Any piece of hardware or software on a computer uses a processor. Processor load refers to the time that the processor spends on a specific task. Low loading processor when executing a task indicates that other devices and programs will get access to it faster. For CD / DVD-ROM drives, there are three factors that affect processor utilization: drive speed CAV, buffer size and interface type.

Direct memory access

Currently, almost all computers are equipped with a controller. Bus Master IDE which allows you to put data directly into RAM bypassing the processor. When using such controllers, the processor load by the CD / DVD-ROM drive (regardless of the interface type) is reduced by up to 11%.

Almost all modern CD-ROM drives (12x and up) and motherboards support direct data transfer to memory. To determine if your system has DMA support, click on the icon System in the window Control Panel... In the tab Devices (Device Manager) click on the "+" sign next to the device group Hard Disk Controllers... If there is a device in the list Bus master then your system supports direct memory access. It is not enough to have a controller to set up DMA Bus Master IDE, we need more devices (hard disks and CD-ROM drives) that will support this mode. Check the type of drives installed on your system and check with the manufacturers for supported features. Hard drives and CD-ROM drives that support MultiWord DMA Mode 2 (16.6 MB / s), UltraDMA Mode 2 (33 MB / s), UltraDMA Mode 4 (66 MB / s) or faster, can use direct memory access.

To activate DMA hard disk or CD-ROM drive, double-click it in the Devices dialog box Properties: System and in the appeared window of properties of this device in the tab Settings) check the box DMA.

Interface

Under interface CD-ROM drive is understood as the physical connection of the drive to the expansion bus. Since an interface is a channel through which data is transferred from a storage device to a computer, its significance is extremely high. The following types of interfaces are used to connect a CD-ROM drive to a computer:

• SCSI / ASPI (Small Computer System Interface / Advanced SCSI Programming Interface) ;
• IDE / AT API (Integrated Device Electronics / AT Attachment Packet Interface) ;
• parallel port;
• USB port;
• Fire Wire (IEEE-1394).

Loading mechanism

There are three fundamentally different types of loading CDs: into storage containers, slide-out trays, and autoloaders.

Pull-out trays

Most simple CD-ROM drives use pull-out trays... In order to replace a disc, it is necessary to slide the tray out of the drive, remove the disc, put it in a transparent plastic box, remove a new disc from another similar box, put it in the tray and push it back.

Containers

This disc loading mechanism was once used in most high-quality CD-ROM drives, as well as CD-R and DVD-RAM... The disc is installed in a special, tight-fitting container with a movable metal flap. It has a lid that is folded back solely in order to place the disc in a container or remove it; the rest of the time, the lid remains closed. When the container is inserted into the drive, a special mechanism moves the metal shutter to the side, opening the path for the laser beam to the surface of the CD.

Autoload mechanism

Some drive models use an autoload mechanism, i.e. you place a CD in the front panel slot and the autoloader sucks it in on its own. However, this mechanism does not allow the use of discs with a diameter of 80 mm, as well as other discs with modified physical formats or shapes.

Other features of CD drives

Of course, the advantages of devices are primarily determined by their technical characteristics, but there are other important factors as well.

In addition to the quality of the design and reliability, when choosing a drive, it is necessary to take into account the following properties:

• dust protection;
• automatic lens cleaning;
• drive type (external or internal).

Automatic lens cleaning

If the lenses of the laser device are dirty, reading the data is slowed down as it takes a lot of time to repeat searches and reads (in the worst case, the data may not be read at all). In such a situation, special cleaning discs should be used. Some modern high-end storage models have a built-in lens cleaner.

CD Recorders

There are two main types of recordable CDs and drives: CD-R (Recordable) and rewritable. CD-RW (Rewritable).

Most CD-ROM writers are devices WORM(write once, read many - write once, read many times), intended for long-term storage. CD-R drives have become the de facto standard for this type of device.They are ideal for Reserve copy systems and similar operations. However, with frequent backups or archiving, despite the low cost of the media, it becomes unprofitable to use CD-R B drives. this case pay attention to rewritable devices CD-RW.

CD-R Drives

CD-R discs that already contain some data can be played or read by almost any standard CD-ROM drive. Disks of this type are very convenient for storing archival data and creating master disks that can be replicated and distributed among employees of small companies.

CD-R discs work in the same way as standard CD-ROMs, reflecting a laser beam off the surface of the disc and tracking changes in reflectivity when trough-to-pad or pad-to-trough transitions occur. On conventional CDs, the spiral track is extruded or stamped in a polycarbonate mass. In turn, CD-R discs contain a pattern of cavities burned into the raised spiral track. Thus, valleys are dark (burned-in) areas that reflect less light. In general, the reflectivity of the depressions and areas remains the same as on stamped discs, therefore conventional floppy drives CD-ROMs and music CD players read both stamped discs and CD-Rs.

CD-R recording begins even before you insert the disc into the drive. The manufacturing process for CD-R media and standard CDs is almost the same. In either case, molten polycarbonate mass is pressed using a forming matrix. But instead of stamping depressions and areas, the matrix forms a spiral groove on the disk (which is called primordial groove)). When viewed from the side of the read (and write) laser located under the disc, this groove is a spiral protrusion, not a depression.

The boundaries of the spiral protrusion (initial groove) have certain deviations from the longitudinal axis (so-called oscillations). The amplitude of the oscillations in relation to the distance between the turns of the track is quite small. The distance between the turns is 1.6 microns, and the transverse deflection of the protrusion reaches only 0.03 microns. Vibrations of the CD-R groove modulate some Additional information which is read by the drive. The sync signal, determined by the wobbling of the track, is modulated along with the time code and other data and is called the absolute time of the original track ( Absolute Time In Pre - groove - ATIP). The timecode is expressed in the format "minutes: seconds: frame" and is entered into the Q subcodes of the frames recorded on the disc. The ATIP signal allows the drive to allocate the required areas on the disk before actually recording frames. Technically, the positioning signal is a frequency drift and is defined by a carrier frequency of 22.05 kHz and an offset of 1 kHz. Changes in the vibration frequency are used to transmit information.

The CD-R manufacturing process is completed by applying a uniform layer of organic dye by centrifugation. Then a golden reflective layer is created. The surface of the disc is then coated with UV-hardened acrylic lacquer, which is used to protect the previously created gold and painted layers of the disc. Research has shown that aluminum used with organic dyes is prone to strong oxidation. Therefore, CD-R discs use gold plating which is highly corrosion resistant and has the highest possible reflectivity. On the surface of the disc, covered with a layer of varnish, a layer of ink is applied by the method of screen printing, which is used for identification and additional protection of the disc. The laser beam used for reading and writing a disc, first passes through a transparent polycarbonate layer, a layer of organic dye and, after reflecting from the gold layer, passes through a layer of dye and polycarbonate mass, after which it is captured by the optical sensor of the drive.

