Characteristics of optical storage media. Lecture on the topic: Optical discs Who and when invented the optical disc
Optical Disc Recovery
1. Research part
1.1 Some history
All the things we use in everyday life have their own fascinating history. The optical disk we are familiar with appeared in 1958. For a long time, determining the development of optical information storage devices, such as CDs, DVDs and, more recently, Blu-Ray discs. At first, the optical disc was used for video recordings. Over time, a disk was invented, which began to be used as a storage medium for music files.
Despite the fact that the first CD format discs went on sale back in 1982, they are still used to this day for recording music files. The DVD format is actively used to record films.
1.2 Types of optical discs
To disks CD-R(they are sometimes also called “blanks”) you can record 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 recording, you can add files to the disk.
Discs CD-RW support deleting and rewriting information, but such discs will not be readable by all drives. Writing and reading disk information is carried out using a laser. CD thickness - 1.2 mm, diameter - 120 mm, capacity - 650 or 700 MB (corresponding to 74 or 80 minutes of sound).
DVDs 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, and the capacity of a mini DVD (80 mm) is 1.6 GB.
Depending on the capacity of DVD, the following types of discs are distinguished:
· DVD-5- single-layer, single-sided disk, capacity - 4.7 GB
· DVD-9- double-layer single-sided disk, 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
Based on the possibility of recording, rewriting and deleting information, DVD discs, like CDs, are divided into ROM, R and RW. But additionally, the following types of disks are distinguished:
· DVD-R for general, DVD-R(G)- a recordable disc intended for home use.
· DVD-R for authoring, DVD-R(A)- a recordable disc for professional purposes.
· DVD-RW- rewritable disc. You can overwrite or erase information up to 1000 times. But you cannot erase part of the information, you can only erase the disk completely and completely rewrite it.
· DVD-RAM use phase change technology. They can be rewritten up to 100,000 times, with a theoretical service life 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 rewriting information up to 1000 times. This format appeared later than DVD-RW.
DVD+R- a recordable disc similar to DVD-R.
HD DVDs (High Density DVDs) can have a capacity of up to 15 GB, and double-layer ones - up to 30 GB. Their main competitor is BD, Blu-ray Disc holds from 23 to 66 GB depending on the number of layers. A prototype of a four-layer disk with a capacity of 100 GB has been announced, and it is also planned to release ten-layer disks with a capacity of up to 320 GB.
.3 Optical disk device
In its structure, a CD-R disc resembles a layer cake, the “filling” of which consists of active, reflective and protective layers, which are sequentially applied to a polycarbonate base - a plastic circle with a hole for fixing on the spindle of the reading drive. At the same time, the 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 a laser beam, which “burns” the pits that encode 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 the change in the active layer is the essence of the reliability of information storage. One type of active layer that is widely used today is cyanine. Cyanine is the original type referred to in the Orange Book standard and is widely used.
1.4 Re-writable discs (CD-
RW)
The difference between such discs and CD-Rs lies in the design 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 recording will be irretrievably lost. In addition, such discs can easily be 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 layer-by-layer structure of one half of the disk is shown in the figure.
The principle of recording on a DVD disc
A record 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 to prevent the formation of crystallization centers. Thus, the growth of the crystalline phase does not occur, and the substance remains in an amorphous state.
.5 Erase fromDVD-disk
To erase, the substance must be returned to its crystalline state. Again, using a laser, the amorphous substance is heated to 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 disks include: relatively large volume, ease of use, prevalence, low cost, resistance to magnetic influences.
1.7 Disadvantages of optical discs
Perhaps the disadvantages include the lack of resistance to mechanical damage (scratches, ultraviolet radiation, temperature...).
1.8 Difficulties in device design
The main problems of the device that need to be solved are:
Select suitable power electric motors
When rubbing, the plastic clogs the pores of the sponge, to avoid this you need to moisten the sponge with water.
1.9 Alternative
Sanwa Supply will offer a very unique innovation called CD-RE1AT.
This miracle of technology restores damaged optical discs, as it is able to apply a special protective layer to their surface that fills scratches. Externally, the product weighs like a regular portable CD/DVD player with a hinged top cover, under which there are two seats to accommodate the two recovery and two cleaning heads included in the package. The cost of this disk restorer in Japan is about 50 euros. Nothing is known about the sale of such devices in Kazakhstan.
2. Experimental part
.1 Calculations for demonstration model
The operating principle of the device is to smooth out scratches and clean the optical disc. I used two electric motors, one rotating disk, the second lapping, a sponge, parts from a DVD, a lower pulley, a rubber casing, goyim paste, an empty can from disks, rubber glue, solvent, a power supply from a phone.
