Information capacity of a CD disc. CD - information capacity. Types of disks by capacity

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 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 uses only 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 NML with IDE interface, capable of recording 25 GB of original 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, when the error correction code is valid in only one dimension (along 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 have received common name 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 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. Writing multiple sessions to disk results in a loss of approximately 23 MB disk space at each session, and the original standard limited to 99 the number of tracks (phonograms) that could be recorded on a disc. 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 write mode is not fully compatible with logical file ISO system 9660, since in this case you need to know exactly which files will be written during the session in order to fill in the FS service tables (Path Tables and Primary Volume Descriptors), which indicate the physical location of the files on the 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 operating system UDF 2.5 required special UDF software for the drive that supported 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, the CD-RW system operates in 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 amplify 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 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 rates 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 (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. OSD coating is more than 2000 times thicker than hard drive and tapes, 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 differs 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 from high 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 the set of “ application levels", which are 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 record players can read DVD ROMs, 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 nanomechanical 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 according to new technology, allowing 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 working together 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 developed technology high density recording information: it is now possible to store 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 value of 0.62 µm was chosen so that existing DVD video players and DVD drives ROMs could read HD-burn discs after 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.

At the end of 1997 - beginning of 1998, discs and DVD drives began to appear on the market. This standard was created with the expectation of replacing different media in several areas at once - both in the video industry and in the information technology, and in sound recordings, and even perhaps in the game cartridge industry. According to the developers, it should be a kind of “universal” carrier, unusually capacious and reliable.

The capacity of a standard (single-sided, single-layer) disc is 4.7 GB, that is, almost eight times the capacity of a regular CD-ROM. In MPEG-2 format, a DVD can record approximately 130 minutes of video with audio in eight languages ​​and subtitles in 32 languages.

The use of double-layer, double-sided discs allows you to quadruple the capacity of DVD media with a slight increase in the cost of the drives and discs themselves. The top layer of such disks is made translucent, and the inner layer is completely reflective. To read information, the laser beam is focused on the surface of the inner layer, “ignoring” the interference created by the upper layer.

Discs created using this slightly modified laser technology, just like traditional CDs, use recesses for storing data, arranged in the form of a spiral track that “curls” across the entire surface of the disc. As with a CD, when reading information, a precisely focused laser diode emits a beam that is reflected from the grooves on the rotating disk and then hits the light-sensitive element. Thus, acting according to the binary system (“there is a signal - there is no signal”), the computer reads information from the media. In terms of size, CDs and DVDs are absolutely the same - DVDs are just a little thinner. Naturally, like CDs, DVDs are produced in two form factors: 12 cm (4.7 inches) and 8 cm (3.1 inches). The most common, as in the case of CDs, will most likely be the 12 cm form factor - after all, this is what most disk drives and DVD players are designed for.

What are the differences between DVD and CD? First of all, DVD discs have a smaller diameter of the recesses, they are located on the track with a smaller “step”, and there are much more tracks on the disc. The use of smaller notches is made possible by the use of a high-frequency laser, which sends a “dense” beam. While the laser is in regular device CD-ROM has a wavelength of 780 nanometers, DVD devices use a laser with a wavelength of 650 or 635 nm, which allows the beam to cover twice as many notches on one track and twice as many tracks. In addition, the disc's storage surface area is slightly larger than that of a CD-ROM, and DVD also features a new sector format and a more robust error correction code. All these innovations made it possible to achieve approximately seven times greater capacity DVDs than traditional CDs.

But a sevenfold increase in disk capacity is far from the limit. Perhaps the most interesting thing about DVD specifications is the ability to create double-sided and dual-layer discs.

A double-sided disc is easy to make: since a DVD disc can be only 0.6 mm thick (half the thickness of a regular CD-ROM), it is possible to connect two discs back to back to create a double-sided DVD. True, you will have to manually turn it over, but with the development of DVD technology, there will be drives that can read both sides without user intervention.

