What is cd dvd rom. What you should know about CD-ROM, CD-R and CDRW discs. What does a CD-ROM consist of?

In the period 1994-1995 in basic configuration personal computers no longer include floppy drives with a diameter of 5.25 inches, but instead the installation of a floppy drive has become standard CD-ROM having the same external dimensions.

Abbreviation CD-ROM (Compact Disc Read-Only Memory) translated into Russian as CD-ROM-based read-only storage device . The operating principle of this device is to read numerical data using a laser beam reflected from the surface of the disk. Digital recording on a CD differs from recording on magnetic disks in its very high density, and a standard CD can store approximately 650 MB of data.

Large volumes of data are typical for multimedia information(graphics, music, video), so disk drives CD-ROM classified as multimedia hardware.

Today, multimedia publications are gaining an increasingly stronger place among other traditional types of publications. For example, there are books, albums, encyclopedias and even periodicals ( electronic magazines), released on CD-ROM.

The main disadvantage of standard disk drives CD-ROM is the impossibility of recording data, but in parallel with them there are also write-once devices CD-R (Compact Disk Recorder) and rewritable devices CD-RW .

The main parameter of disk drives CD-ROM is the data reading speed. It is measured in multiples. The reading speed in the first production samples was taken as the unit of measurement, which was 150 KB/s. Thus, a drive with double the read speed provides performance of 300 KB/s, with quadruple speed - 600 KB/s, etc. Currently, the most common devices are CD-ROM reading with a productivity of 48x-52x. Modern examples of write-once devices have a performance of 16x-32x, and write-multiple devices - up to 32x.

By 1995, Philips and Sony developed a high-capacity compact disc, Multimedia CD. Toshiba and several other companies have created a different CD technology and also with increased capacity. The battle for the market has begun. Then the two largest groups, CITWG (Computer Industry Technical Working Group) and HVDAG (Hollywood Video Disc Advisory Group), came together to fight against the emergence of these incompatible standards. In 1995, through joint efforts, the new standard – DVD. It was intended primarily for the film industry, as a substitute for video cassettes, and therefore the abbreviation stood for Digital Video Disc. Then this format was renamed Digital Versatile Disc - digital versatile disk. However, in 1997, Philips and Sony left the consortium. Subsequently, other DVD manufacturers followed suit.

On this moment There are several DVD formats and this creates some confusion in the market because not all formats are compatible. There are DVD – R, DVD – ROM, DVD – RAM, DVD – RW. DVD-ROM drives without special modification cannot read DVD-RAM discs (with the exception of DVD-ROMs of the so-called third generation, produced since mid-1999). But DVD–RAM drives can read DVD–ROM, as well as CD–R and CD–RW. The DVD+RW drive is only compatible with DVD-ROMs and regular CDs. And the DVD + RW format is not recognized by many manufacturers at all. First-generation DVD-ROM devices used CLV mode and read from the disc at a speed of 1.38 MB/s (in traditional DVD notation this is 1x). Second generation devices could read DVDs at twice the speed - 2x (2.8 MB/s). Modern DVD-ROMs - third generation devices - use a control rotation mode (CAV) with maximum speed reading 4x-6x (5.5 - 8.3 Mb/s) and more.

The main differences between the DVD standard and CD:

1) a laser with a shorter wavelength is used. If in CD-ROM drives the wavelength is 780 nanometers, then in DVD drives– 635 nanometers. This allows you to reduce the stroke length and increase the speed of data reading.

2) due to the use of more advanced materials, DVD is used to record data in two layers on one side of the disc or one layer on both sides of the disc or two layers on both sides of the disc, depending on the DVD format. Disk capacity varies from 2.6 Gb to 17 Gb.

3) a completely new sector format, a more reliable error correction code, and improved channel modulation are used. Now let's talk about layers in more detail.

Single Side/Single Layer

This is the simplest structure of a DVD disc. This disk can accommodate up to 4.7 GB of data. This capacity is 7 times more capacity regular audio CD and CD-ROM disc.

Single Side/Dual Layer

This type of disk has two layers of data, one of which is translucent. Both layers are read from one side and such a disk can accommodate 8.5 GB of data, i.e. 3.5 GB more than a single-layer/single-sided disc.

Double Side/Single Layer

This disk holds 9.4 GB of data (4.7 GB on each side). The capacity of such a disc is twice that of a single-sided/single-layer DVD disc. However, because the data is on both sides, you will have to flip the disk over or use a device that can read the data on both sides of the disk on its own.

Double Side/Double Layer

The structure of this disk allows you to store up to 17 GB of data on it (8.5 GB on each side).

The thickness of a DV disc is 0.6mm, which is half the thickness standard disk CD. This makes it possible to connect two drives downsides and get a double-sided disc equal in thickness to a regular CD. Another technology creates a second layer to house data, which allows you to increase the capacity of one side of the disk. The first layer is made translucent, so the laser beam can pass through it and be reflected from the second layer.

Among other things, DV discs have the ability to increase recording density. To achieve this, manufacturers take different paths:

1. a more advanced laser is used

2. reduce stroke length

3. reduce the distance between turns

4. increase the data area without changing the overall disk size

5. Increase ECC efficiency

6. apply more efficient modulation

Now about rewritable discs. These include the DVD – RAM format. These discs use a material developed by TDK engineers and it is called AVIST. The recording principle is almost the same as that of a CD. The most important advantages of DVD-RAM format discs are the ability to be rewritten up to 100,000 times and the presence of a recording error correction mechanism. On DVD+RW discs you can record as streaming video either sound or computer data. DVD+RW format discs can be rewritten about 1000 times, but the DVD+RW format is promoted only by its developers - Hewlett-Packard, Mitsubishi Chemical, Philips, Ricoh, Sony and Yamaha and is not supported by the DVD forum. DVD-RW is a rewritable format developed by Pioneer. DVD-RW format discs hold 4.7 GB per side, are available in single-sided and double-sided versions and can be used to store video, audio and other data. DVD-RW discs can be rewritten up to 1000 times. Unlike DVD+RW and DVD-RAM formats DVD-R discs W can be read on first generation DVD-ROM drives.

A major achievement in ensuring compatibility in DVD technology was the adoption in 2000 of a single file system MicroUDF. The MicroUDF file system is a version of the UDF (Universal Disk Format) file system adapted for use in DVDs, which, in turn, is based on the international standard ISO-13346. This file system is gradually replacing the outdated ISO9660, which was created at one time for use in CDs. For the transition period (until computer devices and disks operating in the ISO9660 format go out of circulation), the UDF Bridge file system will be used, which is some combination of MicroUDF and ISO9660. Only MicroUDF can be used to burn Audio/Video DVD discs.

