What is the name of the CD? ...

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A brief history of the creation of CDs. Parameters and properties of different optical media. Difference between BD and CD and HD DVD formats.

Today there is a wide variety of CDs, but knowing the main types, you can quite easily figure out for what specific purpose one or another is needed. optical disk. They differ not only in the amount of information stored, but also in the ability to overwrite files.

CDs were the first to be developed - these CDs, in the late seventies of the last century, were created for storing and listening to music. The very first ones could hold up to 650 MB, a little later the memory capacity became larger - 700 MB.

In 1996, DVDs appeared on the CD market. They are comparable in size to CDs, but with a larger storage capacity of up to 4.7 gigabytes. It also became possible to save video images, and therefore DVD technology was much more expensive.

In the 21st century, almost all computers are equipped with a standard DVD drive. DVD format discs are now in greater demand than CDs, but CD manufacturers haven't stopped there.

Technologies for recording and storing various files are constantly being improved. This is how double-sided and multilayer disks were created, on which the amount of information can be recorded an order of magnitude greater.

The next stage of development is the creation of the BD format, Blu-ray disc or "blue ray" was introduced to the public at the turn of the millennium. The CD got its unusual name from the color of the recording laser.

Over the course of several years, developers perfected the technology, and in 2006 the BD version that still exists today was created. This format was in first place in terms of the volume of stored information - up to 23 gigabytes. Today in everyday life you can use a four-layer disk with a capacity of 100 gigabytes. Disks with ten recording layers and a capacity of 320 gigabytes have also been developed.

Dual Discs are not so well known to the average user; they occupy a separate position among compact discs and combine two formats - CD and DVD. So on one side the music is stored, on the second, in DVD format, the following can be recorded: menus, videos, images, surround sound, subtitles.

Such CDs are characterized by the speed of writing or reading information. Thus, the designation 4x MAX stands for increasing the disk rotation speed four times faster compared to conventional CDs.

Another type of CD is HD DVD. These disks can hold up to 15 GB if they are single-layer. The capacity of double-layer ones doubles. However, today optical media in the HD DVD format are no longer available. They have been supplanted by Blu-ray technology, which is more in demand today.

They were replaced a year ago by new CDs developed on the basis of BD, but in comparison, they are cheaper, since production costs are lower than those of BD. They have not yet received their own name.

New optical media exceeds the capacity of all previous disks - terabytes of memory. Twenty-layer recording technology allows them to accommodate such a volume of information. CD manufacturers plan to increase the capacity of optical media to 15 terabytes.

A CD is a plastic disk with a circular hole in the center. It is written and read on it using a laser. optical information digital format.

At first, such discs were used to store digital music recordings; we are familiar with them under the name “Audio CD”. But after a short time, disks were adapted to store files containing digital information various formats(video, text, programs, music, pictures and photos). Such discs began to be called CD-ROM or “read-only compact disc”, because information could be written to it only once, but it could be read many times. A few years later, discs appeared on which the user could write information himself (CD-R), as well as rewritable discs (CD-RW), information from which could be erased and recorded again.

The file formats recorded on Audio CD and CD-ROM are different. In this regard, players designed to read only Audio CDs are not able to play information from a CD-ROM disc, which requires a special reading device.

The history of the CD begins in the 70s of the last century. It first appeared in 1979. It was a joint development Sony companies and Philips. Sony developed a signal encoding method (similar to that used in professional digital tape recorders), and Philips was behind manufacturing process, which used their proprietary laserdisc technology.

CDs began to be produced on an industrial scale in 1982 in Germany by a company located in the city of Langenhagen. The first music CD released for public sale was introduced in June 1982. On this disc the album of the group “ABBA” - “The Visitors” was released for sale. Giants such as Apple and Microsoft had a great influence on the distribution of CDs.

True, there is another version of the origin of compact discs, according to which their inventor was the American James Russell from the Optical Recording company. Already in 1971, he showed his invention that made it possible to store information. Inspired by Russell optical disks was motivated by a desire to prevent the needles from damaging the pickups of vinyl records with his favorite musical compositions. And eight years later, Philips and Sony repeated his invention.

CDs have a thickness of 0.12 cm and a diameter of 12 cm. They are made of polycarbonate with a thin metal coating applied to it (as a rule, silver, gold, aluminum, etc. are used) and a layer of varnish. Information and images related to the content (artist names, album names, track titles, logos, etc.) are printed on one side of the disc.

There is a protrusion on the outside of the disk that encircles the disk and prevents the working surface with the recorded information from being scratched. In the center there is a round hole with a diameter of 1.5 cm. The CD weighs just under 16 grams.

At first, music was recorded on discs in the “Red Book” format. It was two-channel and had a sampling frequency of 44.1 kHz, as well as pulse code modulation equal to 16 bits. Small scratches extending towards the edge of the disc from the center or vice versa do not affect the reading of information from the disc. This is possible thanks to the Reed-Solomon code, which makes it possible to correct reading errors.

