How CD and DVD discs are structured. CDs as carriers of musical information: features, advantages

2011-05-03T00:55

2011-05-03T00:55

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How does a CD work?

The design of a CD-DA disc (Compact Disk - Digital Audio) and the method of recording sound on it are described by the standard of the companies that proposed it, Sony and Philips, published in 1980 under the name Red Book.

A standard compact disc (CD) consists of three layers: base, reflective and protective. The base is made of transparent polycarbonate, on which an information relief is formed by pressing. A metal reflective layer (aluminum, gold, silver, other metals and alloys) is sprayed over the relief. The reflective layer is covered on top with a protective layer of polycarbonate or neutral varnish - so that the entire metal surface is protected from contact with the external environment. The total thickness of the disc is 1.2 mm.

The information relief of the disk is a continuous spiral path starting from the center and consisting of a sequence of depressions - pits. The spaces between the pits are called lands. By alternating pits and gaps of various lengths, an encoded digital signal is recorded on the disk: the transition from gap to pit and vice versa denotes a unit, and the length of a pit or gap is the length of a series of zeros. The distance between the turns of the track is selected from 1.4 to 2 microns, the standard specifies a distance of 1.6 microns.

How is the audio signal represented on the disc?

The original stereo audio signal is digitized into 16-bit samples (linear quantization) with a sampling frequency of 44.1 kHz. The resulting digital signal is called PCM (Pulse Code Modulation), since each pulse of the source signal is represented by a separate codeword. Every six samples of the left and right channels are formatted into primary frames, or microframes, of 24 bytes (192 bits) in size, arriving at a speed of 7350 pieces per second, which are encoded using a two-level CIRC code (Cross Interleaved Reed-Solomon Code). -Solomon with cross interleaving) according to the scheme: interleaving with a 1-byte delay, C2 level encoding, cross-interleaving with a variable delay, C1 level encoding, interleaving with a 2-byte delay. Level C1 is designed to detect and correct single errors, C2 - group errors. The result is a 256-bit block, the data in which is equipped with error detection and correction bits, and is also “smeared” into the block, which leads to the recording of contiguous audio data in physically non-contiguous areas of the disk and reduces the impact of errors on individual samples.

The Reed-Solomon code has 25% redundancy and can detect up to four erroneous bytes and correct up to four lost or two erroneous bytes. The maximum length of a fully correctable error packet is about 4000 bits (~2.5 mm track length), however, not every packet of this length can be completely corrected.

After the second interleaving, subcode bits are added to each received block - P, Q, R, S, T, U, V, W; each block receives eight subcode bits. Then, every 98 blocks with subcodes are formed into one superframe with a duration of 1/75 sec (the amount of pure audio data is 2352 bytes), also called a sector, in which the subcodes of the first two blocks serve as a sign of synchronization, and the remaining 96 bits of each subcode form the P-word, Q-word, etc. Throughout a track, the sequence of subcode words is also called subcode channels.

Words or subcode channels are used to control the recording format, display fragments of a soundtrack, etc. - for example, channel P is used to mark audio tracks and pauses between them (0 - pause, 1 - sound), and channel Q is used to mark the format of tracks and sectors, record TOC (Table Of Contents) and time stamps, by which playback time is tracked. Channel Q can also be used to record information in the ISRC (International Standard Recording Code), intended to represent information about the manufacturer, release time, etc., as well as to divide the track into separate fragments (in total on audio A disc can have up to 99 audio tracks, each of which can include up to 99 fragments).

Finally, frames thus framed are channel encoded in pit-gap terms using 8/14 (Eight to Fourteen Modulation - EFM) redundancy code, in which the original bytes are encoded into 14-bit words, increasing the intelligibility of the signal. Three link bits are inserted between words to maintain restrictions on the number of adjacent zeros and ones, which facilitates demodulation and reduces the DC component of the signal. As a result, 588 channel bits are obtained from each primary microframe, and the resulting bit stream is written to disk at a speed of 4.3218 (588 x 7350) Mbps. Since EFM coding produces a digital stream in which there are more zeros than ones, a system was chosen to represent units by the boundaries of a pit and a gap, and the number of zeros between ones by the length of a pit or gap, respectively.

At the beginning of the disc there is a so-called lead-in zone, containing information about the format of the disc, the structure of sound programs, addresses of fragments, titles of works, etc. At the end, a lead-out zone is recorded (track number AA), which acts as the boundary of the recorded area of ​​the disc; The P code bit in this zone changes at a frequency of 2 Hz. A number of home players cannot recognize a disc without this zone, but many can do without it. Between the input and output zones, a program memory area (PMA) is recorded, containing the actual audio data. The program area is separated from the input area by a section of 150 empty blocks (2 seconds), which acts as a pre-gap.

The total recording time on a CD is 74 minutes, however, by reducing the standard track pitch and the distance between pits, an increase in recording time can be achieved - at the expense of reducing the read reliability in a standard disk drive.

How are CDs recorded and produced?

The main method of producing disks is pressing from a matrix. The original is formed from the original digital master tape, containing an already prepared and encoded digital signal, by a special high-precision machine on a glass disk coated with a layer of photoresist - a material that changes its solubility under the influence of a laser beam. When the recorded original is processed with a solvent, the required relief appears on the glass, which is transferred by electroplating to the nickel original (negative), which can serve as a matrix for small-scale production, or as a basis for making positive copies, from which, in turn, negatives are taken for mass replication.

Stamping is carried out using the injection molding method: a polycarbonate substrate with a relief is pressed from a negative matrix, a reflective layer is sprayed on top, which is varnished. Informational inscriptions and images are usually applied on top of the protective layer.

Recordable discs (CD-R, “blanks”) are made using the same method, but between the base and the reflective layer there is a layer of organic matter that darkens when heated. In the initial state, the layer is transparent; when exposed to a laser beam, opaque areas equivalent to pits are formed. To facilitate tracking of a track when recording on a disc, a preliminary relief (marking) is formed during the manufacturing process, the track of which contains frame marks and synchronization signals recorded with a reduced amplitude and subsequently overlapped by the recorded signal.

Recorded discs, due to the presence of an organic fixing layer, have a lower reflection coefficient than stamped ones, which is why some players (Compact Disk Player - CDP), designed for standard aluminum discs and not having a margin of read reliability, can play CD-R discs less reliably, than usual.

How are CDs played?

During playback, an audio CD rotates at a constant linear velocity (CLV), at which the speed of the track relative to the playback head is approximately 1.25 m/s. The rotation speed stabilization system maintains it at such a level as to ensure the speed of the read digital stream equal to 4.3218 Mbit/s, therefore, depending on the length of the pits and gaps, the actual speed may vary. The angular speed of the disk varies from 500 rpm when reading the innermost sections of the track to 200 rpm on the outermost ones.

To read information from the disk, a semiconductor laser with a wavelength of about 780 nm (infrared range) is used. The laser beam, passing through the focusing lens, falls on the reflective layer, the reflected beam enters the photodetector, where pits and gaps are determined, as well as the quality of focusing of the spot on the track and its orientation along the center of the track are checked. When focusing is disrupted, the lens moves, working on the principle of a loudspeaker diffuser (voice coil), and when it deviates from the center of the track, the entire head moves along the radius of the disk. In essence, the lens, head and spindle motor control systems in the drive are automatic adjustment systems (ATS) and are constantly monitoring the selected track.

The signal received from the photodetector in 8/14 code is demodulated, as a result of which the CIRC encoding result with added subcodes is restored. Then the subcode channels are separated, deinterleaved and CIRC decoded on a two-stage corrector (C1 - for single errors and C2 - for group errors), as a result of which most of the errors introduced by stamping violations, defects and heterogeneity of disk materials, and scratches on it are detected and corrected. surface, unclear definition of the pit/gap in the photodetector, etc. As a result, a stream of “clean” audio samples is sent to the DAC for conversion to analog form.

In sound players, after the corrector, there is also an interpolator of varying complexity, which approximately restores erroneous samples that could not be corrected in the decoder. Interpolation can be linear - in the simplest case, polynomial or using complex smooth curves.

To perform de-interleaving, any CD-reading device has a buffer memory (standard volume - 2 kB), which is also used to stabilize the speed of the digital stream. Decoding can use several different strategies, in which the probability of detecting group errors is inversely proportional to the reliability of their correction; the choice of strategy is left to the discretion of the decoder developer. For example, a CD player with a powerful interpolator might choose a strategy that emphasizes maximum detection, while a CDP with a simple interpolator or CD-ROM drive might choose a strategy that emphasizes maximum correction.

What are the parameters of the audio signal on a CD?

Standard digitization parameters - sampling frequency 44.1 kHz and sample bit depth 16 - determine the following theoretically calculated signal characteristics:

• Frequency range: 0..22050 Hz
• Dynamic range: 98 dB
• Noise level: -98 dB
• Total Harmonic Distortion: 0.0015% (at maximum signal level)

In real CD recording and playback devices, high frequencies are often cut off at 20 kHz to create a margin for the steepness of the filter's frequency response. The noise level can be as low as 98 dB with a linear DAC and a noisy output amplifier, or higher if resampled at a higher frequency using a Delta-Sigma, Bitstream or MASH DAC and low-noise amplifiers. The coefficient of nonlinear distortion strongly depends on the used DAC output circuits and the quality of the power source.

A dynamic range of 98 dB is determined for a CD based on the difference between the minimum and maximum levels of the audio signal, but at a small signal the level of nonlinear distortion increases significantly, which is why the real dynamic range, within which an acceptable level of distortion is maintained, usually does not exceed 50-60 dB.

What is jitter?

Jitter is a rapid jitter in the phase of a digital signal relative to the duration of the period, when the strict uniformity of the pulse fronts is violated. Such jitter occurs due to the instability of clock generators, as well as in places where the clock signal is isolated from a complex signal using the PLL (Phase Locked Loop) method. Such selection takes place, for example, in the demodulator of the signal read from the disk, resulting in the formation of a reference clock signal, which, by correcting the disk rotation speed, is “adjusted” to the reference frequency of 4.3218 MHz. The frequency of the clock signal, and therefore its phase and the phase of the information signal, continuously fluctuates at different frequencies. An additional contribution may be made by the uneven arrangement of pits on the disk, caused, for example, by poor-quality pressing or unstable recording.

However, ripples in the disk signal are fully compensated for by the decoder's input buffer, so that any jitter or knock that occurred before the signal was placed in the buffer is eliminated at this stage. Sampling from the buffer is controlled by a stable oscillator with a fixed frequency, but such oscillators also have a certain, albeit much less, instability. In particular, it can be caused by interference in the power supply circuits, which, in turn, can occur when the ACS is activated and the disk speed or head/lens position is adjusted. On low-quality discs, these corrections occur more often, giving some experts reason to directly link the stability of the output signal with the quality of the disc, although in fact the reason is insufficiently good decoupling of CDP systems.