To protect against illegal copying, two specifications have been developed: DVD-R(A) and DVD-R(G). These two versions of the same specification use different laser wavelengths when recording information. Thus, discs can only be written on equipment that meets their specifications. Disc playback can be performed equally successfully on any equipment that supports the DVD-R format. DVD-R(A) (DVD-R for Authoring) is used in professional applications. In particular, support for a special format (Cutting Master Format) allows you to use these discs to record the original replica of information (pre-mastering) instead of the usual use of DLT tapes for these purposes.

DVD-R(G) (DVD-R for General) is intended for wider use. Disks of this format are protected from the possibility of bit-by-bit copying of information onto them from other disks. The format is supported in mass storage devices (for example, in robotic DVD libraries offered by Pioneer itself).

Dimensions 120 × 1.2 mm Capacity 650-879 MB Reading speed (1×) 150 Kb/s (data from CD-ROM Mode 1)
172.3 Kbps (audio from CD-DA) Highest reading speed 72× (10.8 Mb/s) Life time 10-50 years

CD-ROM drives are a popular and cheapest means for distributing software, computer games, multimedia and other data. CD-ROM (and later DVD-ROM) became the main medium for transferring information between computers, displacing the floppy disk from this role (it is now giving way to more promising solid-state media).

Often the term CD-ROM mistakenly used to refer to the drives (devices) themselves for reading these disks (correctly - CD-ROM Drive, CD drive).

Technical details

A compact disc is a 1.2 mm thick polycarbonate substrate, covered with a thin layer of metal (aluminium, gold, silver, etc.) and a protective layer of varnish, on which a graphic representation of the contents of the disc is usually applied. The principle of reading through the substrate was adopted because it allows for very simple and effective protection information structure and remove it from the outer surface of the disk. The diameter of the beam on the outer surface of the disk is about 0.7 mm, which increases the system's immunity to dust and scratches. In addition, on the outer surface there is an annular protrusion 0.2 mm high, which allows the disk, placed on a flat surface, not to touch this surface. There is a hole with a diameter of 15 mm in the center of the disk. The weight of the disc without the box is approximately 15.7 g. The weight of the disc in a regular (not “slim”) box is approximately 74 g.

CDs are 12 cm in diameter and originally held up to 650 MB of information. However, starting around 2000, 700 MB disks began to become increasingly widespread, subsequently completely replacing the 650 MB disk. There are also media with a capacity of 800 megabytes or even more, but they may not be readable on some CD drives. There are also 8-centimeter disks that can hold about 140 or 210 MB of data and CDs shaped like credit cards (so-called business card disks).

CD-ROM under an electron microscope

Information on the disk is recorded in the form of a spiral track of so-called pits (recesses) extruded into a polycarbonate base. Each pit is approximately 100 nm deep and 500 nm wide. Pit length varies from 850 nm to 3.5 µm. The spaces between pits are called lands. The pitch of the tracks in the spiral is 1.6 microns.

There are read-only disks (“aluminum”), CD-R - write-once, CD-RW - write-multiple. The last two types of discs are designed for recording on special burner drives.

CD business card

CD business card is an optical disk made in the format of a business card (repeats its size 90×50 mm).

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See what "CD-ROM" is in other dictionaries: Rom

- (Roma) ... Deutsch Wikipedia Rom: Großmacht und Weltreich

See what "CD-ROM" is in other dictionaries:- Rom hatte vor dem Pyrrhoskrieg jahrzehntelange höchst aufreibende Kriege geführt und brauchte Ruhe. Es beschäftigte sich damit, allerlei Nachbereinigungen vorzunehmen, um die Herrschaft Schritt für Schritt zu sichern, und errichtete in aller… … Universal-Lexikon

- (Roma), die merkwürdigste Stadt auf der Erde, gegenwärtig die Hauptstadt des Kirchenstaats, liegt unterm 41°53 54 nördl. Breite, 10°9 30 östl. Länge zu beiden Seiten der Tiber, 3 etc. Ml. von deren Mündung auf den bekannten 7 Hügeln (mons… … Herders Conversations-Lexikon ROM hacking

- is the process of modifying a video game ROM image to alter the game s graphics, dialogue, levels, gameplay, or other gameplay elements. This is usually done by technically inclined video game fans to breathe new life into a cherished old game,… … Wikipedia ROM

- bezeichnet: Rom, die Hauptstadt Italiens Provinz Rom, die nach der Stadt Rom benannte italienische Provinz Römisches Reich, in der Zeit vom 6. Jahrhundert v. Chr. bis zum 6. Jahrhundert n. Chr. Zweites Rom, Konstantinopel, antique Hauptstadt des… … Deutsch Wikipedia Rom (Begriffsklärung)

- Rom bezeichnet: Römisches Reich, in der Zeit vom 6. Jahrhundert v. Chr. bis zum 6. Jahrhundert n. Chr. Römische Kurie, die Zentralbehörde des Heiligen Stuhls für die römisch katholische Kirche einen männlichen Angehörigen der Roma… … Deutsch Wikipedia When in the early 80s of the last century Sony and Philips released audio CDs (Compact Disc - CD), no one could have imagined what a valuable information carrier they would become in the near future. Durability, random access and Sound CDs brought them to the attention of everyone and contributed to their widespread distribution. The first CD-ROM drive for PCs was released in 1984, but it took several years before it became an almost mandatory component of high-end PCs. Now games, software applications, encyclopedias and other multimedia programs are distributed on CD-ROMs (figuratively speaking, now “from an expensive luxury, a CD-ROM drive has turned into a cheap necessity”). Actually, the “multimedia revolution” owes a lot to cheap high-capacity CD-ROMs. While an audio CD was designed to reproduce high-quality digital sound for 74 minutes, a computer CD-ROM can store 660 MB of data, more than 100 top-quality photographs, or a 74-minute TV movie. Many disks store all of these types of information, as well as other information.

CD-ROM drives play important role in the following aspects of the computing system:

• Software support: Most important reason that the modern PC must have a CD-ROM drive, is a huge number of software applications distributed on CDs. Nowadays floppy disks are practically not used for this.
• Performance: Since many programs now use the Cd-ROM drive, the performance of the drive becomes important. Of course, it is not as critical as performance hard drive and PC components such as the processor and system memory, but is still important.