The technology for creating dual-layer discs is a little more complex: data is recorded in two layers - a lower one and a translucent upper one. Working at one frequency, the laser reads data from the translucent layer, while working at another, it receives data “from the bottom”.

The first layer (closest to the laser) is translucent. Thanks to this, by changing the laser focus, it is possible to read information both from the first layer and from the second layer located behind it. Since the focus switching time is quite short, the use of two layers makes it possible to obtain a disc with a “continuous” capacity of 8.5 GB (the DVD-9 standard is a single-sided double-layer disc (DL/SS, Fig. 2), with a capacity of 8.5 GB, respectively).

The storage capacity of dual-layer DVD discs is not twice that of single-layer discs, as you might expect, but slightly less: in order to minimize interference caused by the laser beam passing through the outer layer, the minimum size of the grooves on the tracks has been increased from 0.4 mm to 0.44 mm. By the way, as a result, the speed of reading information from such disks has increased slightly.

DVD drives have quite slow speed disk rotation, even compared to legacy three-speed CD-ROM devices. However, since DVDs pack data more densely than CDs, the transfer speed matches that of nine-speed CD-ROM drives, which translates to 1.3 Mbps. Drives operating at this speed are called dual-speed drives.

The second generation of DVD devices will have double the speed. This will not affect the quality of the played video (1.3 MB is enough to ensure smooth and clear video), but it will increase the speed of loading software from DVD-ROM.

There are also two options for recordable DVDs. This is a DVD-R and DVD-RAM standard. The first standard is similar to CD-R - data can only be written to a disc once. The laser beam “burns out” depressions in a special layer applied to the disk.

Another standard, DVD-RAM, allows you to write data to a disc multiple times. It is based on phase change technology: a laser beam heats a special reflective magnetic layer applied to the disk, and then, under the influence of a magnetic head, depressions are formed in this layer. When hardened, the layer retains the shape obtained as a result of the impact of the head, and therefore the data. When overwriting, it is enough to repeat the operation. The number of read/write cycles for this technology is estimated at millions of times.

Based on their design, there are four types of DVD discs:

DVD-5(Single-sided, single-layer disc) is the first version of the DVD: a single-sided disc with single-layer recording and a maximum capacity of 4.7 GB. A DVD consists of 0.6mm film coated with aluminum and adhered to a clean backing. The sputtering technology is the same as for a regular CD. The aluminum film is 55 nanometers thick, the same as for audio CDs and CD-ROMs;

DVD-9(Single-sided, double-layer disc) is a two-level, single-sided disc with a maximum capacity of 8.5 GB. A translucent layer is created that reflects 18-30% of laser radiation. This allows information to be read from the top layer. And at the same time, the translucent layer will transmit enough radiation so that the signal from the lower highly reflective layer is also readable. Information levels separates highly homogeneous adhesive (the thickness of the adhesive layer is 40-70 microns) used to connect the two halves of the disk. This distance is necessary to distinguish between the signal reflected from the 1st and 2nd levels. The optimal material for the translucent layer is gold, but silicon and silver alloys are used. Data is read from the inner or outer layer by refocusing the optical system.

DVD-10 (Double-sided, single-layer disc) - a single-layer double-sided disc with one information layer and a maximum capacity of 9.4 GB (in fact, it is a double DVD-5 without a blank backing). Two disks covered with metal films are connected together. One laser is used to read information from 2 sides of the disk;

DVD-18 (Double-sided, double-layer disc) - a double-sided disc with two information layers and a maximum capacity of 17 GB. The structure of DVD-18 is the same as that of DVD-9.

VCD- disks

A universal platform has emerged for interactive media that combines VHS video with CD-quality sound. Consumers get the video quality they are accustomed to from VHS tapes and CD-quality audio. You can view it interactively. Additional information- text, graphics, tests and questionnaires - can significantly expand familiar formats up to the possibility of accessing the Internet. Or, on the contrary, full-screen video and high-quality sound are added to computer CD-ROMs.