I cut the sponge in the form of a cylinder,
Goi paste dissolved in solvent
I glued the resulting dried sponge cylinder soaked in a solution of goya paste onto the lower pulley for attaching the disk.
I cut the disc cover in the shape of a disc, cutting out the top part.
I screwed the electric motor 3 centimeters from the edge and put the pulley with the sponge on the electric motor rotor.
A second motor was screwed to the bottom of the box onto the rotor, which was covered with a thick rubber cambric so that the disk placed on the finger would rotate.
Since this is just a demo model, I used two 12 volt motors from the DVD, one spinning the 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 of a working device for disk recovery
.1 Manufacturing and assembly of a disk cleaning device
For the frame of the device I took a 15x15 corner
To rotate the disk
1. I took the electric motor from a breeze heater 220 (v) 0.7 (w)
2. Two pulleys from a tape recorder
Bushing with bearings from the radio
Passenger from a tape recorder.
DVD parts for mounting the disc.
To wipe the disk
6. I took the second electric motor from a 12 (v) 2 (a) screwdriver.
7. The pulley from the tape recorder is small.
Paste GOI
Rubber glue,
Solvent
Power supply from a tape recorder.
.2 Practical work on making a model
1) First, we cut the corners to 15x15x300
2) An electric motor was welded onto the corners to rotate the disk, and a pulley from a tape recorder was placed on the rotor of the electric motor.
A pulley from a tape recorder was glued onto the bushing with bearings from the radio, and parts from the DVD for attaching the disk were glued onto the pulley.
Holes were drilled in the metal plate to attach the bushing.
The plate was welded to the frame so that the belt was tensioned.
Checking in action, 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 a tape recorder was put on the rotor of the electric motor, and a cylinder-shaped sponge soaked in a mixture of goya paste was glued on.
2 pieces of corners 15x15x150 were welded vertically to the frame.
We welded a plate horizontally to the corners and drilled two holes for mounting the motor.
In the plate on which the electric motor is screwed, oval holes were cut out to adjust the surface of the drive, and the electric motor was removed to replace the sponge soaked in the goya paste mixture.
To give the look, the frame was lined with plywood and painted.
9. The power supply was made of plywood; a 12-volt transformer with a diode bridge was screwed into the box inside. There are two sockets screwed on the outside, one with 12 volts, the other with 220 volts and a common switch for turning off and on the power.
Conclusion
Data recovery from an optical disk is a reality thanks to special programs. The fact is that the operating system, if it cannot correctly read information from some part of the disk, immediately interrupts the copying and completely deletes the already copied part of the data. Special programs that use mechanisms for reading disks and make it possible to copy the necessary files help to bypass this function (they do not guarantee 100% recovery of all information from a damaged disk).
These programs read information from damaged disks by directly accessing them. At the same time, bypassing standard Windows OS tools. Utilities repeatedly try to read the damaged disk sector, and at the same time, if read errors occur, they can continue copying (or reading) information, which makes it possible to “pull” lost files from 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.
Recovering data from an optical disk is not a simple and labor-intensive 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 losing the entire text that you wrote for a whole month.
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 strange squares on the screen, or you hear some strange sound, but again, this much better than losing your favorite materials altogether.
To restore the physical part of the disk plane, our optical disc cleaning device will help.
Bibliography
optical disk laser restoration
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
A data carrier in the form of a plastic or aluminum disk, intended for recording and/or playback of sound (CD), images (video), alphanumeric information, etc. using a laser beam. Recording density St. 108… … Big Encyclopedic Dictionary
A disk containing digital data readable using optical technology. [GOST 25868 91] Equipment topics. periphery processing systems information EN optical disk...
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
A data carrier in the form of a plastic disk designed for recording and playing back sound (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 transparent material (glass, plastic, etc.) with metallization. layer, on which microscopy, recesses (pits) are formed using digital optical recording, 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
147 optical disk: A disk containing digital data read 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” – a disk containing digital data read using optical technology... Records management and archiving in terms and definitions
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... ... Natural science. encyclopedic Dictionary
Blu Ray Discs (BD) are a new generation of storage media for storing high-definition video (HDTV) and high-density data. The Blu Ray standard was jointly developed by a group of consumer electronics and computer companies... Technical Translator's Guide
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- , Kuzmenko Galina. The training manual presents the content side of the manifestation of the psychological and pedagogical skills of a trainer in the development of social and emotional intelligence in a system of significant qualities...