Information is recorded on the disk by tracks (pits) twisting in the shape of a spiral. The pits have standard widths and depths of 500 nm and 100 nm, respectively. But the length of the pits differs from each other and has a variation range from 850 nm to 3.5 microns.

The following types of discs exist: CD-ROM – read-only, CD-R – write-once, CD-RW – rewritable. To record information on CDs, special writing devices (drives) are used. There are also Shape CDs, which are optical media. CD-ROM type, which are made in the shape of stars, hearts, airplanes, cars, etc. As a rule, such discs are used as carriers of video or audio information by people associated with show business. The "Shape CD" was patented by German producer Mario Koss in 1995. It is worth noting that discs of this type should not be used in computer drives, since they are faster than music ones, which can cause the disc to collapse and damage the drive.

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 track 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 designed in this way are channel encoded in pit-gap terms using an 8/14 redundancy code (Eight to Fourteen Modulation - EFM), 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 (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 (track number AA) is recorded, 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 systems automatic adjustment(SAR) and are in constant monitoring mode of 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. Several different strategies can be used for decoding, 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 supply.
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 " thin elements", in particular - higher harmonics, however, 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 the signal that has undergone analog processing as “warmer” and “live”, but many modern methods Signal processing is only acceptably implemented in digital form.

Can two identical disks 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 to 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). Identity of digital data when replays several disks can be considered a sufficient sign of the reliability of both the disks 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 influences, including “subtle” and unstudied ones, of people on the equipment and on each other are 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 of the convenient and safe methods requires the participation of two hands - thumb The left hand presses lightly on the latch, loosening it, while the other hand removes the disc from the latch. One-handed method when forefinger weakens the latch, and the large and medium ones remove the disk, requires more precise coordination of forces, without which it is easy to bend the disk or break the latch petals.
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 major achievements of DVD is that it has managed to combine all the uses of a CD for data, video, audio (or a combination thereof) within a single physical space. file structure called UDF, or Universal Disk 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).

Since 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 more early versions they couldn't do that. 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 names files.

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, newest algorithm ECC error correction and provides a 2.5:2 compression ratio based on ALDC (Adaptive Lossless Data Compression), resulting in 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 allows for 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 capacity greater 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 scanning speed tolerances, and reducing the likelihood of write-read errors (this raises 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 in pairs decimal digits, it is impossible for the disk capacity to exceed 99 minutes.

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 Failure

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 have been removed in the ISO 23346 “Universal Disk Format"(Universal Disc Format - UDF), 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 CD-RW disc Meets CD specification requirements for minimum 60% modulation. 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 software uses the defect control capabilities of UDF 2.5, the problem is that the software must have full information about 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, achieving data transfer standards competitive with hard drive(30 MB/s) 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 (like a hard drive) and uses a thick, clear acrylic layer similar to a protective coating reverse side 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 media layer", and the ability to read a disc on a particular player or drive depends on its ability to support the corresponding physical layer no matter what data is recorded. The specification of the content itself is subject to the set of “ application levels", which are defined by the DVD Forum. For example, typical movies are released on circulation ROM disks(physical layer), and uses the DVD video format (application layer).

All writing players can read DVDs ROM, but everyone uses Various types discs 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 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 through collaboration large quantity 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 application of two new principles that allow you to record twice as more information on regular media - 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, new system RS-PC error correction 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 disks. 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 films;
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 DVD formats also has many application formats such as DVD video and DVD audio.

Even though in the 21st century humanity has switched to using flash memory, the CD format still remains very popular and in demand among users. Compact discs, as the abbreviation CD (Compact Disk) stands for, unlike volatile media, have higher information reliability, low cost and 100% compatibility with all reading devices. The only difference that CDs have among themselves is information capacity. It remains to figure out which manufacturer’s product you need to buy, and what pitfalls can be encountered in the race for large containers.

World standard

Few people know that the world community owes the creation of the CD, whose information capacity according to the standard is 650 megabytes, to Sony Corporation. Back in 1982, the Japanese created a portable audio media that replaced vinyl discs. Beethoven's 9th Symphony, beloved by most Japanese, with a duration of 73 minutes, determined the size of the disc. When converting audio data into megabytes, the information capacity of the CD must be at least 640 MB.

Considering the recording of the pause and additional information for playback devices, approximately 10 megabytes were added. The physical size of the disk is 5.25 inches - the current ATX format for all personal computers.

Baseline

Even though the standard capacity of a CD is 650 megabytes, it will be difficult to find such a product in the store lately. But without much difficulty you can buy one with an information capacity of 700 and 800 megabytes. Such discs in the country's markets are nothing more than a marketing ploy by manufacturers trying to attract potential buyers. It’s clear: the greater the capacity, the more you can record. Only the manufacturer is silent that, with a constant physical size, such capacity is achieved due to high recording density, which not all recording devices can produce. Also, not every playback device is capable of correctly reading data from high-capacity media.

"Lottery" with high-density discs

Even though the manufacturer talks about 100% compatibility of its discs with all kinds of multimedia devices, the buyer should know that there is a possibility that the player or computer will not be able to play music correctly or open data files. And the larger the CD capacity, the higher this risk. Discs with a recording density of 700 megabytes are very popular in the domestic market. Users are attracted by their low cost. Such discs can be written and read by almost all devices without any problems.

