What is an optical drive in a computer? Optical Discs and Optical Disc Drives

Optical disc

Optical disk

a data carrier in the form of a plastic disk intended for recording and reproducing sound (CD), images (video disc), alphabetic digital information, (CD-ROM, DVD), etc. using a laser beam. The first optical discs appeared in 1979. Philips created them for recording and playing back sound. An optical disc consists of a rigid, optically transparent base, on which a thin working layer and an additional protective layer are applied. Thanks to the optical reading method, optical discs are much more durable than gramophone records. The diameter of a standard CD is 120 mm (4.5 inches), thickness - 1.2 mm, center hole diameter - 15 mm. CDs are made from very durable transparent plastic - polycarbonate or polyvinyl chloride. A label is placed on one side of the disc, and the other side has a mirror surface that shimmers with rainbow colors. This is a recording zone, the spiral track of which consists of pits - recesses of various lengths. The distance between two adjacent spiral tracks is 1.6 microns, i.e. the recording density is 100 times greater compared to a conventional gramophone record. The width of the pits is 0.6–0.8 µm, and their length is variable. It reflects the length of the sequences of "1" recorded digital signal and can vary from 0.9 to 3.3 µm. Information in the form of pits is protected from mechanical damage on one side by transparent disc material, and on the other by a layer of plastic and a label. Compared to mechanical sound recording, it has a number of advantages: a very high recording density and the complete absence of mechanical contact between the medium and the reading device during the recording and playback process. Music CDs are recorded at the factory. Like gramophone records, they can only be listened to. Using a laser beam, the signals are recorded digitally on a rotating optical disk. As a result of recording, a spiral track is formed on the disc, consisting of miniature grooves and smooth areas. In playback mode, a laser beam focused on a track moves across the surface of a rotating optical disk and reads the recorded information. In this case, the depressions are read as ones, and the areas that evenly reflect light are read as zeros.

Contactless reading of information from a CD is carried out using an optical head or laser pickup. The optical head consists of a semiconductor laser, an optical system and a photodetector that converts light into electricity. The reading laser beam is focused on a spiral track with pits located deep in the disk. The head never comes into contact with the disk - it is always at a strictly defined distance from it, ensuring that the track of pits is in the focus of the optical system.

Multimedia technology allows you to combine text and graphics with sound and moving images on a personal computer. Optical compact devices are used as information storage media in such multimedia computers. CD-R discs OM (Compact Disk Read Only Memory - i.e., read-only memory on a CD). Outwardly, they do not differ from audio CDs used in players and music centers.

The capacity of one CD-ROM reaches 650 MB; in terms of capacity, it occupies an intermediate position between floppy disks and a hard magnetic disk (hard drive). A CD drive is used to read CDs. Information on a CD is written only once in an industrial environment, and on a personal computer it can only be read. The most popular ones are published on CD-ROM various games, encyclopedias, art albums, maps, atlases, dictionaries and reference books. All of them are equipped with convenient search engines that allow you to quickly find the material you need. The memory capacity of two CD-ROMs is enough to accommodate an encyclopedia larger in volume than the Great Soviet Encyclopedia.

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

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

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

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

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

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

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

OPTICAL 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 represent... ... Scientific and technical encyclopedic dictionary

Working with optical discs Optical disc An image of an optical disc, ISO image Emulator optical disks ods Software to work with file systems optical discs Recording technologies Recording modes Batch recording Types ... ... Wikipedia

Data carrier in the form of a disk made of transparent material (glass, plastic, etc.) with metallization. layer, on which 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

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

Unlike an NMD, an optical disk has only one physical track in the form of a continuous spiral, running from the inner diameter to the outer one. But a physical track can be divided into several logical ones. If for NMD it is possible to record on different tracks, then recording on optical discs occurs sequentially in a spiral.