All this is provided by the videoCD (VCD) format and its extension - Video CD Plus. On the one hand, VCD users are offered familiar qualities, on the other hand, conveniences that they did not previously have. Finally, VCDs will play on most PCs and Macs, CDi players, 3DO-np consoles, video game machines like the Sega Saturn or Amiga CD32, and various hi-fi systems. Eventually, virtually all CD devices will play VCDs.

It is necessary to distinguish between Laser Video Discs (LD) and VCD. These are products based on different technologies, and if the LD player was purchased before 1995, then most likely it will not be able to play VCDs.

Having replaced large and heavy 30-centimeter laser video discs (LDs), VCDs clearly outperform them in terms of recording time, physical size, convenience, and availability. additional functions, but are slightly inferior in recording quality.

LD is digital recording practically uncompressed video (if you do not take into account losses when sampling the analog signal) in contrast to the compressed MPEG-1 standard used on VCD. It is clear that the quality of LD discs is slightly higher than that of VHS tapes. The VHS format has a resolution of approximately 200-300 lines. (Not to be confused with computer pixel resolution!) Lines in this case indicate the greatest number of discernible changes in the vertical direction and depend on the quality of the tape and playback equipment. Although the quality of LD recording is approximately 1.5 times higher, it does not exceed the quality of S-VHS or Hi-8. It is claimed that a video CD will look approximately the same as VHS, but will retain the same quality one hundred and fifty years after the recording. In addition, on a VCD there will be no flickering of lines, oscillation of small parts, and the unpleasant “effects” of magnetic tapes will disappear. The sound on VCD is initially of high quality - without hissing, buzzing and deafening on audio tracks magnetic tape.

The videoCD format is determined by the presence of an ISO 9660 XA (XA - Extended Architecture) track, that is, having only mode2 sectors (with error correction - form1 or without it - form2), and one or more MPEG tracks (entirely from form2 sectors) . VCDs are used in VCD players and CDi devices. MPEG tracks can also be viewed on computers equipped with a suitable hardware or software MPEG player.

Once the VCD is installed in the VCD player, a “menu” appears with a number of items through which the user goes to other “menus”, calls up a video demonstration or other options. All video sequences are stored in MPEG format.

To record a VCD on a computer, as a rule, a disk image file is created. This file contains interactive links, video, text and graphics. A CD burner with the appropriate software transfers it to a special gold-plated CD (also called a master), which can then be duplicated mechanically for cheap matrices with aluminum coating.

Along with MPEG video, you can put a huge amount of information on the disk. It is possible to vary the volume of video, audio, text and graphic content.

Moreover, VCD discs can be played on computers starting with i486, and without the use of a special MPEG card, which the market is flooded with today (they are distributed as set-top boxes for all graphics cards).

Perspectives DVD .

The current “red laser” DVD technology already has practically no “safety margin” - the volume of up to 17 GB is the limit. But:

• The next generation of optical discs has already been developed (for the DVD-RAM standard). In them, writing/reading will be performed by a violet laser (short-wave “blue laser” technology) with a wavelength of 405 nm, which will allow up to 27 GB to be placed on one side of the disk, and 50 GB in a two-layer version. In such discs, which are called Blu-Ray Discs, the distance between tracks ( tracking pitch) is reduced to 0.32 µm, and the minimum pit size is 0.138 µm. Moreover, the new discs allow you to store up to 13 hours of standard definition video.

Main function external memory A computer is the ability to long-term store a large amount of information (programs, documents, audio and video clips, etc.). A device that provides recording/reading of information is called a drive or disk drive, and information is stored on media (for example, floppy disks).

In floppy magnetic disk drives (FMD or floppy disks) and hard magnetic disk drives (HDD or hard drives), recording, storing and reading information is based on the magnetic principle, and in laser drives - the optical principle.

Flexible magnetic disks.

