Optical discs briefly. Recovery of optical discs. Differences between CDs, DVDs and Blu-ray discs
CD(Compact Disc) - an optical storage medium in the form of a plastic disk with a hole in the center, the process of writing / reading information to / from which is carried out using a laser. CDs are becoming faster and cheaper. Information is recorded on a CD in an industrial way. The most widespread are 5-inch CDs with a capacity of 670 MB. According to their characteristics, they are completely identical to conventional music CDs. The data on the disk is written in the form of a spiral (in contrast to the hard drive, the data on which are arranged in the form of concentric circles). In terms of physics, a laser beam determines the digital sequence of ones and zeros written on a CD, no matter how microscopic pits (pits, pit) on its spiral. Today, with a computer with a CD burner, you can make a disc in less than an hour.
DVD(Digital Versatile Disk, formerly Digital Video Disk), that is, a multi-purpose digital disk is 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 is sufficient to satisfy any manufacturer of computer games and encyclopedias, which would normally require several CD-ROMs to release, causing user inconvenience. The DVD-Video specification, around which so many copies broke, only provides for the recording of full-length film programs with high image quality, multi-channel sound and international settings. The DVD-Audio specification considers the standard for recording only sound, although it assumes a much higher quality, multi-channel and the ability to put on the same disc not only 74 minutes. 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 DVDs according to their data structure:
- DVD-video - contain 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 beam and disc - disk) - 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. new technology cardinal changes appeared in the logical structure of the disk, 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 precisely, and, consequently, to place data on the disk with a higher density. The shorter wavelength of the blue-violet laser allows more information to be stored on 12 cm discs of the same size as CD/DVD.
16. Personal computers. Device. Main characteristics.
A computer is an electronic device designed to work with information, namely introduction, processing, storage, output and transmission of information. In addition, a PC is a single two entities - hardware and software parts (which is reflected in the following diagram).
According to the definition of a computer, computer components can be divided into devices that perform certain functions related to information.
A data carrier in the form of a plastic or aluminum disk intended for recording and/or reproducing sound (CD), images (Video CD), alphanumeric information, etc. using a laser beam. The recording density of St. 108… … Big Encyclopedic Dictionary
A disc containing digital data that can be read using optical technology. [GOST 25868 91] Equipment topics. periphery. processing systems information EN optical disk …
OPTICAL DISC, in computer technology, 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 feature... ... Scientific and technical encyclopedic dictionary
A data carrier in the form of a plastic disc designed for recording and playing back sound (compact disc CD), images (video disc), alphanumeric information, multimedia (CD ROM, DVD), etc. using a laser beam. The first optical ... ... Encyclopedia of technology
Data carrier in the form of a disk made of a transparent material (glass, plastic, etc.) with metallized microscopy, depressions (pits), which together form spiral or annular ... ... 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
147 optical disk: A disk 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
According to GOST 25868–91, “Peripheral equipment for information processing systems. Terms and Definitions” is a disk containing digital data readable using optical technology… Office work and archiving in terms and definitions
A data carrier intended for recording and/or reproducing information using focused laser radiation. It consists of a rigid (usually optically transparent) base, on which a light-sensitive or reflective layer is applied and ... ... Natural science. encyclopedic Dictionary
Blu Ray (BD) discs are a new generation of storage media for high-definition video (HDTV) and high-density data. The Blu Ray standard was jointly developed by a group of consumer electronics and computer ... Technical Translator's Handbook
Books
- , Kuzmenko Galina. The training manual presents the content side of the manifestation of the psychological and pedagogical skills of the coach in the development of social and emotional intelligence in the system of significant qualities ...
What can be a carrier of information? That on which everything that we need to remember can be preserved, for human memory is short-lived. Our ancestors left important data on the ground, and on stone, and on wood, and on clay until paper appeared. It turned out to be a material that meets the most important requirements for a data carrier. It was light, durable, easy to record and compact.
These requirements are met by modern storage media - optical(these are CDs or laserdiscs). True, at the transitional stage (since the beginning of the 20th century), between paper and disks, magnetic tape helped us a lot. But her days are over. To date, the most convenient and reliable receptacle and storage of information are disks.
And how to put the information on the disk? The concept of "recording a cassette" has been known to us for more than a dozen years. We are also talking about disks. Only this process has become much easier and cheaper.
Today we will talk about optical storage media: device, recording technology, main differences.