Thanks to mass production, modern CD-ROM drives are faster and cheaper than before. The vast majority of software applications are now distributed on CD-ROM, and many programs (such as databases, multimedia applications, games, and movies) can be run directly from CD-ROM, often over the network. Today's CD-ROM drive market offers internal, external and portable drives, single-disc and multi-disc drives, SCSI and EIDE drives, and a variety of standards.

Most CD-ROM drives have easy-to-use controls on the front panel that allow you to use the drive to play and listen to audio CDs. Typically there are the following controls:

• Stereo headphone output: A small jack socket for connecting headphones and listening to an audio CD.
• Rotary knob for volume control: To adjust the audio output volume.
• Start and Stop buttons: Used to start and stop playback of an audio CD. On some drives, these buttons are the only controls.
• Next Track and Previous Track buttons: These buttons move to the next track and previous track of an audio CD.

CD-ROM drives came into being after PC drive bays were standardized, so they are designed to fit a standard 5.25" drive bay. The height of a CD-ROM drive is 1.75", which corresponds to a standard "half-height" drive bay. Most drives have a metal casing that has holes for mounting screws, making it easy to mount the drive in the bay. A retractable tray is usually used to install a disc.

CD-ROM Disk Structure

A CD-ROM drive can be compared to a floppy disk drive because both drives use removable(removable) media. It can also be compared with a storage device on hard drives x, since both drives have a large capacity. However, a CD-ROM is neither a floppy disk nor a hard disk. If floppy and hard disk drives use magnetic(magnetic) media, then in CD-ROM it is used optic(optic) medium. The basic CD-ROM has a diameter of 120 mm (4.6") and is a kind of 1.2 mm thick "sandwich" of three coatings: a back layer of transparent polycarbonate plastic, a thin aluminum film and a varnish coating to protect the disc from external scratches and dust.

In traditional production process Pure polycarbonate plastic is stamped with millions of tiny depressions called pitami(pits), on a spiral that unfolds from the center of the disk outward. The pitas are then covered with a thin aluminum film, which gives the disc its characteristic silver color. A typical pit is 0.5 µm wide, 0.83 to 3 µm long and 0.15 µm deep. Distance between tracks ( track pitch- pitch) is only 1.6 microns. Track density is more than 16,000 tracks per inch (Tracks Per Inch - TPI); For comparison, a floppy drive has a TPI of 96 and a hard drive has a TPI of 400. The length of the unfolded and extended spiral is about four miles.

Of course, CDs must be handled with care. The working side of the disk is most sensitive to damage. Despite the fact that the aluminum layer is protected from damage and corrosion by a varnish coating, the thickness of this protective layer is only 0.002 mm. Careless handling or dust can lead to small scratches and tiny cracks through which air can penetrate and oxidize the aluminum coating, rendering the disc inoperable.

Operating principle of a CD-ROM drive

With the exception of very complex error checking, the operation of a CD-ROM drive is very similar to that of an audio CD player. Data is stored in the same way as on all CDs. Information is stored in 2 KB sectors on a spiral track that starts at the center of the disk and "unwinds" to the outer edge of the disk. Sectors can be read independently.

The player reads information from pits and lands(lands) of a spiral CD track, starting from the center of the disc and moving towards the outer edge. For reading, an infrared laser beam with a wavelength of 780 nm is used, which is generated by a low-power gallium arsenide semiconductor. The beam passes through a layer of transparent coating onto a metal film. Although the laser is low-power, it can damage the retina if it enters an unprotected eye. When the disk rotates at a speed of 200 to 500 revolutions per minute (Rotations Per Minute - RPM), the beam is reflected from the pits and the frequency of the light changes.

The areas around the pits, called lands, are also involved in the reading process. The reflected light passes through a prism to a photosensor whose output is proportional to the volume of light received. The light reflected from the pits is 180 degrees out of phase from the light reflected from the lands, and the differences in intensity are measured by photovoltaic cells and converted into electrical pulses. As a result, a sequence of variable-length pits and lands stamped onto the surface of the disc is interpreted as a sequence of ones and zeros, from which the data stored on the disc is reconstructed (using a digital-to-analog converter, the digital data of an audio CD is converted into audio signals). Since only the laser beam directly “touches” the surface of the media, there is no wear on the media.

Everything would be relatively simple if the surfaces of CD-ROM disks were completely flat and could rotate without horizontal deviation. In fact, the drive required complex electronic circuits, ensuring the focusing of the laser beam on the surface of the disk and directing it exactly to the track being read.

Several methods have been developed to provide radial track tracking, but the three-beam method is the most common. The laser beam is not simply directed at the surface of the disk, but is emitted by a semiconductor device and passes through a diffraction grating, which creates two additional light sources on each side of the main beam. When passed through collimator lenses, the three rays become parallel, and then they pass through a prism called polarizing beam splitter(polarized beam splitter). The splitter allows the incoming rays to pass through, and the returning reflected rays are rotated 90 degrees to a photodiode, which interprets the signal.

The intensities of the two side beams are measured, which should be the same as long as the beams remain on each side of the track. Any lateral movement of the disk leads to imbalance and the servo motor corrects the lens. Vertical offset is accounted for by dividing the receiving photodiode into four quadrants and placing them midway between the horizontal and vertical focal points of the beam. Any deflection of the disk causes the spot to become elliptical, causing an imbalance of currents between opposite pairs of quadrants. In this case, the lens moves up or down, providing a circular spot shape.

Compact disc technology has built-in error correction systems that can correct most errors caused by physical particles on the disk's surface. Every CD-ROM drive and every audio CD player uses error detection. cross-interleaved Reed-Solomon code(Cross Interleaved Reed Solomon Code - CIRC), and the CD-ROM standard provides a second level of correction using the Layered Error Correction Code algorithm. In CIRC code, the encoder adds 2D parity information to correct errors and also interleaves data on disk to protect against burst errors. It is possible to correct burst errors up to 3500 bits (length 2.4 mm) and compensate burst errors up to 12,000 bits (length 8.5 mm) caused by small scratches.

Digital audio

On records and tape cassettes sound signal written as analog signal. Therefore, we hear all imperfections in the recording as interference (hissing and whistling) or other defects. To eliminate these defects, CDs use digital methods of storing “samples” as numbers. Conversion process analog signal in digital it's called sampling(sampling), or digitization(digitizing). The analog signal is sampled many times per second and at each survey the amplitude is measured and rounded to the nearest representable value. Obviously, the higher sampling frequency(sampling rate) and the more accurately the values ​​assigned to the amplitudes ( dynamic range- (dynamic range), the better the representation of the original.