The area on an optical CD that contains data is called IPformation Area(information area). This section starts with a diameter of 44 mm, ends 2 ... 3 mm before the edge of the disk and contains the following three zones (in the order of their placement from the center of the disk):

1) input directory zone (Lead-in Zope);
2) data zone (Data Zope), which contains data written to the disk;
3) zone of the source directory (Lead-out Zope) with an end-of-disk mark.

At the end of the outer track and at the beginning of the inner track there is a middle zone (MiddleZope), which does not contain data. This area is used to allow the laser beam to change focus to read data from the internal track.

The input directory area in CD discs contains the TOC content (Table of Contents), recording addresses, number of titles, total recording time, volume and name of the disc. The data area of ​​a CD has the following data structure. The basic data unit of a CD is frame (frate), which contains 24 coded bytes, one control byte and eight bytes for error correction. The frame is preceded by 24 bits, any of which has a fixed value (pattern) and three merge bits. When the laser is brought to the frame, the beginning of the frame is determined by the template; 98 frames form a sector, the smallest addressable unit of data on a CD. The sector contains 3234 encoded bytes (2352 information bytes and 882 error correction and control bytes). Of the 2352 bytes, user information can occupy 2048 (in mode “1”) or 2336 bytes (in mode “2”). This organization of data recording on CDs and the use of error correction algorithms allows for high-quality reading of information with a probability of error per bit of 10-10.

Generalized structure of an optical disk drive

The simplified structure of the GCD is shown in Fig. 3.
Several recording methods are used for GCD: ablative - by burning holes in the opaque medium of the medium; by using local change reflectance coefficient of the environment; transferring the storage medium from the crystalline phase to the amorphous one and vice versa; transformation of the magnetic state of the structure; changing the color of the local area. The first two methods are used for “non-erasable” recording, and the rest are used for repeated rewriting of information on the GCD.

When recording, a beam of a semiconductor laser diode, controlled by the recording data through a collimator, mirror and objective lens, burns a hole in the information layer of the disk. The presence of a hole corresponds to the entry “1”. During reading, an unguided laser beam (received from a beam splitter) enters the work surface through another beam splitter, a mirror and a lens.
In reading mode, the mirror moves. Light from the laser passes through a polarization-separation prism, hits a polarizing filter (the light is polarized in a certain plane), and then is focused on the surface of the optical disk. If a laser beam hits the flat surface (lands) of a CD-ROM or DVD-ROM disc, the light is reflected almost entirely. If the light hits the recess (pits), then most of the light is scattered. The reflected light passes through a beam splitter to a photodiode, the signal from which is processed by electronic readout circuits. Precise alignment of the beam on the track is ensured by the track servo unit, focusing by the focusing servo unit, and a constant number of revolutions by the disk rotation servo unit (see Fig. 3).

Based on the capabilities of recording discs, optical disc drives are divided into drives with the ability to both read and write discs (recordable drives) and read-only drives , and by disk type - to CD drives And DVD drives.

Figure 4

The optical drive consists of: main functional units:

- boot device;
- disk drive;
- optical block;
- track drive;

- data encoding-decoding block;
- systems automatic regulation;
- audio unit;
- connectors.

Boot device There are two types of disk drives: container (caddy) And tray. In the first type of floppy drive, the disk is placed in a plastic container and inserted into the drive (this container performs the same functions as a 3.5-inch floppy disk container). In the second type of drive, the disc is placed on a tray (Fig. 3), which is pulled out after pressing the Eject button. After pressing the button again or lightly pressing the tray, it is pushed into the drive (pop-up mechanism).

On the front panel of the drive, in addition, there are: a device operation indicator (busy, light bulb), a jack for connecting headphones or a stereo system (for listening to audio CDs), and a sound volume control (also for audio CDs).
There is also a hole with which you can remove the CD even in an emergency, for example, if the Eject button does not work. You need to insert a thin rod 2-3 cm into this hole, then the tray will slide out.

Optical block contains optical system drive shown in Fig. 4. To read data from CDs, a laser with a wavelength of 780 nm (in the infrared range) is used, and for reading from DVDs, a laser with a wavelength of 650 nm (red) is used. Therefore, DVD drives that read from CDs and DVDs typically contain two lasers with separate optical systems or a common optical system (switchable between one or the other laser).