The reflective layer and the organic dye layer have the same optical properties as unlabeled compact disc. In other words, the track of an unrecorded (blank) CD-R disc is perceived by the CD-reader as one long pad. The laser beam of the CD-R drive has the same wavelength (780 nm), but the power of the laser used for recording, in particular for heating the colored layer, is 10 times higher. A pulsed laser heats the organic dye layer to 482-572 ° F (250-300 ° C). At this temperature, the dye layer literally burns out and becomes opaque. As a result, the laser beam does not reach the gold layer and is not reflected back, which achieves the same effect as when canceling the reflected laser signal that occurs when reading stamped CDs.

While reading the disc, the drive reads non-existent depressions, which are areas with low reflectivity. These areas appear when the organic dye is heated; therefore, the process of recording a disc is often called burning out... The burnt areas of the dye change their optical properties and become non-reflective. These properties can only be changed once, which is why CD-Rs are called write-once media.

Storage devices CD-RW are backward compatible with CD-R devices and allow you to read or write data to CD-R media.

CD-RW features the following:

• they can be overwritten;
• have a higher cost;
• have a lower write speed;
• have a lower reflectivity.

In addition to the high cost and rewritability of data, storage media CD-RW They also differ in a lower (two or more times) write speed. This is because the laser takes longer to process each area of ​​the disc while recording is being performed. Disks CD-RW also have a lower reflectivity, which limits their readability. Carriers CD-RW e.g. not readable by many standard CD-ROMs and CD-Rs Therefore for recording music discs or compatibility with drives different types it is better to use CD-R discs. It should be noted that the MultiRead technology, which is currently supported by almost all drives with a speed of 24x and higher, allows you to read discs CD-RW without any problem. This feature is identified by the MultiRead logo printed on the casing of the CD-ROM drive.

To create the appearance of depressions on the surface of a disc, CD-RW drives and media use a phase-change process. The discs are created on a polycarbonate substrate containing a preformed wavy spiral groove, the vibrations of which determine the positioning information. The upper part of the base is covered with a special dielectric layer (insulation), after which a recording layer is applied, another dielectric layer and an aluminum reflective layer. The surface of the disc is then coated with UV-hardened acrylic lacquer, which is used to protect the previously created layers of the disc. Dielectric layers above and below the recording layer are designed to shield the polycarbonate substrate and reflective metal layer from the intense heat used during the phase change recording process.

CD-R discs are burned by heating specific areas of the organic dye (i.e., the recording layer). In turn, the recording layer CD-RW is an alloy of silver, indium, antimony and tellurium (Ag-In-Sb-Te), with the possibility of phase transformations. As the reflective part of the recording layer, an aluminum alloy is used, which is no different from that used in conventional stamped discs. During a read or write operation laser device located on the underside of the disc. When viewed from the laser side, the spiral groove will appear as a protrusion, with the recording layer of the disc located on its upper plane.

The Ag-In-Sb-Te alloy used as the recording layer has a polycrystalline structure with a reflectivity of 20%. While writing data to disk CD-RW the laser can operate in two modes, which are called P-write and P-erase. In P-recording mode, the laser beam heats the recording layer material to a temperature of 500-700 ° C (932-1229 ° F), which causes it to melt. In the liquid state, the molecules of the alloy begin to move freely, as a result of which the material loses its crystalline structure and goes into amorphous(chaotic) state. The reflectivity of the material solidified in the amorphous state is reduced to 5%. When reading a disc, areas with different optical properties are perceived in the same way as the depressions of a conventional stamped CD-ROM disc.

In wipe mode, the active material layer heats to about 200 ° C (392 ° F), which is well below the melting point but sufficient to soften the material. When the active layer is heated to the specified temperature, followed by slow cooling, the structure of the material is transformed at the molecular level, i.e. transition from amorphous to crystalline state. This increases the reflectivity of the material up to 20%. The areas with higher reflectivity serve the same function as the areas of a pressed CD.

Although this mode of laser operation is called P-erase, data is not directly erased. Instead, technology is applied direct data overwrite, when using which the plots CD-RW lower reflectivity are not erased, but simply overwritten. In other words, during data recording, the laser is constantly on and generates pulses of different power, thereby creating areas of amorphous and polycrystalline structure with different optical properties.

Drive Compatibility: MultiRead Specifications

The Optical Storage Technology Association (OSTA) has developed an industry standard, test system, and logo to indicate the compatibility of a drive to ensure certain levels of compatibility. These are all called MultiRead specifications. The following specification levels currently exist:

• MultiRead for CD-ROM drives;
• MultiRead2 for DVD-ROM drives.

In addition, a similar MultiPlay standard has been developed, which is intended for device owners DVD-Video and CD-DA.

MultiRead and MultiRead2 Standards for CD / DVD Drives

Carrier	MultiRead	MultiRead2
CD-DA (Digital Audio)	x	x
CD-ROM	x	x
CD-R	x	x
CD-RW	x	x
DVD-ROM	-	x
DVD-Video	-	x
DVD-Audio	-	x
DVD-RAM	-	x

x - the drive will read from this medium.

The presence of one of these logos guarantees an appropriate level of compatibility. If you are purchasing a CD-ROM or DVD drive and want to read rewritable or writable discs, make sure the drive has the MultiRead logo. For DVD drives, the MultiRead version will be much more expensive due to the additional cost of the dual laser mechanisms. Almost all DVD-ROM drives used in computer systems, have a dual reading mechanism that allows you to read data from CD-R discs and CD-RW.

Shape CD (shaped CD) - an optical digital information carrier of the CD-ROM type, but not strictly round in shape, but with the outline of the outer contour in the form of various objects, such as silhouettes, cars, airplanes, hearts, stars, ovals, in the form credit cards, etc.

It is usually used in show business as a carrier of audio and video information. The record was patented by producer Mario Koss in Germany (1995). Usually discs with a shape other than circular are not recommended for use in computer CD-ROM drives, because high speeds Rotating the disc may burst, which can lead to complete failure of the drive.