A variety of data processing and storage tools have become an integral part of our lives. Printed paper archives are a thing of the distant past. What are modern storage media?
Optical disc: history of creation
The first device for storing audio recordings was produced by Sony back in 1979. It was, as it is now, a plastic disk with a round hole in the center. Initially, it was used only for recording audio files, and information was applied to it using a special Pulse Code Modulation encoding method. It consists in the fact that text or sound passes through an analog-to-digital converter and turns into a set of bits.
Later, in 1982, mass production of discs began in Germany. They began to be purchased for storing various files. Soon they hit the shelves of not only music stores.
How does a CD work? To make the base, a 1.2-mm thick polycarbonate plate with a diameter of 120 mm is used, which is first coated with a thin layer of metal (gold, aluminum, silver, etc.) and then varnish. It is on the metal that information is applied in the form of pits (recesses) extruded along a spiral path. Reading of files recorded on an optical disc occurs using a laser beam with a wavelength of 780 nm. It is reflected from the surface of the plate, changes phase and intensity, hitting the pits. Land is usually called the intervals between pits. The pitch of one track located in a spiral is about 1.6 microns.
Types of optical discs
There are several types of Digital Versatile Disc (DVD), Blu-ray Disc (BD). They all have different capacities for recording information. For example, DVDs are produced in capacities ranging from 4.3 to 15.9 GB, while CDs are only available in capacities up to 900 MB.
Discs are also distinguished by the frequency of recording: single and multiple. In such media, the relief structure of the pits is formed differently. Rewriting is possible thanks to organic material, which darkens under the influence of a laser and changes the reflectance. In common parlance, this process is called burning.
Optical media may also differ in shape. Shaped CDs are usually used in show business as storage of audio and video files. They come in any shape (square, airplane or heart). They are not recommended for use in CD-ROM drives because they may burst at high speeds.
CDs and their types
The CD-R optical disc is a read-only storage medium. You can write files to it only once without the right to add or edit. Initially, the capacity of such discs reached only 650 MB or 74 minutes of audio recording. Devices are now available that can hold up to 900 MB of information. Their advantage is that all standard CDs support reading.
A CD-RW laser disk has the same amount of memory, but files can be written to it multiple times (up to 1000 times). For this, standard computer programs are used. The downside is that not all devices are ready to work with this format. CD-RWs cost a little more than CD-Rs.
CDs containing audio and video recordings do not have any degree of protection and can be copied and played. But media with certain data are protected from copying by StarForce technology.
ROM format discs are written at the factory and are only capable of reproducing data. It is impossible to edit such media. But optical devices like RAM can be rewritten up to 10 thousand times and last up to 30 years. Such disks are produced in additional cartridges; their reading is not supported by conventional disk drives.
DVD media and their characteristics
Digital Versatile Disc is a digital multi-purpose storage medium. Its structure is more dense and holds a lot of information (up to 15 GB). This optical disc resembles two CDs glued together. Storing and reading a large amount of information is possible thanks to the use of a red laser, which is 650 nm, and a lens with a maximum numerical aperture. DVDs have one or two recording sides, and one or two working layers on each side. These indicators determine their capacity.
As well as are divided into several formats. DVD-R or DVD+R are media that can only be written to once. The recording standard for such discs was developed by Pioneer in 1997. “Minus” and “plus” devices differ in the material of the reflective layer and special markings.
DVD RW optical discs (DVD+RW, DVD-RW) have the ability to rewrite information multiple times. Moreover, the “plus” media allows you to make changes in places necessary at your discretion. Universal drives help solve the problem of format incompatibility (+RW and -RW).
What is Blu-ray Disc?
This type of optical disc allows you to store and record digital data at high density. To reproduce information (even high-definition video), a blue laser beam of 405 nm is used, which narrows the spiral path by half. Files located very close to each other are sensitive to mechanical damage, so the disk must be given special care. Recently, media have been produced with a special coating that can be wiped with a regular dry cloth.
There are single-use and reusable Blu-ray discs, as well as multi-layer discs (from 2 to 4 layers). The capacity of the most “layered” media reaches 128 GB. Moreover, it has a standard 12-centimeter diameter. A double-layer standard Blu-ray disc can hold up to 50 GB of information. A device is in development that reaches a capacity of 300-400 GB, which can be read by modern disk drives. For video cameras, smaller diameter disks (80 mm) with a memory capacity of up to 15 GB are used.
For copy protection, Blu-rays are equipped with ROM-Mark digital watermarks and Mandatory Managed Copy technology.