Flexible magnetic disks are placed in a plastic case. This storage medium is called a floppy disk. The floppy disk is inserted into the disk drive, which rotates the disk at a constant angular speed. The magnetic head of the drive is installed on a specific concentric track of the disk, onto which information is written (or read).

The information capacity of the floppy disk is small and is only 1.44 MB. The speed of writing and reading information is also low (about 50 KB/s) due to the slow rotation of the disk (360 rpm).

In order to preserve information, flexible magnetic disks should be protected from exposure to strong magnetic fields and heat, as this can lead to demagnetization of the media and loss of information.

Hard magnetic disks.

Hard disk (HDD - Hard Disk Drive) refers to non-replaceable disk magnetic storage devices. First hard drive was developed by IBM in 1973 and had a capacity of 16 KB.

Hard magnetic disks are several dozen disks placed on one axis, enclosed in a metal case and rotating at high angular speed. Due to the many tracks on each side of the disks and the large number of disks, the information capacity of hard disks can be tens of thousands of times greater than the information capacity of floppy disks and reach hundreds of GB. The speed of writing and reading information from hard drives is quite high (about 133 MB/s) due to the fast rotation of the disks (7200 rpm).

A hard drive is often called a hard drive. There is a legend explaining why hard drives got such a fancy name. The first hard drive, released in America in the early 70s, had a capacity of 30 MB of information on each working surface. At the same time, O. F. Winchester's repeating rifle, widely known in America, had a caliber of 0.30; Maybe the first hard drive rumbled like a machine gun during its operation, or it smelled of gunpowder - it’s not clear, but from then on they began to call it hard drives hard drives.

During the operation of the computer, malfunctions occur. Viruses, power outages, software errors - all this can cause damage to information stored on your hard drive. Damage to information does not always mean its loss, so it is useful to know how it is stored on the hard drive, because then it can be restored. Then, for example, if the boot area is damaged by a virus, it is not at all necessary to format the entire disk (!), but, having restored the damaged area, continue normal operation while preserving all your invaluable data.

Hard drives use fairly fragile and miniature elements. To preserve information and the performance of hard drives, it is necessary to protect them from shocks and sudden changes in spatial orientation during operation.

Laser drives and disks.

In the early 80s, the Dutch company Philips announced a revolution in the field of sound reproduction. Its engineers came up with something that is now very popular - This laser discs and players.

Over the past few years, computer compact disc (CD) readers, called CD-ROMs, have become an almost essential part of any computer. This happened because various software products began to take up a significant amount of space, and delivering them on floppy disks turned out to be prohibitively expensive and unreliable. Therefore, they began to be supplied on CDs (the same as regular music ones).

Laser disk drives use the optical principle of reading information. On laser discs CD (CD - Compact Disk, compact disc) and DVD (DVD - Digital Video Disk, digital video disc), information is recorded on one spiral-shaped track (like on a gramophone record), containing alternating sections with different reflectivity. A laser beam falls on the surface of a rotating disk, and the intensity of the reflected beam depends on the reflectivity of the track section and acquires values ​​0 or 1. To preserve information, laser disks must be protected from mechanical damage (scratches), as well as from contamination. Laser discs store information that was recorded on them during the manufacturing process. It is impossible to write new information to them. Such discs are produced by stamping. There are CD-R and DVD-R discs on which information can only be written once. On CD-RW and DVD-RW discs, information can be written/rewritten many times. Disks of different types can be distinguished not only by markings, but also by the color of the reflective surface.

Burning to CDs and DVDs using regular CD-ROMs and DVD-ROMs is not possible. To do this, you need CD-RW and DVD-RW devices with which read-once write and read-write-rewrite are possible. These devices have a fairly powerful laser that allows you to change the reflectivity of surface areas during the recording process. The information capacity of a CD-ROM reaches 700 MB, and the speed of reading information (up to 7.8 MB/s) depends on the disk rotation speed. DVD discs have a much larger information capacity (single-layer, single-sided disc - 4.7 GB) compared to CD discs, because lasers with a shorter wavelength are used, which allows the optical tracks to be placed more densely. There are also dual-layer DVDs and double-sided DVDs. Currently, the reading speed of 16-speed DVD drives reaches 21 MB/s.

