entranceOptical disk stores information. Characteristics of optical media
Recording and reading information in optical drives is performed contactlessly using a laser beam. Such devices include, first of all, CD-ROM, CD-R, CD-RW and DVD (ROM, R and RW) storage devices.
CD-ROM devices. In the CD-ROM devices (Compact Disk Read-Only Memory - CD only for reading) The carrier of the information is optical disk (CD) manufactured on flowing production with stamping machines and read-only.
The CD is a transparent polymer disc with a diameter of 12 cm and a thickness of 1.2 mm, for one side of which a reflective aluminum layer was sprayed, protected from damage to a layer of transparent varnish. The thickness of the spraying is a few ten thousandths of the millimeter.
The information on the disk is represented in the form of a sequence of depressions and protrusions (their level corresponds to the surface of the disk) located on a spiral track emerging from the area near the disk axis (only a few hundred tracks are placed on the radius on the surface of the rigid disk). The capacity of such a CD reaches 780 MB, which allows you to create reference systems based on it and training complexes with a large illustrative base. One CD according to information capacity is almost 500 floppy disk. Reading information from CD-ROM occurs with a sufficiently high speed, albeit noticeably less than the speed of the hard disk drives.
CD-R drives (CD-RECORDABLE). They allow, along with reading conventional CDs to record information on special CD-R optical discs. The information volume of such discs is 700 MB.
An entry on such discs is carried out due to the presence of a special light-sensitive layer from an organic material dark with heating. In the process of recording, the laser beam heats the selected points of the layer, which darken and cease to skip the light to the reflective layer, forming areas similar to the valves.
Recording information on CD-R discs is a cheap and operational way to store large amounts of data.
CD-RW drives (CD-Rewritable). Make it possible to make multiple record on the disk. The information volume of such discs is 700 MB.
CD-ROM drive - allows only to read information from any CD. Accordingly, each other devices will vary with the speed of reading and cache. CD-R drive - read and record, and the CD-RW drive not only reads, but also overwrites (erases information and writes a new one on top). Such drives are varying reading / write / restart (last only for CD-RW) and cache size.
DVD drives (Digital Versatile Disc, general purpose digital disk). The first DVDs appeared on the market somewhere in 96-97 years of the last century. DVD is an excellent medium for data of any type and is used as an ordinary computer media.
Outside the DVD looks like a regular CD, and even at the closer look it is hard to notice the difference. However, DVD features are much more. DVDs can store 26 times more than CD-ROM data.
DVD technology has become a huge jump in the media. A standard one-sided single-layer disk can store 4.7 GB data. But DVDs can be manufactured using a two-layer standard that allows you to increase the number of stored on one side of the data to 8.5 GB.
In addition, DVD discs are double-sided, which increases the capacity of the disk capacity to 17 GB. True, to read the DVD, a new device is necessary (DVD-ROM), but the DVD technology is compatible with the CD technology, and the DVD-ROM drive reads the CD discs, and different formats.
You can find various combined drives for optical disks on sale. For example, DVD-CD R / RW allows you to read DVD and CDs and record / overwrite on CDs. Another option is DVD-RW - CD-RW. Allows you to read, write and overwrite DVDs and CDs.
Our life has a diverse processing and storage tools. In the distant past, printed paper archives remained. What are modern storage media?
Optical disk: creating history
The first audio recorder was manufactured by Sony in the distance in 1979. It was the case as now, a plastic disk with a round hole in the center. Initially, it was used only to record audio files, and the information on it was applied by a special method of encoding Pulse Code Modulation. It lies in the fact that text or sound passes through an analog-to-digital converter and turns into a set of bits.
Later, in 1982, the mass production of disks began in Germany. They began to buy for storage of a variety of files. Soon they hit the counters not only music stores.
How is the CD? For the manufacture of the base, 1,2-millimeter polytecarbonate 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 a metal that information is applied in the form of a pit (deepening), squeezed over a spiral track. Reading files recorded on an optical disk occurs with a laser beam with a wavelength of 780 nm. It reflects from the surface of the plate, changes the phase and the intensity, falling onto the pit. Landa is customary to call gaps between the pit. The step of one track located in the spiral is about 1.6 microns.
Types of optical disks
There are several types of Digital Versatile Disc (DVD), Blu-Ray Disc (BD). All of them have a different capacity to record information. For example, DVD discs are made with a capacity from 4.3 to 15.9 GB, and CD is only up to 900 MB.
Also distinguish discs on multiplicity recording: single and multiple. In such carriers, the relief structure of the peit is formed in different ways. Overwriting is possible due to the organic material, which darkens under the action of the laser and changes the reflection coefficient. In the surprise, such a process is called burning.
