorely lacking. 
The discs of the new format did not look different from ordinary CDs. But the amount of information was increased from 650 MB to 4.7 GB. It is also important that DVD players could play regular CDs without any problems, and therefore there were no problems with standards. With the advent of DVD, it has become possible to obtain high quality sound and picture at home. The format quickly became popular. Today the DVD Forum includes more than 250 companies around the world. And it’s hard to believe that at one time some analysts jokingly deciphered the title of the DVD as “Dead, Very Dead”, predicting the imminent death of the standard.
Some standardization problems only arose when the first recordable DVDs were introduced. Two standards have appeared in the world - DVD + R and DVD-R. Each of them had its own advantages and disadvantages, incomprehensible to the average user. However, users did not have any particular problems. You just had to make sure that the disc you purchased was supported by the available player (DVD-R was more common). Yes, universal players and recorders that support both standards appeared quite quickly. Today, not all users are even aware of the existence of various standards.
DVD repeated the history of CD. Highly specialized discs (and DVD was originally developed only for work with video) have become a universal storage medium. The cost of the turntables has dropped from a few hundred dollars to several dozen. The price of the media themselves is estimated at pennies.
Optical disc classification
Each of the groups of media 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-R DL, DVD + R DL);
3. rewritable discs (CD-RW, DVD-RW, DVD + RW, DVD-RAM).
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 disc 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 capacity), 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.At present (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 disc 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 with 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 brought into two different stable states of aggregation by heating, 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 / sec for DVD-drives
Currently, 52x-speed CD-drives are widely used - up to 7.8 MB / sec.
CD-RW discs are recorded 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 disc, 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 according to the standard technology, then the other is translucent, applied below the first and has a transparency of about 40%. To read double-layer discs, complex optical heads with a variable focal length are used. The laser beam, passing through the semitransparent layer, first focuses on the inner information layer, and upon completion of its reading it refocuses to the outer layer.
