D. Aleco not all buyers worries hard, which CD drive will be installed in their computer. Well, ask his speed, and that's all. But sometimes a person still asks about the performance of the CD-ROM, which he is offered to choose from, how reliable they are and will be able to read all the discs, including poorly manufactured pirated. Honestly, answer is not so easy.

Mitsumi CR-4802TE drive 40-speed Mitsumi FX-4010M

For example, we are well for sale CD-ROM from Samsung. They like me that they are almost no noisy and at the same time quite productive. However, it was already necessary to hear that these CD-ROM were often breaking, firms that sell them call high return interest and often fear to give them a long warranty. I do not know. I have not yet come across this problem, these drives work on acquaintances to me computers normally and cope with our duties for more than a year.

Nevertheless, there are alternative proposals. The choice of CD-ROM is quite wide, and for the price of the drives of different brands differ non-essential. In particular, the significant proportion of the market belongs to devices from Mitsumi, you're about it, of course, heard. Someone her drives like, there is no one - the case of taste. Two drives that I recently tried in work, made a good impression on me, although there were no significant advantages over other models. They say, however, they are more reliable than SAMSUNG CD-drives. I received this information from people who traded them and other drives. Perhaps this is so.

40-speed Mitsumi FX-4010M
Of course, speed, 40 times higher than the nominal speed of reading musical compacts, is the maximum. In most cases, this drive reads data at a lower speed.

Mitsumi, specializing in the supply of the most popular market peripheral devices - Keyboards and mice, flopopes and optical CD drives, not newcomer and has a number of own know-how and technological developments. In the FX-4010M drive, for example, a combination of two methods for reading information is used with a constant angular (CAV) and linear (CLV) speed. In the first case, when reading data from the periphery of the disk, the maximum speed is achieved. The second technology provides a constant reading speed, regardless of how much data blocks from the center of the disk are removed. The combination of these technologies guarantees good performance and reliability.

The FX-4010M drive for passport data with an average access time of 65 milliseconds at the maximum 40-fold speed should provide 6,000 kilobytes of data per second. It is equipped with an ATAPI IDE interface and uses Ultra DMA-33 mode, in which the external data transfer rate reaches 33 megabytes per second. Of course, data transmission at this speed is possible when it is removed from the buffer, and not when reading from the disk. Mitsumi FX-4010M buffer is not very large - 256 kilobytes.

This drive has two more interesting features. Thanks to the original design of the FX-4010M, you can be installed both in horizontal and vertical position. At the same time there are no latches as in other CD-ROMs capable of working in a vertical position. Accordingly, the disk stacked easily, it does not cling to anything, and do not carefully watch if it is inserted correctly. In the vertical position, the compact is fixed by two grooves of the tray, which are not used at normal horizontal installation, and they can not be noticed at all.

Another feature is support for multiple digital CD formats, including the newly appeared CD-Text. His, by the way, not yet all drives understand. In addition, FX-4010M is able to read both stamped CD-ROM and CD-R and CD-RW discs, including multirest.

Testing Mitsumi FX-4010M to performance has shown that this drive differs little from its 40-speed fellow, for example Pioneer DR-944. However, when testing, I drew attention to an interesting pattern, other drives have so clearly not manifested. The better the disk is made, the easier it is read from it, the higher the performance. I explain. When using a CD-R disc, the speed turned out to be constant throughout the disk, which is in the inner, which at an external radius it was about 2.190 KB / s. That is, the CLV scheme was used. When I put a factory CD for good quality, almost up to half, ranging from the center, he read on CAV technology and productivity linearly grew from the initial 2,170 KB / s. Then, when, apparently, the drive experienced difficulties with reading data at an increasing speed, it switched to CLV, the reading speed at the same time reached 4,150 KB / s, and at this level it remained until the end of the disc. The reading of the Pirate CD also began on CAV technology, but literally on the fifth part of the MITSUMI FX-4010M disk was forced to go to the CLV.

This affected the speed, and not on the reliability of data reading - even the shaded old Bulgarian compact compact, which I use as a "bad" disk to check the CD-ROM to endurance, was read. Although with creak, but completely. By the way, about noise. Mitsumi FX-4010M when working is noise. Less than the same Pioneer DR-944, but still significantly louder than the CD-ROM from Samsung.