Purpose of MiniDVD media
Mini DVD optical media is a smaller copy of the regular Digital Versatile Disc. It is 8 cm in diameter and is used in photo and video cameras. A single-sided disk holds up to 1.4 GB of information, respectively, a double-sided one - 2.8 GB. In terms of format, they come in MiniDVD-R (one-time recording) and MiniDVD-RW (multiple recording).
A standard 12cm drive is not designed to read Mini DVDs. When using such drives in a laptop, you should use a drive motor spindle. Sometimes there are reading problems. Usually in such cases the computer displays the message “the driver for the optical drive was not found.” To solve the problem, you should contact an experienced programmer.
It's no secret that the story began with gramophone records. Storing information at home is problematic, and only audio was stored on it. The principle of operation is not a secret, but vinyl disc has been popular for over a hundred years and is still used and preserved by collectors and DJs today. It was funny to watch how the needle, while scrolling the disk, seemed to shake on a perfectly even spiral. The principle of sound production was built on this. When the depth and width of the groove changed, the sound wave changed and was further amplified by the pipe (gramophones, gramophones). With the development of electronics, the principle of collecting information was made on a piezoelectric needle and a modern, until recently, record player was obtained.
The 70s are here. And there was a leap in storage media (we will skip magnetic tapes). They invented a disk made of polycarbonate, which was transparent, coated with aluminum. Polycarbonate served as the basis and protected the spraying from external influences, and depressions were burned into the spraying in a spiral. The principle of capturing and recording information is based on this, as you can see we have not gone far from the gramophone record. A thin beam reflected from the coating surface and arrived at the light receiver, which in turn determined the changes and created ones and zeros based on the information received. And then according to the ABC principle Morse information is converted into music, movies, photos, files, etc.
Now let's look at the notation on CDs:
But with DVD disks, everything turned out much more complicated. This disk was created to store large amounts of information and was developed by a large number of companies (DVD-R and DVD-RW). Different coatings had different characteristics and household players from different companies began to conflict with discs, hence the loss of versatility. Therefore, having united, they invented a new type of disk, called DVD+R and DVD+RW, they are, oddly enough, cheaper. Now it doesn’t matter which disc to use, since household players have adapted it. The only difference is in the re-writable discs, DVD-RW must be completely erased before recording, and DVD+R Just erase the “header” and put the recording on top.
As they say, no matter how much you give us, it’s not enough for us. Therefore, progress did not stop there, double sided And two-layer and two in one discs. Well with bilateral, everything is simple, the coating was applied on both sides, and like an audio cassette you need to turn the disc over. Double layer- this is one of the layers closest to the laser, made translucent, and you don’t need to get up from the couch to turn the disk over. Well, with the last option, take two two-layer and glue them together.
Now we have reached the peak of developments in the modern optical disk world, this is - HD-DVD and Blu-ray.
HD-DVD- this is a disk that was made based on our workaholic described above, but using a blue laser.
Blu-ray- a completely different development, a blue laser is used.
If you remember the spectrum (rainbow), you will see that from a blue beam you can get a much thinner beam, so these disks turned out to be much more voluminous. But this will be discussed in the next topic.
It seems like that’s all for today. It remains only to tell a little about storage and use of the disk. The disc is not tasty, there is no need to chew it, well, unless someone has a lack of plastic in the body. And also this is not a tool for playing on nerves, so you don’t need to run your claws over it. It is advisable not to bend it, although it is difficult to break, but fragments can end up where they shouldn’t, and this will affect your body. Also, the constant bending is disrupted by the coating inside, it cracks and the zeros of the unit will no longer coincide. Don't fry it in the sun, it's an element D It’s not needed at all, but it will turn into a thin product and you won’t shove it anywhere. Do not insert a disk with a crack into the drive, otherwise you will have to spend money either on repairs or on buying a new one.
I hope YOU literate and you don’t need to list everything point by point, you need to treat things with care and they YOU they will be grateful for this.
Lecture 4
Peripherals
Optical disks: main characteristics and purposes
CD-disks, their types, history of creation
Optical music CDs replaced vinyl CDs in 1982, around the same time as the company's first personal computers. IBM
These devices were the result of a fruitful collaboration between two giants of the electronics industry = a Japanese company Sony and Dutch Philips.
The strictly defined capacity of CDs is associated with such an interesting story.