More optical media may differ form. Figure CDs (Shaped CD) are usually used in show business as audio and video keepers. They are arbitrary shape (square, in the form of an airplane or heart). It is not recommended to use them in the CD-ROM drives, because at high speeds of rotation they can break.
CDs and their types
The optical disc CD-R is a media carrier that is read only. You can write files to it only once without adding and editing. Initially, the capacity of such discs reached only 650 MB or 74 minutes of audio recordings. Now devices that accommodate up to 900 MB of information are available. The advantages of them are that reading is supported by all standard CDs.
The CD-RW laser disk has the same memory, only the files on it can be recorded repeatedly (up to 1000 times). For this, standard computer programs. The minus is that not all devices are ready to work with this format. CD-RW are a bit more expensive than CD-R.
CDs with audio and video recordings do not have any degree of protection, they can be copied and reproduced. But the media with certain data is protected from copying StarForce technology.
ROM format discs are recorded in the factory and can only play data. Edit such a carrier is impossible. But RAM optical devices can be overwritten up to 10 thousand times and they are up to 30 years. Such discs are manufactured in additional cartridges, their reading is not supported by conventional drives.
DVD carriers and their characteristics
Digital Versatile Disc is a digital multipurpose information carrier. The structure is more dense and accommodates a lot of information (up to 15 GB). Such an optical disc is reminiscent of two CD glued together. Storage and reading a large amount of information possible due to the use of a red laser, which is 650 nm, and lenses with a maximum numerical aperture. DVDs have one or two recording parties, as well as one or two operating layers on each side. These indicators determine their container.
As divided into several formats. DVD-R or DVD + R are media to which you can only write information once. The record standard on such disks was developed by Pioneer in 1997. "Minus" and "positive" devices are characterized by a reflective layer material and special markup.
DVD RW optical discs (DVD + RW, DVD-RW) have the ability to multiple information overwriting. Moreover, the "positive" medium allows you to make changes to your discretion. Universal drives help solve the problem of incompatibility of formats (+ RW and -RW).
What is Blu-ray Disc?
This type of optical disk allows you to store and record digital data with high density. To play information (even high definition video) uses a blue laser beam in 405 nm, which narrows twice the spiral track. Files that are very close to each other are sensitive to mechanical damageTherefore, the disk should have a special care. Recently, carriers are made with a special coating that can be wiped with a conventional dry napkin.
There are blu-ray discs of the disposable and multi-sized record, as well as multi-layered (from 2 to 4 layers). The capacity of the "layered" carrier itself reaches 128 GB. In this case, it has a standard 12-centimeter diameter. Two-layer standard disk Blu-ray accommodates up to 50 GB of information. The development contains a device that reaches a capacity of 300-400 GB, which can read modern drives. For camcorders, drives of smaller diameter (80 mm) with memory capacity up to 15 GB are used.
To protect from copying Blu-Ray, equipped with digital Rom-Mark and Mandatory Managed Copy technology.
MINIDVD carrier destination
The MINI DVD optical medium is a reduced copy of the usual Digital Versatile Disc. It is in diameter 8 cm and is used in photo and video cameras. One-sided disk accommodates up to 1.4 GB of information, respectively, bilateral - 2.8 GB. According to the format, they are miniDVD-R (once recording) and miniDVD-RW (multiple).
Standard 12-centimeter drive is not designed to read Mini DVD. When using such disks in a laptop, the drive motor spindle should be applied. Sometimes there are problems with reading usually in such cases the computer gives the inscription "not found driver for a drive optical disks" To solve the problem, you should contact the experienced programmer.
External memory
Optical disks
Optical (laser) discs are currently the most popular media. They use the optical principle of recording and reading information using a laser beam.
Information on the laser disk is written on one spiral-shaped track starting from the center of the disk and containing alternating plots of depressions and protrusions with different reflectivity.
When reading information from optical disks, the laser beam installed in the drive falls on the surface of the rotating disk and is reflected. Since the surface of the optical disk has sections with different reflection coefficients, the reflected beam also changes its intensity (logic 0 or 1). The reflected light pulses are converted using photocells to electrical pulses.
In the process of recording information on optical discs, various technologies are used: from a simple stamping to a change in the reflective ability of the area of \u200b\u200bthe disk surface with a powerful laser.
There are two types of optical disks:
CDs (CD - Compact Disk, CD), which can be written to 700 MB of information; DVDs (DVD - Digital Versatile Disk, digital universal disk), which have a significantly greater information capacity (4.7 GB), as the optical tracks on them have a smaller thickness and are placed more tight.
DVDs can be two-layer (Capacity 8.5 GB), while both layers have a reflective surface carrying information.