Mitsumi CR-4802TE drive

This is another CD drive from Mitsumi, which you just need to know. More than once in the letters complained that the writing CD drives that I wrote are too expensive and are of interest except for "rich broths." Like, when the drive is worth $ 300 and clean discs are not cheaps - once recorded CD-Rs are an average of $ 1.5, and rewritable CD-RW from $ 10 - this method of storing information cannot be considered more convenient and affordable than on the hard drive, where the gigabytes of data today It is necessary to pay something about $ 15.

this opinion can argue. Winchester is sooner or later (and usually earlier than you thought) is filled with data, the utility of which is not so easy to judge. (I wrote about this problem in "kg", N№22). And more than three IDE hard drives to the computer you do not put (including the availability of CD-ROM), so that the maximum capacity of the disk subsystem is available today (prepared for the release and 20-gigabyte hard drives, but they are not yet available and they will be almost twice as expensive 10-gigabyte) will be 30 gigabytes. It will cost this pleasure of $ 450 or a little less.

If you buy a CD-RW drive, such as Mitsumi CR-4802Te, which is worth $ 185 today, it opens the possibility of storage in the workplace unlimited data. At least as long as you do not turn the entire room with compacts. What will increase 30 gigabytes when using CDs? It will take approximately 45 disks of 650 megabytes each. Approximately because the container of the hard drives is indicated in thousands of bytes, and 650 megabytes are really placed on the matrix.

My own experience It shows that on rewritable CD-RW makes sense to store no more than a third of files, for the rest, the CD-R discs are perfectly suitable (by the way, the information on them can be added as accumulated). So, $ 195 will leave for compacts with a total capacity of 30 gigabytes, plus the drive - total $ 380. As you can see, no more than the purchase of hard drives of the same container. And do not forget that hard disks You do not put more than three, and the matrices can buy and buy: 45 pieces - not so much. In the future, of course, the Winchesters will be cheaper. Like CD matrices.

Well, ok, enough about the bucks. The MITSUMI CR-4802TE drive allows you to record CD-R discs at four-time speed (600 KB / s), CD-RW - with double (300 KB / s). It reads the usual CD-ROM with an 8-fold speed, the maximum data reading rate is 1,200 KB / s. These are passport details. Testing them confirmed. When testing, the CD-R disc read speed was 1.220 KB / s on a smaller radius and 1.210 on the periphery of the disk. This reminded me of a situation with a Mitsumi FX-4010M drive. The main thing is that the passport details during the test confirmed. The average access time, by the way, specified in the documentation is 200 milliseconds. When testing with ZD CD WinBench 99, it turned out to be significantly less - 164 milliseconds.

The CR-4802TE drive is equipped with a 2 megabyte buffer - twice as large than many type CD-drives of this class. Using the ATAPI interface facilitates the installation. Although the Ultra DMA-33 mode is not supported, in this case it does not affect performance. The CR-4802TE has both analog and digital audio output, which provides high quality playback and copying music CDs. This drive supports a lot of CD formats, including ISO 9660, Red Book, Yellow Book, Orange Book Part 2, White Book, CD-I and CD Extra. It allows you to record CD-R discs in several receptions, which are called sessions or sessions, which is very convenient when creating libraries utilities and archiving of working data. For repeatedly rewritable CD-RW drives, direct access can be used as if it was a magneto-optical drive.

Included with Mitsumi CR-4802TE, the Winon CD version 3.6 CD recording program comes. For direct access, the Cequadrat PacketCD version 3.00.169 should be installed. The drive is clearly intended for the European market. In the installation instructions there is a section in Russian. The compact offers the user's manual in many languages, including in Russian, but for some reason an English-language description opens. Unfortunately, when testing, I found that with Mitsumi CR-4802Te does not want to work Adaptec Easy CD Creator, which I consider the most convenient for the user. But WinonCD 3.6 has rich capabilities, although its interface is somewhat more complicated.

Bringing the impressions of Mitsumi CR-4802Te in a couple of offers, I will say that this is today the cheapest drive working with CD-R and CD-RW discs, characterized by good performance and convenient for use. In addition, he copes well with the cheapest "unnamed" matrices, who, by the way, having not wanted to record a more expensive CD-recorder of Yamaha. Perhaps for amazing cheap CR-4802TE and hidden some pitched stones, but during testing I did not find them. For the needs of the usual user, the capabilities of this drive is quite enough.

Roman Sobolenko

Full CD-ROM.

CD-ROM Drive is a complex electropline-mechanical extension to read information with lase disks. Typical DPEIV consists of electrical cards (sometimes two and even the TPEC - the spindle control circuit and the optoprifier amplifier separately), the spindle node, the optical reading head with its proceeding and the mechanics of the disk pumping.

HA Electronic Circuit Features:

• the gain and coition circuit with the OPOGOLOGO;
• schemes of the FAAP signal and SAR spindle;
• pPPRESSOP Operation of Reed-Solomon code;
• sAR schemas focusing ray and dynamic tracking;
• updation scheme for optogloval proceedings;
• pPPRESSOP UPPERTANCE (logic);
• buffer memory;
• interface with controller (IDE / SCSI / Other);
• interface connectors and audio output;
• mode switching block (jumpers / jumpers).