Executive Director of the company Sony Akio Morita decided that CDs should meet the needs of classical music lovers only - nothing more and nothing less. After the development team conducted a survey, it turned out that the most popular classical piece in Japan at that time was Beethoven's 9th Symphony, which lasted 72-73 minutes. Therefore, it was decided that the CD should be designed for exactly 74 minutes of sound, or more precisely, 74 minutes and 33 seconds. Thus was born the standard known asRed Book (RedBook ). When 74 minutes were converted into megabytes, the result was 640 MB.
Philips specialists determined the minimum requirements for the quality of sound recording and regulated, for example, such characteristics of audio CDs as their size, data encoding method and the use of a single spiral track. In particular, the sampling frequency of stereo signals was determined at the level of 44.1 kHz (for one channel 22.05 kHz), and the bit depth of each = 16 bits.
The two companies mentioned above also played a leading role in the development of the first specification for digital compact discs = the so-calledYellow Book| (YellowBook), or simply CD-ROM. She served as the basis for creating CDs with a comprehensive presentation of information, that is, capable of storing not only audio, but also text and graphic data ( CD-DigitalAudio, CD-DA ). In this case, the drive, reading the disc header, itself determined its type = audio or digital data. In this format, however, the logical and file formats of CDs were not regulated, since the resolution of these issues was completely left to the manufacturing companies. This, in particular, meant that a CD that complied with the Yellow Book requirements could only work on a specific drive model. This state of affairs, especially in connection with the great commercial success of CDs, of course, could not satisfy the manufacturers of such devices. In the common interests, it was urgent to find a compromise.
That is why the specification became the second de facto standard for digital CDs HSG (HighSierraGroup), or simply HighSierra . This document was, generally speaking, advisory in nature and was proposed by the major manufacturers of digital compact discs in order to ensure at least some compatibility. This specification already defined both logical and file formats of CDs.
The specification created turned out to be so attractive that the standard ISO -9660 (1988) for digital compact discs, in principle, coincided with the main provisions HSG . Please note that all CDsmeeting the requirements of the standard ISO-9660, which defines their logical and file formats, are compatible with each other. Specifically, this document specifies how to locate the contents of a CD. The basic format proposed in HSG -specifications, was in many ways similar to the floppy disk format. As you know, the system track (track 0) of any floppy disk not only identifies the floppy disk itself (its density, type of OS used), but also stores information about how it is organized into directories, files and subdirectories.
Leading Data Track on a CD begins with a service area necessary for synchronization between the drive and the disk. Next is the system area, which contains information about disk structuring. The system area also contains directories for this volume with pointers or addresses to other areas of the disk. The significant difference between the structure of a compact disc and, for example, a floppy disk is that on CD The system area contains the direct address of files in subdirectories, which should make them easier to find.
The physical device of the CD.
The CD consists of made of several layers combined into a single, round, thin plate. The diameter of the vast majority of CDs is 120 mm, which is equal to five inches. A standard 5-inch disk contains 640-700 MB of information.
CD - ROM , created industrially, consists of three layers (Fig. 3.19,A). The disc base, made of transparent polycarbonate, occupies the main volume of the disc. When a base is made by stamping or injection molding, an information pattern is applied to it, resulting in a transparent plastic plate that is smooth on one side and contains many microscopic depressions on the other (sometimes called pits, fromEnglish pit - recess), the depth of which is measured from the surface ( land ). Next, a reflective metal layer is applied to the base (most often aluminum, although other metals or alloys can be used), and then a protective coating of a thin polycarbonate film or special varnish, on which printing is often placed - various drawings and inscriptions
Rice. 3.19. CD structure ("); surface micrograph CD ( 6 )
CD drive ( CD - ROM ). Reading information from a CD, just like writing it, occurs using a laser beam, but, of course, with less power.
The laser emits coherent light consisting of synchronized waves of the same length (Fig. 3.20,A). The beam, hitting a light-reflecting surface, is deflected through a splitting prism to a photodetector, which interprets this as “1”, and when it enters the cavity, it is scattered and absorbed - the photodetector records “0”.
Unlike hard drives, whose tracks are concentric circles, a CD has one physical track in the shape of a continuous spiral, running from the outside to the inside of the disk. However, one physical track can be divided into several logical ones: each of its 360-degree fragments is treated as a separate track, by analogy with magnetic disks.
CD - R . Write-once optical disc type ( Write Once / Read Many storage - WORM ) has been known since the late 1980s.
When writing data to WORM physical marks (marks) are made on the surface of the media with a low-power laser and since these marks cannot be erased, the recording is done only once.