Figure 5. Optical drive design: 1 - tray; 2 - track drive; 3 - interface control bus; 4 - optical system; 5 - floppy drive; 6 - disk

To write data to the disk, a separate recording laser is used, which operates in a pulsed mode with variable power (to “burn” the disk, change the phase state from crystalline to amorphous, and return to the crystalline state). Typically, the recording and reading lasers have a common optical system. The surface of the optical disk moves relative to the laser head with a constant linear speed, and the angular velocity changes depending on the radial position of the head. Thus, reading of internal tracks is carried out with an increased, and external - with a reduced number of revolutions. The servomotor, upon command from the internal microprocessor of the drive, moves the reflecting mirror. This allows the laser beam to be precisely positioned on the track. The beam penetrates the protective layer of plastic and hits the reflective layer of aluminum, silver or gold on the surface of the disc. When it hits the protrusion, it is reflected onto the detector and passes through a prism, which deflects it onto a light-sensitive diode. If the beam hits the pit (pit), it is scattered, and only a small part of the radiation is reflected back and reaches the photosensitive diode. On the diode, light pulses are converted into electricity; bright radiation is converted to “1”, weak radiation – to “0”. Thus, the pits are perceived by the drive as logical zeros, and the smooth surface as logical ones. Note that the pits formed by the laser beam are very small in size. Approximately 30-40 depressions correspond to the thickness of a human hair, which is approximately 50 microns.

Drive track according to commands that come from the built-in microprocessor, it moves the optical system to the desired track on the disk for writing or reading. During recording, the laser performs the desired operation (“burning” or phase change) according to the commands of the encoding-decoding unit, and during reading, the beam reflected from the disk hits the photodetector, the signals from which enter the encoding-decoding unit and the automatic tracking system.

Encoding-decoding block is a signal handler that is written to or read from the disk. It consists of an encoder, a decoder, a random access memory and a control controller. The encoding device prepares data for recording on disk, performing character conversions according to EFM (for CD disks) or RLL (2.10) (for DVD disks) encodings and adds clock signals and service information to the data. The decoder extracts data from the digital stream, restoring its original form. The random access memory serves as a buffer memory, and the controller manages error correction modes for data recorded in all formats supported by the drive.

When writing or reading data from a disk, disturbances in the positioning of the laser beam may occur due to radial beats of the disk. To avoid data loss, optical drives use automatic tracking system using control signals. There are several ways to isolate these signals. However, the most common is the method in which the laser beam after the first lens (see Fig. 1.) enters the diffraction gratings, where it is split into three beams, one of which is used to read data, and the other two are used by the track tracking system. Pulse signals from the photodetector enter the amplifier of the automatic control system, where tracking error signals are separated and the reading signal is corrected.

Audio block The optical drive was inherited from CD players. It turns audio data from digital form to analog. After amplification, this data is transmitted either to an external device or to headphones.

Next to the computer interface connector and the power connector, optical drives also have connectors for connecting to a sound card or audio unit of the motherboard.

On the front panel of the drive, in addition, there are: indicator device operation (busy, light bulb), nest for connecting headphones or a stereo system (for listening to audio CDs), volume control sound (also for audio CD).
It is also provided hole, with which you can remove the CD even in an emergency, for example, if the Eject button does not work. You need to insert some thin stick into this hole about 2-3 cm, then the tray will slide out.

Optical Disc and Drive Specifications

Optical disc characterized by its type(CD or DVD) and capacity. The capacity of a disk is determined by its type and size (diameter). Optical discs are available in 120 mm (4.7 inch) and 80 mm (3.1 inch) diameters.
CDs measuring 120 mm have a capacity of 650 or 700 MB (depending on the recording mode), and discs measuring 80 mm - capacity 185 MB. Sometimes used to record data optical business cards(оtісalbusiness сards) - CD-R discs rectangular in size 80 x 61 mm and capacity 50 MB.