Rewritable device standards and DVD discs

Drive and DVD media compatibility

Storage devices	CD-ROM	CD-R	CD-RW	DVD-Video	DVD-ROM	DVD-R	DVD-RAM	DVD-RW	DVD + RW	DVD + R
DVD-Video player	R	?	?	R	-	R	?	R	R	R
DVD-ROM drive	R	R	R	R	R	R	?	R	R	R
DVD-R drive	R	R / W	R / W	R	R	R / W	-		R	R
DVD-RAM drive	R	R	R	R	R	R	R / W	R	R	R
DVD-RW drive	R	R / W	R / W	R	R	R / W	-	R / W	R	R
DVD + R / RW drive	R	R / W	R / W	R	R	R	R	R	R / W	R / W
DVD-Multi drive	R	R / W	R / W	R	R	R	R / W	R / W	R	R
DVD +/- R / RW Drive	R	R / W	R / W	R	R	R / W	R	R / W	R / W	R / W

The history of rewritable devices and DVDs began in April 1997, when companies in the DVD Forum introduced specifications for rewritable DVDs.

DVD (Digital Versatile Disc) is a digital versatile disc or, more simply, a high-capacity compact disc. Virtually every DVD-ROM drive is a CD-ROM drive, i.e. drives of this type can read both regular CDs and DVDs. Digital versatile discs use the same optical technology as compact discs and differ only in higher recording densities. The DVD standard significantly increases the amount of memory and therefore the size of applications that can be recorded on CDs. CD-ROMs can hold a maximum of 737 MB of data (an 80-minute disc), which at first glance seems like a pretty good figure. Unfortunately, this is no longer enough for many modern applications, especially with the active use of video. DVDs, in turn, can contain up to 4.7 GB (single layer disc) or 8.5 GB (dual layer disc) of data on each side, which is about 11.5 times more than standard CDs. The capacity of double-sided DVDs is, of course, twice the capacity of single-sided ones. However, at present, the disc has to be turned over to read the data from the second side.

Up to two data layers can be recorded on a DVD, and the capacity of a standard single-sided single-layer disc is 4.7 GB. The new disc has the same diameter as CD discs, but is half the size (0.6 mm). Applying MPEG-2 compression, the new disc can fit 133 minutes of video - a full-length movie with three channels of quality audio and four channels of subtitles. Using both layers of a single-sided disc, a 240-minute movie can be recorded on it. There is no cabalism in terms of the capacity of optical discs. DVDs were directly related to the production of films, and the film industry has long considered this type of media to be cheaper and more reliable than videotapes.

Digital versatile discs have replaced CDs and videotapes. Purchased or rented DVDs perform the same functions as a VCR tape, but provide better sound and picture quality. Like CDs, which were primarily intended for music recordings, DVDs can be used for a variety of purposes, including storing computer data.

Note!

It is very important to understand the difference between DVD-Video and DVD-ROM. The first disc contains only video and is playable in a DVD player, while the second includes Various types data and is read using a DVD drive in your computer. These two types of discs can be compared to a music CD and a CD-ROM. DVD drives are capable of playing DVD-Video movies (using a hardware or software MPEG-2 encoder), but DVD-Video players cannot be used to access DVD-ROM data.

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How is the CD organized?

A standard disc consists of three layers: a polycarbonate substrate, on which the disc relief is stamped, a reflective coating of aluminum, gold, silver or other alloy sprayed onto it, and a thinner protective layer of polycarbonate or varnish, on which inscriptions and drawings are applied. Some discs of "underground" manufacturers have a very thin protective layer, or do not have it at all, which makes the reflective coating quite easy to damage.

The informational relief of the disc consists of a spiral path running from the center to the periphery, along which grooves (pits) are located. Information is encoded by alternating pits and spaces between them.

What recording formats are used in the CD-ROM?

The CD-ROM uses the same technology as the conventional CD-DA sound system. The standards for recording arbitrary data on compact discs issued by Philips and Sony are known as Yellow book("Yellow book"), Green Book("Green book"), Orange book("Orange book"), White Book("White paper") and Blue Book("Blue Book"); they all complement the basic CD-DA standard described in Red Book("The red book").

Separate "audio tracks" are used for data recording. The mentioned standards do not refer to the disc as a whole, but only to the format of individual tracks, and tracks of different formats can coexist on the same disc. To read them, you need a player that either supports all the formats on the disk, or allows unknown ones (many CD-ROM players and drives cannot skip tracks of unknown formats).

The Yellow Book defines the basic formats for writing data to disk: CD-ROM mode 1 and CD-ROM mode 2. In both formats, within each of the track frames, 2352 bytes in size, which are also called sectors, 12 bytes of synchronization are allocated, 4 bytes of the sector header and 2336 bytes for writing data. Due to the presence of the syncronization and header bytes, it is possible to accurately find the required data sector, which is extremely difficult in an ordinary audio disc.

In the mode 1 format, used in most CD-ROMs, 288 bytes are allocated from the data area for recording EDC / ECC codes (Error Detection Code / Error Correction Code), thanks to which data discs are read much more reliably than audio discs with the same workmanship. The remaining 2048 bytes are reserved for storing data.

In the mode 2 format, the correction codes are not used, and all 2336 bytes of data in the sector are allocated for writing information. It is assumed that the recorded information either already contains the correction codes, or is insensitive to minor errors left after the correction with the low-level Reed-Solomon code. This format is intended primarily for recording compressed audio signals and images.

A mode 1 disk that combines sound and data is called the Mixed Mode Disk. At the same time, data is recorded on the first track, and sound information is recorded on all subsequent ones. Most audio players do not distinguish the format of the tracks and, when they hit the data track, try to reproduce it, which can damage amplifiers and speakers.

The mode 2 format is practically not used in its pure form - on its basis the CD-ROM / XA (eXtended Architecture) formats of two versions (Green Book) have been developed. In the first option, 8 bytes of the sub-header, 4 bytes of EDC and 276 bytes of ECC are allocated from a data block of 2336 bytes, leaving 2048 bytes for data, as in the "mode 1" format; in the second option ECC is not used and 2324 bytes are left for data. On the same track of the XA format, the sectors of both the first and the second options can be met. The advantage of this approach is the possibility of simultaneous reading in real time of data and audio and / or video information, without unnecessary movement between tracks.

Format CD-I (CD-Interactive - interactive CD), described in the Orange Book, provides recording of video on tracks of the XA format and playing it using a special CD-I player on a household TV in parallel with listening to sound. Tracks of the CD-I format are not included in the disc table of contents (TOC), so they are not visible on hardware that does not support this format.

For compatibility with standard audio players, the CD-I Ready format ("ready for playback on a CD-I player") has been proposed, which uses an extended pause before the first audio track, ignored by most conventional players, to record the image.

For compatibility with the device for reading discs in the XA format, the CD-Bridge format ("CD-bridge") was proposed, which is included in the general disc table of contents tracks of the CD-I format, containing the address labels of both formats - CD-I and XA.

