Optical discs concept types of purpose show. Characteristics of optical storage media. CDs and their types

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 minimum requirements to 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 requirements of the Yellow Book could only work on specific model drive. 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 resulting specification 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, similar to 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 the 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 disks may not be fully readable for more than earlier versions 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 separate 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 (“reading 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 movies;

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. Incompatible with some CD-R drives and CD-RW 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.

Recorded formats DVDs 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 terms of speed 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 you to read information from different types CD and DVD media.

3. CD- RW- drives that allow you to read information from optical discs belonging to the group of compact discs, 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 speed characteristics optical drives conventional units are used, and they 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 speed reading 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 monochrome images to the decorative surface of disks High Quality directly into 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 developed by specialists MitsubishiKagakuMedia (MKM) and HP . Unlike other technology - DiscT@2, LightScribe involves applying images not to the working layer of the disk, but from 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 a recording drive to apply an image to its decorative surface.

Of course, the implementation 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 signed agreements to sell licenses to use this technology to some large manufacturers recording drives (in particular, 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 ) - new generation optical drives high density, 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, 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.

Important characteristic new media is the volume. Native Compatibility BD with disks previous generations not provided for by the standard, but 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.

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.

Recording music and films on optical media is a familiar process, like using magnetic cassettes twenty years ago, but it is 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.

Information carriers

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 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 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 written 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. Initially, representatives of the computer industry relied on the “plus” format, and consumer electronics manufacturers promoted the “minus” format 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, disc 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 under ideal storage conditions - 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, media is exposed to high temperatures and mechanical stress. 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 - pit). 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 playing a disc, 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 DVDs, only one of the layers undergoes further processing, as described in steps 2–3, while for dual-layer DVDs, both layers are processed further. 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 disk rotating at a constant speed in the area of ​​the central hole and is evenly distributed over the surface of the carrier.

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 do not need a protective layer of varnish.

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

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 disk 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 the 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 rotation speeds.

CDs and their types

Optic CD-R disc is a carrier of information that is read-only. 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 purpose standard computer programs. 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 such as 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 standard for recording on 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 very close to each other are sensitive to mechanical damage, so the disc must be specially cared for. 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. Double layer standard disk Blu-ray holds 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.

Hello everyone, friends! As they say, a generation has grown up that has never used an optical disc. What it is and why such storage media are needed, I will tell you in today’s article.

How it all began

Laser and optical technologies began to be developed long before the appearance of the familiar personal computers. At that time, computers had already appeared, but they worked on diodes and triodes, that is, they were warm and tube-based, and information was loaded into them using punched paper tapes.

Soviet scientists Nikolai Basov and Alexander Prokhorov, awarded the Nobel Prize in 1964, are considered pioneers in the development of laser data recording and reading technology.

It is typical that drives on optical disks for storing information on a computer were not even considered at that time - all developments were aimed at creating music players, which would eventually replace the “gramophones” on vinyl records and become an alternative to magnetic tape.

American engineer James Russell caught the idea of ​​using optical disks for data storage and patented the invention in 1969. This method became the prototype of the modern DVD disc. For unknown reasons, at that time, the technology was not developed.
They remembered it only in 1990, when Pioneer patented a CD of its own design. It remained the leader in disc production in the USA and Japan until the advent of the DVD format. Such disks were flexible and had a number of disadvantages.

The structure of a modern disk with a substrate that reflects a laser beam was developed by Philips engineer Peter Kramer. In fact, it was this invention that became the basis for all modern disks, including rewritable types of RW.

What happened next

The basis of the disk is a thin sensitive layer of metal (most often aluminum) capable of reflecting a laser beam. The grooves burned during laser recording (they are called piits) do not reflect laser radiation. The lands, that is, the remaining untouched areas, reflect this ray.

The laser head, in addition to the emitter itself, contains a lens and a reading device. Thus, pit and land can be encoded as one or zero, that is, in the binary code familiar to any computer.

Interpreting this code into a format more acceptable for humans is the task of other hardware components of the computer.

Naturally, any technology develops and becomes more advanced. In total, engineers showed the world four generations of disks, which differed from each other in a key characteristic - storage capacity.

Thus, the famous CD belongs to the first generation and holds only 700 MB of data, the DVD is a second generation disc and can already record 4.7 GB, and the third generation Blu-ray contains 25 GB.