Optical drives have the following main characteristics:

Compatibility;
- data transfer speed;
- average access time;
- cache memory capacity;
- error rate;
- reliability;
- device type;
- interface type;
- list of supported formats;
- audio path parameters.

All optical disc drives have a 5.25-inch form factor and are compatible in disc sizes, that is, they can read both 120 mm and 80 mm discs, as well as optical business cards (for reading discs of the latter two types, there is a provision in the drive tray special recess).

Compatibility different types floppy drives means the ability to read and write other types of disks.
Data transfer rate - This is the maximum speed at which data is exchanged between the drive and the computer. This is the most important characteristic of an optical drive, which is almost always given along with the model name, and it is not specified by the number of megabytes per second, as for other devices external memory, but by an increase factor relative to the base speed. The first CO drives had a data transfer rate of 150 kB/s, just like CD players. This basic speed is clearly insufficient for reading, for example, video data. Therefore, the rotation speeds of disk drives and, accordingly, data transfer rates began to increase (at first twofold). Such drives (with a data transfer rate of 300 kB/s) became known as 2x drives. Subsequently, drive speeds increased even more. Disk drives now have maximum speed transfers 54x (16.2 MB/s) and higher (up to 76x).

For DVD drives, due to their higher data density and higher rotation speed, 1x corresponds to a data transfer rate of 1.32 MB/s, which means that a 1x DVD drive is approximately the same as a 9x CD drive. The maximum value for DVD drives is now 16x or 21.13 MB/s.

The figures given are valid for reading data. For data recording, maximum data transfer rates are lower and are now equal to 40x for recording CD-R drives, 24x for CD-RW drives and from 2x to 8x for DVD drives. Typically, for CD-RW drives, both the write speed and the read speed are indicated separately, and for DVD record drives, the DVD write speed, CD write speed, DVD and CD read speeds.

For recording optical discs (R or RW), the maximum permissible recording speed or range of permissible speeds (for example, 24x or 1x-24x) is usually indicated.

Average access time - This is the time (in milliseconds) that the drive needs to remain on the media with the necessary data. Obviously, working on the internal areas of the disk requires less access time than reading information from external areas. Therefore, the drive data sheet lists the average access time as the average value for performing several data reads from different (randomly selected) disk sections. The average access time for CD-ROM drives is 100 ... 200 ms, and for new DVD drives it is 40 ... 250 ms.

Cache memory capacity - This is the capacity of the optical drive's random access memory, which is used to increase the speed of access to data recorded on the media (buffer memory). If you use special driver programs to control the drive, you can pre-write the contents of the disk into the cache memory. Then accessing a fragment of the requested data is much faster. Cache capacity modern devices- from 64 to 2.048 MB.

The drive buffer is a memory for short-term storage of data after it is read from the CD-ROM, but before it is sent to the controller board and then to the CPU. This buffering allows the disk device to transfer data to the processor in small chunks, rather than taking up its time by slowly sending a constant stream of data. Important characteristic floppy drive is buffer fill level, which affects the playback quality of animated images and videos. This value is defined as the ratio of the number of data blocks transferred to the buffer from the drive and stored in it until the start of their output to system bus, to the total number of blocks that the buffer can hold. Too much fill can cause delays in output from the buffer to the bus; On the other hand, a buffer that is too low will require more attention from the processor. Both of these situations lead to jumps and stuttering during playback.

On CD-ROM burners, buffer memory is very important because it ensures that information flows smoothly onto the CD-R or CD-RW. This allows for more reliable recording, since you cannot allow a track to stop recording, otherwise the entire disc may be damaged.

The reading quality level is characterized error rate(Error Rate). This parameter displays the optical drive's ability to correct read/write errors. Typically the error rate is 10-10...10-12. The error rate is an estimate of the probability of an information bit being corrupted when it is read. If the drive reads data from a dirty or scratched area of ​​the disk, it records a group of bad bits. If the error cannot be eliminated due to the excessiveness of the noise-resistant code (used during writing and reading), then the drive reduces the data reading speed and repeats it many times. If the error correction mechanism cannot cope with the failure, then the message “Sector not found” appears on the computer monitor. not found). If the failure is resolved, the drive switches to the maximum data reading speed.