Orange Book also defines the format of recordable CD-R discs (CD-Recordable), which can be recorded in several receptions (sessions), as well as have an initial session stamped during production (the so-called Hybrid Disk). Each session contains the Lead In, the actual data and the Lead Out.

The White Book describes the VideoCD format based on CD-Bridge and used for storing motion pictures encoded in AVI, MPEG and the like. The Blue Book describes the CD-Xtra format, which consists of two sessions - an audio session and a data session.

The organization of the file system on a CD-ROM is described by the ISO 9660 standard. Level 1 of this standard includes the file system formats MS-DOS and HFS (Apple Macintosh). The nesting of MS-DOS directories cannot exceed 8, and the name length is 8 + 3 characters. Level 2 describes a filesystem with long names and nesting levels up to 32. The Rock Ridge extension describes the UNIX filesystem format.

A special case of CD-R is the Kodak Photo CD format, used for multi-session recording of photo collections. Photo CD uses the CD-Bridge format, formatted in the ISO 9660 file system. Photo CDs can be played by special players on a consumer TV or read by computer CD-ROM drives.

How does the CD-ROM drive work?

A typical drive consists of an electronics board, a spindle motor, an optical readhead system, and a disk loading system.

The electronics board contains all the control circuits of the drive, the interface with the computer controller, the interface and output connectors sound signal... Most drives use one electronics board, however, in some models, separate circuits are carried out on auxiliary small boards.

The spindle motor is used to drive the disc in rotation at a constant or variable linear speed. Maintaining a constant linear velocity requires changing the angular speed of the disc depending on the position of the optical head. When searching for fragments, the disk can rotate at a higher speed than when reading, therefore, a good dynamic performance is required from the spindle motor; the engine is used for both acceleration and braking of the disc.

A stand is attached to the spindle motor axis, to which the disk is pressed after loading. The surface of the stand is usually covered with rubber or soft plastic to prevent the disc from slipping. Pressing the disc to the stand is carried out using a washer located on the other side of the disc; the stand and washer contain permanent magnets, the force of which forces the washer through the disc to the stand.

The optical head system consists of the head itself and its movement system. The head contains a laser emitter based on an infrared laser light-emitting diode, a focusing system, a photodetector and a preamplifier. The focusing system is a movable lens propelled by an electromagnetic voice coil system, made by analogy with the movable system of a loudspeaker. Changes in the strength of the magnetic field cause the lens to move and refocus the laser beam. Due to its low inertia, such a system effectively monitors the vertical beats of the disc, even at significant rotational speeds.

The head movement system has its own drive motor, which drives the carriage with an optical head using a gear or worm gear. To eliminate backlash, a connection with an initial voltage is used: for a worm gear - sprung balls, for a toothed gear - pairs of gears sprung to different sides.

The disc loading system is carried out in two versions: using a special case for the disc (caddy), inserted into the receiving opening of the drive, and using a pull-out tray (tray), on which the disc itself is placed. In both cases, the system contains a motor driving a tray or case, as well as a frame moving mechanism, on which the entire mechanical system is fixed, together with a spindle motor and an optical head drive, into a working position when the disc rests on the spindle motor support.

When using a conventional tray, the drive cannot be set to any position other than horizontal. In drives that can be mounted in a vertical position, the design of the tray provides latches that hold the disc when the tray is extended.

On the front panel of the drive, there is usually an Eject button for loading / unloading a disc, an indicator of access to the drive and a jack for connecting headphones with an electronic or mechanical volume control. In a number of models, the Play / Next button has been added to start playing audio discs and transition between audio tracks; The Eject button is usually used to stop playback without ejecting the disc. On some models with a mechanical volume control, made in the form of a knob, playback and transition are carried out by pressing the end of the control.

Most drives also have a small hole on the front panel, designed for emergency ejection of the disc in cases where it is impossible to do it in the usual way - for example, when the drive of the tray or the entire CD-ROM is removed from the drive, when the power is lost, etc. You need to insert a pin or a straightened clip into the hole and press gently - this removes the lock of the tray or disc case, and you can pull it out manually.

Through which interfaces does the CD-ROM work?

SCSI, IDE - CD-ROM connects directly to a SCSI or IDE (ATA) trunk, specifying the device number for SCSI or Master / Slave for IDE. IDE CD-ROMs usually run in the ATAPI (ATA Packet Interface) standard.

Sony, Mitsumi, Panasonic are the three most common interfaces supported by many sound cards and individual adapters. Mitsumi and Panasonic use a 40-pin interconnect cable for IDE and Sony use a 34-pin for floppy drives.

There are also CD-ROMs with the so-called Proprietary Interface - the manufacturer's own interface, supplied with an adapter and a connecting cable.

Currently, CD-ROMs are available only with SCSI and IDE interfaces.

Why does the CD-ROM drive spin at different speeds during operation?

The information on the CD is recorded with a constant linear density, therefore, to achieve a constant read speed, the rotation speed varies depending on the movement of the read head. The standard speed of rotation of the disk is 500 rpm when reading from internal zones and 200 rpm - when reading from external ones (information is written from the inside to the outside).

What does “n-speed” CD-ROM mean?

At the standard rotational speed, the data transfer rate is about 150 kb / s. In two- or more-speed CD-ROMs, the disc rotates at a proportionally higher speed, and the transfer speed is proportionally increased (for example, 1200 kb / s for an 8-speed one).

Due to the fact that the physical parameters of the disk (heterogeneity of mass, eccentricity, etc.) are standardized for the main speed of rotation, at speeds greater than 4-6, significant oscillations of the disk already occur, and the reliability of reading, especially for disks of illegal production, may get worse. Some CD-ROMs can reduce the rotation speed of the disc during read errors, but most of them then cannot return to maximum speed until the disc is replaced.

At speeds above 4000-5000 rpm, reliable reading becomes virtually impossible, therefore latest models 10 or more speed CD-ROMs limit the upper limit of rotation speed. At the same time, on external tracks, the transmission speed reaches the nominal (for example, 1800 kb / s for 12-speed models, and in relation to the internal ones - it drops to 1200-1300 kb / s.

Why "illegal" discs often read worse than "branded" ones?

The standard for compact discs determines their physical and optical parameters: thickness and reflectivity of the aluminum layer, depth and shape of pits (recording elements), distance between tracks, transparency of the protective layer, eccentricity, etc. Leading CD manufacturers have proven technologies and reliable equipment to meet these parameters; the equipment and technologies of illegal manufacturers often do not provide this.

Mechanics and optics of different CD-ROM models have different tolerances and adjustment possibilities, which is why some models can confidently read discs that are virtually unreadable by other models. Also, as a result of operational wear, the parameters of the drive deteriorate with time, which leads to a deterioration in the reading of disks, which were confidently read on the new drive.