What do the abbreviations AAD, DDD, ADD mean?

The letters of this abbreviation reflect the audio waveforms used to create the disc: the first for the original recording, the second for processing and mixing, and the third for the final master signal from which the disc is formed. "A" denotes analog form, "D" denotes digital form. The master signal for a CD always exists only in digital form, so the third letter of the abbreviation is always "D".

Both analog and digital signal forms have their advantages and disadvantages. When recording and processing a signal in analog form, its “fine elements” are most fully preserved, in particular higher harmonics, but the noise level increases and the amplitude-frequency and phase-frequency characteristics (AFC/PFC) are distorted. When processed in digital form, higher harmonics are forcibly cut off at half the sampling frequency, and often even lower, but all further operations are performed with the highest possible accuracy for the selected resolution. A number of experts evaluate a signal that has undergone analog processing as “warmer” and “live”, but many modern signal processing methods can only be implemented acceptably in a digital version.

Can two identical discs sound different?

First of all, you need to make sure that the discs actually contain an identical digital audio signal. A complete binary match between two discs at the pit and gap configuration level is virtually impossible due to minor material defects and distortions during die processing and pressing, but due to redundant encoding, the vast majority of these errors are corrected during decoding, providing the same “high level” digital stream.

You can compare the digital contents of discs by reading them in a CD-ROM drive that supports Read Long or Raw Read mode - reading “long sectors”, which are actually CD-DA superframes with a capacity of 2352 bytes each. You can read more about this in the CD-ROM FAQ or in the manual for audio reading programs (CD-DA Grabbers/Rippers). You can also compare discs using studio equipment that can read discs in digital form on a DAT tape recorder.

There can be several reasons for digital differences between discs that sound similar. Some CD-ROM drives and other digital CD-DA reading devices can, in order to prevent direct copying, introduce subtle distortions into the signal (for example, using smoothing polynomials), and most drives that support full frame reading commands do this inaccurately and inaccurately. When making copies (reprints) of audio discs, especially in a pirated way, they are often copied with resampling to another frequency (for example, 48 kHz in DAT) followed by resampling to the original one, or even through an analog path with double digital/analog conversion. A number of versions of CD-R burning software also intentionally or accidentally distort the original data so that the copy is not the same as the original.

It should be noted that even if the digital contents of two disks coincide when comparing them in some system (CD-ROM, special devices for comparing the original/copy, etc.), this does not mean at all that on this or that CDP they are also Identical digital signals will be decoded. Therefore, the most reliable way to determine the cause of differences in sound is to use a CDP with a digital output, from which recording is being carried out on some storage device while listening to both discs. Subsequent digital comparison of the resulting signalgrams will show at what point in the player the changes that are audible to the ear are introduced into the signal.

Of course, before comparing the original and the copy in this way, you need to make sure that the results of reading the same discs multiple times are repeatable. Various digital signalgrams in this case may indicate unreliable disk reading or poor operation of digital interfaces (receiver, transmitter, cable, connectors). The identity of digital data during repeated playback of several discs can be considered a sufficient sign of the reliability of both the discs themselves and the reading, decoding and intermodular transmission systems.

The auditory comparison of the sound of discs must be correct - the most recognized is the double-blind test. The essence of the method is that the expert (listener) should not see the manipulations with the equipment and the person performing them, and this person himself, who randomly changes the disks, should not know the features of their contents. In this way, any influence, including “subtle” and unstudied, of people on the equipment and on each other is eliminated as much as possible, and the expert’s opinion is considered extremely unbiased.

What is HDCD?

High Definition Compatible Digital is a “super-system” for CD audio encoding, using the standard CD-DA format. An audio signal with a higher bit depth and sampling frequency is subjected to digital processing, as a result of which the main part is isolated from it, encoded, as usual, using the PCM method, and additional information clarifying small details is encoded in the least significant bits of samples (LSB) and masked spectral regions . When playing an HDCD disc on a regular CDP, only the main part of the signal is used, but when using a special CDP with a built-in decoder and HDCD processor, all information about the signal is extracted from the digital code.

How to handle CDs?

Avoiding mechanical damage to any of the surfaces, exposure of the disc to organic solvents and direct bright light, impacts and kinks of the disc. Inscriptions on recordable discs may only be made with pencils or special felt-tip pens, excluding pressure and the use of ballpoint or fountain pens.

When removing a disc from the box, be careful not to bend it. One convenient and safe method requires the use of two hands - the thumb of the left hand presses lightly on the latch, loosening it, while the other hand removes the disc from the latch. The one-handed method, when the index finger loosens the latch and the thumb and middle finger remove the disk, requires more precise coordination of forces, without which it is easy to bend the disk or break the latch tabs.

A dirty disc can be washed with warm water and soap or a non-aggressive surfactant (shampoo, washing powder), or specially produced liquids. Shallow scratches on the transparent layer can be polished using polishing pastes that do not contain organic solvents and oils, or regular toothpaste.

What is a “green marker” and why is it needed?

Many users and experts claim that a disc treated in this way produces cleaner sound in high-end devices, attributing this to a more accurate reading of digital information from the disc, which in its original form supposedly cannot be reliably read in most drives. However, a carefully designed system (drive and decoder) is able to correctly read not only untreated discs, but also discs of average quality, and even slightly dirty and scratched ones, so possible reasons for improved sound should not be sought in the disc. The most likely explanations for this phenomenon seem to be the same factors that create different sounds of copies of discs that match the digital content.

Where can I find more information on CDs?

Technical characteristics of CD-R disc.

CD-R is a thin disk made of transparent plastic - polycarbonate - 1.2 mm thick, with a diameter of 120 mm (standard) or 80 mm (mini). The capacity of a standard CD-R is 74 minutes of audio or 650MB of data. However, at the moment (2006) a CD-R with a capacity of 702MB of data (more precisely 736,966,656 bytes) or 79 minutes 59 seconds and 74 frames can be considered standard. This capacity is achieved by slightly exceeding the tolerances described in the Orange Book standard (CD-R/CD-RW). There are also 90 minute / 790MB and 99 minute / 870MB discs on the market, which are much less widespread.

The polycarbonate disk has a spiral track to guide the laser beam when writing and reading information. On the side where this spiral track is located, the disc is covered with a recording layer, which consists of a very thin layer of organic dye and then a reflective layer of silver, its alloy or gold. This reflective layer is coated with a protective photopolymerizable varnish and cured with ultraviolet radiation. And already on this protective layer various inscriptions are applied with paint.

A blank CD-R is not completely empty; it has a service track with ATIP servo marks - Absolute Time In Pregroove- absolute time in the service track. This service track is needed for the tracking system, which keeps the laser beam while recording on the track and monitors the write speed (i.e., makes sure the pit length is constant). In addition to synchronization functions, the service track also contains information about the manufacturer of this disc, information about the material of the recording layer, the length of the track to be recorded, etc. The service track is not destroyed when data is written to the disk and many copy protection systems use it to distinguish the original from the copy.

The first companies to begin producing CD-R blanks were Taiyo Yuden, Kodak, Maxell and TDK. Since then, the CD-R standard has been further developed to provide increasingly faster recording speeds and currently (2006) the maximum possible CD-R recording speed is 52x, i.e. 52 times greater than that defined in the Orange standard. Books" (1x = 150 KB/s). These improvements consist mainly of new materials for the recording layer, better track geometry and technology for applying the recording layer. Low-speed 1x recording is still used today for recording special “audio CD-Rs”, since CD recording decks were standardized at this speed.

Blank CD-R blanks have a service track with recorded data. This track contains time stamps and is used when recording so that the laser beam writes along a spiral track, just like on regular CDs. Instead of printing pits as physical indentations in the blank material as in the case of a CD, when recording a CD-R, data is written onto the disc using a high-power laser beam to physically “burn through” the organic dye of the recording layer. When the dye is heated above a certain temperature, it breaks down and darkens, changing the reflectivity of the “burnt” area. Thus, when recording, by controlling the laser power, alternating dark and light spots are obtained on the recording layer, which are interpreted as pits when reading.

When reading, the laser has significantly lower power than when writing, and does not destroy the dye of the recording layer. The beam reflected from the reflective layer hits the photodiode, and if the beam hits a dark - “burnt” - area, then the beam almost does not pass through it to the reflective layer and the photodiode registers the weakening of the light flux. During reading, the “blank” in the drive rotates on the spindle, and the reading beam remains stationary and is directed by the tracking system to the data track. Alternating light and dark sections of the track generate a change in the luminous flux of the reflected beam and are translated into a change in the electrical signal, which is then converted into bits of information by the electrical drive system - “decoded”.

Burning the recording layer is an irreversible chemical process, i.e., a one-time process. Therefore, information recorded on a CD-R cannot be erased, unlike CD-RW. CD-Rs, however, can be written in sections called sessions.

There are three main types of recording layer used for CD/DVD:

Cyanine (English) Cyanine) - Cyanine dye has a blue-green (sea wave) tint to the working surface. This material was used in the very first CD-R blanks and was patented by Taiyo Yuden. This dye is chemically unstable, which is the reason for the short period of guaranteed storage of recorded information. The dye may fade over several years. Although many manufacturers use additional chemical additives to increase the stability of cyanine, such drives are not recommended for backup or long-term storage of archival data.
Azo - Metallized azo dye, has a dark blue color. Its formula is patented by Mitsubishi Chemicals. This dye is chemically resistant and its ability to store information is calculated for decades (the companies themselves write about 100 years).

Phthalocyanine (English) Phthalocyanine) - A slightly later development of the active recording layer. Phthalocyanine practically colorless, with a pale shade of light green or golden color, which is why discs based on the phthalocyanine active layer are often called “golden”. Phthalocyanine- a slightly more modern development. Discs based on this active layer are less sensitive to sunlight and ultraviolet radiation, which increases the durability of recorded information and somewhat more reliable storage in adverse conditions (companies claim hundreds of years).
Unfortunately, many manufacturers use various additives in the recording layer to make cyanine discs similar in color to phthalocyanine discs. Therefore, you cannot simply determine the material of the recording layer by color. Also, the “golden” reflective layer does not guarantee that it is a phthalocyanine CD-R.
There are several methods for writing data to CD-R:

Disc-At-Once, DAO (Disk at a Time) - the entire disc is recorded in one session, from start to finish without interruption. First, special information is written to the disc indicating the start of recording. lead-in), after this the data is “burned”, and then the disk is “closed”, i.e. a special sequence of bits is written, which indicates the impossibility of adding information to this “blank” (eng. lead-out). This method is well suited for recording live concert performances, without pauses between songs, and also as master discs for subsequent duplication at the factory.