For CD, a sampling rate of 44.1 kHz and a 16-bit dynamic range are used. This means that 44,100 samples are taken per second and the amplitude of the signal at each sample is described by a 16-bit number, giving 65,536 possible values. This sampling rate provides a frequency response sufficient for sounds with a pitch of 20 kHz. However, some "audiophiles" believe that this is not enough to convey psychoacoustic effects that occur beyond the range of human hearing. Sound is recorded on two tracks to achieve a stereo effect.

Simple calculations show (44,100 samples per second * 2 bytes * 2 channels) that one second of sound is described by 176,400 bytes with a corresponding data transfer rate of 176.4 KB/s. A single-speed CD-ROM drive transfers data at this speed, but part of the data stream contains error correction information, which reduces the effective data transfer rate to 150 KB/s. A CD can store 74 minutes of encoded stereo audio data, which, after adding error detection and correction overhead, gives a standard CD capacity of 680 MB. The table shows all the considered parameters.

Rotational speed

Constant linear speed

The first generation of single-speed CD-ROM drives was based on the design of audio CD players. Technology was used to rotate the disk constant linear speed(Constant Linear Velocity - CLV), i.e. the disk spun like an audio CD, providing a data transfer rate of 150 KB/s. The data track must pass under the read head at the same speed on the inner and outer parts of the disk. To do this, you have to change the rotation speed of the disk depending on the position of the head. The closer to the center of the disk, the faster the disk must spin to ensure a constant flow of data. The disc rotation speed in audio CD players ranges from 210 to 540 rpm.

Because there are more sectors at the outer edge of the disk than at the center, CLV technology uses a servo motor that slows the rotation speed of the disk as it moves to the outer tracks to maintain a constant data transfer rate from the laser read head. The drive's internal buffer memory controls the rotation speed by using a crystal oscillator to clock the data output of the buffer at a specific speed and keep the buffer 50% full when data is read into it. If data is read too quickly, the 50% duty cycle threshold is exceeded and a command is sent to slow down the spindle motor speed.

If audio CDs need to be read at a constant speed, then this requirement is not necessary for CD-ROM discs. Essentially, the faster the data is read, the better. As CD-ROM technology improved, speeds continually increased and in 1998, drives with 32 times the data transfer speed of 4.8 MB/s appeared.

For example, a four-speed drive using CLV technology must spin the platter at about 2120 rpm when reading internal tracks and 800 rpm when reading external tracks. Variable rotation speed is also necessary when reading audio data, which is always read at a constant speed (150 KB/s) regardless of the computer data transfer speed. The most important factors in variable speed drives are the quality of the spindle motor that spins the drive and the software that controls the drive, as well as the positioning system that must quickly and accurately move the read head to the desired position to access the data. Simply increasing the rotation speed is not enough.

Another factor is the level of CPU time usage: as the rotation speed and, consequently, the data transfer rate increases, the time that the processor must spend processing data from the CD-ROM drive also increases. If other tasks require processor time at the same time, the CD-ROM drive has less data processing capability and data transfer speeds will be reduced. A properly designed CD-ROM drive should minimize processor time at a given rotation speed and data transfer rate. It is clear that the internal performance of a fast drive should be greater than that of a slow one.

For CD-ROM drives, the data buffer capacity is always given. Of course, a 1MB buffer is definitely better than a 128KB buffer in terms of data transfer speed. However, without a good drive management program, the marginal performance gains are hardly worth the expense of additional buffer memory.

Constant angular velocity

CLV technology remained the dominant CD-ROM drive technology until Pioneer, which released the first four-speed drive, released the DR-U10X ten-speed drive in 1996. This drive operated not only in the usual constant linear speed mode, but also in the constant angular velocity(Constant Angular Velocity - CAV). In this mode, the drive transmits data at a variable speed and the spindle motor rotates at a constant speed, as HDD.

Overall performance is strongly influenced by access time(access time). As the speed of a CLV drive increases, access times often become worse because it is more difficult to accommodate the sudden changes in spindle motor speed required to maintain a constant and high data transfer rate due to the inertia of the drive itself. The CAV drive maintains a constant rotation speed, which increases data transfer speed and reduces seek time as the head moves to the outer edge. If in the first CLV drives the access time was 500 ms, then in modern CAV drives it has decreased to 100 ms.

Pioneer's revolutionary drive design allowed operation in CLV and CAV modes, as well as mixed mode. In mixed mode, CAV mode was used to read near the center of the disk, and when the head approached the outer edge, the drive switched to CLV mode. Pioneer's drive marked the end of the era of CLV-only drives and the transition to the so-called Partial CAV drives as the main type of Cd-ROM drives.

This situation remained until the development of a new generation digital signal processors(Digital Signal Processor - DSP), which could provide 16 times the data transfer speed, and in the fall of 1997, Hitachi released the first CD-ROM drive using only CAV (Full CAV) technology. It overcomes many of the problems with Partial CAV drives, in particular the need to control head position and vary rotation speed to maintain a constant data transfer rate and maintain approximately constant access time. The new drive did not require waiting for the spindle motor speed to calm down between transitions.

Most 24-speed Full CAV CD-ROM drives in late 1997 used a constant 5000 rpm disk speed with data transfer rates of 1.8 MB/s at the center and rising to 3.6 MB/s at the outer edge. By the summer of 1999, a 48-fold data transfer rate from an external track was achieved at 7.2 MB/s at a disk rotation speed of 12,000 rpm, which corresponded to the rotation speed of many high-speed hard drives.

However, spinning the drive at such high speeds created problems of excessive noise and vibration, often in the form of a whistling sound caused by air escaping from the drive enclosure. Since the CD-ROM disc is clamped in the center, the strongest vibration occurs at the outer edge of the disc, i.e. where the data transfer rate is maximum. Since only a small number of CD-ROMs store data at the outer edge, most high-speed drives rarely achieve their theoretical maximum data transfer rates in practice.

Applications

The question soon arose about which applications took advantage of the speed of CD-ROM storage. Most media drives have been optimized to use 2-speed and, at best, 4-speed drives. If the video is recorded to be played back in real time at a data transfer rate of 300 KB/s, then there is no need to exceed twice the speed. Sometimes a faster drive could quickly read information into the buffer cache, where it would then be played back, freeing the drive for other work, but this technique was rarely used.