But with CDs with a recording density of 800 megabytes, problems may arise. Not every writing device is capable of correctly recording information onto a medium. Judging by numerous reviews, the user often believes that the problem is in the burner drive and, scolding it, does not even suspect that in this case the manufacturer is to blame for producing a low-quality CD.

About the manufacturing plants

It's funny that the majority of buyers prefer expensive and well-known brands, whose names and logos are printed on the surface of the media, completely ignoring cheap, little-known CDs whose information capacity is suitable for the consumer. Often there is no difference between an expensive and a cheap disc, because they have the same manufacturer and the same batch number. It's all about advertising. One seller advertises his product and inflates the price, while the other sells discs at a low cost. An example would be discs from BASF and Intenso. The difference in price is colossal, and the CD is from the same batch. Before buying media, you should pay attention not to the sticker, but to reviews about the manufacturer. Recently, due to high competition, a lot of marketing research has been carried out, the results of which are picked up by computer magazines and Internet resources, so the buyer should not have problems finding information.

We will talk about CDs, the maximum information capacity of which is no more than 700 megabytes. Having studied the popular ones, we can conclude that there have been no significant changes in the optical media market over several decades.

Serious brands have only strengthened their positions, and manufacturing plants of low-quality products stay afloat only thanks to advertising. Regarding the types of disks by capacity, you can safely give your preference to the brands Mitsui, HP, Sony&Philips, 3M, Verbatim and FujiFilm. Professionals recommend refraining from purchasing CDs from brands such as Princo, Memorex, Arita, BASF, Dysan, MMore and JTEC. Not only do poor quality media have many errors during playback, but also the size of the CD is actually 5-20 megabytes smaller than what the seller stated on the packaging.

Active layer color

Often, when purchasing from a seller, you can hear that the quality of recording on a CD media directly depends on the color of the active layer - the darker it is, the better the safety of information, regardless of the type of disc capacity. Assuring the buyer that black music CDs with a protective vinyl layer, although they cost an order of magnitude more, will last for centuries, successfully complete the deal. In fact, the appearance of the disk, including the color of the active layer, is created according to the requirements that the customer sets to the manufacturing plant. Along with such indicators as capacity, there is a “design” column, in which the color of the active layer is indicated. But the column “active layer material” is responsible for the shelf life. For example, inexpensive cyanine can be destroyed under the influence of direct sunlight in ten years, but expensive phthalocyanine will allow you to read information from a disk without problems after a century.

Write speed

The size of a CD is always accompanied by an indication that can be set to the writing device when recording information onto optical media. Without going into technology, it is important for any user to know that the higher this figure, the less time will be spent on all types of disks in capacity have different time indicators, which differ slightly from each other. On average, at “1x” speed, recording will take about 40 minutes, and a disc with the “52x” parameter will be recorded in one minute.

In addition to the capabilities of the disc, you need to pay attention not only to the recording speed characteristics of the writing device, which are indicated on the front panel. You should also read the instructions for the device on which you plan to play the CD. For example, many car radios cannot play music from media recorded at speeds exceeding 24x.

Capabilities of the protective layer

A spontaneous purchase at the market or in a store forces you to produce a beautifully designed CD. A photo of your favorite character or the title of a movie instantly attracts attention, and the disc adds to your home collection. In any case, every person has ever come to the idea that in addition to recording information on a medium, it would be nice to design the appearance of a CD by applying your own drawing or photograph to its surface. There is no problem with this. It is enough to purchase a disk marked “Printable”. The surface of the protective layer is equipped with a special coating that can absorb ink from an inkjet printer, similar to matte photo paper. Naturally, to apply a picture you will need a printer whose functionality supports printing on CDs.

Business card disk

In big business, according to the rules of good manners between partners or contractors, the proposal should be in the form of a visual presentation, which many businessmen often prefer to familiarize themselves with in their free time. In a mailbox, a presentation can get lost among a large volume of email, and it’s unaffordable to give out flash drives to potential partners for free. In such cases, a business card disk will save you. Many printing companies provide this service. At the customer’s request, the manufacturer can add a logo or contact information to a CD disc cut to the size of a regular business card. For such a CD, information capacity is not critical. The 120-180 megabytes available for recording are quite enough to record several presentations. Such a business card, having non-standard dimensions, can be reproduced without problems on any optical disc reader.

About MiniDiscs

The mini-format of CDs is still quite popular among owners of video cameras and audio players with an 8 cm format factor. Among all existing standard types of disks, such a CD can hold no more than 210 megabytes per storage medium. But its price breaks records, exceeding several times the cost of the most expensive 5.25-inch CDs. It's all about the manufacturer. As practice and numerous tests show, the manufacturer, fulfilling the requirements stated by corporations producing audio and video equipment, produces a disc highest quality. Any user can verify this by simply comparing the characteristics of different disks by testing with specialized software.