Is it possible to visually determine the quality of a disc?

Approximately - you can. It is necessary to carefully examine the working surface of the disc - it should be even, and there should be no scratches, cloudy areas, bulges or depressions, as well as "streaks" on the reflecting layer. Then look at the disc at the light (with the side facing you) - it may be slightly transparent, but without obvious holes in the reflecting layer. The more transparent the disc, the higher the probability of its erroneous reading.

Cheap discs (especially made in China) usually do not have a protective varnish layer on the other side - even a small scratch on this side can lead to a complete failure to read the corresponding area of ​​the disc.

What is the quality of playing audio discs on CD-ROM?

Playing audio discs is a side function for CD-ROMs, and is usually done "according to the residual principle" - a simple (often 12- or 14-bit) DAC and a simple output amplifier. Mass CD-ROMs are significantly inferior to stationary Hi-Fi players, some models are approaching inexpensive portable players. In any case, the signal quality at the headphone output (front panel) is worse than at the line output (back panel) due to additional distortion during amplification.

In addition to DAC quality, most CD-ROMs do not oversample the digital signal to improve signal-to-noise ratio, nor interpolate and mask for smoothing and partial compensation for uncorrected errors. The lack of interpolation and masking leads to noticeable distortions and clicks when discs are read erroneously, while read errors are not so noticeable on a sound player.

Many modern CD-ROMs have an additional audio output in a digital format (S / PDIF - Sony / Philips Digital Interface Format) on the rear panel, which can be connected to a studio or consumer equipment that has an S / PDIF input or AES / EBU, which allows you to play sound from a disc with virtually no distortion (some distortion may be introduced by the CD-ROM decoder).

What is the maximum capacity of a CD?

Approximately 650 MB (* 1024 * 1024 bytes) - 74 minutes of recording, data flow - 153600 bytes / s. This recording length is determined by the standard, however, with a tighter arrangement of the tracks or the pits themselves on the disc, more sounding time or data volume can be obtained. Such disks with deviations from the standard can be read unstably by some drives, or not read at all.

What are CD-R and CD-E?

CD-Recordable and CD-Erasable CD burning system. The terms CD-R and CD-E refer to both the recorder and the discs themselves.

For one-time recording, so-called "gold" discs are usually used, which are a regular CD, in which the reflective layer is made of gold film, and the transparent layer of plastic immediately overlapping to it is made of a material that darkens when heated. In the process of recording, the laser beam heats up the areas of the plastic, which darkens and stops transmitting light to the reflective layer, forming a "gap" between the "pits" - unchanged transparent areas of the plastic.

To make it easier to follow the information track during the recording process, CD-R discs are made with auxiliary markings. When reading, tracking is performed as usual on the recorded pit track.

Some versions of the software (for example, CDR Publisher) allow you to burn bootable discs. To boot from such disks, the computer BIOS must support this feature (latest versions of AWARD and Phoenix BIOS).

Why is there noise when recording pure WAV to CD-R?

Perhaps the reason is that some sound editors (for example, Cool Edit and Sound Forge) put their service information at the end of the WAV file, formatting it as an additional record in full accordance with the RIFF format. However, some CD-R software ignores the audio length field, treating the entire remainder of the file after the title as a single audio fragment, with the result that the service information gets to the disc in digital audio format and is played as noise or clicks at the end of the program. To eliminate this phenomenon, it is necessary either to prohibit the audio editors from saving service information in the WAV file, or to remove it using other programs.

During the multisession recording of individual audio tracks, at the beginning and at the end of each session, the lead-in and lead-out zones are formed, hitting which during playback causes a random signal to appear. It is recommended to record audio discs in one session, forming a full sound file if the CD-R software does not allow you to combine files during the recording process.

In addition to the above, noise on recorded audio discs can occur due to instability of the data stream in the CD-R (overflow of the internal buffer or interruption of the stream), deviations from the normal parameters of the recorded signal, the operating mode of the laser or the speed of rotation of the disc, factory disc defects, as well as due to the fault of the card readers, unable to copies of disks. In the case of poor-quality recording of data discs, the situation is often saved by large volumes of correction codes provided in CD-ROM formats.

Can I use a different model of IDE CD-ROM driver?

In most cases, yes, if the CD-ROM runs in ATAPI standard. However, some drivers may not work correctly with other CD-ROM models.

To read video discs, you need support from the drive itself and its driver, as well as the video format unpacking (player) program. Some combinations of drive, controller, driver and unpacking program are incompatible with each other. You can try to change the driver or the unpacking program. There are also cases when, when CD-ROM is installed on one channel from HDD, video discs are played much slower.

You can - for this you need a CD-ROM that supports the Read Long command and is able to find audio sectors in direct access mode (for example, many of the drives with a SCSI interface, most Panasonic models), and a special program - grabber - to read full audio sectors, for example, CDGRAB, CDDA, CDT, etc. Often these programs include a list of CD-ROM models that support the long read command. Due to slight differences in interfaces, some drives do not work with some of these programs, but may work with others.

One of the main problems when reading audio disks is sync errors between sectors. They occur when the program reading the disk does not have time to issue a command to read the next sector before the overflow of the internal CD-ROM buffer starts and data from the beginning of the sector is lost. In this case, the CD-ROM is forced to perform positioning, and the frame-by-frame structure of audio discs makes it impossible to start reading exactly from the right place. As a result of such failures in the file generated by the program, there are dropouts or the appearance of several extra signal samples. To combat synchronization errors, some programs have a mode in which the correctness of joining of neighboring sectors is checked. If you use CD-ROMs with a larger buffer size, the chance of errors is reduced.

Positioning overshoots are often mistakenly referred to as "jitter". In fact, the term jitter is used to denote the phase jitter of a digital signal due to rapid fluctuations in the flow rate generated by a change in the rotational speed of the disk and its vertical beating. In a sense, sync disturbances are also phase errors of a higher level, but the jitter term is not entirely correct to use for them.

What are the reasons for the poor performance of the Samsung-631 CD-ROM drives?

In addition to the low quality of the mechanism itself and the reading system, in these drives there is an insufficient pressure of the disc to the spindle, which is why the discs slip during acceleration and braking. The reason for the weak clamping is the large gap between the spindle magnet and the metal disc, which is drawn by the magnet. Michael Svechkov (2: 460 / [email protected]) recommends to glue a steel washer with a thickness of 1-2 mm to the magnet, choosing it so that the gap between the magnet and the metal disc is minimal, however, with the thinnest discs, they should not touch each other, otherwise the operation of the tray pull-out system will be disrupted.