Reading huge images from PhotoCDs turns out to be an ideal use for a fast CD-ROM drive, but having to decompress the images when reading from the disk requires only 4x the data transfer speed. In fact, the only application that really requires high data transfer rates is copying serial data to a hard drive - in other words, installing software applications.

Fast CD-ROM drives are only really fast when transferring sequential data, not random access. The ideal application for high continuous data transfer rates is high-quality digital video, recorded at a correspondingly high speed. MPEG-2 video implemented in digital versatile disks(Digital Versatile Disc - DVD) requires a transfer rate of approximately 580 KB/s, while the MPEG-1 standard according to the White Paper for VideoCD requires a transfer rate of only 170 KB/s. Thus, a standard 660MB CD-ROM will be read in just 20 minutes, so high-quality video will only be of practical use on DVDs with significantly larger capacities.

Interfaces

There are three main connections on the back of CD-ROM drives: power, audio output sound card and data interface.

Nowadays, most CD-ROM drives use an IDE data interface, which theoretically can be connected to the IDE controller found in almost every PC. The original IDE hard drive was designed for the AT bus, and the old IDE interface allowed you to connect two hard drives - a master and a slave. Subsequently, the ATAPI specification allowed one of them to become an IDE CD-ROM drive. The EIDE interface went one step further by adding a second IDE channel for two more devices, which could be hard drives, CD-ROM drives, and tape drives.

Work on one of these devices must be completed before accessing any other device. Connecting a CD-ROM drive to the same channel as the hard drive will reduce PC performance because the slower CD-ROM drive will block access to the hard drive. In PC with two hard IDE drives The CD-ROM drive should be isolated by connecting it to the secondary IDE channel, and the hard drives should be connected as master and slave to the primary channel. Hard disks will compete with each other, but without the participation of a slow CD-ROM drive. The disadvantage of the EIDE interface is that the number of connected devices is limited to four and all devices must be mounted internally, so expansion may be limited by the size of the PC case.

The SCSI-2 standard allows up to 12 devices, which can be internal or external, to be connected to one host adapter. SCSI allows all devices on the bus to be active at the same time, although only one device can transmit data. Physical localization of data in devices is relatively time-consuming, so while one device is using the bus, any other device can position the heads to perform read and write operations. Latest Specification Fast Wide SCSI supports a maximum data transfer rate of 20 MB/s compared to EIDE's 13 MB/s, and with built-in intelligence, SCSI devices require less processor attention than IDE devices.

The advantages of the SCSI interface over IDE also manifest themselves when using PC resources, in particular IRQ interrupt request lines. Due to the large number of additional cards and devices, modern PCs place increased demands on the use of IRQ, leaving little room for further expansion. The primary EIDE interface is typically allocated IRQ 14 and the secondary EIDE interface IRQ 15, so four devices are added by two interrupt lines. The SCSI interface is less resource-intensive because, regardless of the number of devices on the bus, only one IRQ line is required for the host adapter.

All in all, SCSI interface provides greater PC expansion potential and provides better performance, but is significantly more expensive than the IDE interface. The modern preference for internal EIDE drives turns out to be more convenient and cheaper than technical excellence, so the SCSI interface is chosen only for external drives CD-ROM.

Comparison of DMA and PIO mode

Traditionally, CD-ROM drives used to transfer data. programmable I/O(Programmable Input/Output - PIO), not direct memory access(Direct Memory Access - DMA). This was justified in early developments because the hardware implementation was simpler and suitable for low data rate devices. The disadvantage of this method is that the data transfer is controlled by the processor. As the data transfer speeds of CD-ROM drives increased, so did the load on the processor, so 24- and 32-speed drives occupied the entire processor in PIO mode. The load on the processor depends on several factors, in particular, on the used PIO mode, IDE/PCI bridge circuitry in the computer, CD-ROM drive buffer capacity and circuitry, and CD-ROM drive device driver.

Transferring data using DMA is always more efficient and takes only a few percent of the processor's time. Here, a special controller controls the transfer of data directly to system memory and only the initial memory allocation and minimal acknowledgment(handshaking). However, performance depends on the device, not the system. DMA devices must provide the same performance regardless of the system they are connected to. DMA has long been standard on most SCSI systems, but only recently has it become widely used for IDE interfaces and devices.

TrueX technology

To allow users to run applications directly from a CD without transferring to a hard drive, Zen Research took an original approach to improving the performance of CD-ROM drives when developing TrueX technology - improving data transfer speeds and access times, rather than simply spinning the disk faster. A typical CD-ROM uses a single focused laser beam to read digital signal, encoded by tracks of tiny pits on the surface of the disk. The Zen Research method uses application-specific large integrated circuit(Application-Specific Integrated Circuit - ASIC) to illuminate multiple tracks, detect them simultaneously, and read from the tracks in parallel. The ASIC contains analog interface elements, such as a Digital Phase-Locked Loop (DPLL), a digital signal processor, a servo motor controller, a parallel-to-serial converter, and an ATAPI interface. If necessary, you can connect an external SCSI or IEEE 1394 interface circuit.

A split laser beam, used in conjunction with a multi-beam detector array, illuminates and detects multiple tracks. A conventional laser beam is passed through a diffraction grating, which splits it into seven discrete beams (such accumulators are called multi-beam- multibeam), illuminating seven tracks. Seven beams are fed through a mirror to the lens and then to the surface of the disk. Focusing and tracking are provided by the central beam. Three beams on each side of the center are read by the detector array when the center beam is on the track and focused. The reflected rays return along the same path and are directed by a mirror to the detector array. The multibeam detector has seven detectors aligned with reflective tracks. Conventional detectors are provided for focusing and tracking.

Although the mechanical elements of the CD-ROM drive are slightly modified (the rotation of the disk and the movement of the read head remain the same), the format of the disk media follows the CD or DVD standard, and the usual approach is used for searching and tracking. TrueX technology can be used in CLV and CAV drives, but Zen Research is targeting CLV to provide consistent data transfer rates across the entire drive. In either case, higher transmission speeds are achieved at lower platter speeds, reducing vibration and improving reliability.

Kenwood Technologies released the first 40-speed TrueX CD-ROM drive in August 1998, and six months later developed a 52-speed drive. Depending on the working environment and media quality, the Kenwood 52X TrueX CD-ROM drive provides data transfer rates of 6.75 - 7.8 MB/s (45x - 52x) across the entire disk. For comparison, a typical 48-speed CD-ROM drive provides 19x speeds on the internal tracks and reaches 48x speeds only on the outer tracks. At the same time, its rotation speed is more than twice as high as compared to the drive from Kenwood Technologies.