Track-At-Once, TAO (Track at a time) - data is written one track (session) at a time and left “open” (i.e., no record is made of “closing” the disk), which indicates the possibility of further recording of information to this disk. In addition, this allows you to record audio CDs with an additional “computer” track. An audio disc can only be read on a CD player after the table of content (TOC - Table Of Content) has been written. Once the TOC is recorded, adding tracks becomes impossible.

Packet Writing is a not very common type of recording in which the disk is “formatted” and in the future data can be written to it or previously recorded data can be made “invisible”, i.e. such a CD-R becomes similar to arbitrary disks. reading and writing. However, any data change (deletion, write, change) on the disk must be written to additional packets, and after all the packets have been written, the disk becomes unavailable for further changes - read-only. Not supported by all drives, leading to compatibility issues.

Session-At-Once, SAO (Session at a time) - SAO mode is used when recording in CD-Extra format. When using this format, it is possible to record both audio information (CD-DA) and the program part on the disc. When recording, the audio tracks are burned first, and then the data.

Multisession - a recording mode that allows you to later add information to the disc. Each session contains information about the beginning of the session (lead-in), then data and information about the end of the session (lead-out). When recording in multi-session mode, information about the structure of previous recordings is copied to the new session and can be edited. Thus, the user can destroy information about the structure of already unnecessary or outdated records without including it in a new table of content (TOC - Table Of Content). It is possible to “erase” unnecessary information from a CD, although in fact it physically continues to remain on the CD. Information can be recovered using special software.

Storage conditions and average lifespan of recorded CD-Rs.

At the moment (2006), the average CD-R lifetime is only estimated based on accelerated aging tests, since this optical media technology is too young and has no practical data on this matter. It is believed that with proper care, CD-Rs should withstand at least a thousand reading cycles and store recorded information for several hundred years. Unfortunately, some common disk mishandling practices can reduce this figure to one to two years. Therefore, if the main purpose of recording is long-term storage of information, you should handle CD-R blanks with care.

The characteristics of recorded CD-R material are subject to deterioration over time, just like most other recording media. Write-once optical discs, CD-Rs, use a dye in the recording layer that, when exposed to heat, changes properties that affect data storage. The degradation process can cause the recorded data track to move within the layer, causing the drive to be unable to read the data from the disk.
Many cheap recording “blanks” from little-known companies, as well as nameless, “bald”, “technological” blanks, have a lifespan of about two years. Some of these higher quality “blanks” have a longer service life - about five years. It is very difficult to distinguish low-quality “blanks” from high-quality ones, since only a few manufacturers (for example, Taiyo Yuden) care about the lifespan of their products. Due to price wars, disc quality is often sacrificed to achieve the lowest possible cost.
Recommendations for storing and working with CD-R blanks:

Store vertically, each in a separate case or slim case. While in them, the discs do not come into contact with the surface of the recording layer on the walls of the case.

Avoid bending the blank. To remove a disc from the case, under no circumstances should you “pull” it by the edges. Instead, you need to press down on the spindle that holds it, which will allow you to remove the disc without force or bending.
The “blank” should be held by the thin edges around the perimeter, and try not to touch the transparent protective layer, so as not to contaminate this surface with fingerprints.

Store in a cool, dry place. Optimum temperature 5-20°C (41-68°F), humidity 30-50%. Sharp changes in these values ​​are also undesirable.
Avoid direct sunlight. It can heat up the case and the disc it contains. Prolonged exposure of the disc to direct ultraviolet light (including sunlight) also negatively affects its performance. However, small doses of X-ray radiation, such as during airport security, or magnetic fields should not cause significant damage to the disks.
If possible, use felt-tip pens or water-based markers with a soft nib when writing notes on the writing surface. The best place to mark is a small space on the disk around the central hole, about one centimeter wide, usually completely transparent. Felt pens based on alcohol solvents are considered less harmful to the disc than those based on xylene or toluene solvents. Typically, permanent markers are made from xylene or toluene and are therefore not recommended for marking on a disc. Many manufacturers produce felt-tip pens specially designed for writing on optical media (CD/DVD).

Never use stickers on discs. The adhesive in the stickers can chemically attack the disc, and in high-speed CD drives, the stickers cause the disc to wobble. There are known cases when a disk shattered into pieces inside the drive, which led to loss of information and failure of the drive.
Scratches on any surface of the disc are unacceptable. Even a small scratch on the “outer” surface with the recording layer can lead to partial or complete loss of information. Contrary to popular belief, small scratches on the “transparent” (“inner”) side of the disk are less dangerous, but can also lead to read and write problems. You cannot write on disks with ballpoint pens, since mechanical stress on the disk usually renders it unusable.
Contact with water is also undesirable for the disk, especially for “technological” “blanks”.
Disk Cleanup
As a rule, you only need to clean a CD-R disc if you have problems reading information from it. The error correction codes used in CD-Rs generally cope well with fingerprints and scratches on the transparent side.
Accumulated dust can be removed by wiping the disc with a soft cloth, moving from the center to the rim of the disc in a radial direction. Do not wipe the disc in a circular motion, as circular scratches will be parallel to the track and are more difficult to deal with than radial scratches. Another preferable way to remove dust is to blow it away using a jet of air from a can of compressed air, which is sold in stores.
Fingerprints or dirt can be removed by using a soft cloth dampened with denatured alcohol (ethyl or isopropyl) and then wiping the disc dry using the same radial motion.
Never use acetone, nail polish thinner, kerosene, gasoline or other petroleum-based solvents. Such aggressive solvents can literally dissolve the disc itself or make its surface cloudy and unusable. Use only alcohol solvents.
CD-RW format discs.
Technical specifications.
CD-RW (Compact Disc-ReWritable) is a type of compact disc developed in 1997 for recording information multiple times.
CD-RW is a further development of the recordable laser compact disc CD-R, however, unlike it, it allows not only recording information, but also repeatedly erasing already recorded data. This format was introduced in 1997, and during its development was called CD-Erasable (CD-E, Compact Disc Erasable). CD-RW is in many ways similar to its predecessor CD-R, but its recording layer is made of a special alloy that can be heated into two different stable states of aggregation - amorphous and crystalline. This alloy is usually made of silver (Ag), indium (In), antimony (Sb) and tellurium (Te). When recording (or erasing), the laser beam heats a section of the track and transfers it to one of the stable states of aggregation, which are characterized by varying degrees of transparency. The reading laser beam has lower power and does not change the state of the recording layer, and alternating sections with different transparency form a picture similar to the pits and pads of conventional stamped CDs.

CD-RW "blanks" allow you to rewrite information about 1000 times. With the exception of the ability to erase recorded information, for the user, working with CD-RW blanks is very similar to working with write-once CD-Rs. Data is recorded in sessions, you can add new files and “hide” already recorded ones. With each new session, the free space on the disk decreases, and when it runs out, it will be possible to completely erase information from the entire disk or part of it, after which it will again be available for new recording. Later, a new format for recording CD-RW blanks appeared - Universal Disk Format (UDF, Packet Writing), which hides technical difficulties from the user and allows you to “format” the “blank” and work with it as with an ordinary large floppy disk accessible for reading/writing/deleting /change. The volume of such UDF formatted discs is approximately 530MB, as opposed to the usual 700MB when recording in sessions (more precisely, 700MB can be written in only one session on the entire disk).

The recorded CD-RW does not fully meet the requirements described in the Red Book (CD-ROM) and Orange Book Part II (CD-R) standards - more specifically, they have a weaker reflected signal. And therefore such discs are not readable in older CD drives manufactured before 1997. CD-R is considered a more suitable backup media standard because... The information recorded on them can no longer be changed and manufacturers of blanks indicate a longer data storage time for CD-R discs than for CD-RW discs.

During normal recording on a CD-RW - not UDF, you need to periodically erase the disc completely. There are two types of erasing - “full” and “quick”. As the name suggests, with a “full” erasure, the entire information track is overwritten, roughly speaking, with zeros, and the old information is destroyed. A “quick” erase clears only a small part of the disk from the beginning, which happens much faster, but it is technically possible to restore the data. Therefore, if there is a need to maintain confidentiality of information, then complete erasure should be used.
CD-ROM format discs.
Compact disc (“CD”, “CD-ROM”, “CD ROM”) is an optical storage medium in the form of a disk with a hole in the center, information from which is read using a laser. The compact disc was originally created for digital audio storage (the so-called Audio-CD), but is now widely used as a general-purpose data storage device (the so-called CD-ROM). Audio CDs have a different format from data CDs, and CD players can usually only play them (a computer can, of course, read both types of discs). There are discs containing both audio information and data - you can listen to them on a CD player or read them on a computer. With the development of mp3, manufacturers of household CD players and music centers began to provide them with the ability to read mp3 files from CD-ROMs.
The abbreviation "CD-ROM" stands for "Compact Disk Read Only Memory" and refers to the compact disc as a storage medium for general use (as opposed to an audio CD). "CD ROM" means "Compact Disc Read Only Memory". A CD-ROM is often mistakenly called a CD-ROM drive.
DVD-R/RW format discs.
Technical characteristics of DVD-R disc
Externally, DVDs are almost impossible to distinguish from regular CDs. They are the same size and look very similar to each other. However, it will no longer be possible to read a DVD disc on a regular CD drive. To do this, you will need a drive that supports the DVD format, which, by the way, reads regular CDs without any problems.
All information on DVD is stored in the MicroUDF (Micro Universal Disk Format) file system. It was officially approved in 2000. MicroUDB supports high-capacity media and large file sizes. File names are written in unicode format, which ensures DVD compatibility with all PC operating systems, as well as with a variety of household appliances.
A significant difference between DVD and CD is the ability to record double-layer discs. On one single-sided disk (there are also double-sided ones, with an information surface on each side) you can store twice as much information. Both layers have a reflective surface, only one of them has high transparency (up to 40%). When writing/reading, the beam simply changes focus, which makes it possible not to hit both layers at the same time.

The higher capacity of DVD discs is due not only to the possibility of double-layer recording of discs, but also to a higher density of information recording. Higher recording density was achieved by reducing the distance between information tracks on the spiral. This distance for CDs is 1.6 microns. DVD discs have 0.74 microns. The volume of DVD discs, depending on their specific type, can be from 4.7 to 17 GB.
DVD types:

There are three types of DVDs based on their data structure:
DVD-Video - contain films (video and sound);
DVD-Audio - contains high quality audio data (much higher than that on audio CDs);
DVD-Data - contain any data.
There are four types of DVD media:
DVD-ROM - factory-stamped discs;
DVD+R/RW - discs of single (R - Recordable) and multiple (RW - ReWritable) recording;
DVD-R/RW - discs of single (R - Recordable) and multiple (RW - ReWritable) recording;
DVD-RAM - rewritable discs with random access (RAM - Random Access Memory).
A DVD may have one or two working sides and one or two working layers on each side. The capacity of the disk depends on their number:

• single-layer, single-sided (DVD-5) hold 4.7 gigabytes of information,
• double-layer single-sided (DVD-9) hold 8.7 gigabytes of information,
• single-layer double-sided (DVD-10) hold 9.4 gigabytes of information,
• double-layer, double-sided (DVD-18) holds 17.4 gigabytes of information.