In addition, the information container of DVDs can be even doubled (up to 17 GB), since information can be recorded on two sides.Currently (2006) the market received optical discs (HP DVD and Blu-Ray), the information container of which is 3-5 times higher than the information capacity of DVDs due to the use of a blue laser with a wavelength of 405 nanometers.
Optical drive drives are divided into three types:
- Without the possibility of recording - CD-ROM and DVD-ROM
(ROM - Read Only Memory, read only memory).
On the cD-ROM disks And the DVD-ROM stores information that was recorded on them in the manufacturing process. The recording on them is not possible.- With a single recording and multiple reading -
CD-R and DVD ± R (R - Recordable, recorded).
On disks CD-R and DVD ± R, information can be recorded, but only once. The data is recorded on the disk of the high power laser beam, which destroys the organic dye of the recording layer and changes its reflective properties. Driving a laser capacity, on the recording layer, the alternation of dark and light spots is obtained, which, when reading, is interpreted as logic 0 and 1.- With the possibility of overwriting - CD-RW and DVD ± RW
(RW - Rewritable, overwritten). cD-RW discs And DVD ± RW information can be recorded and erased repeatedly.
The recording layer is made of a special alloy, which can be heated in two different stable aggregate states, which are characterized by varying degrees of transparency. When writing (erasing), the laser beam heats the pathway and translates it into one of these states.
When reading the laser beam has a smaller power and does not change the state of the recording layer, and alternating areas with different transparency are interpreted as logic 0 and 1.The main characteristics of optical drives:
disk capacity (CD - up to 700 MB, DVD - up to 17 GB) data transfer rate from carrier in rAM - Measured in fractions, multiple speed
150 KB / s for CD drives (such a read speed of information was at the first CD drives) and
1.3 MB / s for DVD drives (such a read speed of information was at the first DVD drives)
Currently, 52x-high-speed CDs received widespread - up to 7.8 MB / s.
The CD-RW recording of the discs is performed at a lower speed (for example, 32x multiple).
Therefore, the CDs are marked with three numbers "reading speed x CD-R recording speed CD-RW" (for example, "52x52x32").
DVD drives are also marked with three numbers (for example, "16x8x6"access time - the time required to search for information on the disk is measured in milliseconds (for CD 80-400ms). When complying with the storage rules (storage in vertical cases) and operation (without scratching and contamination), optical media can maintain information for decades.
Additional information about the structure of the disks
The disc created by the industrial method consists of three layers. An information pattern is applied to the disc on the disk created from transparent plastic by the method of stamping. For stamping there is a special prototype matrix of the future disc, which squeezes the tracks on the surface. Next, the base is sprayed with a reflective metal layer, and then from above also protective layer From a thin film or special varnish. Various drawings and inscriptions are often applied to this layer. Information is read from the working side of the disk through the transparent foundation.
Recorded and rewritable CDs have an additional one layer. In such discs, the base does not have an information pattern, but there is a registering layer between the base and reflecting layer, which can be changed under the influence of high temperature. Recording the laser warms the specified areas of the registering layer, creating an information pattern.
The DVD can have two registering layers. If one of them is performed according to standard technology, then the other - translucent, applied below the first and has transparency about 40%. For reading two-layer disks, complex optical heads with variable focal length are used. Laser beam, passing through a translucent layer, first focuses on the internal information layer, and upon completion of its reading, it is refocused on the outer layer.
Optical carriers are CDs with a diameter of 12 cm (4.72 inches) or a mini-disks with a diameter of 8 cm (3.15 inches). Optical media consist of three layers:
1) polycarbonate base (outer side of the disk);
2) an active (registering) plastic layer with a variable state phase;
3) the finest reflective layer (the inner side of the disk).
In the center of the CD, there is a round hole worn on the spindle of the CD drive.
Recording and reading information on a CD is carried out by a head that can emit a laser beam. There is no physical contact between the head and the surface of the disk, which increases the service life of the CD. The phase of the second plastic layer, crystalline or amorphous, varies depending on the cooler speed after heating the surface with a laser beam during the recording process performed in the drive. With slow cooling, plastic goes into crystalline state and information is erased ("0" is written); With a quick cooling (if the microscopic point is heated), the plastic element goes into an amorphous state ("1" is written). In view of the difference in the reflection coefficients from crystalline and amorphous microscopic points of the active layer, during reading, the intensity of the reflected beam is perceived by the reading head occurs. The surface of the disk is divided into three areas. The initial area (LEAD-IN) is located in the center of the disk and is read first. It contains the contents of the disk, the address table of all records, the disc label and other service information. The average area contains basic information and takes most of the disk. The final area (LEAD-OUT) contains a label of the end of the disk.