Reliability optical drives, expressed in terms of MTBF (mean time between failures - MeanTimeBetweenFailure), is 50...125 thousand hours, which is almost an order of magnitude longer than the obsolescence period of the device.

Hot stamped discs (CD-ROM and DVD-ROM) provide up to 10,000 cycles of error-free data reading. DVD-RAM discs can be rewritten up to 100,000 times.

By device type Optical drives, like other external storage devices, can be either internal or external.

Connecting CD-ROM drives. The first connection method is based on the fact that one IDE interface channel can support two built-in devices. The CD-ROM drive is connected to the I/O board via IDE interface along with hard drive according to the master/slave principle. However, in this case, the speed of data exchange with the hard drive is reduced. One way to solve this problem is to connect CD-ROM devices to various channels one EIDE interface or to two different IDE controllers. If the CD-ROM has a SCSI interface, then it is connected to the SCSI controller accordingly. It is also possible to connect CD-ROM drives via the sound card controller. It should also not be forgotten that modern motherboards may contain built-in SCSI and IDE controllers, which generally eliminates the need for an additional I/O card to connect CD-ROM drives.

Connecting audio channels. Almost every CD-ROM drive has a built-in digital-to-analog converter(DAC), as well as an output connector for outputting stereo signals. If there is audio information on the CD, the DAC converts it into analog form and supplies the signal to the headphone jack, as well as to the audio output connectors of the drive, from which the signal in turn goes to the amplifier and speaker system directly or through sound card. The advantage of the active output is that the audio signal from the CD-ROM is additionally processed by the sound card.
An important characteristic of a CO-ROM drive is scroll supported by him formats for recording data on CDs. You can write data to optical discs using different formats X. To record data such as documents, programs use the CD-ROM (ISO) and DVD-ROM (ISO) formats, as well as CO-DOM (UDF) and DVD-ROM (UDF).

CD-ROM formats (1S0) and DVD -ROM (IS0), sometimes called CD-ROM and DVD-ROM formats, they are defined in the IS0 9660 standard. This standard specifies three format levels. The level 1 format defines the names of the recorded files as MS DOS file names, that is, file names can contain up to eight characters using the specified three extension characters. The files to be written must occupy several sectors one after another (non-fragmented recording). The Level 2 format allows the use of long file names, and the Level 3 format additionally allows files to be written over several sections of the disk (fragmented recording) in batch mode. In order to be able to record long names defined in the Windows operating system, the company Mісrosofі added ISO format 9660 level 1 Joliet specification. Varieties of the IS0 9660 format are the CD-ROM (Boot) and DVD-ROM (Boot) formats, in which a special section (in addition to the content) is written to the disk (at the beginning of the disk), which allows the optical disk to be used as a boot disk.

If the ISO 9660 standard is intended to ensure compatibility between CD-ROM and DVD-ROM discs used on different computer systems, then the UDF format (UniversalDiskFormat - universal format discs) is designed for compatibility between read-only optical discs (ROM) and recordable optical discs (R or RW) in different operating systems. This format, like IS0 9660, allows long file names and data recording. Data is written to an optical disc in small portions using the Packet Writing (for CDs) or Incremental Writing (for DVDs) mode.
Audio CD formats And Audio DVD used for recording music. These are two different formats. Format Audio DVD provides better quality music recording.

Video CD (VCD) and VideoDVD formats used for recording films. These are also two different formats with different additional features(for example, regarding the choice of language for dubbing a film). Format VideoDVD Provides better quality movie recording. High-quality movie playback on CDs is ensured by the Super Video format. CD. To record movies in Video DVD format onto CO discs, use the mini-DVD format.