CD-ROM standards

To understand CDs themselves and which drives can read them, you first need to become familiar with disc formats. Typically, CD standards are issued in the form of books with colored covers and the standard itself is named after the color of the cover. All CD-ROM drives are compatible with Yellow Book and Red Book standards and also have built-in digital-to-analog converters(Digital-to-Analog Converter - DAC), which allows you to listen to Red Book audio discs through headphones or audio output.

Red Book

The Red Book is the most widely used CD standard and describes the physical properties of a compact disc and digital audio encoding. It defines:

• Audio specification for 16-bit Pulse Code Modulation (PCM).
• Disk specification, including its physical parameters.
• Optical styles and parameters.
• Deviations and block error rates.
• Modulation and error correction system.
• Control and display system.

Each piece of music recorded on a CD meets the Red Book standard. It basically allows for 74 minutes of audio and splits the information into tracks(tracks - tracks). A later addendum to the Red Book describes the CD Graphics option using subcode channels R through W. The addendum describes various applications of the subcode channels, including graphics and MIDI.

Yellow Book The Yellow Book was released in 1984 to describe an extension of the CD for storing computer data, i.e. CD-ROM (Compact-Disc Read-Only Memory). This specification contains the following:

• Disc specification, which is a copy of part of the Red Book.
• Modulation and error correction system (from the Red Book).
• Optical styles and parameters (from the Red Book).
• Control and display system (from the Red Book).
• A digital data structure that describes the sector, ECC, and EDC structure of a CD-ROM disc.

CD-ROM XA

As a separate extension of the Yellow Book, the CD-ROM XA specification contains the following:

• Disc format, including Q channel and sector structure when using Mode 2 sectors.
• Data retrieval structure based on the ISO 9660 format, including file interleaving, which is not available in Data Mode 2.
• Audio coding using levels B and C of ADPCM modulation.
• Coding of video images, i.e. still images.

The only CD-ROM XA formats currently available are the CD-I Bridge formats for the Photo CD VideoCD plus of Sony's Playstation system.

Green Book

The Green Book describes the CD-Interactive (CD-I) disc, player and operating system and contains the following:

• CD-I disc format (track and sector structure).
• Data retrieval structure based on the ISO 9660 format.
• Audio data using levels A, B and C of ADPCM modulation.
• Real-time still video encoding, decoder and visual effects.
• Compact Disc Real Time Operating System(CD-RTOS).
• Basic (minimum) system specification.
• Movie extension (MPEG cartridge and software).

A CD-I disc can store 19 hours of audio, 7,500 still images, and 72 minutes of full-screen full-motion video (MPEG) in standard CD format. CD-I discs are now obsolete.

Orange Book

The Orange Book identifies CD-Recordable discs with multisession capability. Part I defines magneto-optical rewritable CD-MO (Magneto Optical) discs; Part II defines CD-WO (Write Once) discs; Part III defines rewritable CD-RW (Rewritable) discs. All three parts contain the following sections:

• Disc specification for unrecorded and recorded discs.
• Pre-groove modulation.
• Organizing data, including linking.
• Multi-session and hybrid discs.
• Recommendations for reflectivity measurement, power control, etc.

White Book

• Disc format including track usage, VideoCD information area, segment playback area, audio/video tracks and CD-DA tracks.
• Data retrieval structure that satisfies ISO format 9660.
• MPEG encoding of audio/video tracks.
• Playback segment element encoding for video sequences, still images and CD-DA tracks.
• Playback sequence descriptors for programmed sequences.
• User data fields for data scanning (fast forward and backward scanning is allowed).
• Examples of playback sequences and playback controls.

Up to 70 minutes of full-motion video are encoded in the MPEG-1 standard with data compression. The White Paper is also called Digital Video (DV). A VideoCD disc contains one data track recorded in CD-ROM XA Mode 2 Form 2. This is always the first track on the disc (Track 1). This track records the ISO 9660 file structure and application CD-I program, as well as the VideoCD Information Area, which contains general information about VideoCD. After the data track, video is recorded on one or more subsequent tracks during the same session. These tracks are also recorded in Mode 2 Form 2. The session is closed when all tracks have been recorded.

Blue Book

The Blue Book defines the Enhanced Music CD specification for multi-session pressed discs (i.e. non-recordable discs) containing audio and data sessions. The discs can be played on any audio CD player and PC. The Blue Book contains the following:

• Disc specification and data format, including two sessions (audio and data).
• Directory structure (ISO 9660), including directories for CD Extra information, images and data. The CD Plus information file format, image file formats, and other codes and file formats are also defined.
• MPEG still image data format.

Compact discs that comply with the Blue Book specification are also called CD-Extra or CD-Plus. They contain a mixture of data and audio recorded in separate sessions to prevent playback of data tracks and possible damage to high-quality home stereo systems.

CD-I Bridge

CD-I Bridge is a Philips and Sony specification for discs intended for playback on CD-I players and PCs. It contains the following:

• The disc format that defines CD-I Bridge discs as meeting the CD-ROM XA specification.
• Data retrieval structure in accordance with ISO 9660. Mandatory application program CD-I, which is stored in the CDI directory.
• Audio coding that includes ADPCM and MPEG.
• Video encoding for CD-I and CD-ROM XA compatibility.
• Multi-session disk structure, including sector addressing and volume space.
• Data for CD-I, since all CD-I players must read CD-I Bridge data.

Photo CD

The Photo CD specification is defined by Kodak and Philips based on the CD-I Bridge specification. It contains the following:

• General disk format, including program area layout, index table, volume descriptor, data area, Q-channel subcode skew, CD-DA clips, and microcontroller-readable sectors.
• Data retrieval structures, including directory structure, INFO.PCD file, and microcontroller-readable sector system.
• Image data encoding, including description of image encoding and image packets.
• ADPCM files for simultaneous playback of sound and images.

There is a lot of information on CD-ROM drives on the website http://www.cd-info.com/.

How to choose a DVD drive for your computer

The fact that DVD media is slowly but surely disappearing into oblivion is difficult to dispute. They repeat the fate of their predecessors - floppy disks and CDs. No “revolutionary” solutions such as the release of double-layer or double-sided DVDs could radically change the situation, and the digital media market in small batches is falling into the hands of flash memory and Blu-ray disc manufacturers. However, the DVD format is still the most widespread in the distribution of movies, software, games and music (together with CDs), so the DVD drive is still considered an integral part of a personal computer.