CD-R became the very first recordable optical media. They had the ability to record only once. The data were stored when the working layer was heated by a laser, causing its chemical reaction (at t? = 250°C). At this point, dark spots are formed in places of heating. That's where the concept of "burn" came from. DVD-R discs are burned in a similar way.
The situation is slightly different with CD, DVD and Blu-ray discs that have an overwrite function. Such dark dots do not form on their surface, because. the working layer is not a dye, but a special alloy, which is heated by a laser up to 600°C. Then, the areas of the disk surface that fell under the laser beam become darker and more reflective.
At the moment, in addition to CD discs, which can be considered pioneers in a number of optical media, discs such as DVD and Blu-ray have appeared. These types of discs are different from each other. For example, capacity. A Blu-ray disc can hold data up to 25 GB, a DVD disc can hold up to 5 GB, and a CD disc can hold up to 700 MB in total. The next difference is the way data is read and written to Blu-ray drives. The blue laser is responsible for this process, the wavelength of which is one and a half times less than that of the red laser of CD or DVD drives. That is why on the surface of Blu-ray discs, equal in area to discs of other types, you can record information many times larger.
laser disc formats
The three types of laser discs listed above can also be classified according to their formats:
1. CD-R, CD-RW discs are the same in size (up to 700; sometimes 800 MB, but such discs are not readable by all devices). The only difference is that CD-R is a one-time recordable disc, while CD-RW is reusable.
2. DVD-R, DVD+R, and DVD-RW format discs differ only in the ability to rewrite DVD-RW discs multiple times, but otherwise the parameters are the same. 4.7 GB is the size of a standard DVD and 1.4 GB is the size of an 8 cm DVD.
3. DVD-R DL, DVD+R DL are double-layer discs that can hold 8.5 GB of information.
4. Formats BD-R - Blu-ray discs are single-layer, 25 GB and BD-R DL - Blu-ray discs are double-layer, 2 times larger.
5. Formats BD-RE, BD-RE DL Blu-ray discs - rewritable, up to 1000 times.
Discs with "+" and "-" signs are a relic of format disputes. Initially, it was believed that "+" (for example, DVD + R) is the leader for the computer industry, and "-" (DVD-R) is the quality standard for consumer electronics. Now almost all equipment easily recognizes discs of both formats. None of them have clear advantages over each other. The materials for their production are also identical.
what are optical discs
The disc itself, which is used at home to record information, is no different in size from commercially produced discs. The structure of all optical media is multilayer.
- The basis of each is the substrate. It is made of polycarbonate, a material resistant to various external environmental influences. This material is transparent and colorless.
- Next comes the working layer. For recordable and rewritable discs, it differs in its composition. For the former, it is an organic dye, for the latter, a special alloy that changes the phase state.
- Then comes the reflective layer. It serves to reflect the laser beam, and may include aluminum, gold or silver.
- Fourth - protective layer. The protective layer, which is a hard varnish, covers only CDs and Blu-ray discs.
- The last layer is the label. This is the name of the top layer of varnish that can quickly absorb moisture. It is thanks to him that all the ink that falls on the surface of the disc during the printing process dries quickly.
the process of transferring information to disk
Now a drop of scientific theory. All optical storage media have a spiral track running from the very center to the edge of the disk. It is along this track that the laser beam records information. The spots formed during the "burning" of the laser beam are called "pits". Areas of the surface that remain untouched are called "lands". In binary language, 0 is pit and 1 is land. When the disc starts playing, the laser reads all the information from it.
"Pits" and "lands" have different reflectivity, therefore, the drive easily distinguishes all dark and light areas of the disk. And this is the very sequence of ones and zeros inherent in all physical files. Gradually, it became possible to increase the accuracy of focusing due to the development of technologies that have achieved a reduction in the wavelength of a laser beam. Now a much larger amount of information can be placed on the same area of the disk as before. the distance between the laser and the working layer directly depends on the wavelength. Shorter wave means shorter distance.
disc burning methods
- Recording a disc in domestic conditions occurs with the help of a laser beam. It is also called "burning" or "cutting".
Recording in the industrial production of discs is called stamping. In this way, discs with recording of music, movies, computer games are produced in large quantities. All the information that gets on the disk during stamping is a lot of tiny depressions. Something similar happened when gramophone records were made.
organization of the recording process on optical media
Stage 1. Media type recognition. We loaded the disc and wait until the recorder gives out information about the appropriate recording speed and the most optimal power of the laser beam.
Stage 2. The recording management program queries the recorder about the type of media being used, the amount of free space, and the speed at which the disc should be burned.