Devices based on flash memory.

Flash memory is a non-volatile type of memory that allows data to be written and stored on chips. Devices based on flash memory do not have moving parts, which ensures high data security when used in mobile devices.

Flash memory is a chip housed in a miniature package. To write or read information, drives are connected to a computer via a USB port. The information capacity of memory cards reaches 1024 MB.

Answers:

Gennady:
The problem is in the marketing of disc manufacturers (as well as hard drive manufacturers), they believe that 1 GB is 1000 MB, not 1024. Actual size DVD-5 disc: 4.37 GB - Nero says everything right! Briefly about “+\-” technologies: minus is more suitable for recording DVD-Video, it is compatible with a large number of stationary DVD players (older players may not understand the “plus” format), and plus is more suitable for recording data, because . by its structure it is less prone to errors and failures.

Khailov Konstantin Yurievich:
Everything is written correctly on the disk. Don't forget that there are 1024 kilobytes in 1 megabyte. This is where the difference comes from. Next. There is no fundamental difference between “+” and “-” technologies. It used to be that "-" played better on home DVD players, while "+" had better performance. high-quality recording(data is stored more securely). Over time, manufacturers have improved these technologies and now there is no difference. So it's not for everybody. It is better not to use Overburn, because... It often happens that this disk will be readable on you, but not on other slightly older drives. In general, the meaning of this technology is to reduce the length of the notch ( in simple language speaking).