These formats are the most common, since they allow you to record music and films, as well as text data, graphic data and programs, on optical discs. These formats are supported by most disk drives and optical disc writing programs. There are also other formats, mostly designed for types of data that are used much less frequently, for example, Photo CD from Kodak, Record and play back high-quality digital photos. Both photos and music can be recorded in IS0 9660 or UDF formats as regular graphics or sound files.

A new, promising format is the format Mt. (Mount) Rainier, also known as format EasyWrite. This format writes data to an optical disk in the same way as to a floppy disk. Using this format, the optical disk can be accessed (read or written) from any application without calling special programs reading and writing to optical discs.

CD formats are sometimes named by the color of the cover of the books in which these formats are described. So, the very first format CD - Audio CD is described in the “red” book. The “yellow” book describes the CD-ROM (IS0) format, the “orange” book describes the CD-R and CD-RW formats, the “green” book describes the CD-ROM format CD-I(now almost never used), in “blue” - Enhanced CD and in “white” - Video CD.

Optical media are 12 cm (4.72 in) CDs or 8 cm (3.15 in) MiniDiscs. Optical media consists of three layers:

1) polycarbonate base (outer side of the disk);

2) active (recording) layer of plastic with a changeable state phase;

3) the thinnest reflective layer ( inner side disk).

In the center of the CD is a round hole that fits onto the CD drive spindle.

Writing and reading information onto 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 disc, which increases the life of the CD. The phase of the second plastic layer, crystalline or amorphous, changes depending on the cooling rate after the surface is heated by the laser beam during the recording process performed in the drive. When the plastic cools slowly, it turns into a crystalline state and the information is erased (a “0” is written); upon rapid cooling (if only a microscopic point is heated), the plastic element goes into an amorphous state (written “1”). Due to the difference in reflection coefficients from crystalline and amorphous microscopic points of the active layer during reading, the intensity of the reflected beam perceived by the reading head is modulated. The surface of the disk is divided into three areas. The Lead-In area is located in the center of the disk and is read first. It records the contents of the disk, a table of addresses of all records, the disk label and other service information. The middle area contains basic information and occupies most of disk. The Lead-Out area contains the end-of-disk mark.

The information on a CD is encoded with great redundancy using a Reed-Solomon correction code, which ensures the restoration of the original information if it cannot be read from the disk.

A CD can withstand several hundred rewrite cycles. Information is read when the CD is rotated at a frequency of more than 10,000 rpm.

Depending on the read/write capabilities, all CDs can be divided into three types:

1) ROM (Read Only Memory) – read only; recording is not possible;

2) R (Recordable) – for writing once and reading multiple times; the disc can only be written to once; the recorded information cannot be changed and is read-only;

3) RW (ReWritable) – for repeated writing and reading; information on the disk can be overwritten many times.

These types of discs differ in the material from which the second plastic layer is made.

Let's consider the types of CDs (CD (Compact Disc), DVD (Digital Versatile Disc) and Blu-Ray, which have the same size of 4.72 inches.

CD capacity is 650 or 700 MB. Music CDs refer to CDs and are intended only for reading music from them. CD access time – 0.05-0.3 s.

The DVD format is a development of CDs; their volume is 4.7 GB due to denser recording. DVDs continue to improve. There are several competing DVD formats: DVD-, DVD+ and DVD-RAM.

Blu-ray format is further development DVD and allows you to record 25 GB of information on one layer.

The names of CD and DVD formats depending on read/write capabilities are presented in the table.

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

Record music and movies on optical media– the process is as familiar as using magnetic cassettes twenty years ago, but it’s much cheaper. How do the types of media differ and how is information recorded on them?

Stamping and burning

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

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

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

Storage media

Discs intended for recording at home have the same thickness (1.2 mm) and the same diameter (12 or 8 cm) as discs on which data is recorded industrially. Optical media have a multilayer structure.

Substrate. The base for the discs, which is made of polycarbonate, is a transparent, colorless and quite resistant to external influences polymer material.