If normal CD - ROM made by mechanical stamping of recesses (marks, “pits”), when writing CD - R A laser is used to “burn out” marks in an organic dye. Once heated to a critical temperature, the “burned” area becomes opaque (or absorbent) and, when read, reflects less light than adjacent areas that were not heated by the laser. This technology imitates the way information is read from a regular CD when light is completely reflected from the surface (" land "), but is dissipated by a depression (" pit »).
Unlike technology WORM , disks CD - R do not allow you to erase previously recorded data, but they do allow you to sequentially add them over several sessions (or sessions) to free areas of the disk. The problem is that such multi-session discs may not be fully readable on earlier versions of players, computers, or when using outdated operating systems.
CD - R disposable without the ability to add
CD + R disposable with the ability to add
CD - RW - rewritable CD ( rewritable CD ). A standard was proposed in mid-1997 CD - RW (known as Orange Book III ), which allows the user to record over old data or delete individual files. Specifications CD - RW guarantee compatibility within the CD reader family as well as compatibility with CD - ROM .
Recording layer placed between layers of dielectric, which remove excess heat from it during the recording process.
As a recording medium CD - RW usually uses a transparent composition composed of compounds of silver, indium, antimony and tellurium. During the recording process, a focused laser beam selectively heats areas of the material above the melting point (500-700 °C), and after sufficiently rapid cooling, the substance passes into the so-called amorphous state.
When abraded, the layer is heated to a temperature that is below the melting point but above the crystallization temperature (200 °C) for sufficient time, and the atoms return to an ordered (transparent) state.
To obtain these effects in the recording layer, the writing laser of the device CD - RW uses three power levels:
high, so-called “recording power”, creates opaque (absorbing) areas in the recording layer;
medium (“erasing power”), melts a section of the recording layer and converts it to a reflective (transparent) state;
low (“read power”), does not change the state of the sensitive layer and can be used to read data.
Transparent areas allow the metallized layer to reflect light, while opaque areas absorb it. The problem that arises is that the disk reflects less light than CD - ROM or CD - R and therefore the disks CD - RW can only be read on devices that support the new specification Multiread (Multi-reading).
Overcoming buffer insufficiency. By the end 1999 G. performance doubled to 8x/24x, but a problem known as buffer underrun (or write buffer underrun) arose when the speed of the machine and the MD began to lag behind the speed of the devices CD - R (the device is ready to write to the disk, but the information in the write buffer is already exhausted and there is “nothing to write” - as a result, the disk turns out to be damaged). To avoid such effects, firstly, they began to use cache memory located on the writing device. CD -player (sizes from 256 KB to 2 MB), secondly, devices began to adapt to the speed of information flow, reducing or increasing the recording speed.
DVD media
Track width DVD is 0.8 or 0.74 µm, and the minimum pit length is 0.44 or 0.40 µm. To read data in DVD -drives use a red laser with a wavelength of 650 nm and an optical system with a numerical aperture of 0.6. Capacity standard DVD is 4.7 GB (for 80 mm media - 1.4 GB). Unlike CDs, DVD -carriers can be double-layered or double-sided. Double layer capacity DVD is 8.5 GB, double-sided - 9.4 GB. Double-sided discs are essentially two identical media glued together (the disc must be flipped over to read the second side).
Universal digital disk (digital versatile disc - DVD) is a type of storage device that, unlike CDs, was designed for wide use from the moment it entered the market.
There are five physical DVD formats (or books) , which are not much different from the various “shades” of CD:
DVD-ROM is a high-capacity read-only storage medium;
DVD-video is a digital storage medium for films;
DVD audio - audio storage only; format similar to audioCO;
DVD-R - write once, read many times; format similar to CD-R;
DVD-RAM is a rewritable (erasable) version of DVD, which was the first to appear on the market and subsequently found DVD-RW and DVD+RW formats as competitors. The same size as a standard CD (diameter 120 mm, thickness 1.2 mm), DVDs provide up to 17 GB of storage with transfer speeds faster than CD-ROM, access times similar to CD-ROM, and are available in four versions :
DVD-5 - single-sided single-layer disc with a capacity of 4.7 GB;
DVD-9 - single-sided double-layer disc 8.5 GB;
DVD-10 - double-sided single-layer disc 9.4 GB;
DVD-18 - capacity up to 17 GB on a double-sided, double-layer disc.
For the first At a glance, a DVD is no different from a CD: a plastic disc with a diameter of 120 mm and a thickness of 1.2 mm, both use lasers to read data recorded in the grooves of a spiral track. However, DVD's sevenfold increase in data capacity over CD was largely achieved by pushing all the tolerances of its predecessor system.