Capacity can be determined by eye - you need to look at how many working (reflective) sides the disc has and pay attention to their color: double-layer sides are usually gold in color, and single-layer sides are silver, like a CD. Any of the media can have any data structure (see above) and any number of layers (double-layer DVD-R and DVD-RW appeared at the end of 2004).

The DVD-R(W) recording standard was developed by DVD-Forum as the official specification for (re)recordable discs. However, the license price for this technology was too high, and therefore several manufacturers of record drives and recording media united in the “DVD plus RW Alliance”, which developed the DVD+R(W) standard, the cost of a license for which was lower. At first, DVD+R(W) blanks (blank discs for recording) were more expensive than DVD-R(W) blanks, but now the prices are equal.

The writing standards “+” and “-” are partially compatible. Currently, they are equally popular - half of the manufacturers support one standard, half the other. There is debate as to whether one of these formats will displace its competitor or whether they will continue to coexist peacefully. All DVD drives can read both disc formats, and most burners can also write both types of discs.
Unlike CDs, where the structure of an audio disc is fundamentally different from a data disc, DVDs always use the UDF file system.
The DVD read/write speed is indicated as a multiple of 1350 Kb/s, that is, a 16-speed drive provides reading (or writing) of discs at 16? 1350 = 21600 Kb/s (21.09 Mb/s).
DVD regional locking.
Film studios are interested in controlling the distribution of their films released on DVD in different countries. This is due to the fact that the time of release of films in cinemas and the time of their release into wide video distribution in different countries is different. It is generally accepted that a movie should be released on video distribution only after it has premiered in cinemas. So, for example, a film released on video in the USA can only begin to be shown in cinemas in Europe, which violates this rule.
That is why, when the DVD standard was approved, a code was introduced that limited the use of a DVD-Video disc within one zone.
Thus, the DVD-Video disc and DVD player are assigned a region code. And if, when playing the disc, these codes do not match, the film will not be played.
Regional protection is optional and may be used at the discretion of the disc manufacturer. It is not any kind of cryptographic system, but just one byte in the disc header that is checked before the disc starts playing. A DVD player may have multiple region codes, in which case it can play discs from several different "zones". Many Chinese players generally ignore regional protection.
A total of 8 regional zones were introduced:

The restriction can be removed by editing the firmware of the drive, which however leads to loss of warranty. Typically, when flashing the firmware, the region code is changed to 0. However, there are DVDs with a special region code check that cannot be played with such a region code. DVD players with a changeable DVD zone can solve this problem (usually changing is possible only up to 5 times, further changes can only be made after flashing the firmware).
This protection is used only on DVD-Video discs.

Blu-Ray Disc format discs.

Blu-ray Disc or abbreviated BD (from the English blue ray - blue ray and disc - disk) is the next generation of optical disc format - used for storing high-definition video (with a resolution of 1920X1080 pixels) and high-density data.
The Blu-ray standard was jointly developed by a group of consumer electronics and computer companies led by Sony, which are members of the Blu-ray Disc Association (BDA). Compared to its main competitor, the HD DVD format, Blu-ray has a larger information capacity per layer - 25 instead of 15 gigabytes, but at the same time it is more expensive to use and support.

At the Consumer Electronics Show (CES), which took place in January 2006, it was announced that the commercial launch of the Blu-ray format would take place in the spring of 2006.
Technical characteristics of BD.
A single-sided Blu-ray disc (BD) can store 23.3, 25, or 27 GB - enough capacity to record approximately four hours of high-definition video with audio. The dual-layer disc can hold 46.6, 50, or 54 GB - enough to record approximately eight hours of HD video. Also in development are disks with a capacity of 100 GB and 200 GB using four and eight layers, respectively. TDK Corporation has already announced a prototype of a four-layer disk with a capacity of 100 GB.
The BD-RE (BD Re-Writable) standard will be available along with BD-R (Recordable) and BD-ROM formats. Almost all manufacturers of optical media have announced their readiness to release rewritable and recordable discs simultaneously with the release of the BD-ROM format onto the market.
In addition to the standard 12 cm discs, 8 cm disc variants will be released for use in digital cameras and video cameras, with capacity planned to be 15 GB for a double-sided version.
The table below shows the sizes of current and upcoming Blu-Ray discs.

Blu-ray technology uses a blue-violet laser with a wavelength of 405 nm to read and write. Conventional DVDs and CDs use red and infrared lasers with wavelengths of 650 nm and 780 nm, respectively.

This reduction made it possible to narrow the track by half compared to a conventional DVD disc - to 0.32 microns - and increase the data recording density.

The shorter wavelength of the blue-violet laser allows more information to be stored on 12 cm discs of the same size as a CD/DVD. The effective "spot size" on which a laser can focus is limited by diffraction and depends on the wavelength of the light and the numerical aperture of the lens used to focus it. Reducing the wavelength, using a larger numerical aperture (0.85, compared to 0.6 for DVD), a high-quality two-lens system, and reducing the thickness of the protective layer by a factor of six (0.1 mm instead of 0.6 mm) made it possible to carry out better and more correct flow of read/write operations. This made it possible to write information to smaller points on the disk, which means storing more information in the physical area of ​​the disk, and also increase the read speed to 36 Mbit/s. In addition to optical improvements, Blu-ray Discs also feature improved encoding technology that allows them to store more information.

Hard coating technology.

Due to the fact that on Blu-Ray discs the data is located too close to the surface, the first versions of the discs were extremely sensitive to scratches and other external mechanical influences, which is why they were enclosed in plastic cartridges. This shortcoming caused a lot of uncertainty as to whether the Blu-ray format could hold its own against the HD DVD standard, its main competitor. HD DVD, in addition to its lower cost, can exist without cartridges just like the CD and DVD formats, making it more understandable to consumers and also more interesting to manufacturers and distributors who may be concerned about the added costs of cartridges.

The solution to this problem appeared in January 2004, with the advent of a new polymer coating that gave the discs incredible protection against scratches and dust. This coating, developed by TDK Corporation, is called "Durabis", and allows the BD to be cleaned with paper towels - which can damage CDs and DVDs. The HD DVD format has the same disadvantages, since these discs are based on old optical media. According to press reports, “naked” BDs with this coating remain functional even when scratched with a screwdriver.

HD DVD format discs.

HD DVD High Definition DVD- High-definition DVD) - recording technology from Toshiba (in collaboration with NEC and Sanyo). HD DVD is similar to rival Blu-ray Disc technology, which also uses the same standard-sized discs (120 millimeters in diameter) and a blue laser with a wavelength of 405 nanometers. The HD DVD Alliance has been joined by Microsoft and Intel, and includes non-exclusive support from the three major film studios: Paramount Pictures, Universal Studios and Warner Bros.

Single-layer HD DVD has a capacity of 15 GB, double-layer - 30 GB. Toshiba also announced a three-layer drive that will store 45 GB of data. That's less capacity than rival Blu-ray, which supports 25 GB per layer and 100 GB per layer, but HD DVD advocates say multi-layer Blu-ray discs are still in development. Both formats are backward compatible with DVD and both use the same video compression techniques: MPEG-2, Video Codec 1 (VC1, based on the Windows Media 9 format) and H.264/MPEG-4 AVC. HD DVD is often misspelled "HD-DVD" because people think the name is similar to the previous generation "DVD-R/RW".

Blu-ray Disc or abbreviated BD (from the English blue ray - blue ray and disc - disk) is the next generation of optical disc format - used for storing high-definition video (with a resolution of 1920? 1080 pixels) and high-density data.

The Blu-ray standard was jointly developed by a group of consumer electronics and computer companies led by Sony, which are members of the Blu-ray Disc Association (BDA). Compared to its main competitor, the HD DVD format, Blu-ray has a larger information capacity per layer - 25 instead of 15 gigabytes, but at the same time it is more expensive to use and support.

Blu-ray (lit. "blue-ray") takes its name from the short-wavelength 405 nm "blue" (technically blue-violet) laser, which allows you to write and read much more data than DVD, which has the same physical volume, but uses a red laser of a longer wavelength (650 nm) for recording and playback.

HVD format discs

Holographic Versatile Disc is an improved optical disc technology, still in development, that will significantly increase data storage capacity compared to Blu-ray and HD DVD. It uses a technology known as holography, which uses two lasers, one red and the other blue-green, collimating into a single beam. The blue-green laser reads data encoded in a grid pattern from a holographic layer close to the surface of the disc, while the red laser is used to read servo signals from a regular CD layer deep within the disc. Servo information is used to track the read position, similar to the CHS system in a conventional hard drive. On a CD or DVD, this information is embedded in the data.

These discs have a storage capacity of up to 3.9 terabytes (TB), which is comparable to 6,000 CDs, 830 DVDs or 160 single-layer Blu-ray discs. HVD also has a data transfer rate of 1 GB/sec. Optware is set to release a 200GB drive in early June 2006 and Maxell in September 2006 with a 300GB capacity.

Holographic Disc (HVD) structure

1. Green laser read/write (532nm)
2. Red positioning/indexing laser (650nm)
3. Hologram (data)
4. Polycarbonate layer
5. Photopolymeric layer (layer containing data)
6. Distance layers
7. Dichroic layer
8. Aluminum reflective layer (red light reflective)
9. Digit basis
P. Petes (PIT)

Types of printing on discs

At the moment, the following types of printing on the surface of CD/DVD-R discs are presented on the technology market:

Offset printing method.

Silkscreen printing.

Thermal printing on CD/DVD-R discs.

Inkjet printing (Ink-Jet) on CD/DVD-R discs.

The offset printing method is most often used for printing industrial runs on CDs and DVDs. Its main feature is that the image technology on CDs and DVDs is practically no different from traditional printing, so the image is full-color and of fairly high quality, although somewhat inferior to felt printing in color brightness. A protective layer of clear varnish is usually applied over the image.

Silk-screen printing is a printing method in which paint is applied to paper by pressing it through a special mesh (stencil). Hence the second name for silk-screen printing – screen printing. Silk-screen printing is the main method of applying images to compact discs produced in medium circulations, and is most suitable for printing simple images with no more than five colors, while ensuring high clarity and color rendering quality. Hence the main drawback - silk-screen printing is poorly suited for transmitting photographic quality images. However, up to ninety percent of all optical discs produced in the world are screen-printed.