Neo:
The actual size of a DVD disc is 4.7, but you can only burn 4.44. The fact is that recording the system track, which is needed to recognize it in a DVD player, requires space, and therefore the disk capacity is less... On the question of the plus or minus of DVD. Plus or minus DVD. Let's start with the fact that there is no definite answer to the question, just as, in fact, there is no answer to many other questions related to DVDs. This is such a mysterious and enigmatic format. For example, the development of the DVD standard began back in September 1995, and was carried out by a group of 10 very large corporations: Hitachi, JVC, Matsushita, Mitsubishi, Philips, Pioneer, Sony, Thomson, Time Warner and Toshiba (all of them together made up called the DVD Consortium, which then became the current DVD Forum in 1997). However, despite such a number of participants, the abbreviation DVD itself does not have an exact decoding. You can read it as a Digital Video Disc or Digital Versatile Disc. It is quite possible that this is caused by competition that arose from the very beginning of the development of the format. The fact is that initially there were two groups of developers. One was headed by Sony and Philips and they worked on MMCD (Multimedia Compact Disc). The other included Toshiba and Time Warner, their development was called SD (Super Disc). It was only under external pressure that the companies united into the aforementioned DVD Consortium and adopted a common DVD standard. Fortunately, the great battle Betamax vs. VHS was still fresh in memory, and no one wanted two competing standards. By the way, the above-mentioned external pressure was led by IBM, for which special thanks to it. Five types of DVD discs were initially standardized: DVD-ROM, DVD-Video, DVD-Audio, DVD Recordable (DVD-R), and DVD RAM. DVD-ROM and DVD-Video appeared on the market in 1996 and still exist in the same form. However, of greater interest are the recorded DVD-R discs and DVD RAM. DVD-R discs originally came to market in 1997 and had a capacity of 3.95 billion bytes (or 3.68 GB). In 1999, the DVD-R 2.0 specification was adopted, according to which the recording capacity of the disc increased to 4.37 GB and thus became equal to the stamped DVD-ROM. Since then, the DVD-R standard has remained virtually unchanged. As for DVD-RAM, it was conceived as a rewritable format. DVD-RAM discs are based on phase change recording technology (as in CD-RW) with some elements borrowed from magneto-optical disc technology. DVD-RAM entered the market in 1998 and for some time remained the only rewritable DVD disc. Initially, their capacity was 2.4 GB, but then also increased to the standard 4.37 GB. However, DVD-RAM was quite inconvenient to use (in particular, due to the mandatory protective cartridge), so very soon they had an alternative in the form of DVD-RW. This format was developed by Pioneer based on the already existing DVD-R and was first called DVD-R/W or DVD-ER (that is, erasable). The first DVD-RW readers and discs appeared on the market in 1999 (at first they were sold exclusively in Japan and entered the world market only two years later, in 2001). The price of a DVD-RW disc was then about $30. From the very beginning, DVD-RW capacity was equal to a standard DVD disc, that is, 4.37 GB. DVD-RW is based on the same phase-change recording technology as CD-RW discs. However, the development of DVD standards did not end with the advent of CD-RW as an alternative to DVD-RAM. The fact is that initially all the above-mentioned formats were created specifically for video recording. Almost simultaneously with the advent of DVD-RAM, a group of companies, which included Sony, Philips, Hewlett-Packard, Ricoh and Yamaha, organized an alternative organization, the DVD+RW Compatibility Alliance, which, accordingly, was developing and promoting an alternative format for rewritable DVD discs, DVD+RW. Moreover, in order not to aggravate the conflict within the DVD Forum, this format was initially declared as intended exclusively for storing computer data. What prompted the creation of the DVD+RW Alliance by companies that were already members of the DVD Forum? Mainly patent disputes. Almost all of the major participants owned their own set of patents on optical storage media technologies. Accordingly, each participant tried to include their own technologies in the standard and exclude competitors’ technologies. Therefore, when the DVD+RW format finally entered the market in 2001, it turned out to be incompatible with either DVD-RAM or DVD-RW. And this despite the fact that basic technology they used the same thing - changing the phase of the working substance and a laser with a wavelength of 650 nm. DVD+RW was eventually followed by the DVD+R write-once disc format based on it. This happened in 2002, after which, in fact, the main confrontation between the two recording formats + and - R/RW began. So what is the difference between these formats? But in general, from the user’s point of view, nothing. There are undoubtedly technical differences in the principles of track tracking, addressing and marking. These differences make + and - drives completely incompatible with each other. But enough time has passed since the release of DVD+RW / DVD+R that all modern drives understand both, which is usually indicated in the specifications. As for DVD players, older ones (and certainly those released before 2002) may not understand DVD+RW / DVD+R discs. But all modern technology reads both equally well. We can say that the standard with a “plus” is more modern and therefore better. But practice shows that over three years of coexistence, “plus” and “minus” have reached a certain parity. In addition, the next generation of optical discs is already looming on the horizon - BluRay, which in a few years will begin to replace DVDs and will finally transfer this issue to the academic category.

Shurovik:
Don't forget that a GB is 1000 MB in decimal and 1024 in binary. Divide 4,700,000,000 B by 1024 three times to get the capacity in binary GB. That turns out to be 3.78 GB. That's right. For a home user, there is no difference between “+” and “-” disks. Unless "+" discs are readable on older drives. And their recording speed is higher.

Victor:
Go to www.cd4user.net. By the way, they have a good newsletter on these issues.

Vladimir:
Overburn cannot be used on DVD. 2-3 MB of additional space on a DVD will not make a difference, and if it’s more, the disc will go to waste.

Vasily:
A small correction for Shurovik: 4,700,000,000 B divided by 1024 3 times - you get 4.38 GB.

This is a question from the archives. Adding replies is disabled.

Optical discs are a popular storage medium. Most users are only familiar with CDs and DVDs; in fact, there are many more types of discs. The Land of Soviets will tell you what there are types of disks, and will help you understand their diversity.