Since its introduction in 1984, CD-ROM drives have gone no less glorious than floppy drives. Finding a PC that doesn't have a drive that can read CD-ROMs is even harder today than a PC without a floppy disk drive. The maximum rotational speeds of the disks have increased to 12 thousand rpm. Few of today's hard drives can boast of such speeds, and in fact, in a CD-ROM, removable media of a larger diameter, which may not be very well balanced, rotate at such a speed. At such speeds, increased vibration and, as a result, an increase in the frequency of errors can even cause uneven ink application in the overprint of a disc or an inscription made with a felt-tip pen on one of its halves. Therefore, the "race for X" stopped after reaching the 60X mark, and in practice the 40X speed is considered “reliable and sufficient”. It should be understood that 40 or 60X (6 or 9 MB / s) is just the maximum data transfer rate that is achieved only on the outer tracks of the disc. The exception was drives made according to the TrueX technology developed by Zen Research, when several tracks are read at the same time. Thanks to this technology, Kenwood managed to D1 lead "X" to 72, but the production of such devices turned out to be economically unprofitable and has now been discontinued.

The experience gained in the process of improving CD-ROM drives was not in vain. The first such devices used the constant linear velocity (CLV) mode, which came from the audio CD industry. The data transfer rate in the IX drive was equal to 150 kb / s and was constant on all tracks, for which, when the head moved from the center of the disk to its periphery, the rotation speed decreased proportionally. Since the data disc does not have to be read at a constant speed, CD-ROM manufacturers have also adopted the inherent constant angular velocity (CAV) mode or a combination of the two to reduce access time. This technology is called partial-CA \ or zoned-CLV and involves partitioning the disk by radius into several zones, each of which uses its own rotation speed, and reading can be performed both in CAV and CLV modes. Now this technology is widely used in storage devices.

General arrangement of a three-beam optical system of a CD-ROM drive

An important stage in ensuring the compatibility of the four major CD formats - CD-Digital Audio (CD-DA), CD-ROM, CD-Recordable (CD-R), and CD-Rewritable (CD-RW) - has been adopted by the optical storage industry association (Optical Storage TechHeTlogy Association, OSTA) MultiRead specification. Devices marked with the appropriate logo guarantee that all four formats can be read.

An interesting novelty was presented at the recent CeBIT "2002 exhibition in Hanover by flexs-torm GmbH - the world's first flexible CD-disk. The 0.1-mm flexCD can be read by existing drives using a special adapter, which is made of two hard plastic circles.

The flexCD is claimed to be 10 times faster than a traditional CD-ROM, at just 0.3 seconds, at a significantly lower manufacturing cost. It is assumed that it will find wide application for the distribution of advertising and other informational materials. It can be easily sewn into magazines, sent in envelopes, or even distributed as labels on the packaging of any products.

CD-R, CD-RW

Write-once optical discs (WORM) were introduced in the late 1980s. In 1990, Orange Book II appeared, setting out the specifications for recordable CDs. In 1993 Philips released the first CD-R drive. As "blanks" for recording, we used ordinary polycarbonate discs coated with a special dye (cyanine, phthalocyanine or azo dye), on top of which was sprayed the thinnest reflective layer of a noble metal, usually pure silver or gold. During recording, a laser beam focused on the dye layer physically "burned out" it, forming opaque areas similar to the "pits" on a conventional stamped CD.

CD-R media do not fully meet the definition of WORM (write once, read many times) because Part II of the Orange Book provides for multi-session recording. Each session consists of one or more data tracks, leading and trailing blanks, and a corresponding TOC entry on the disc. The presence of unused sections leads to the loss of 13.5 MB of space on the CD-R during each next session.

At the end of the last century, CD-R drives, which by that time had reached write / read speeds of 8X / 24X, were replaced by more versatile CD-RW drives, which allow writing not only write-once discs, but also rewritable ones.

Unlike organic dyes used to form the active layer in CD-R discs, in CD-RW discs the active layer is a special polycrystalline alloy (silver-indium-antimony-tellurium), which turns into a liquid state at a strong (500-700 ° C ) heating by laser. With the subsequent rapid cooling of the liquid sections, they remain in an amorphous state, therefore, their reflectivity differs from polycrystalline sections. The return of amorphous areas to the crystalline state is carried out by weaker heating below the melting point, but above the crystallization point (about 200 ° C). Above and below the active layer are two layers of dielectric (usually silicon dioxide), which remove excess heat from the active layer during recording; from above, all this is covered with a reflective layer, and the entire "sandwich" is applied to a polycarbonate base, in which spiral grooves are pressed out, necessary for precise positioning of the head and carrying address and time information.

The CD-RW drive uses three laser modes, which differ in beam power: write mode (maximum power that ensures the transition of the active layer to a non-reflective amorphous state), erase mode (returns the active layer to the reflective crystalline state) and read mode (the lowest power, which does not affect the state of the active layer).

Cutting a CD-RW or DVD + RW media

The biggest problem that has always plagued manufacturers of optical disc recorders is buffer underruns. Since the writing is at a constant (linear or angular) speed, there must always be data in the drive buffer to write. If for some reason (CPU overload with other tasks, interface problems, program crash, etc.) data starts to flow too slowly, a situation may arise when there is no data in the drive buffer to write the next block. In the drives of the first generations, this led to irrecoverable damage to the "blank" in the case of CD-Rs or the need to erase and rewrite CD-RWs. At the end of 2000, Sanyo patented the BURN-Proof technology (Buffer UndeRuN-Proof, that is, buffer underrun protection), which allowed recording to stop if the amount of data in the buffer fell below a certain threshold, and resume from the same place when filling the buffer. Nowadays variations of these technologies (each company calls them differently: Yamaha has it "SafeBurn", Acer has "Seamless Link", Ricoh has "JustLink") used by almost all manufacturers of CD-RW drives.

Plextor uses a combination of Sanyo's technology and its own called "PoweRec" (Plextor Optimized Writing Error Reduction Control). In this case, the recording process is periodically paused using the BURN-Proof method and the recording quality is checked to determine if the speed can be increased.

It seems that the process of growth of "X" in CD-RW drives, which has been going by leaps and bounds in the last year or two, is approaching its logical conclusion, as it happened with CD-ROMs. In any case, TEAS recently released a drive with write / rewrite / read speeds of 40X / 12X / 48X. In addition to an 8MB buffer and 72ms data access time, the new drive is one of the first drives on the market to support EasyWrite technology, based on the Mount Rainier group (which includes Philips, Microsoft, Compaq and Sony) specifications to enable batch writing to CD-RW (by transferring files in the same way as writing to a floppy disk) is easy and fast, without the use of special drivers such as Direct CD.