Firstly, the tracks are placed more densely, the DVD track pitch (distance between them) is reduced to 0.74 microns, more than 2 times compared to 1.6 microns for a CD.
Secondly, the DVD specification allows information to be read from more than one layer by changing the focus of the reading laser beam.
Third, DVD allows you to use double-sided discs.
The DVD format has been plagued with compatibility issues from the very beginning. Some of these are now permitted, but others, particularly rewritable and video disc compatibility, remain. Incompatibility with some CD-R and CD-RW drives has been a long-standing problem. The blanks used in some of these devices cannot properly reflect the laser beam used in DVD-ROM readers, which makes them "unreadable". For CD-RW media, this problem was easily solved by the Multi-Reading standard and by equipping the DVD-ROM device with lasers with two different wavelengths. However, getting DVD-ROM drives to reliably read all CD-R media is a much bigger challenge. The laser of a DVD reader has difficulty reading CD-Rs due to the reduced reflectivity of the surface in light at 650 nm, while at 780 nm it is almost the same as for CD-ROMs.
Recordable DVD Disc Formats There are five versions of recordable DVDs:
DVD-R regular;
DVD-RAM (rewritable);
DVD-RW;
DVD+RW.
All recordable DVD formats include a set of specifications that define the physical characteristics of the recording environment. This level of operation is the "physical layer of the media", and the ability to read a disc on a particular player or drive depends on its ability to support the appropriate physical layer regardless of what data is written.
CD drives can only work with media belonging to the group CD. DVD drives allow you to work with DVD and CD media. The classification of optical discs is given below:
In each of the media groups, there are three main types of disks:
1. read-only disks ( CD-ROM, DVD-ROM);
2. write-once discs ( CD- R, DVD- R, DVD+ R, DVD- RDL, DVD+ RDL);
3. rewritable discs ( CD-RW, DVD-RW, DVD+ RW, DVD-RAM).
Differences between formats
DVD+ R/RW devices are in no way inferior to storage devices DVD-R/RW , and with some improvements they can outperform their competitors in performance and reliability. For example, the write speed of drives DVD+ RW higher than most devices DVD-RW . Some disks DVD-R are recorded at a speed close to that of DVD+ R , and with the advent of models DVD-RW The performance gap has narrowed even further.
Another difference between the “-” and “+” technologies is the way the disks in the drives are rotated. Drives CD, DVD-ROM and DVD-RW - These are constant line rate devices that provide a constant data transfer rate when reading disks. In these drives, the disks spin more slowly when reading information from external, longer tracks.
Types of optical drives
Depending on the functions available, optical drives can be divided into several main types.
1. CD- ROM- drives that allow reading information from media belonging to the group of compact discs.
2. DVD- ROM- drives that allow reading information from different types CD and DVD media.
3. CD- RW- drives that allow you to read information from optical discs belonging to the CD group, as well as write to CD-R and CD-RW.
4. DVD- ROM/ CD- RW- so-called combined drives that allow you to read information from different types CD and DVD -media, as well as recording on CD-R and CD-RW.
5. DVD- RW, DVD+ RW, DVD± RW- universal recording drives that allow you to read information from different types CD and DVD media, as well as recording on CD-R, CD-RW , writable and rewritable DVD (set of supported DVD -carriers depend on the specific model).
To measure the speed characteristics of optical drives, conventional units are used, which differ for CD and DVD formats. The data read speed of 150 KB/s was chosen as the reference point (1x) for the CD group media. Therefore, 8x for CD drive corresponds to a data transfer rate of 1200 KB/s, 12x - 1800 KB/s, etc.
In case of DVD devices, the single speed is already 1350 KB/s. So 4x for DVD media corresponds to a speed of 5400 KB/s - which is equivalent to 36x on the scale CD .
In the characteristics of drives that support reading and/or writing of different types of opticaldisks, the maximum speed for each of them is usually indicated. Short designationThe speed characteristics of the carrier are called the speed formula. For example, in the case of a drive DVD - ROM speed formula 8/52 means maximum reading speed equivalent to 52x for CD and 8x for DVD . For drive CD - RW speed formula 32/24/48 means the maximum recording speed on CD - R And CD - RW respectively 32x and 24x and maximum speed readings 48x.
TechnologyLightScribe
One of the most interesting technological innovations of 2005 in the field of recordable optical discs was the technology LightScribe . It allows you to apply high-quality monochrome images to the decorative surface of discs directly in the recording drive.