Stage 3. We indicate all the necessary data requested by the program, and make a list of files that require writing to disk.
Stage 4. The program transfers all the data to the recorder and monitors the entire “burning” process.
Stage 5 The recorder sets the power of the laser beam and starts the recording process.
Even with media of the same format, the quality of the recording can be drastically different. In order for the recording quality to be high, you should pay attention to the speed specified in the recording. There is a "golden rule" - fewer errors at lower speed and vice versa. The recorder itself, namely, its model, also plays a significant role.
signature on optical discs
It is advisable to immediately sign the disk on which some information appeared, in order to avoid confusion. This can be done in different ways:
- printing text on blanks, the surface of which is varnished and allows you to print texts and images using an MFP with a special tray.
- using a recorder, with the support of special technologies that apply text and a single-color image to a special surface. The cost of such disks can be 2 times higher than the cost of simple disks;
- a signature made independently by hand (with a special marker);
- LabelTag technology - the text is applied directly to the disk work surface. The inscription may not always be well read;
- labels printed separately on any of the printers. Their use is not welcome, because. they can damage the surface of the disc, come off at the time of its playback.
duration of storage of optical storage media
On the labels of new discs, you can see a period that indicates how long you can save data on this medium. Sometimes this figure corresponds to 30 years. In reality, such a period is practically impossible. During its existence, the disk can be subjected to various influences and damage. If it was recorded at home, then its shelf life is reduced even more. Only ideal storage conditions will keep all the data on the disks safe and sound.
Recovery of optical discs
1. Research part
1.1 Some moments of history
All things that we use in everyday life have their own fascinating history. The optical disc familiar to us appeared in 1958. For a long time, defining the development of optical storage media such as CDs, DVDs and, more recently, Blu-ray discs. At first, the optical disc was used for video recordings. Over time, a disc was invented, which began to be used as a carrier for music files.
Despite the fact that the first discs of the CD format went on sale back in 1982, they are still used to record music files to this day. For recording movies, the DVD format is actively used.
1.2 Types of optical discs
On disks CD-R(they are sometimes also called “blanks”) you can write down your information, but it will be impossible to erase or change it. If there is free space left on the disk, and you enabled the option to add information when writing, you can add files to the disk.
Disks CD-RW support deletion and overwriting of information, but such discs will not be read by all drives. Recording and reading information discs are carried out using a laser. CD thickness - 1.2 mm, diameter - 120 mm, capacity - 650 or 700 MB (corresponds to 74 or 80 minutes of sound).
DVD discs allow you to store more information than CDs, due to the use of a laser with a shorter wavelength. The capacity of a standard size DVD (120 mm) can range from 4.7 GB to 17 GB, while the capacity of a mini DVD (80 mm) is 1.6 GB.
Depending on the capacity of DVD, there are such types of discs:
· 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-layered on one side and single-layered on the other, capacity - 13.24 GB
· DVD-18- double-layer double-sided disc, capacity - 17.1 GB
Whenever it is possible to write, rewrite and delete information, DVD discs, like CDs, are divided into ROM, R and RW. But in addition, there are such types of disks:
· DVD-R for general, DVD-R(G)- a write-once disc intended for home use.
· DVD-R for authoring, DVD-R(A)- a write-once disc for professional purposes.
· DVD-RW- rewritable disc. You can overwrite or erase information up to 1000 times. But you can not erase part of the information, you can only erase the disc completely and completely overwrite it.
· DVD-RAM using phase change technology. They can be overwritten up to 100,000 times and have a theoretical lifespan of up to 30 years. But they are expensive, are produced mainly in special cartridges and are not supported by most drives and players.
· DVD+RW are based on CD-RW technology and support overwriting information up to 1000 times. This format appeared later than DVD-RW.
DVD+R is a write-once disc, similar to DVD-R.
HD DVDs (High Density DVDs) can have a capacity of up to 15 GB, and dual-layer - up to 30 GB. Their main competitor is BD, Blu-ray Disc holds from 23 to 66 GB depending on the number of layers. A prototype of a four-layer disc with a capacity of 100 GB has been announced, and ten-layer discs with a capacity of up to 320 GB are also planned.
.3 Optical disc device
By its structure, a CD-R disc resembles a layer cake, the “filling” of which consists of active, reflective and protective layers, which are successively applied to a polycarbonate base - a plastic circle with a hole for fixing it on the spindle of the reading drive. At the same time, the basis of a CD-R disc is no different from that used in the technology of manufacturing compact discs by casting: the characteristics of the plastic must be such that the laser beam passing through it is properly focused and does not cause destruction of the disc.