Working layer. For recordable CDs and DVDs, it consists of an organic dye, and for rewritable CDs, DVDs (RW, RAM) and Blu-ray discs, it is formed by a special alloy that can change the phase state. The working layer is surrounded on both sides by an insulating substance.

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

Protective layer. Only CDs and Blu-ray discs are equipped with it. It is a hard varnish coating.

Label. A layer of varnish is applied on top of the disc - the so-called label. This layer is able to absorb moisture, so that the ink that appears on the surface of the media during printing dries quickly.

Differences between CDs, DVDs and Blu-ray Discs

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

Media formats

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

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

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

DVD-R/DVD+R. Recordable DVDs hold 4.7 GB of information. miniDVD with a diameter of 8 cm – 1.4 GB.

DVD-R DL/DVD+R DL. The DL prefix stands for Dual Layer (DVD-R) or Double Layer (DVD+R), which corresponds to two-layer media. Capacity – 8.5 GB. An eight-centimeter disk can hold up to 2.6 GB.

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

DVD-RAM. These media have the same storage capacity as single-layer DVDs. There are also double-layer discs that hold twice as much information. DVD-RAM can withstand up to 100 thousand write cycles, but only a few DVD players work with these discs. Data is recorded not on a spiral track, but in sectors on ring tracks, like on plates hard drive. Marks defining sector boundaries are clearly visible on the surface of DVD-RAM - by their presence it is easy to distinguish this type of media from others.

BD-R/BD-R DL. An abbreviation used to refer to recordable Blu-ray Discs. BD-R media has one working layer that can hold 25 GB of data. BD-R DL are equipped with two working layers, so their capacity is 2 times higher.

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

"Plus" and "minus"

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

Neither of them has clear advantages over the other. Both types of media use the same materials. Therefore, there are no significant differences between “plus” and “minus” disks from the same manufacturer.

Recording quality

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

Recorder and Media Compatibility

Not every recorder is capable of recording to discs of all formats without exception. There are certain restrictions.

CD recorders. Cannot work with DVDs and Blu-ray discs.

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

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

Signatures on discs

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

Printable blanks. The top side of these discs is varnished. On such a surface you can print text and images using inkjet printers and MFPs equipped with a special tray. The price of the discs is no different from regular ones.

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

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

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

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

Data storage period

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

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

Transferring information to disk

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

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

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

Media production

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

1. To cast a plastic substrate, polycarbonate, heated to 350 °C, is fed into a mold using injection molding. A microscopic spiral track in the form of a groove (Pre-Groove) is created on the surface of the base using a matrix. This track not only records data, it also contains a signal to synchronize the recorder spindle drive. After cooling the substrate to 60 °C, a central hole is made, then the temperature is reduced to 25 °C and further processing begins. DVDs typically consist of two polycarbonate layers, each 0.6mm thick. For single-layer recordable DVD further Only one of the layers is processed, as described in steps 2–3, and for double-layer DVDs, both are processed. CDs and Blu-ray discs have only one layer 1.2 mm thick.

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

3. The reflective layer is applied to the disk using ion-plasma sputtering. In a vacuum chamber, an aluminum, silver or gold plate is bombarded with charged ions, which knock out metal atoms from it - it remains on the surface of the working layer of the blank. For rewritable CDs, DVDs and Blu-ray discs, all working and reflective layers are created using ion-plasma sputtering. In four chambers, the first insulator layer, the working layer, the second insulator layer and the reflective layer are sequentially applied to the disk. When producing Blu-ray discs, these operations are performed in reverse order.

4. Two polycarbonate bases are glued together. For CDs and Blu-ray discs, instead of a second base, a varnish coating is applied, which is dried under an ultraviolet lamp. The varnish coating of Bly-ray discs is particularly durable, while DVDs are protective layer no varnish needed.

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

CDs, DVDs and Blu-ray discs are optical storage media on which you can store electronic form movies, music or other digital data. They operate primarily with digital code. On the one hand, these storage media are digital information and communication technologies, on the other hand, they are technical tools for any type of digitization, calculations, recording, archiving, processing, transmission and presentation of digital content.