More recently, information has appeared that the ML (MultiLevel) multilevel recording technology developed by the Calimetrics company has been embodied in a prototype CD-RW drive created by TDK corporation, which allows recording up to 2 GB of information on the same media and without changing the optical part of the drive. that is, to triple the information capacity of the media. At the same time, the recording speed on CD-R can reach 48X. To do this, you just need to install the ML ENDEC codec chip developed and already produced by Sanyo into the drive. TDK is a member of the ML Alliance, created at the end of 2000, which, in addition to Calimetrics, includes Sanyo, Mitsubishi Chemical, Plextor, TEAC, Yamaha and Verbatim. ML-discs will also be supported by major CD-R and CD-RW writing software manufacturers Ahead Software (Nero) and Roxio (EasyCD Creator).

It is expected that the use of this technology will also increase the capacity and transfer speed of DVD + RW recording media by at least two times.

Insufficient capacity (650 or 700 MB) CD-ROM and the impossibility of further improving performance made people think about a new format for optical discs. The history of its origin, in contrast to the simple and clear history of the creation of the CD, is full of contradictions, collisions and intrigues. Initially, the new disc was supposed to replace VHS videotapes. At the origins of DVD (originally this abbreviation was decoded as "Digital Video Disk", that is, "digital video disc", and later, when they began to record not only video on DVD, it turned into "Digital Versatile Disk", that is, "digital multifunction disc "), were on the one hand Matsushita Electric, Toshiba and the Time / Warner film company, which developed Super Disc (SD) technology, and on the other, the" parents "of the Sony and Philips CD with their Multimedia CD (MMCD) technology ... Since these two formats were completely incompatible with each other, in 1995, under pressure from the giants of the IT industry (Microsoft, Intel, Apple and IBM), the DVD Consortium was created to develop a single standard, which included the main manufacturers of drives and media for them. a total of 11; the name was subsequently changed to DVD Forum.

Similar to the multi-colored "books" defining CD formats, there are 5 documents describing the DVD-ROM, DVD-Video, DVD-Audio, DVD-R (DVD Recordable) and DVD-RAM (Recordable DVD) formats. Recently, there have also been two new rewritable disc formats - DVD-RW and DVD + RW, and one - write-once DVD + R.

Unlike CD-ROMs, which are only single-sided and single-sided, DVDs can also be double-sided and double-sided. Thus, there are 4 DVD options: DVD-5 (single sided single layer, 4.7 GB capacity), DVD-9 (single sided double layer, 8.5 GB), DVD-10 (double sided single layer, 9.4 GB) and DVD-18 (double-sided, dual-layer, 17 GB).

How did you manage to place 7-25 times more information on a disk of exactly the same size? First of all, due to the use of a red laser with a wavelength of 635 or 650 nm instead of an IR laser with a wavelength of 780 nm. Reducing the wavelength made it possible to reduce the minimum size of the "pits" (depressions on the surface of the polycarbonate base of the disc covered with a reflective layer that carry information) from 0.83 to 0.4 microns, and the track spacing from 1.6 to 0.74 microns, which gave the overall gain in capacity is 4.5 times. The rest was obtained through the use of more efficient error correction codes, which significantly reduced the percentage allocated to these codes in each data packet.

The possibility of making double-layer disks (the reflective material of the first layer is semitransparent, so that it is possible to focus the laser on the second reflective layer lying above it) made it possible to raise the capacitance almost twice (in fact, somewhat less, since it is not possible to achieve the same density in the semitransparent layer) records as in fully reflective). A double-sided disc, which is like two one-sided, glued together with reflective layers inward (the total thickness of the disc remains equal to 1.2 mm), has doubled the possible capacity of the DVD, although in this case there is a certain inconvenience: the disc has to be turned over manually ...

Direct Dubbing to DVD + RW

Increasing the density of the data on the disk led to an automatic increase in the data transfer rate at the same speed of rotation of the medium. Thus, in a CD-ROM IX drive, data is transferred at a speed of 150 kb / s, while in a DVD-ROM IX, the transfer rate reaches 1250 kb / s, which corresponds to 8X CD-ROM. Modern DVD drives have reached speeds of 16X, which, as you can easily calculate, gives 128X for CD-ROMs! Various technical solutions are used to ensure DVD compatibility with CD media, including a change of focusing lenses, two lasers with wavelengths of 780 and 650 nm, or a special holographic element that provides the correct focus for each type of media. The adoption of the OSTA-developed UDF (Universal Disc Format) specification, or rather a subset of it called MicroUDF, as the main format of the DVD file system, removed the problems associated with the need to develop new formats whenever a new class of data appears that needs to be written to disk. ... Since this specification also includes the ISO-9660 standard file system for CD-ROMs, compatibility issues with operating systems that support this system are addressed. DVD-ROM discs use the intermediate UDF Bridge format (this format lacks support for Microsoft's long and Unicode ISO 9660 file extension called Joliet), while DVD-Video discs use the full UDF format. DVD-Video files should not exceed 1 GB in size, should not be fragmented (each file should occupy one connected area of ​​the disc), and links to them recorded in 8.3 format should be located in the VIDEO_TS directory, which should be the first on the disc. Audio files are located in a separate area of ​​the disc (DVD-Audio zone), and links to them - in the AUDIO_TS directory.

Video is recorded on DVD, usually in MPEG-2 format. DVD-Video discs can use several different copy protection systems, the most famous and simpler of which, causing a lot of inconvenience to users, is regional coding. The whole world is divided according to this system into seven regions (the countries of the former USSR fall into the fifth region along with India, Africa, North Korea and Mongolia). A DVD-Video disc intended, say, for the first region (USA), in theory, should not be read by a drive or player for the fifth region. In practice, however, in Russia, multi-regional drives and discs are most often used.

DVD-R for General, DVD-R for Authoring, DVD-RAM, DVD-RW, DVD + RW, DVD + R

Total for this moment There are six recordable DVD formats (in chronological order of their appearance): DVD-R for General, DVD-R for Authoring, DVD-RAM, DVD-RW, DVD + RW, and DVD + R. Now the situation is developing in such a way that the first four formats are likely to become a thing of the past. The alliance of major writable optical drive manufacturers, which includes such "whales" as HP, Sony, Ricoh and others, united around DVD + RW and DVD + R technologies, it seems, will not leave them any chance, although the company Pioneer, which first proposed DVD-RW format at the end of 1999 and which achieved its approval in the DVD Forum (DVD + RW has not yet received such approval, despite the fact that all members of the DVD + RW Alliance are among the founders of the DVD Forum), is not going to give up its positions.