The active (or recording) layer is the layer on which, in fact, information is recorded, i.e. it is he who is exposed to the laser beam, which "burns" (burn) pits (pits), encoding information (logical zeros and ones). In other words, during recording, the active layer changes its structure under the influence of a laser beam, and the subsequent irreversibility of changes in the active layer is the essence of information storage reliability. One type of active layer widely used today is cyanine. Cyanine is the original type referenced in the Orange Book standard and is widely used.
1.4 Rewritable discs (CD-
RW)
The difference between such discs and CD-Rs lies in the arrangement of the recording layer. The intermediate layer of special organic material can be either amorphous or crystalline. Amorphous substances tend to crystallize over time. No matter how we store a CD-RW, after a few years the record will be irretrievably lost. In addition, such discs can be easily erased by simple heating.
Structure of DVD discs
The principle of burning a DVD is not much different from the principle of burning a CD. The basis for recording and storing data on DVD-RAM and DVD-RW discs is the technology of changing the phase state of matter. The layered structure of one half of the disc is shown in the figure.
How to burn to DVD
The recording of amorphous regions is shown in this graph. A short high power laser pulse melts the recording material. This is followed by cooling below the crystallization temperature. The result of cooling is the prevention of the formation of crystallization centers. Thus, the growth of the crystalline phase does not occur, and the substance remains in the amorphous state.
.5 Erase fromDVD-disk
For erasing, it is necessary to return the substance to a crystalline state. Again, with the help of a laser, an amorphous substance is heated to a temperature T. Heating (or rather, annealing) continues for a time sufficient to restore the crystalline state of the substance. This time must be longer than the so-called crystallization time.
.6 Advantages of optical discs
The advantages of optical discs include: relatively large volume, ease of use, prevalence, low cost, resistance to magnetic influences.
1.7 Disadvantages of optical discs
Perhaps the disadvantages include - not resistance to mechanical damage (scratches, ultraviolet, temperature ...).
1.8 Difficulties in device design
The main device problems to be solved are:
Choose the right power electric motors
When rubbed, the plastic clogs the pores of the sponge, to avoid this, you need to moisten the sponge with water.
1.9 Alternative
Sanwa Supply will offer a very original innovation in terms of functionality called CD-RE1AT.
This miracle of technology restores damaged optical discs, as it is able to apply a special protective layer on their surface that fills in scratches. Externally, the product weighs similar to a conventional portable CD/DVD player with a hinged top cover, under which there are two seats for accommodating two recovery and two cleaning heads included in the package. The cost of this disc restorer in Japan is about 50 euros. Nothing is known about the sale of such devices in Kazakhstan.
2. Experimental part
.1 Demonstration Model Calculations
The principle of operation of the device is to smooth out scratches and clean the optical disc. I used two electric motors, one spinning disk, the second lapping, a sponge, parts from the DVD lower pulley, rubber cambric, goy paste, an empty can of disks, rubber glue, solvent, a power supply from the phone.
Sponge cut out in the form of a cylinder,
Goyi paste dissolved in solvent
The resulting dried sponge cylinder soaked in a solution of goy paste, I pasted on the lower pulley for mounting the disk.
I cut out the cover from the disks in the form of a disk, cutting out the upper part.
I screwed the electric motor from the edge by 3 centimeters and put a pulley with a sponge on the rotor of the electric motor.
To the bottom of the box, I screwed the second motor onto the rotor, which I put on a thick rubber cambric so that the disk put on the finger rotates.
Since this is just a demo model, I used two 12 volt motors from a DVD, one spinning disk, the second lapping, motor speed (250 rpm) and power (0.1a).
I connected two electric motors in parallel to the power supply from the phone.
3. Diagram-drawing of the operating device for disk recovery
.1 Manufacture and assembly of the disc cleaner
I took a 15x15 corner on the frame of the device
To spin the disk
1. I took the electric motor from the heater breeze 220 (v) 0.7 (w)
2. Two pulleys from a tape recorder
Bushing with bearings from the radio
Passik from the tape recorder.
Parts from the DVD to mount the disc.
To clean up a disk
6. I took the second electric motor from a screwdriver 12 (v) 2 (a).
7. The pulley from the tape recorder is small.
Paste GOI
adhesive rubber,
Solvent
Tape recorder power supply.
.2 Practical work on model making
1) First cut the corners at 15x15x300
2) An electric motor was welded to the corners by welding to rotate the disc, a pulley from the tape recorder was put on the rotor of the electric motor.