The sophisticated Holographic Versatile Disc, which is theoretically capable of holding up to 3.9 TB of data, is still imperfect and is constantly being improved.

Interestingly, regardless of classification, all these disks have the same standard size: 12 cm for regular and 8 cm for mini-disc. The difference in capacity is achieved by narrowing the width of the tracks - it is logical that with such a trend, more of them will fit in the same area.

How it all ended

The purpose and design of optical storage devices remains unchanged today: any information can be stored on them. The disadvantages include the limited service life of the disk: with regular use, the protective layer is scratched, which makes it difficult for the read head to work.

In addition, the reading speed from such media is limited (depending on the format) and is no longer sufficient in the 21st century.

Having experienced their heyday, such drives are gradually losing popularity. The reason lies in the development of more advanced data storage technologies and the widespread use of high-speed Internet.

Agree, there is no point in looking for a point selling discs (it’s not a fact that you will even find one today) and paying money when the music, movie or game you are interested in can be downloaded from the Internet in half an hour, most often for free.

The popularization of the Holographic Versatile Disc is hampered by the price: both the disc itself and the drive capable of reading it are significantly more expensive than older formats.

I'm not saying that disks have completely disappeared from everyday use, far from it. Moreover, in some places, in the old fashioned way, they still even use floppy disks. However, the scale that existed five years ago no longer exists and will not exist again.

The same thing will eventually happen with the flash drives popular today - but not before more advanced technology is invented and made available to the masses.

Thank you for your attention, friends, and see you next time! I will be grateful to everyone who shares this publication on social networks.

CD(Compact Disc) is an optical storage medium in the form of a plastic disk with a hole in the center, the process of writing/reading information to/from which is carried out using a laser. CDs are becoming faster and cheaper. Information is recorded on a CD using an industrial method. The most widely used are 5-inch CDs with a capacity of 670 MB. Their characteristics are completely identical to regular music CDs. Data on the disk is written in the form of a spiral (unlike a hard drive, on which the data is arranged in the form of concentric circles). From a physics point of view, the laser beam determines the digital sequence of ones and zeros written on the CD, in the form of microscopic pits (pits) on its spiral. Today, with a computer with a CD burner, you can make a disc in less than an hour.

DVD(Digital Versatile Disk, formerly Digital Video Disk), i.e., a multi-purpose digital disc is a type of CD that stores from 4.7 to 17 GB of information, which is quite enough for a full-length film. This volume can satisfy any manufacturer of computer games and encyclopedias, the production of which usually required several CD-ROMs, causing inconvenience for the user. The DVD-ROM specification considers disks and DVD technology as a means of storing computer data with enormous capacity. The DVD-Video specification, around which so many copies were broken, only provides for the recording of full-length film programs with high image quality, multi-channel sound and international settings. The DVD-Audio specification considers a standard for recording only audio, assuming, however, significantly higher quality, multi-channel and the ability to place more than 74 minutes on the same disc. music, but also a variety of related information. It becomes clear that the rapid decline in prices for DVD devices may lead to the displacement of CD drives in the near future, even if old media are used. There are four types of DVDs based on their data structure:

• DVD-video - contains films (video and sound);
• DVD-Audio - contains high quality audio data (much higher than that on audio CDs);
• DVD-Data - contain any data;
• mixed content.

BD(Blu-ray - English blue ray - blue ray and disc - disk) - an optical media format used for recording and storing digital data, including high-definition video with increased density. The Blu-ray standard was jointly developed by the BDA consortium. new technology There were dramatic changes in the logical structure of the disk, cost and other parameters. The wavelength of the blue laser was shortened to 405 nm, which made it possible to position the beam much more accurately, and therefore place data on the disk with greater density. The shorter wavelength of the blue-violet laser allows you to store more information on 12 cm discs of the same size as a CD/DVD. BD is a new generation product, the most progressive, meeting the “requirements of our time” than CDs and DVDs.

16. Personal computers. Device. Main characteristics.

Computer is an electronic device designed to work with information, namely introduction, processing, storage, output and transmission of information. In addition, a PC is a single entity of two entities - hardware and software (which is reflected in the following diagram).

According to the definition of a computer, the components of a computer can be divided into devices that perform specific functions related to information.