The most important advantage of the DVD + RW format (and its variants for DVD + R write-once media) is the compatibility of the recorded media with the vast majority of conventional DVD-ROM drives and consumer DVD players. DVD-RW discs have this property only when they are recorded in the "compatible" mode, in which recording with a variable bit rate is impossible and the so-called "finalization" of the disc is required, which takes up to 15 minutes. Another most valuable feature is the use of these drives for writing (and, of course, reading) CD-R and CD-RW discs.

DVD + RW is an evolution of DVD-RW technology. For recording, a phase change technology is used, completely similar to that used in CD-RW. Precise positioning of the head is ensured by undulating grooves along the entire spiral track of the disc. Thanks to them, it becomes possible for the so-called lossless linking, that is, ensuring the consistency of the recorded video file even with long interruptions in the data transfer from the PC. You can even edit specific sections of an already recorded file!

Direct Dubbing to DVD + RW

DVD + RW drives can record single and double-sided discs in 4.7 GB and 9.4 GB respectively. Dual layer discs are not supported.

The write-once format DVD + R, unlike CD-R, which preceded CD-RW, appeared quite recently, after the successful start of the rewritable DVD + RW. The first DVD + RW / + R drives began to appear only in the spring of 2002. One of the first such drives, Ricoh MP5125A, records DVD + RW and DVD-R discs at 2.4X, CD-R discs at up to 12X, CD- RW - up to 10X. The maximum read speeds for DVD are 8X, and for CD 32X, access times are 140 and 120 ms, respectively. Compatibility has been an issue that has plagued DVD drives since their inception. It was only at the end of 1999 that third-generation drives appeared on the market, in which the problems of compatibility with CD-R, CD-RW, DVD-RAM and DVD + RW discs were solved. The table below summarizes the compatibility data of optical media and drives of various formats ("Read" means the ability to read the media of this type in the corresponding drive, "Write" means the ability to write). Note that "Yes" does not mean that any drive of this type will read (write) any disk of the corresponding type. This only means that what has been said will be carried out as a rule.

Meet in our time a computer without CD-ROM / DVD drive almost impossible. A wide variety of programs, music, documents, digital photographs, etc. are recorded on CDs and DVDs. You can purchase both discs with already recorded data (for example, a music CD or DVD with a movie), as well as special discs on which you can (one or more times, depending on the disc and drive) burn any information you need.

In addition to the not entirely correct name “ drive», CD / DVD reading and writing devices are also called optical drives. Word storage device generally refers to all devices intended for storing or reading data. For example, HDD can be called a disk drive. Optical refers to a method for reading data from discs. In CD / DVD drives, reading and writing data from discs is carried out using a special laser beam.

There are several types in total CD-ROM and DVD drives, with and without recording support. Let's consider them in more detail.

• Regular floppy drive CD— ROM only reads data from disks CD, CD— R and CD— RW. It cannot be used to write data to any discs. Such drives are the cheapest, but they are outdated and are not installed in new computers.
• Drive CD— ROM with the ability to record. Unlike the previous version, this drive can be used to write data to discs with write once (CD-R) or rewrite (CD-RW).
• Drive DVD. This drive combines the capabilities of the two previous drives, i.e. allows you to write and read data from CDs, and can also read data from DVDs.
• Drive DVD with the ability to record. This is the most versatile and popular drive option and is recommended for purchase. With this drive, you can read and write any discs, including CD, CD-R, CD-RW, DVD + -R / RW.
• Also, every year, drives with support for reading Blu-rey discs are becoming more and more popular.

Basic types of optical discs

As you already understood, the recording capabilities depend not only on the drive, but also on the discs themselves. Let's study the main ones that exist in currently types of optical discs.

• CD, or CD. The simplest option for an optical disc. These discs sell either music (music CDs) or various programs. You cannot write anything to such a disc.
• CD-R disc... On such a disk, you can once write down the information you need. It is no longer possible to add it later. A single CD-R disc can store up to 880 MB of data, depending on the size of the disc. These drives are most commonly used for storage important information, which will not need to be changed in the future. This can be music, video files, etc.
• CD-RW disc. This disc has the same capacity as CD-R discs, but you can write data on it many times and delete any data you do not need. In total, such a disk is designed for about 1000 rewriting cycles, which is more than enough, for example, for periodically recording Word documents, then deleting them and writing new files. CD-RW discs are more expensive than CD-R discs.
• DiskDVD-ROM,orDVD Video. It is on these discs that DVD movies are sold. You cannot record anything on such a disc. In this case, the volume of a single-layer DVD is 4.7 GB, which is several times more than the volume of CDs.
• DiskDVD— Rand diskDVD+ R. Just like CD-R discs, DVD-R and DVD + R discs can be one just write the data you need. Unfortunately, at one time the companies - manufacturers of optical discs and drives took up arms against each other and became irreconcilable enemies, as a result of which two completely incompatible standards appeared, DVD + R and DVD-R. Fortunately, the manufacturers of optical drives have solved this problem and now for most drives it does not matter at all which disc to take; both types of discs will be supported.
• DiskDVD+ RWandDVD— RW. By analogy with CD-RW discs, DVD + RW and DVD-RW discs can be used to record data many times Given the disc size of 4.7 GB, it is very convenient for storing and backing up a variety of data, for example, your music collection, etc. ... The problem of incompatibility of standards exists here, and it was solved in the same way - by the release of universal small format drives that support any type of disc.
• Diskblu— rey we have a huge volume that allows you to record up to 80 gigabytes of information! Agree this is a lot for optical drive! In most cases, I record video with high definition on such discs, which allows me to achieve the maximum quality of the film! The cost of such a drive can reach up to 2000 rubles!

Optical drive speed

The speed of the optical drive is usually indicated in this way 52x / 24x / 52x... This means that CD-R discs are written from 52x, disc recording CD-RW happens at a speed 24x, and reading CD-R / RW discs - also at 52x. In this case, the indicator 1x means a data transfer rate equal to 153 KB / s. Now let's calculate the speed of the drive with a read speed of 52 x. To do this, multiply 52 by 153, the result will be 7956 KB / s, i.e. almost 8 MB / s.

Compared to CD-ROM drives, rewritable DVD drives read and write data much faster. The speed of a 1x DVD-ROM drive is 1.35 MB / s, which is the same as 9x speed for a CD-ROM. Therefore, the performance of modern DVD-ROM drives a read speed of 20x corresponds to 180x for CD-ROM drives (27 MB / s), although, of course, this speed does not exist for CD-ROM drives.