CD and DVD are abbreviations, but the concept of Blu-ray disc has a slightly different nature.

CD is short for Compact Disc.

DVD is short for Digital Video Disc. A little later, the name “digital versatile disc” (English: Digital Versatile Disc) appeared, since DVD can be used not only for recording video.

Blu-ray Disc gets its name from the blue laser (as opposed to white laser) that reads information from the disc and also writes information.

The compact disc (CD-ROM) has long been the main medium for transferring information between computers. Now it has practically given up this role to more promising solid-state media, which work much faster and take up less space.

Story

For the first time, the idea of ​​optical recording appeared in 1965, at the American Battelle Memorial Institute, Ohio. This technology was still extremely primitive at that time - photographs were applied to the disk using a photographic method. dark spots and dashes. To read the information, the disk was illuminated with a special lamp. The founder of the technology was the American physicist James Russell. But as is usually the case, he did not earn a penny from his invention. The scientist patented his technology in 1970. He also came up with the idea of ​​using a laser as a light source.

The Compact Disc was developed in 1979 by Sony. Sony used its own PCM signal encoding method - Pulse Code Modulation, previously used in digital professional tape recorders. In 1982, mass production of CDs began at a plant in Langenhagen near Hannover, Germany. The release of the first commercial music CD was announced on June 20, 1982.

According to Philips, more than 200 billion CDs have been sold worldwide in 25 years. Even though more and more people are choosing to purchase music files online, CD sales still account for about 70% of all music sales, according to IFPI.

Microsoft and Apple Computer made significant contributions to the popularization of CDs. John Sculley, then CEO of Apple Computer, said in 1987 that CDs would revolutionize the world of personal computing. One of the first mass-produced multimedia computers/entertainment centers using CDs was the Amiga CDTV (Commodore Dynamic Total Vision), later CDs were used in the Panasonic 3DO and Amiga CD32 game consoles. First standard

In 1979, Philips and Sony entered into an agreement to jointly develop a new media. A year later, the company introduced a new standard called CD-DA (Compact Disk Digital Audio). It was a disc with a diameter of 12 centimeters and a playing time of just over an hour. The format turned out to be surprisingly successful and convenient. It quickly won the hearts of both manufacturers and buyers.

The CD format has unconditionally ruled the market for 15 years. During this time, it ceased to be just a music disc, turning into a universal storage medium. However, by the mid-90s of the last century, the amount of information that one CD could contain became sorely insufficient.

The new format discs looked no different from regular CDs. But the volume of information was increased from 650 MB to 4.7 GB. It is also important that DVD players could play regular CDs without any problems, and therefore there were no problems with standards. Thanks to the advent of DVD, it became possible to obtain high quality sound and images at home. The format quickly became popular. Today, DVD Forum includes more than 250 companies around the world. And I can no longer believe that at one time other analysts jokingly deciphered the name of the DVD as “Dead, Very Dead,” predicting the imminent death of the standard.

Some standardization problems only emerged when the first recordable DVDs appeared. Two standards have appeared in the world - DVD+R and DVD-R. Each of them had its own advantages and disadvantages, which were unclear to the average user. However, users did not encounter any particular problems. You just had to make sure that the disc you purchased was supported by your existing player (DVD-Rs were more common). Yes, universal players and recorders supporting both standards appeared quite quickly. Today, not all users even know about the existence of various standards.

DVD repeated the history of CD. Highly specialized discs (DVD was originally developed only for working with video) have become a universal storage medium. The cost of players has dropped from several hundred dollars to several dozen. The price of the media itself is estimated at pennies.

Classification of optical discs

In each of the media groups, there are three main types of disks:

1. read-only discs (CD-ROM, DVD-ROM);

2. write-once discs (CD-R, DVD-R, DVD+R, DVD-R DL, DVD+R DL);

3. rewritable discs (CD-RW, DVD-RW, DVD+RW, DVD-RAM).