Types of CDs

CDs or compact discs, were originally intended for recording and playing music, but are now used to store almost any computer information. Writing and reading disk information is carried out using a laser. CD thickness - 1.2 mm, diameter - 120 mm, capacity - 650 or 700 MB (corresponding to 74 or 80 minutes of sound). There are mini CD with a diameter of 80 mm, but their capacity is smaller - 190-200 MB (21 minutes of sound). Mini CD can be read on any media except car radio. There are curly cds of various shapes, they are produced mainly for commercial purposes. Such disks are not recommended for use in computer drives, because they can burst at high rotation speeds.

CD discs can be divided into CD-ROM, CD-R and CD-RW. This division is determined by the ability to write information to the disk and the purpose of the disk. Information on disk CD-ROM recorded by the manufacturer, it cannot be changed or deleted, you can only read the data. To disks CD-R(they are sometimes also called “blanks”) you can record your information, but it will be impossible to erase or change it. If there is any left on the disk free space, and when recording you enabled the option to add information, you can add files to the disk. Discs CD-RW support deleting and rewriting information, but such discs will not be readable by all drives.

Types of DVDs

DVDs allow you to store more information than CDs due to the use of a laser with a shorter wavelength. The capacity of a standard size DVD (120 mm) can range from 4.7 GB to 17 GB, and the capacity of a mini DVD (80 mm) is 1.6 GB.

Depending on the capacity of DVD, the following types of discs are distinguished:

• DVD-5— single-layer, single-sided disk, capacity — 4.7 GB
• DVD-9— double-layer single-sided disk, capacity — 8.5 GB
• DVD-10— single-layer double-sided disk, capacity — 9.4 GB
• DVD-14- double-sided disc, double-layer on one side and single-layer on the other, capacity - 13.24 GB
• DVD-18- double-layer, double-sided disc, capacity - 17.1 GB

Dual-layer discs contain two layers of information on one side and are marked with the abbreviation DL. A double-sided disk is actually two disks glued together with non-working surfaces. Naturally, the thickness of such a disc is controlled to match the thickness of a conventional single-layer DVD.

Where possible, recording, overwriting and deleting DVD information Disks, like CDs, are divided into ROM, R and RW. But additionally, the following types of disks are distinguished:

• DVD-R for general, DVD-R(G)- a recordable disc intended for home use.
• DVD-R for authoring, DVD-R(A)— a one-time recordable disc for professional purposes.
• DVD-RW- rewritable disc. You can overwrite or erase information up to 1000 times. But you cannot erase part of the information, you can only erase the disk completely and completely rewrite it.
• DVD-RAM use phase change technology. They can be rewritten up to 100,000 times and have a theoretical service life of up to 30 years. But they are expensive, are produced mainly in special cartridges and are not supported by most drives and players.
• DVD+RW are based on CD-RW technology and support rewriting information up to 1000 times. This format appeared later than DVD-RW.
• DVD+R- A recordable disc similar to DVD-R.

It is clear that no single drive or player fully supports all DVD formats. Majority modern drives Support both DVD-R(W) and DVD+R(W) formats. But older drives and home players released before the advent of the DVD+R(W) format will only read DVD-R(W) discs. There are "super multi" drives that support all types of discs, including DVD-RAM.

Other types of disks

Standing apart are the so-called Dual Discs. These discs combine CD and DVD formats. On one surface of such a disk music is recorded in CD format, and on the other - five-channel sound, video, menus, subtitles, images, etc. in DVD format.

HD DVDs (High Density DVDs) can have a capacity of up to 15 GB, and double-layer ones - up to 30 GB. Their main competitor is BD, Blu-ray Disc holds from 23 to 66 GB depending on the number of layers. A prototype of a four-layer disk with a capacity of 100 GB has been announced, and it is also planned to release ten-layer disks with a capacity of up to 320 GB.

The confrontation between BD and HD DVD is called the “fight of formats.” But leading film studios abandoned the use of HD DVD in favor of BD discs, so the release and support of the HD DVD format was officially discontinued.

So, there are many types of optical discs. You should choose a disk for recording information based on its capacity, the ability to rewrite information and the model of your drive or home player. Knowing the main types of disks, you will never get confused in their rich assortment.