The principle underlying the technology LightScribe , quite simple. As is known, under the influence of a laser beam, the active layer of recordable discs loses its transparency. By illuminating some areas of the working layer with a laser and leaving others untouched, a monochrome image can be formed using a recording drive.
At the beginning of 2004 the company HP announced the creation of an improved direct disc labeling system ( DirectDiscLabelingSystem ), which later received the commercial name LightScribe . This technology was developed by specialists MitsubishiKagakuMedia (MKM) and HP . Unlike other technology - DiscT@2, LightScribe involves applying images not to the working layer of the disc, but on the reverse side - where the label is usually located (of course, recordable discs for this must be equipped with an additional photosensitive layer).
To take advantage of technology LightScribe , you need to have three components: LightScribe -compatible recording drive, media with an additional photosensitive layer and special software. In this case, after finishing recording information, the user can turn the disk over and use the recording drive to apply an image to its decorative surface.
Of course, the implementation of additional features will entail a slight increase in prices for recording drives and blank media. True, according to HP , implementation of support LightScribe will lead to an increase in the cost of the recording drive by about $10. Regarding media LightScribe , they are understandably more expensive to produce than conventional recordable discs, but the price difference will also be negligible.
In 2005 HP has signed agreements to license the use of this technology to some major record drive manufacturers (notably LG, Toshiba, Philips and Lite-On (Sony)).
High-density optical media
Improvements in the capabilities of media systems and, as a consequence, the need for high quality data (video and audio) have led to the fact that this type of information has become cramped on the standard DVD . The development of new formats has been and is being carried out by various companies, but two standards have matured for commercial use.
1. Blu- rayDisc(from English blueray - “blue ray”, abbreviated BD ) is a new generation of high-density optical storage devices developed by a consortium of companies led by Sony . This standard has no common roots with DVD . The recording density per layer is 25 GB.
Note
When choosing a name for the new standard, the developers had to distort the word blue, since if spelled correctly it could not be used to register a trademark.
2. HDDVD ( High- DefinitionDVD) - new generation format developed Toshiba and NEC versus Blu-ray. HDDVD recognized as an evolutionary development of the standard DVD . The recording density of discs of this format is 15 GB per layer.
Until the end of 2007, it was not clear which standard would become dominant in the industry. However, the beginning of 2008 put the finishing touches on “ i". Toshiba Company announced the abandonment of this project in favor of the construction of factories for the production of flash memory, which it considers more promising.
Regarding Blu-ray , then it did not become popular and widespread overnight. As it turned out, the positions DVD are still strong, but consumers are in no hurry to switch to the new format. The rapid spread of the “blue ray” is also hampered by the high cost of the devices themselves. In light of global economic turmoil, it is still unclear how price dynamics for this type of device will develop in 2010. Discs Blu-ray retained the same dimensions that were characteristic of their predecessors CD and DVD : 120 and 80 mm. Due to the technological features of the coating, they were initially very sensitive to various types of mechanical stress. The developers of the prototypes even thought about protecting the media with a special cartridge. In the future, such a nuance would clearly not be in favor of the new standard. Therefore, engineering minds were still able to solve this problem. A new polymer coating has been found that can protect data from external influences. According to some sources, new disks can remain functional even if scratched by a screwdriver. It should be noted that these impressive capabilities have led to increased production costs for these media.
In Blu-ray technology A blue-violet laser with a wavelength of 405 nm is used for reading and writing. Let us remember that the usual DVD and CD use red and infrared lasers with wavelengths of 650 and 780 nm, respectively. This reduction made it possible to narrow the track by half compared to the usual DVD - up to 0.32 microns - and increase the data recording density.
Base speed 1x for BD is 36,864 Kbps, which is 27 times more than DVD , and is 243 times greater than CD . 2x bit rate players are capable of exceeding 73,000 Kbps.
An important characteristic of new media is volume. Native Compatibility BD with disks of previous generations is not provided for by the standard, however the association BDA recommends that all manufacturers implement support DVD to ensure backward compatibility.
Disk versions with a capacity of 100 GB and higher are in the process of development.
Latest generation of optical discs
Holographic multi-purpose disk (HolographicVersatileDisc) - a promising technology for the production of optical disks, which involves significantly increasing the amount of data stored on the disk compared to And .
It uses technology known as , which uses two : one - red, and the second - green, combined into one parallel beam. laser reads data encoded in a grid with layer close to the surface of the disk, while a laser is used to read auxiliary signals from a conventional CD layer deep within the disk. Auxiliary information is used to track reading position like a system on a regular hard drive. On or this information is embedded in the data.