Thermal printing on CDs, DVDs.
Thermal printing technology consists of a combination of high temperature and short-term pressure (pressure) on the print head, as a result of which the dye from the ink ribbon is transferred to the surface of the disk, and the size of each portion is microscopic. Naturally, the paint is chosen in such a way that it is embedded in almost any paint and sticks to it very well. Therefore, such devices are best suited for printing mainly inscriptions or complex designs (for example, logos).

The most important advantage of CD and DVD thermal printers over inkjet printers is that almost all of them can print on any CD without the need for special coatings, as well as the high moisture resistance and durability of the resulting images.

Inkjet printing (Ink-Jet) on CDs, DVDs.
This is the highest quality and fastest way to print on CDs and DVDs, which are also ideal for creating small print runs. Using this method, it becomes possible to accurately display photographs with small elements, complex patterns or small text.

Inkjet printing is not possible on any discs, but only on special, “printable” CD/DVD discs that have a micro-rough coating (Ink-Jet Printable), which effectively imprints the ink sprayed by the print head. An attempt to print on discs whose packaging does not say “Printable”, even if they seem suitable for printing in appearance, will most likely end in failure: droplets of ink will not be able to absorb into the surface of the disc and will “spread” to the sides as soon as it is inserted into drive. In addition, the printed surface is very sensitive to moisture. To fix the image, the discs can be coated with a special varnish or laminated, and the surface of the disc becomes glossy. However, many consumers, especially those who “print” discs for personal use, are quite satisfied with the image without varnish.

Glossary of terms

Universal Disk Format is a file system used on rewritable CDs.

Discs marked “termo printable” (with a white layer) are used for thermal printing.

Discs marked “no printing” - silk-screen printing and offset printing.

Discs marked “Ink-jet printable” – inkjet printing.

Disc packaging – “Spindl”

Good afternoon friends!

Today we will talk about perhaps the most common storage media - CD and DVD discs.

As you know, it is a machine in which flows of information circulate.

And such information needs a carrier. The main storage device is a hard drive (hard drive). But it is hidden in the depths of the computer.

Nowadays, when the speed of information exchange increases, there must be other media with quick and convenient access. And such media exist - these are flash drives (“flash drives”), CDs, DVDs, Blu-ray discs.

The disc can be quickly inserted into the drive (without disassembling the computer), recorded information on it and stored. Currently, an alternative to such media has emerged - all kinds of cloud data storage services, but it is premature to write them off. Let's look at CDs and DVDs in a little more detail.

How CDs and DVDs work

CD (Compact Disc) is a 1.2 mm thick plastic disc with a centering hole in the middle. Information can be located on one or both (DVD) sides of the disc. The information side is one long spiral groove starting from the center.

The information is read low-power laser. As is known, the entire diversity of the information flow is provided through quanta (bits) of information, each of which can have a value of 0 or 1. 0 can be interpreted as the absence of a signal, 1 - its presence.

At the bottom of the information groove of the disk there are alternating protrusions (platforms) and depressions.

The laser beam, continuously reflected from the protrusions and depressions of the groove, enters the receiver through the optical system. There is some confusion with the terms "ledge" and "valley". If you look at the disk from above (from the side where the paper sticker is), it will be a depression.

But reading occurs from the bottom (information) part of the disk, so for the laser beam it will be a protrusion. When reflected from the protrusion, the wavelength of the laser beam is shorter - by half the wavelength. Therefore, the wave is extinguished, which is equivalent to the absence of a signal.

The transition from the platform to the ledge and vice versa is interpreted as 1.

If such a transition does not occur (for some time), then this is interpreted as 0.

DVD ( Digital Versatile Disc, universal digital disk) is designed in a similar way, but its groove pitch is smaller (0.7 µm), and the length and height of the protrusions are also smaller. Therefore, with the same disk diameter, more information can be written to it.

Information disks produced in mass quantities are made by stamping from polycarbonate using a metal matrix. A reflective layer of aluminum is applied to the side where the grooves are. Then a thin layer of varnish is applied to this surface and a paper label is glued. DVD capacity - 4.7 Gb.

Dual layer and double sided DVDs

There are dual-layer DVDs, which have two identical discs with grooves.

In such cases, a translucent gold coating is applied to the disk closest to the laser (on the groove side), so that the beam can pass through it and read data from the “far” layer.

For stable reading, the grooves in double-layer discs are made wide e than in single-layer ones, so the disk capacity is 8.5 Gb (and not 9.4 Gb, as might be expected). The transition to the “near” or “far” disk in two-layer disks is carried out by changing the focusing of the laser beam.

Due to the fact that the pads and protrusions in DVDs are smaller than in CDs, the DVD laser operates at a shorter wavelength (CD wavelength is 780 nm, DVD wavelength is 650 nm). There are also double-sided DVDs, each side of which can consist of one or two grooved discs. Thus, the maximum capacity of a DVD can be 17 Gb. The individual grooved discs (both single-sided and double-sided discs) are glued together into one unit.

Write-once discs

Write-once discs are also available CD-R And DVD-R(R – recordable, recordable). There are several types of recordable discs for DVDs, due to the fact that several companies were involved in developing recording standards.

Now we will not delve into boring and dry details and specify the differences between one standard and another.

Recorded discs are, naturally, similar in structure to stamped ones, but the groove contains one long protrusion (from the laser side) along the entire length of the groove, without depressions. Another difference is that before applying the reflective coating, a thin layer of transparent varnish is applied to the disc from the groove side.

When recording information, the laser current increases, its beam heats the varnish layer to a temperature of 250 - 300 0C. The varnish fades and becomes opaque. This operation is also called "by burning» . Naturally, there is no smoke! But, if you look at the disc from the recording side in reflected light, you can distinguish between the recorded and non-recorded zones.

When reading information, the beam is reflected from the reflective layer in those places where the varnish has not been burned out. Where the varnish has been burned, no reflection of the beam occurs.

Re-writable discs

There are also rewritable discs. CD-RW, DVD-RW(RW – rewritable, rewritable). In such disks, on the side where the groove is located, instead of a layer of transparent varnish, a thin film of a metal alloy is applied, which can change its phase state under the influence of heat. The alloy can be in two states - in crystalline and in amorphous.

Moreover, the reflection coefficients for different states are different. In the initial (unwritten) state, the alloy film is in a crystalline state and has a certain reflectance. When recording, the laser beam heats the alloy film to a temperature of 500 - 700 degrees, the alloy in these places melts and turns into an amorphous state.

In this case, the reflection coefficient decreases greatly, and this is perceived by the reading circuit as the absence of a signal. You can erase the data if you transfer the alloy film back to the crystalline state. To do this, it is heated with the same laser beam to a temperature of 200 degrees. This is not enough to melt, but it is enough to soften.

Upon subsequent cooling, a transition from the amorphous to the crystalline state occurs. Data erasing occurs when discs are rewritten. In this case, the laser beam generates pulses of different powers, creating areas with a crystalline and amorphous structure.

Digital data on the disc is recorded in redundant code.

This is necessary to correct errors that will always occur, if only because the surface of the disk is scratched. Therefore, discs must be handled with care. and grab them only by the outer edges. Fingerprints on the information side may lead to reading errors. Because of this, the disk will take longer to read than it could or “slow down”.

If there are a lot of scratches on the disc, the disc will also take a long time to read (if it takes at all). The reading speed of a defective disk may depend on the specific drive model (on the firmware “hardwired” into it).

How to remove a disk from a faulty drive?

In conclusion, let us mention one useful detail. Sometimes a DVD drive fails right before your eyes, and the disc remains in it.

In such cases, when you press the eject button, no action occurs. You can remove the disk by disassembling the drive. But it's long and troublesome! For such emergencies, there is a small hole on the front of the drive.

To remove the disk, you need to insert a metal pin into this hole (you can straighten the paper clip) until it stops and press lightly.

In this case, the moving part of the drive will move out slightly. You can then manually slide it out to its normal open position and remove the disc. Did you think this was a hole for ventilation?

That's all for today, dear readers.

Vsbot was with you.

All the best!

Audio Compact Disc (CD-DA) FAQ

All rights in relation to this text belong to the author. When reproducing the text or part of it, copyright is required. Commercial use is permitted only with the written permission of the author.

How does a CD work?

The design of a CD-DA disk (Compact Disk - Digital Audio) and the method of recording sound on it are described by the standard of the companies Sony and Philips that proposed it, published in 1980 under the name Red Book.

A standard compact disc (CD) consists of three layers: base, reflective and protective. The base is made of transparent polycarbonate, on which an information relief is formed by pressing. A metal reflective layer (aluminum, gold, silver, other metals and alloys) is sprayed over the relief. The reflective layer is covered on top with a protective layer of polycarbonate or neutral varnish - so that the entire metal surface is protected from contact with the external environment. The total thickness of the disc is 1.2 mm.

The information relief of the disk is a continuous spiral path starting from the center and consisting of a sequence of depressions - pits. The spaces between the pits are called lands. By alternating pits and gaps of various lengths, an encoded digital signal is recorded on the disk: the transition from gap to pit and vice versa denotes a unit, and the length of a pit or gap is the length of a series of zeros. The distance between the turns of the track is selected from 1.4 to 2 microns, the standard specifies a distance of 1.6 microns.

How is the audio signal represented on the disc?

The original stereo audio signal is digitized into 16-bit samples (linear quantization) with a sampling frequency of 44.1 kHz. The resulting digital signal is called PCM (Pulse Code Modulation) because each pulse of the source signal is represented by a separate codeword. Every six samples of the left and right channels are formatted into primary frames, or microframes, of 24 bytes (192 bits) in size, arriving at a speed of 7350 pieces per second, which are encoded using a two-level CIRC code (Cross Interleaved Reed-Solomon Code). -Solomon with cross interleaving) according to the scheme: interleaving with a 1-byte delay, C2 level encoding, cross-interleaving with a variable delay, C1 level encoding, interleaving with a 2-byte delay. Level C1 is designed to detect and correct single errors, C2 - group errors. The result is a 256-bit block, the data in which is equipped with error detection and error correction bits, and is also “smeared” down to the block, which leads to the recording of contiguous audio data in physically non-contiguous areas of the disk and reduces the impact of errors on individual samples.

The Reed-Solomon code has 25% redundancy and can detect up to four erroneous bytes and correct up to four lost or two erroneous bytes. The maximum length of a fully correctable error packet is about 4000 bits (~2.5 mm track length), but not every packet of this length can be completely corrected.