A typical PRP consists of an electronic circuit board, a spindle engine, an optical reading head system and a disk headband system. HA Electrical Panel Passed All Updating Pliode Schemes, Internet Control Plot, Internet Passions and Sound Outputs. Most of the FIPS uses one electronic card, however, in some models, individual schemes are submitted for auxiliary small fees.

Recording, reading and subsequent information processing define the general functional CD-ROM scheme presented on the functional scheme. In addition to the above systems, it turns on a synchron generator, providing synchrons all CD-ROM nodes, and an EFM demodulator that converts 14-bit code parcels from a disk to an 8-bit serial code. The following information enters the digital data processor, which in conjunction with the system control processor is the heart of the entire device. Here is the inverse data enabling and error correction. The task of overcoming data when writing information is "Stretching" of each information byte for several recording frames. At the same time, if the loss of even several frameworks of information occurs as a result of mechanical damage to the disk surface, the result of reverse interleave data will be the presence of minor errors in separate bytes. Such errors corrects error correction scheme.

When, at the beginning of the 80s of the last century, Sony and Philips released sound cDs (Compact Disc - CD), no one could assume what valuable media they will be in the near future. Durability, the possibility of arbitrary access and high sound quality CD attracted universal attention to them and contributed to their widespread. The first CD-ROM drive (CD-ROM DRIVE) was released in 1984, but several years have passed before it became an almost mandatory component of high-quality RS. Now the games, software applications, encyclopedias and other multimedia programs are distributed on CD-ROM, now "from expensive luxury CD-ROM drive turned into a cheap necessity"). Actually, the "multimedia revolution" is obliged to many cheap CD-ROM of a large capacity. If the sound CD was designed to reproduce high quality digital sound Within 74 minutes, the computer CD-ROM can store 660 MB of data, more than 100 photos highest quality or television duration of 74 minutes. Many discs store all these types of information, as well as other information.

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

• Support software : The most important reason for the modern RS should Have a CD-ROM drive, is a huge number of software applications distributed on CDs. Now flexible disks are practically not used for this.
• Performance: Since now many programs use the CD-ROM drive, the performance of the drive takes important importance. Finite, it is not so critical as performance hard disk And such components of PC, as a processor and system memory, but still is important.

Thanks to mass production, modern CD-ROM drives have become faster and cheaper than before. Now the vast majority of software applications are distributed on the CD-ROM, and many programs (for example, databases, multimedia applications, games and movies) can be performed directly from the CD-ROM, and often on the network. The modern CD-ROM storage market offers domestic, external and portable devices, one-piece and multi-disc devices with automatic disk changing, drives with SCSI and EIDE interfaces, as well as many standards.

Most CD-ROM drives have convenient controls on the front panel, allowing you to use the drive to play and listen to sound CDs. Usually there are such controls:

• Entry to stereo headphones: A small jack (Jack - Jack) to connect headphones and listening to sound CD.
• Rotary Pen for Volume Control: To adjust the volume of the audio output.
• Start and Stop buttons: Designed to start and stop playing audio CD. In some drives, these buttons are the only controls.
• NEXT TRACK and PREVIOUS TRACK buttons: These buttons allow you to go to the next track and the previous audio CD track.

CD-ROM drives appeared after the drives in the RS are standardized, so they are calculated on the standard storage compartment 5.25. The height of the CD-ROM drive is 1.75 ", which corresponds to the standard half-height compartment (Half-Height). Most drives have a metal casing in which there are holes for fixing screws, which ensures simple installation of the drive in the compartment. To install the disk, a retractable tray (tray) is usually applied.

CD-ROM disk structure

The CD-ROM drive can be compared with the drive on a flexible disk, as in both drives it is used removable (Removable) Media. It can be compared with the drive on hard disks, since both drives have a large capacity. However, CD-ROM is neither flexible or hard disk. If in drives on flexible and hard drives used magnetic (Magnetic) media, then in CD-ROM applies optic (optic) carrier. The basic CD-ROM has a diameter of 120 mm (4.6 ") and is a kind of" sandwich "with a thickness of 1.2 mm of three coatings: rear layer of transparent polycarbonate plastic, thin aluminum film and lacquer coating to protect the disk from external scratches and dust.