Let's start, as usual, with the basics. "Scientifically" a DVD drive is optical drive, a device designed for reading and writing data from digital media, which include, in particular, CD-R, CD-RW, DVD-/+R and DVD-/+RW discs. Many still remember the times when a DVD burner was more of a luxury than a necessity. Today, finding a simply “reading” disk drive on sale is almost impossible, and there is no particular need for it. Even if you rarely or never use this function (recording), this has practically no effect on the final price, so it makes no sense to purchase a regular DVD drive or even a CD-ROM writer. Unless you collect them.

If you buy a computer from scratch, then by default the internal one (packed in system unit) A DVD drive is included in the package. This applies to both desktop PCs and laptops with netbooks, although the latter are equipped with their own, thinner and more expensive, drive models. The need to separately purchase a DVD drive may arise for only two reasons. Either your drive has failed for some reason (there can be many reasons - from factory defects to carelessness in operating the device), or this model you are not satisfied with some parameters (noise, speed, design, compatibility), but we managed to find out this only while working with the drive.

Drive speed and major media formats

The question arises, what could be wrong with this or that drive? The main parameter that you should pay attention to is the read and write speed. Because in fact, you can only experience this speed if you are going to read or write disks on a truly industrial scale. It is also worth deciding what media you will most often “feed” the device, because the same CDs are read much slower (more than 9 times) than DVDs. It is logical to assume that if most of the information on the market today is sold on DVD media, then you will mostly be stuffing discs of this format into the drive.

Drive speed is indicated in 1x, where 1 corresponds to 150 Kb/s for CD-ROM, and 1.385 MB/s for DVD-ROM. The maximum capacity of a standard CD, on which music albums and small-sized computer games (as well as databases and software) are most often found on sale today, is 700 MB. By today's standards, the size is ridiculous, but quite sufficient for recording a dozen uncompressed music tracks, text files, programs or a disk with corporate information (catalogs, price lists, instructions, etc.). Theoretically, the CD reading speed is limited to 56x, but in practice this figure does not exceed 40x, because the faster the disk rotates in the drive, the more noise it creates during operation.

If you often and enjoy writing discs CD-R (one-time use) And CD-RW (rewritable), then your ability to read these media will be limited to speeds of 40x and 48x, or even 24x (for CD-RW). As for recording, by default the drive will operate at the maximum possible speed, which can be manually changed to a lower speed. 700 megabytes usually fills up within five minutes.

Now let's turn directly to DVD discs, which you will encounter most often, both during the reading and writing process. We remind you that data exchange with DVD media can only be carried out using a DVD drive; a regular CD-ROM cannot cope with this function by definition.

Currently, the following DVD discs are distinguished. This is first and foremost the most common DVD-ROM, which is the basis for film products, games, software and other data produced and sold in series. Writing to DVD-ROM at home is impossible, read only. DVD-ROMs come in single-layer and double-layer formats, with capacities of 4.7 and 8.5 GB, respectively.

The most common disc formats that you will encounter are disposable discs DVD-R and DVD+R, which are most often used to store “heavy” information such as video and software. Why plus and minus? It's simple, negative disks appeared a little earlier at the instigation of the famous company Pioneer, while “plus” technologies belong to the pen of Sony and Phillips. The difference lies in the presence of special markings that make it easier to position the drive head, and the use of different reflective material. At first, these differences were critical for the quality of multiple rewrites (of course, for DVD-RW and DVD+RW discs), but today most drive models can easily cope with any version.

The maximum reading and writing speed on DVD-R and DVD+R discs is, depending on the drive model and the quality of the disc, from 8x to 24x, which when fully loaded with data will be approximately 4 to 8 minutes. There are also two-layer disposable discs with the prefix DL (dual layer) in the name, with a capacity of 8.5 GB. However, the recording speed on these “giants” is no more than 12x.

Media that support rewriting are distinguished between DVD-RW, DVD+RW and DVD-RAM. You've probably already encountered the first two: 4.7 GB disks with a maximum write speed of 8x. As for DVD-RAM, which can be written to simultaneously with the process of reading data, their mass use is limited due to the prohibitive cost.

What else do you need to know about DVD drive speed? Considering the fact that this parameter Since the device directly depends on the media used in it, it is not advisable to try to buy the fastest drive. Discs that support high write and read speeds are expensive and are not sold everywhere. Remember that discs are extremely fragile media, susceptible to scratches, chips and other physical surface deformations. At high rotation speeds, such interference can lead to the destruction of the disk, which simply shatters into fragments and can cause irreparable damage to the drive. As they say, the quieter you go, the further you will go.

Features of connecting the drive and sales packaging

Probably everyone has seen a regular internal disk drive. A rectangle (148x42x198 mm) without unnecessary design frills, weighing under a kilogram. There are also shortened versions (for compact cases) with a length of up to 170 mm and lightweight ones up to 750 grams. The most elegant are, of course, DVD drives for laptops - square in size (130x130 mm) with a thickness of only 13 mm and a weight of 120 grams. However, these devices are very expensive and capricious in terms of installation, which is best left to professionals.

Appearance of a DVD drive for a laptop

The DVD drive, being an internal device, is connected using a cable to the computer's motherboard, and therefore there are two types of connection - through the parallel IDE interface or the serial SATA interface. IDE is now being widely replaced by the more advanced SATA, so when purchasing a drive separately, you should check the insides of your computer, or rather, the connectors on the motherboard, so as not to get into trouble. New board models most likely already work with SATA, so you can safely purchase the appropriate drive. What's the advantage? Theoretically - in speed. But in practice, you most likely will not notice the difference.

Regarding packaging. The fact that used drives are not worth buying is, I hope, clear without further ado, because all computer components have their own limited resource. The store will offer you two options: OEM and Retail. OEM is a package “for the poor”, which includes a plastic bag plus a disk with installation software. As part of the Retail kit, in addition to the drive itself, you will find wires (cable), screws, blank disks, and if the manufacturer is generous, then an audio cable and even replacement panels. Naturally, the second option will cost you a little more than the “polyethylene” one.

Manufacturers and prices

It's no secret that in the niche of DVD drives, a brand or trademark often becomes a determining factor in choosing a particular device. There are many different elements in the system unit, ranging from motherboard, video cards and ending with the power supply and, in fact, the system case itself. But all these components, as a rule, are impersonal, because not everyone would think of going inside to look at the manufacturer of the sound board or motherboard. Many, not very advanced, users focus more on specific parameters rather than on company names. It’s different with DVD drives; they are “facing” the consumer, proudly decorating the system unit with an inscription like NEC, Sony or Plextor.