A pulley from a tape recorder was glued onto a sleeve with bearings from a radio tape recorder, parts from a DVD were glued onto a pulley to mount a disc.
Holes were drilled in the metal platinum for fastening the bushing.
The plate was welded to the frame by welding, so that the belt was stretched.
Checking in the case, fastening the disk and what speed the disk is gaining.
Holes were drilled in the plate for mounting the second electric motor at 12 (v) 2 (a), a small pulley from the tape recorder was put on the rotor of the electric motor and a sponge was glued in the form of a cylinder soaked in goy paste mixture.
Corners 15x15x150 2 pieces were welded vertically to the frame by welding.
A plate was welded horizontally to the corners by welding, two holes for mounting the motor were drilled.
In the plate on which the electric motor is screwed, oval holes were cut out to adjust on the surface of the dick, and the removal of the electric motor to replace the sponge with a mixture of goy paste soaked.
To give a look around the frame, sheathed with plywood and painted.
9. The power supply was made of plywood, a 12-volt transformer with a diode bridge is screwed into the box inside. From the outside, two sockets are screwed on one out 12 volts to the second 220 volts and a common switch for turning off and on the power.
Conclusion
Data recovery from an optical disc is a reality thanks to special programs. The fact is that operating system, if it cannot correctly read information from some part of the disk, it immediately stops copying and completely deletes the already copied part of the data. Bypass this function help special programs that use mechanisms for reading disks and make it possible to copy the necessary files (they do not guarantee 100% recovery of all information from a damaged disk).
These programs read information from damaged disks by accessing them directly. At the same time, bypassing the standard tools of Windows OS. Utilities repeatedly try to read the damaged sector of the disk, and at the same time, if reading errors occur, they can continue copying (or reading) information, which makes it possible to “pull” lost files from disks in their original form. If some sectors are not readable, some programs simply replace them with zeros, which in turn leads to a defect in the file.
Data recovery from an optical disc is not a simple and time-consuming process, often taking a lot of time. In practice, not all files recovered in this way will be usable. For example, if a couple of paragraphs disappear in a text document, then this is much better than the entire text that you wrote for a whole month disappears.
With music and video, everything can also be quite decent - it’s unpleasant, of course, if at some point while listening to your favorite song or watching a video plot you see incomprehensible squares on the screen, or you hear some incomprehensible sound, but again, this much better than losing your favorite materials altogether.
To restore the physical part of the disk plane, our device for cleaning optical disks will help.
Bibliography
optical disc laser recovery
1. http://strana-sovetov.com/computers - types of disks.
2. http://ergosolo.ru/reviews/gadgets/ - smart gadgets.
Http://www.datars.ru/recovery/optics-disc/ - disk recovery
Information carriers - material that is intended for recording, storage and subsequent reproduction of information.
Information carrier - a strictly defined part of a particular information system, which serves for intermediate storage or transmission of information.
Information carrier is the physical environment in which it is fixed.
Paper, photographic film, brain cells, punched cards, punched tapes, magnetic tapes and disks or computer memory cells can act as a carrier. Modern technology offers more and more new types of information carriers. To encode information, they use the electrical, magnetic and optical properties of materials. Carriers 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 line and column. The amount of information is 800 bits or 100 Kb.
2. Magnetic media - as they are used floppy magnetic disks and cassette magnetic tapes.
3. (compact discs) is a metallized plastic compact disc with a diameter of 120 mm and a thickness of 1.2 mm. One of its sides has a reflective aluminum layer, which is covered with a protective varnish to prevent damage. Recording and reading of information is performed by a laser beam on a track going 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. One of its sides has a reflective aluminum layer, which is covered with a protective varnish to prevent damage. Recording and reading of information is performed by a laser beam on a track going in a spiral from the center.
Types of optical discs:
1. CD-ROM (Compact Disk Read Only Memory) - CD, 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 rewrite information.
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 resistance.
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 stroke depth 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. CDs 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 at 44.1 kHz sampling rate and 16-bit bit depth, or a huge amount of MP3 audio. About 180 MB of information is placed on three-inch disks. Sometimes there are discs called "business card" (business card). In appearance and size, they resemble a business card, but in fact they are three-inch discs cut off on both sides. On such a CD is recorded from 10 to 80 MB.