After the second interleaving, subcode bits are added to each received block - P, Q, R, S, T, U, V, W; each block receives eight subcode bits. Then, every 98 blocks with subcodes are formed into one superframe with a duration of 1/75 sec (the amount of pure audio data is 2352 bytes), also called a sector, in which the subcodes of the first two blocks serve as a sign of synchronization, and the remaining 96 bits of each subcode form the P-word, Q-word, etc. Throughout the track, the sequence of sub-code words is also called sub-code channels.

Words or subcode channels are used to control the recording format, indicate fragments of a soundtrack, etc. - for example, the P channel is used to mark audio tracks and pauses between them (0 - pause, 1 - sound), and the Q channel is used to mark the track format and sectors, TOC entries (Table Of Contents) and timestamps that track playback time. Channel Q can also be used to record information in the ISRC (International Standard Recording Code), which is intended to represent information about the manufacturer, release time, etc., as well as to divide the track into separate fragments (all on audio A disc can have up to 99 audio tracks, each of which can include up to 99 fragments).

Finally, frames designed in this way are channel encoded in pit-gap terms using 8/14 (Eight to Fourteen Modulation (EFM)) redundancy code, in which the source bytes are encoded into 14-bit words, increasing the intelligibility of the signal. Three link bits are inserted between words to maintain restrictions on the number of adjacent zeros and ones, which facilitates demodulation and reduces the DC component of the signal. As a result, 588 channel bits are obtained from each primary microframe, and the resulting bit stream is written to disk at a speed of 4.3218 (588x7350) Mbps. Since EFM coding produces a digital stream in which there are more zeros than ones, a system was chosen to represent units by the boundaries of a pit and a gap, and the number of zeros between ones by the length of a pit or gap, respectively.

At the beginning of the disc there is a so-called lead-in zone containing information about the disc format, the structure of sound programs, addresses of fragments, titles of works, etc. At the end the lead-out zone is recorded (track number AA) , which acts as the boundary of the recorded area of ​​the disk; The P code bit in this zone changes at a frequency of 2 Hz. A number of home players cannot recognize a disc without this zone, but many can do without it. Between the input and output zones, a program memory area (PMA) is recorded, containing the actual audio data. The program area is separated from the input area by a section of 150 empty blocks (2 seconds), which acts as a pre-gap.

The total recording time on a CD is 74 minutes, however, by reducing the standard track pitch and the distance between pits, you can achieve an increase in recording time - at the expense of reducing the read reliability in a standard disk drive.

How are CDs recorded and produced?

The main method of producing disks is pressing from a matrix. The original is formed from the original digital master tape, containing an already prepared and encoded digital signal, by a special high-precision machine on a glass disk coated with a layer of photoresist - a material that changes its solubility under the influence of a laser beam. When the recorded original is processed with a solvent, the required relief appears on the glass, which is transferred by electroplating to the nickel original (negative), which can serve as a matrix for small-scale production, or as a basis for making positive copies, from which, in turn, negatives are taken for mass replication.

Stamping is carried out using the injection molding method: a polycarbonate substrate with a relief is pressed from a negative matrix, a reflective layer is sprayed on top, which is varnished. Informational inscriptions and images are usually applied on top of the protective layer.

Recordable discs (CD-R, “blanks”) are made using the same method, but between the base and the reflective layer there is a layer of organic matter that darkens when heated. In the initial state, the layer is transparent; when exposed to a laser beam, opaque areas equivalent to pits are formed. To facilitate tracking of a track when recording on a disc, a preliminary relief (marking) is formed during the manufacturing process, the track of which contains frame marks and synchronization signals recorded with a reduced amplitude and subsequently overlapped by the recorded signal.

Recorded discs, due to the presence of an organic fixing layer, have a lower reflection coefficient than stamped ones, which is why some players (Compact Disk Player - CDP), designed for standard aluminum discs and not having a margin of read reliability, can play CD-R discs less reliably, than usual.

How are CDs played?

During playback, an audio CD rotates at a constant linear velocity (CLV), at which the speed of the track relative to the playback head is approximately 1.25 m/s. The rotation speed stabilization system maintains it at such a level as to ensure the speed of the read digital stream equal to 4.3218 Mbps, so depending on the length of the pits and gaps, the actual speed may vary. The angular speed of the disk varies from 500 rpm when reading the innermost sections of the track to 200 rpm on the outermost ones.

To read information from the disk, a semiconductor laser with a wavelength of about 780 nm (infrared range) is used. The laser beam, passing through the focusing lens, falls on the reflective layer, the reflected beam enters the photodetector, where pits and gaps are determined, as well as the quality of focusing of the spot on the track and its orientation along the center of the track are checked. When focusing is disrupted, the lens moves, working on the principle of a loudspeaker diffuser (voice coil), and when it deviates from the center of the track, the entire head moves along the radius of the disk. In essence, the lens, head and spindle motor control systems in the drive are automatic adjustment systems (ATS) and are constantly monitoring the selected track.

The signal received from the photodetector in 8/14 code is demodulated, as a result of which the CIRC encoding result with added subcodes is restored. Then the subcode channels are separated, deinterleaved and CIRC decoded on a two-stage corrector (C1 for single errors and C2 for group errors), as a result of which most of the errors introduced by stamping violations, defects and heterogeneity of disk materials, and scratches on the disk are detected and corrected. surface, unclear definition of the pit/gap in the photodetector, etc. As a result, the stream of “pure” audio samples is sent to the DAC for conversion to analog form.

In sound players, after the corrector, there is also an interpolator of varying complexity, which approximately restores erroneous samples that could not be corrected in the decoder. Interpolation can be linear - in the simplest case, polynomial or using complex smooth curves.

To perform de-interleaving, any CD-reading device has a buffer memory (standard volume - 2 KB), which is also used to stabilize the bit rate. Decoding can use several different strategies, in which the probability of detecting group errors is inversely proportional to the reliability of their correction; the choice of strategy is left to the discretion of the decoder developer. For example, a CD player with a powerful interpolator might choose a strategy that emphasizes maximum detection, while a CDP with a simple interpolator or CD-ROM drive might choose a strategy that emphasizes maximum correction.

What are the parameters of the audio signal on a CD?

Standard digitization parameters—sampling frequency 44.1 kHz and sample bit depth 16—determine the following theoretically calculated signal characteristics:

• Frequency range: 0..22050 Hz
• Dynamic range: 98 dB
• Noise level: -98 dB
• Total Harmonic Distortion: 0.0015% (at maximum signal level)

In real CD recording and playback devices, high frequencies are often cut off at 20 kHz to create a margin for the steepness of the filter's frequency response. The noise level can be as low as 98 dB with a linear DAC and a noisy output amplifier, or higher if resampled at a higher frequency using a Delta-Sigma, Bitstream or MASH DAC and low-noise amplifiers. The coefficient of nonlinear distortion strongly depends on the used DAC output circuits and the quality of the power source.

A dynamic range of 98 dB is determined for a CD based on the difference between the minimum and maximum levels of the audio signal, but at a small signal the level of nonlinear distortion increases significantly, which is why the real dynamic range, within which an acceptable level of distortion is maintained, usually does not exceed 50-60 dB.

What is jitter?

Jitter is a rapid jitter in the phase of a digital signal relative to the duration of the period, when the strict uniformity of the pulse fronts is violated. Such jitter occurs due to the instability of clock generators, as well as in places where the clock signal is isolated from a complex signal using the PLL (Phase Locked Loop) method. Such selection takes place, for example, in the demodulator of the signal read from the disk, resulting in the formation of a reference clock signal, which, by correcting the rotation speed of the disk, is “adjusted” to the reference frequency of 4.3218 MHz. The frequency of the clock signal, and therefore its phase and the phase of the information signal, continuously fluctuates at different frequencies. An additional contribution may be made by the uneven arrangement of pits on the disk, caused, for example, by poor-quality pressing or unstable recording.

However, ripples in the disk signal are fully compensated for by the decoder's input buffer, so that any jitter or knock that occurred before the signal was placed in the buffer is eliminated at this stage. Sampling from the buffer is controlled by a stable oscillator with a fixed frequency, but such oscillators also have a certain, albeit much less, instability. In particular, it can be caused by interference in the power supply circuits, which, in turn, can occur when the ACS is activated and the disk speed or head/lens position is adjusted. On low-quality discs, these corrections occur more often, giving some experts reason to directly link the stability of the output signal with the quality of the disc, although in fact the reason is insufficiently good decoupling of CDP systems.

What do the abbreviations AAD, DDD, ADD mean?

The letters of this abbreviation reflect the audio waveforms used to create the disc: the first for the original recording, the second for processing and mixing, and the third for the final master signal from which the disc is formed. “A” denotes analogue form, “D” denotes digital form. The master signal for a CD always exists only in digital form, so the third letter of the abbreviation is always "D".

Both analog and digital signal forms have their advantages and disadvantages. When recording and processing a signal in analog form, its “fine elements” are most fully preserved, in particular higher harmonics, but the noise level increases and the amplitude-frequency and phase-frequency characteristics (AFC/PFC) are distorted. When processed in digital form, higher harmonics are forcibly cut off at half the sampling frequency, and often even lower, but all further operations are performed with the highest possible accuracy for the selected resolution. A number of experts evaluate a signal that has undergone analog processing as “warmer” and “live”, however, many modern signal processing methods can only be adequately implemented in a digital version.

Can two identical discs sound different?

First of all, you need to make sure that the discs actually contain an identical digital audio signal. A complete binary match between two discs at the pit and gap configuration level is virtually impossible due to minor material defects and distortions during die processing and pressing, but due to redundant encoding, the vast majority of these errors are corrected during decoding, providing the same “high level” digital stream.

You can compare the digital contents of discs by reading them in a CD-ROM drive that supports Read Long or Raw Read mode - reading “long sectors”, which are actually CD-DA superframes with a capacity of 2352 bytes each. You can read more about this in the CD-ROM FAQ or in the manual for audio reading programs (CD-DA Grabbers/Rippers). You can also compare discs using studio equipment that can read discs in digital form on a DAT tape recorder.

There can be several reasons for digital differences between discs that sound similar. Some CD-ROM drives and other digital CD-DA reading devices can, in order to prevent direct copying, introduce subtle distortions into the signal (for example, using smoothing polynomials), and most drives that support full frame reading commands do this inaccurately and inaccurately. When making copies (reprints) of audio discs, especially in a pirated way, they are often copied with resampling to another frequency (for example, 48 kHz in DAT) followed by resampling to the original one, or even through an analog path with double digital/analog conversion. A number of versions of CD-R burning software also intentionally or accidentally distort the original data so that the copy is not the same as the original.