The information on the CD is encoded with great redundancy by the corrective code of the Reda Solomon, providing the restoration of the original information when it is not possible to read it from the disk.
The CD withstands several hundred cycles of overwriting. The reading of information is carried out when the CD rotation with a frequency of more than 10,000 revolutions / min.
Depending on the read / record feature, all CDs can be divided into three types:
1) ROM (Read Only Memory) - read-only; recording is not possible;
2) R (Recordable) - for one-time recording and multiple reading; The disc may be once recorded; Recorded information cannot be changed and it is read-only;
3) RW (Rewritable) - for multiple recording and reading; Information on the disk can be rewritten repeatedly.
These types of discs differ in the material from which the second plastic layer is made.
Consider the types of CDs CD (Compact Disc), DVD (Digital Versatile Disc - digital universal (multilateral) disc) and Blu-ray, having the same 4.72 inches size.
CD volume is 650 or 700 MB. Music disks relate to CD and are only designed to read music from them. Access time to CD - 0.05-0.3 s.
DVD format is the development of CD, their volume is 4.7 GB due to a more dense recording. DVD continue to be improved. There are several DVD competing formats: DVD-, DVD + and DVD-RAM.
Blu-ray format is further development DVD and allows you to record 25 GB of information per layer.
The names of CD and DVD formats depending on the read / write feature are presented in the table.
It's no secret that the story began with gramplastics. Save information at home is problematic, and only sound was stored on it. The principle of operation is not a secret, so vinyl disk It was popular for more than a hundred years, and until now, collectors and DJs use and keep them. It was cool to look like a needle, while scrolling the disk, walked in a word like on perfectly smooth spirals. On this, the principle of obtaining sound was built. When changing the depth and width of the groove, changed sound wave And further enhanced pipe (gramophones, patephones). With the development of electronics, the principle of information removal was made on a piezoelectric needle and received modern, until no long ago, the recorder of the recorder.
So the 70s came up. And there was a jump in the media of the information (we will miss the magnetic ribbons). Invented a disc made from polycarbonate, having transparency, with aluminum spraying. Polycarbonate served as the basis and defended sputtering from external influences, and on spiral spirals were deepened. The principle of removal and write information on this is based on how you see not far away from the recordlasty. The thin ray was reflected from the surface of the spraying and came to a light reproduction, which in turn determined the changes and relatively received information was created units and zeros. And then on the principle of alphabet Morse Information is converted to music, movies, pictures, files, etc.
Now we will deal in the notation on CDs:
But S. DVD disks, everything has developed much more difficult. This disk was created for storing information in a large amount and engaged in developments a large number of firms. (DVD-R and DVD-RW). Miscellaneous spraying had a variety of characteristics and household players, various firms, began to conflict with discs, universality was lost from here. Therefore, uniting, invented a new type of disk, called name DVD + R and DVD + RWThey cost, oddly enough, cheaper. Now without any difference how to use the disk, as household players adapted. There is a difference only in overwriting disks, DVD-RW. need to fully erase before recording, and DVD + R. It is enough to erase the "cap" and impose an entry from above.
As they say, how much do we do and everything is not enough for us. According to this, progress did not stop bilateral and two-layer And two in one discs. Well, S. double-sided, Everything is simple, spraying caused from both sides, and how the audio cassette needs to turn the disk. Two-layer - This is one of the hotels near the laser, made translucent, and do not need to get up from the sofa to turn the disk. Well, with the last option, undress two two-layer and glue together.
So we reached the peak of developments modern Mira optical disk, it is - HD-DVD and Blu-Ray.
HD-DVD. - This is a disk that was made on the basis of our hard workers described above, but the use of a blue laser.
Blu-ray. - Absolutely different development, a blue laser is used.
If you recall the spectrum (rainbow), it will be seen that with a blue beam, you can get much thinner than the beam, so these discs are much more common. But this will be in the next topic.
It seems to today, everything. It remains only a little about the storage and use of the disk to tell. The disk is not tasty, it is not necessary to gnaw it, well, if only someone has a lack of plastic in the body. And also this is not a tool for the game on the nerves, therefore it is not necessary to drive claws on it. It is advisable not to bend, although it breaks difficult, but the fragments can fall before, and this will affect your body. Also, constant bend violates inside the spraying, it cracks and zeros of units, no longer be the coincidence. In the sun does not fry him, he is an element D. I do not need at all, but to turn into a zyuchny product and it's not a pitch anyway. Do not insert a disc with a crack to the drive, otherwise it will have to spend either for repairs or to buy a new one.
I hope YOU competent and you do not need everything on items to list, to things need to be careful and they YOU Thank you for it.