In the late 1970s, Sony and Philips began to jointly develop a single standard for optical storage media. Philips has created a laser player, and Sony has developed a technology for recording on optical media. At the suggestion of Sony Corporation, the size of the disk was 12 cm, because. this volume made it possible to record the entire Ninth Symphony of Beethoven. In 1982, in a document called Red Book (Red Book), the standard for processing, recording and storing information on laser discs was published, as well as the physical parameters of the disc, i.e.: 1. The physical size of the disc. 2. Disk structure and data organization. 2. Recording data in a single stream from the center to the periphery. 3. Reading 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 (sector). Sectors are combined into a track (track). A maximum of 99 tracks can be recorded on a disc.
During the recording and reading of information, when the laser beam moves from the center to the periphery, the disk rotation speed is ↓. This is necessary to ensure the ability to read and write the same amount of information in the same time. Therefore, without the use of CLV technology, when playing, for example, musical works, there would be a change in the speed of performance.
Due to the relatively small size of laser discs compared to vinyl records, they have become known as compact discs, or CD (Compact Disk) for short. The first CDs were designed for recording and playing music and allowed up to 74 minutes of high-quality stereo sound to be stored. The standard for such discs was called CD-DA (Compact Disk Digital Audio).
With the development of the computer industry, there was a need for a technology that allows you to store on CDs not only digital sound, but also various data. Computer programs couldn't fit on floppy disks, and user files got bigger and bigger.
In 1984 a standard called the Yellow Book was published. Sony and Philips reorganized the structure of CDs and began to use new error correction codes - EDC (Error Detection and Correction) and ECC (Error Correction Code). The sector has become the main unit of data placement. 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 when the laser beam moves from the center to the periphery, the data flow increases. Modern CD drives support both technologies. Computer laser discs were called CD-ROM - Compact Disk ReadOnly Memory (literally - "read-only memory on CDs"). In the late 1990s, the CD-ROM drive became a standard part of every computer, and the vast majority of programs were distributed on CD-ROMs.
The consumer market expanded rapidly, production volumes increased, and the largest manufacturers began to develop technology that allows the user to independently burn any information on a CD. In 1988, the world's first CD-R (Compact Disk Recordable) was released by Tajyo Yuden. The biggest challenge faced by CD burner designers is finding highly reflective materials. Tajyo Yuden successfully coped with the task. The alloy of gold and cyanine they used to make these drives was over 70% reflective. The same company developed a method for applying an active organic layer to the surface of a disc, as well as a technology for dividing a disc into tracks.
DVD, DVD-R, DVD-RW, CD, CD-R, and CD-RW discs are produced 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 was originally deciphered as Digital Video Disc (Digital Video Disc), but later its meaning was changed to Digital Versatile Disc (Digital double-sided disc). The disc was fully compatible with the Red Book (Red Book) and Yellow Book (Yellow Book) standards. DVD is externally identical to CD, but allows you to record information that is 24 times larger in volume, that is, up to 17 GB. This was made possible by changing the physical characteristics of the disk and the use of new technologies. The distance between the tracks decreased to 0.74 µm, and the geometric dimensions of the pit were reduced to 0.4 µm for a single-layer disk and 0.44 µm for a two-layer disk. The data area has increased, the physical sizes of the sectors have decreased. A more efficient error correction code, RSPC (Reed Solomon Product Code), has been used, and more efficient bit modulation has become 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. Each side can have one or two working layers.
Burning single-layer DVDs is similar to burning CDs, but burning dual-layer discs is quite different from the process described earlier.
Dual-layer discs of the DVD-2 and DVD-9 types 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: it should reflect the laser beam well in the process of reading the outer layer and at the same time be as transparent as possible when reading the inner layer. Commissioned by Philips and Sony Corporation, 3M has created a material that meets these requirements: having a reflectance of 40% and the necessary transparency. DVDs are 0.6mm thick. For physical compatibility with CDs on DVDs, a 0.6 mm thick polycarbonate substrate was additionally glued.
The CD specification does not provide for any copy protection mechanism - discs can be freely duplicated and played back. However, starting in 2002, various Western record labels began to attempt to create copy-protected CDs. The essence of almost all methods is to deliberately introduce errors into the data written to the disc, so that the disc is played on a household CD player or music center, but not on a computer. The result is a game of cat and mouse: such discs are not readable on all household players, and on some computers they are readable, it turns out software, which makes it possible 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) + OPTICAL.
The surface of the magneto-optical disk is coated with a special material whose properties change under the influence of temperature and magnetic fields. All these discs differ from each other in diameter and the number of working surfaces. The amount of information is up to 10 GB.