It should be noted that even if the digital contents of two disks coincided when comparing them in some system (CD-ROM, special devices for comparing the original/copy, etc.), this does not mean at all that on this or that CDP they are also Identical digital signals will be decoded. Therefore, the most reliable way to determine the cause of differences in sound is to use a CDP with a digital output, from which recording is being carried out on some storage device while listening to both discs. Subsequent digital comparison of the resulting signalgrams will show at what point in the player the changes that are audible to the ear are introduced into the signal.

Of course, before comparing the original and the copy in this way, you need to make sure that the results of reading the same discs multiple times are repeatable. Various digital signalgrams in this case may indicate unreliable disk reading or poor operation of digital interfaces (receiver, transmitter, cable, connectors). The identity of digital data during repeated playback of several discs can be considered a sufficient sign of the reliability of both the discs themselves and the reading, decoding and intermodular transmission systems.

The auditory comparison of the sound of discs must be correct - the most recognized is the double-blind test. The essence of the method is that the expert (listener) should not see the manipulations with the equipment and the person performing them, and this person himself, who randomly changes the disks, should not know the features of their contents. In this way, any influence, including “subtle” and unstudied, of people on the equipment and on each other is eliminated as much as possible, and the expert’s opinion is considered extremely unbiased.

What is HDCD?

High Definition Compatible Digital is a “super-system” for CD audio encoding, using the standard CD-DA format. An audio signal with a higher bit depth and sampling frequency is subjected to digital processing, as a result of which the main part is isolated from it, encoded, as usual, using the PCM method, and additional information clarifying small details is encoded in the least significant bits of samples (LSB) and masked spectral regions . When playing an HDCD disc on a regular CDP, only the main part of the signal is used, but when using a special CDP with a built-in decoder and HDCD processor, all information about the signal is extracted from the digital code.

How to handle CDs?

Avoiding mechanical damage to any of the surfaces, exposure of the disc to organic solvents and direct bright light, impacts and kinks of the disc. Inscriptions on recordable discs may only be made with pencils or special felt-tip pens, excluding pressure and the use of ballpoint or fountain pens.

When removing a disc from the box, be careful not to bend it. One convenient and safe method requires the use of two hands - the thumb of the left hand presses lightly on the latch, loosening it, while the other hand removes the disc from the latch. The one-handed method, when the index finger loosens the latch and the thumb and middle finger remove the disk, requires more precise coordination of forces, without which it is easy to bend the disk or break the latch tabs.

A dirty disc can be washed with warm water and soap or a non-aggressive surfactant (shampoo, washing powder), or specially produced liquids. Shallow scratches on the transparent layer can be polished using polishing pastes that do not contain organic solvents and oils, or regular toothpaste.

What is a “green marker” and why is it needed?

Many users and experts claim that a disc treated in this way produces cleaner sound in high-end devices, attributing this to a more accurate reading of digital information from the disc, which in its original form supposedly cannot be reliably read in most drives. However, a carefully designed system (drive and decoder) is able to correctly read not only untreated discs, but also discs of average quality, and even slightly dirty and scratched ones, so possible reasons for improved sound should not be sought in the disc. The most likely explanations for this phenomenon seem to be the same factors that create different sounds of copies of discs that match the digital content.

Where can I find more information on CDs?

One of the greatest achievements of DVD is that it has managed to combine all the uses of a compact disc for data, video, audio (or a combination thereof) within a single physical file structure called UDF, or Universal Disc Format. Developed by OSTA (Optical Storage Technology Association), the UDF format ensures that any file can be accessed on any drive installed on a consumer's computer or video player. In addition, the format is compatible with standard operating systems because it takes into account the CD ISO 9660 standard. UDF overcomes the incompatibility problems that plagued the CD when the standard had to be rewritten every time new applications such as multimedia, interactive systems or video were introduced.

The version of UDF that both rewritable and read-only Discs satisfy is a subset of the UDF specification version 2.02, which is known as MicroUDF (M-UDF).

Because UDF was not supported by Windows until Microsoft released Windows 98, DVD manufacturers were forced to use an intermediate format called UDF Bridge, which was a hybrid of UDF and ISO 9660. Windows 95 OSR2 supported UDF Bridge, but earlier versions did not could. The UDF Bridge specification does not explicitly include Joliet extensions for ISO 9660, which are needed for long filenames. Windows 98 recognizes UDF, so these systems have no problems with either UDF or long file names.

DVD video only uses UDF with all the data required by UDF and ISO 23346 to be compatible with computer systems, and does not use ISO 9660 at all. DVD video files cannot be larger than 2 GB in size and must be written as a separate extent (that is, in a contiguous sequence). The first directory on the disk must be the VIDEO_TS directory containing all files, and all file names must be in 8+3 format (8 bytes for name, 3 for extension).

DVD audio discs use UDF to store data in a separate "DVD audio zone" on the disk, specified as the AUDIO_TS directory.

Mammoth format

Exabyte has been a leader in the NML industry for over 20 years. The company was the first to propose the use of 8 mm tapes for data storage based on a mechanism similar to Sony video cameras, and more than 2.5 million of such drives were produced. Such mechanisms are sufficient for low-reliability applications, but are less suitable for today's server applications. Introduced in 1996, the Mammouth standard is a more advanced and reliable technology and represents Exabyte's answer to the requirements of this range of the server market.

The ML drive does not use a capstan, eliminating the tape storage portion that creates unpredictable wear on the media. AME technology (Advanced Metal Evaporated) or metal deposition by evaporation is used. This ensures anti-corrosion resistance and wear resistance of the tape, and the shelf life increases to 30 years. The smooth surface of the ML increases the wear time of the heads to 35 thousand.

Data on the ML is organized into segments (sections), each of which can be written, erased, or read as a whole. This organization allows storage capacity to be increased to support applications such as multimedia and video servers. For error correction, the two-level Reed-Solomon ECC method is used. In this case, errors are corrected “on the fly” by rewriting blocks within the same track.

In 2000, the Exabyte Mammoth-2 drive was released, setting new standards for speed and capabilities. The drive has a transfer speed of 22 MB/s, 8 mm AME tape can load a maximum of 60 GB. NML uses the Ultra2/LVD SCSI interface, a 32 MB buffer - a multi-channel head, the latest ECC error correction algorithm and provides a compression ratio of 2.5: 2 based on ALDC (adaptive lossless data compression), giving a capacity of 250 GB per tape. The subsequent fiber optic version offered an increase in the original transfer speed to 30 MB/s.

Advanced digital recording technology

Developed by Philips Corporation. The first ADR devices were launched in the spring of 1999, in the form of an NML with an IDE interface, capable of recording 25 GB of raw or 30 GB of compressed information per cartridge.

The tape drive is able to continuously control its movement up or down by even the smallest amount, resulting in high density - up to 292 tracks on 8 mm film. ADR's ability to read or write all eight data tracks simultaneously makes it possible to achieve impressive transfer rates at relatively low speeds. The tape wear is minimal, and it is also possible to control and correct errors in both horizontal and vertical directions. The error correction code (ECC) used here is much more efficient than in conventional systems, where the error correction code operates in only one dimension (the data track). In fact, ECC for ADR can provide 200% data recovery even if up to 24 of the 292 tracks are destroyed along the entire length of the tape.

CD-R and disc capacity

A CD-R contains a pre-applied spiral track divided into blocks, with the address of each block encoded directly into the media. The capacity of the most widely used CD format can be expressed as either 74 minutes or 650 MB. Each second of playback time takes up 75 blocks, so a full CD has a capacity of 74 x 60 x 75 = 333,000 blocks.

The actual capacity of these 333 thousand blocks depends on what exactly is recorded on the disk - audio or data. This is due to the fact that audio has fewer requirements for error-free recording and therefore, in this case, a smaller amount of control, redundant information is recorded in each block. This results in a block capacity of 2353 bytes for audio (2048 for data). Therefore, a 74-minute disc has a capacity of 783,226,000 bytes (746 MB) for audio, but only 682,984,000 bytes (650 MB) for data.

At the end of the 1990s. CD-R media began to appear with a larger storage capacity than the 74-minute maximum allowed by the Audio Compact Disc (Red Book) or CD-ROM (Yellow Book) standards. These technologies are collectively called CD overburning.

Additional capacity was achieved by reducing track pitch, reducing scan speed tolerances, and reducing the likelihood of write-read errors (this introduces compatibility issues with older devices or older CD recordings).

The first of these high-capacity formats provided a read time of 80 minutes and held 360 thousand blocks instead of the usual 333 thousand. In terms of data volume, this meant 703 MB compared to the 650 MB of a standard CD. At the start of the new millennium, even higher capacities appear in the form of 90- and 99-minute formats (approximately 792 and 870 MB respectively). It should be noted that since timestamps on a CD are encoded with a pair of decimal digits, it is not possible for the disc to exceed 99 minutes in capacity.

Overburning requires support for Disc-At-Once mode when writing and for the CD writer to ignore the free space information found on the non-written disc (ATIP) and instead use the data passed from the writing program.

Overcoming buffer insufficiency

By the end of 1999, the specifications had doubled to 8x/24x, but a problem known as buffer underrun occurred when the speed of the machine and the MD began to lag behind the speed of CD-R devices (the device is ready to write to 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 a recording CD player (sizes from 256 KB to 2 MB), and secondly, devices began to adapt to the speed of information flow, reducing or increasing the recording speed.

BURN-Proof technology (Buffer UndeRuN-Proof technology), proposed by Sanyo, consists of constantly monitoring the state of the CD data buffer so that recording is stopped at a certain point if there is a danger of buffer insufficiency (for example, when the buffer fill drops below a specified threshold ), and then resumed by positioning the laser head to the appropriate sector.

Plextor uses Sanyo technology in combination with its own "PoweRec" (Plextor Optimized Writing Error Reduction Control) method. The recording process here is periodically paused (using BURN-Proof technology) to check the recording quality and decide whether to increase or decrease the recording speed.

UDF standard

The ISO 9660 standard used by CD-ROMs and CD-R discs makes it difficult to add data to discs in small chunks. Recording multiple sessions to disk wastes approximately 23 MB of disk space per session, and the original standard limited the number of tracks that could be recorded to disk to 99. These restrictions were removed in the ISO 23346 Universal Disc Format (UDF) standard developed by the Optical Storage Technology Association (OSTA). This standard is independent of operating system type, is designed for writing data on optical media, including CD-R, CD-RW, and DVD devices, and uses a redesigned directory structure that allows the device to efficiently write a file (or "batch") at a time .

Batch recording mode is not fully compatible with the ISO 9660 logical file system, since it requires knowing exactly which files will be written during a session in order to populate the FS service tables (Path Tables and Primary Volume Descriptors), which indicate the physical location of files on disk.

UDF allows you to add files to CD-R or CD-RW discs in portions of one file at a time, without significant overflow of service information, using a technique called “packet writing”. In UDF, even if a file is overwritten, its virtual addressing remains unchanged.