There is always a lot of subjectivity in the selection of a specific brand, because few people have to test drives from different manufacturers at home. Usually we become attached to a particular model, after which we don’t even want to hear about its replacement with something else. Nevertheless, there are quite a lot of players in this market, which we will talk about at the end of the article.

DVD-ROM from Plextor

If you have to deal with the recording process often and a lot, then there are actually two options. Either constantly change cheap devices, or occasionally face the need to buy expensive models. For both of them, the resource is a parameter with a finite value. If you are more satisfied with the second option, then pay attention to the quality of the company Plextor, whose devices are distinguished by high reliability and performance. The cost of Plextor drives is not the only, but the most significant reason why only a select few can afford to communicate with this brand (from 5,000 rubles and above).

The situation is approximately the same with the products of American companies. Dell And Hewlett-Packard (HP). Good, even remarkable quality, high operating speeds, reliability, but the price in the region of 4000-5000 rubles will not please everyone. Moreover, their products are rarely seen on store shelves, and Dell prefers to specialize in ultra-thin laptop models.

Drives available with label ASUS And Sony Optiarc (since 2006, the official merger of two companies - Sony and NEC)- strong middle peasants. At a cost of around 1,000 rubles, they demonstrate high recording quality, and discs created using these drives can be read without problems by devices from other manufacturers, as well as by many DVD players. Not noisy, stylish, practical - optimal ratio prices and quality.

DVD-RW drive Sony Optiarc

Drives from Samsung, Toshiba and Pioneer are considered the most capricious in terms of blank quality. LG and Lite-On drives handle scratched media better than others. Of course, these conclusions were made during testing specific models, which, as we know, can be both successful and not so successful. In other words, you may be incredibly lucky and your Samsung DVD drive will be omnivorous and tireless, while the ASUS drive, highly rated by “experts,” will stumble at every step.

In any case, when buying a DVD drive, pay attention to three things: packaging (OEM or Retail), connection method (IDE or SATA) and speed characteristics. Well, and the design, of course, because a black NEC sticking out on a white case will be striking. Each brand has its own advantages and disadvantages, but in this market, unless we are talking about elite models of semi-professional quality, the main and determining factor is still the price of the device, which for the vast majority of DVD drives varies from 600 to 1,500 rubles.

To 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 either discs with pre-recorded data (such as a music CD or DVD with a movie) or special wheels, onto which you can (one or several times, depending on the disk and drive) write any information you need.

Apart from the not entirely correct name “ drive", devices for reading and writing CD/DVD discs are also called optical drives. Word storage device generally refers to all devices designed to store or read data. For example, HDD can be called a disk drive. The word "optical" refers to the method of reading data from disks. In CD/DVD drives, data is read and written from disks using a special laser beam.

There are several types CD-ROM and DVD drives, with and without recording support. Let's take a closer look at them.

• Regular drive CD— - is the process of modifying a video game ROM image to alter the game s graphics, dialogue, levels, gameplay, or other gameplay elements. This is usually done by technically inclined video game fans to breathe new life into a cherished old game,… … Wikipedia allows only reading data from disks CD, CD— R And CD— RW. You cannot write data to any discs using it. Such drives are the cheapest, but are already outdated and cannot be installed in new computers.
• Drive CD— - is the process of modifying a video game ROM image to alter the game s graphics, dialogue, levels, gameplay, or other gameplay elements. This is usually done by technically inclined video game fans to breathe new life into a cherished old game,… … Wikipedia with recording capability. Unlike the previous option, using this drive you can write data to write-once (CD-R) or write-once-repeat (CD-RW) discs.
• 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 recording capability. This is the most versatile and popular drive option that is recommended for purchase. With this drive you can read and write any disc, including CD, CD-R, CD-RW, DVD+-R/RW.
• Also, drives with support for reading Blu-rey discs are becoming more and more popular every year.

Basic Types of Optical Discs

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

• CD, or CD. The simplest option optical disk. Such 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. You can’t add it later. One CD-R disc can store up to 880 MB of data, depending on the disc capacity. These disks are most often used for storing important information, which will not need to be changed in the future. This could be music, video files, etc.
• CD-RW disc. This disc has the same capacity as CD-R discs, but you can write data to it many times and delete data you don't need. In total, such a disk is designed for approximately 1000 rewrite cycles, which is more than enough, for example, for periodic recording Word documents, their subsequent deletion and recording of new files. CD-RW discs are more expensive than CD-R discs.
• DiskDVD-ROMorDVD Video. It is on these discs that DVD films are sold. You cannot write anything to such a disk. At the same time, the volume of single-layer DVD is 4.7 GB, which is several times more than the capacity of CD discs.
• DiskDVD— Rand diskDVD+ R. Just like CD-R discs, DVD-R and DVD+R discs can be one once write down the data you need. Unfortunately, at one time the companies producing optical discs and drives turned against each other and became irreconcilable enemies, as a result of which two standards that were completely incompatible with each other, DVD+R and DVD-R, appeared. Fortunately, optical drive manufacturers have solved this problem and now, for most drives, it doesn't matter which drive you use; Both types of disks will be supported.
• DiskDVD+ RWAndDVD— RW. Similar to CD-RW discs, DVD+RW and DVD-RW discs can be used to record data multiple times. Given the disc capacity of 4.7 GB, this is very convenient for storing and Reserve copy a variety of data, for example your music collection, etc. The problem of incompatible standards exists here too, and it was solved in the same way - by releasing universal small format drives that support any type of disk.
• Diskblue— rey We have a huge capacity that allows you to record up to 80 gigabytes of information! Agree, this is a lot for an optical drive! In most cases, I record video with increased clarity on such discs, which allows me to achieve maximum film quality! The cost of such a drive can reach up to 2000 rubles!

Optical drive speed

Operation speed optical drive usually indicated this way 52x/24x/52x. This means that CD-R discs are written from 52x, disc recording CD-RW happens at speed 24x, and reading CD-R/RW discs is also at a speed of 52x. In this case, the 1x indicator means a data transfer speed of 153 KB/s. Now let's calculate the speed of a disk 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 similar to the speed of a 9x CD-ROM. Therefore, the speed of modern DVD-ROM drives with a read speed of 20x corresponds to a speed of 180x for CD-ROM drives (27 MB/s), although, of course, such speed does not exist for CD-ROM drives.