At the end of each packet recording session, UDF writes to disk a "Virtual Allocation Table" (VAT), which describes the physical location of each file. Each newly created VAT includes the data from the previous VAT, thus allowing the UDF to locate all files that have ever been written to disk.

By mid-2998, two versions of UDF had been released - UDF 2.02 (the version used on DVD ROMs and video DVDs) and UDF 2.5 (adds support for CD-R and CD-RW). Windows 98 provided support for UDF 2.02. However, in the absence of support for the UDF 2.5 operating system, special UDF software for the drive was required to support batch writing to CD-R and CD-RW.

The first example of such software was DirectCD V2.0 (developed by Adaptec), which supported both batch writing and random deletion of files from CD-RW media. DirectCD V2.0 provided recording of two types of packets - fixed and variable lengths. Fixed-length packets are more suitable for CD-RWs to allow random deletion of files.

MultiRead Specification

Tracks recorded on a CD-RW disc are read in the same way as tracks on a regular CD - by detecting transitions between low and high reflectances and measuring the gaps between transitions. The only significant difference is that the reflection coefficient is lower than for “proper” CDs, as a result of which CD-RW media may not be readable by many older CD-ROM drives or CD players.

Note that the original specifications for CDs required reflectances for the disc surface and grooves to be a minimum of 70% and a maximum of 28%, respectively. These requirements were introduced to ensure reliable data readout by photodiodes of the 1980s.

Currently, due to the improvement of electronics, these requirements turn out to be excessively high.

A CD-RW disc has a surface reflectance of 25-25%. Therefore, a CD-RW system operates within a range of reflectances equal to ⅓ of those of the original CD specification. However, for modern photodiodes this does not pose any problem; it is enough to organize the amplification of the electrical signal.

The MultiRead specification, compiled by Philips and Hewlett Packard and later endorsed by the Optical Storage Technology Association (OSTA), provides the necessary adjustments to address any compatibility issues.

In addition, the maximum and minimum reflectance levels of a CD-RW disc meet the CD specification requirements for a minimum modulation of 60%. The phase change technology for CD-RW is practically independent of the wavelength of the write-read laser.

CD-RW discs can be read by both lasers used in DVD systems (650 nm wavelength) and lasers used in conventional CD drives (780 nm).

Mount Rainier

The specification, proposed by the Mount Rainier group (led by industry leaders Compaq, Microsoft, Philips Electronics and Sony), was intended to make the use of CD-RW media similar to that of HDDs or HDDs - in particular, to perform operations in a data-towing manner with the support of the operating system (“drag and drop”). The Mount Rainier specification contains the following key elements:

• hardware monitoring of defective areas on the disk. Although most batch CD-RW burning programs use the defect monitoring capabilities of UDF 2.5, the problem is that the software must have complete information about the defective areas of the disk. Mount Rainier's approach is to have hardware control so that if an application tries to write to a "bad" sector, that sector will be "hidden" and an alternative one will be offered;
• logical addressing of a 2 KB record. While CD-RW uses a 64 KB block size, Mount Rainier requires support for 2 KB logical addressing, thus keeping CD-RW drives in line with other storage systems that are based on 4 or 2 KB addressability ;
• background formatting. Mount Rainier eliminates both time delays and the need to use software outside the operating system or disk writing software (typically associated with formatting CD-RW media). Formatting is now carried out as a background task, invisible to the user.

OSD technology

The goal of Optical Super Density (OSD) technology was to develop high-capacity (40 GB or more) removable magneto-optical storage media that would have the reliability to meet today's ISO requirements for ML, achieve data transfer rates competitive with hard drive (30 MB /c) and would provide a lower cost per megabyte of memory than other optical and magnetic technologies. In the spring of 1999, Maxoptix Corporation, a leading manufacturer of MO drives, announced the creation of OSD technology.

Achieving the project’s goals was based on a number of innovative technologies:

• OverCoat Incident Recording (OCIR) technology places a recording layer on top of a substrate (similar to a hard drive) and uses a thick, clear acrylic layer similar to the protective coating on the back of a CD or DVD. The OSD coating is more than 2,000 times thicker than hard drive and tape, but much thinner than the substrate used on conventional MO media. Because this allows the lens to be positioned much closer to the recording layer of the disc, the OSD is able to use the higher numerical aperture of the lens, resulting in much higher data recording densities;
• Bulk surface recording - Surface Array Recording (SAR), this uses independent read/write heads on both sides of the media to allow access to both sides of the disk simultaneously. This is different from traditional MO, where users are forced to swap the media to read data stored on the opposite side of the disk;
• Magnetic Field Modulation (MFM) bypasses the limitations inherent in the traditional use of bias when recording data on a disk MO. By using a small magnetic head in close proximity to the disk, the polarity of the magnetic field can be switched at the highest frequency; Magnetic Super Resolution (MSR): Using MFM changes the limiting factor of recording density from laser wavelength to the ability to highlight individual reading marks using a beam spot that can span multiple marks.

Recordable DVD formats

There are five versions of recordable DVDs:

• DVD R regular;
• DVD R authorized;
• 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. The specification of the content itself is subject to multiple "application layers" as defined by the DVD Forum. For example, typical movies are released on ROM discs (physical layer) and use the DVD video format (application layer).

All recording players can read DVD ROM discs, but each uses a different type of disc for recording. DVD R, which was introduced in 1997, can only be written once (sequentially only), while DVD RAM, DVD RW and DVD+RW discs can be rewritten thousands of times.

DVD RAM was the first rewritable format to hit the markets in the summer of 1998. This format is most suitable for recording computer data from rewritable DVD formats for use in computers as it supports defect bypass and CLV (Constant Linear Velocity) zone format, however it is not compatible with most players (due to differences in disc reflectivity and minor format differences).

The DVD RW and DVD+RW formats represent an evolutionary development of the existing CD-RW and DVD R technologies, and therefore provide better compatibility with the rest of the CD/DVD product family. DVD RW first appeared in Japan in late 1999 and was not used anywhere else until 2002. DVD+RW suffered many false starts and appeared in late 2002.

Project Centipede (Millipede)

In late 1999, IBM's Zurich Research Laboratory unveiled the concept that micro- and nano-mechanical systems could compete with electronic and magnetic devices in the field of high-capacity storage devices. Instead of writing bits by magnetizing points on the surface of a disk, the new "Millipede" device melts tiny depressions into the surface of the media.

The technology uses "legs" (tips) mounted on the ends of tiny arms to scan tiny surface details. The tips of the “centipede” (2024 = 32 x 32 in number) are heated by an electrical pulse to 750 F (400 ° C), which is enough to melt a hole in the surface film of the polymer of the disk. The tips leave holes 30-50 nm in size, each representing one bit. To read the data, the centipede determines whether the "leg" is in the hole by recording the temperature of the console.

Technologically, the write-read element consists of an array of 64 x 64 = 4096 micro-levers, occupying 6.4 x 6.4 mm2 and placed on a silicon chip (20 x 20 mm2), manufactured using a new technology that allows direct communication of micro-levers with CMOS electronics. The micro-levers have separate heaters for writing and reading and an electrostatic drive for movement in the z-axis direction.

High data processing speeds can be achieved by the joint work of a large number of tiny “legs”. IBM believes this method will eventually enable storage densities of 500 Gb/in2 to be achieved.

HD-burn technology

Sanyo Electric Co., Ltd. (Japan) announced the release of new BURN-Proof technology, which solved the main problem of recording on CD-R/DVD R-discs and radically improved the characteristics of CD/DVD recorders. On this basis, Sanyo has developed high-density recording technology: it is now possible to fit 2.4 GB of data on a regular 700 MB CD-R disk.

The new technology is called “HD-burn” (High Density Burn) - high-density recording. To implement the new method, a new combined drive Sanyo SuperCombiDrive CRD-DV2 was created. Let us list the features of this technology.

Regular CD-R discs can record a standard amount of information - up to 0.7 GB. Moreover, the discs are fully compatible with CD and DVD drives.

Conventional CD-R discs can store double the amount of information - up to 2.4 GB. At the same time, the discs are fully compatible with DVD drives, taking into account the introduction of changes to the firmware.

In HD-burn mode, 36x write speed and 80x read speed are achieved.

BURN-Proof recording technology is supported without limitation. HD-burn mode also supports CD-RW discs. This achieves 24x recording speed. Working with the HD-burn recorder is supported by several popular software packages, including Nero Burning ROM (manufactured by Ahead Software). HD-burn mode cannot burn CD-DA (Audio CD) format discs.

Discs recorded using high-density technology will not be readable by CD drives.

A disc recorded using HD-burn technology will contain 30 minutes of high quality video (similar to DVD video) with a resolution of 720 x 576 pixels.

The essence of high-density recording technology is the use of two new principles that allow you to record twice as much information on a conventional medium - a CD-R disk:

• the length of the pit (mark) on the disk is reduced to 0.62 microns (for a regular CD - 0.83 microns). This means that HD-burn increases the disk capacity by 2.35 times. The 0.62 µm value was chosen so that existing DVD video players and DVD ROM drives could read HD-burn discs with minor upgrades;
• A different error correction system is used: instead of CIRC (Cross Interleaved Reed Solomon Code), RS-PC (RS-PRODUCT Code) with modulation 8-26 is used, which increases the capacity by another 2.49 times. According to Sanyo, the new RS-PC error correction system is not only more compact, but also significantly more efficient than CIRC. As a result, the capacity of one CD recorded in HD-burn mode is 2 times greater than the capacity of a CD recorded in normal mode - 2.49 x 2.35 = 2.0225.

The spiral pitch (track feed) and recording area remain the same, allowing the use of regular CD-R discs. Other high-density recording technologies require changes in the physical characteristics of the media. For example, Sony's DDCD (Double Density Compact Disc) technology cannot work with regular discs. Figure 3.35, c shows a comparison of the pit length of an HD-Burn disc with ordinary CD and DVD discs.

DVD formats

There are five physical formats (or books) of DVD, 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 - for audio storage only; audio CD-like format;
• 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.

Having the same size as a standard CD (diameter 220 millimeters, thickness 2.2 mm), DVDs provide up to 27 GB of storage with transfer speeds faster than CD-ROMs, access times similar to CD-ROMs, and come 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 20 - double-sided single-layer disc 9.4 GB;
• DVD 28 - capacity up to 27 GB on a double-sided, double-layer disc.

In addition, there is a project for the DVD 24 format - two layers on one side, one on the other, which, being easier to produce, will replace DVD 28 until the need for the latter is fully realized.

It is important to recognize that in addition to the five physical formats, DVD also has many application formats such as DVD video and DVD audio.