In the traditional production process on pure polycarbonate plastic, millions of tiny depressions are stamped, called pitama (Pits), on a spiral, which unfolds from the center of the disk outside. The petes are then coated with thin aluminum film, which gives the disc characteristic silver color. Typical Pete has a width of 0.5 μm, length from 0.83 to 3 μm and a depth of 0.15 μm. Distance between tracks ( pag Road - Pitch) is only 1.6 microns. The density of the tracks is more than 16,000 inch tracks (Tracks Per Inch - TPI); For comparison, the TPI flexible disk is 96, and the hard disk is 400. The length of the unfolded and elongated spiral is about four miles.

Of course, you need to contact CDs neatly. The most sensitive damage is the working side of the disk. Despite the fact that the aluminum layer is protected from damage and corrosion of the lacquer coating, the thickness of this protective layer is only 0.002 mm. Careless handling or dust can lead to the appearance of small scratches and the finest cracks through which the air penetrates and oxidizes the aluminum coating, turning the disk into the inoperable.

The principle of operation of the CD-ROM drive

With the exception of very complex error control methods, the work of the CD-ROM drive is very similar to the player's player of sound CDs. The data is stored in the same way as on all CDs. The information is stored in the sectors of a capacity of 2 KB on a spiral track, which starts in the center of the disk and "unwind" to the outer edge of the disk. Sectors can be read independently.

Player reads information from the pit and landov (Lands) a CD spiral track, ranging from the center of the disk and moving toward the outer edge. An infrared laser beam with a wavelength of 780 nm is used for reading, which generates a low-power arsenide gallium semiconductor. The beam passes through a layer of transparent coating on a metal film. Despite the fact that the laser is low-power, it can damage the retina if he falls into an unprotected eye. When the disk is rotated at a speed of 200 to 500 revolutions per minute (Rotations Per Minute - RPM), the beam is reflected from the pit and the frequency of light changes.

Areas around the pita, called landamiAlso participate in the reading process. The reflected light passes through the prism on the photo sensor, the output of which is proportional to the volume of perceived light. The light reflected from peit differs in phase of 180 degrees from the light reflected from the lands, and the difference in intensity is measured by photovoltaic cells and are converted into electrical pulses. As a result, the sequence of the peit and the lands of the variable length, postponed on the disk surface, is interpreted as a sequence of units and zeros, from which the data stored on the disk is restored (with a digital-analog converter, the digital data of the audio CD is converted into sound signals). Since the surface of the carrier directly "concerns" only a laser beam, the carrier wear does not occur.

Everything would be relatively simple if the surface cD-ROM discs were absolutely flat and could rotate without horizontal deviation. In fact, complex electronic circuits were required as part of the drive, which ensure the focusing of the laser beam on the surface of the disk and directions of it exactly to the reader.

Several methods for ensuring radial tracking track, but the most common three-beam method was most common. The laser beam is not simply headed on the surface of the disk, but is emitted by a semiconductor device and passes through a diffraction grid, which forms two additional light sources on each side of the main beam. When passing through collimator lenses, three beams become parallel, and then they pass through the prism called polarizing beam discrofer Polarized Beam Splitter). The splitter allows the passage of incoming rays, and the returnable reflected rays turn 90 degrees to the photodiode that interprets the signal.

The intensities of two side rays are measured, which should be the same while the rays remain on each side of the track. Any side displacement disk leads to a smaspania and the servo-motor corrects the lens. The vertical displacement is taken into account by the separation of the receiving photodiode by four quadrants and the placement of them in the middle between the horizontal and vertical focal points of the beam. Any disk deviation leads to the fact that the stain becomes elliptical, causing outputs between opposite pairs of quadrants. In this case, the lens moves up or down, providing a circular shape of the spot.

CD technology provides embedded error correction systems that can correct most errors caused by physical particles on the disk surface. In each CD-ROM drive and each player of sound CDs to detect errors Cross-interlacing Reda 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 the CIRC code, the encoder adds information about a two-dimensional charging to correct errors, and also moves the data on the disk data to protect against batch errors. It is possible to correct the packages of errors up to 3,500 bits (length 2.4 mm) and compensate for error packs up to 12,000 bits (length 8.5 mm) caused by small scratches.

Digital sound

On plates and tape recorder cassettes sound signal recorded as Analog signal. Therefore, all the imperfections of the record we hear as interference (hiss and whistle) or other defects. To eliminate these defects in CDs apply digital methods Storage "Samples" (SAMPLES) as numbers. Process conversion analog signal In digital called discretization (sampling), or digitizing (Digitising). Analog signal is interviewed many times per second and with each survey the amplitude is measured and rounded to the nearest representable value. Obviously, the higher sampling frequency (sampling rate) and the more accurately assigned to the amplitudes of the value ( dynamic range - (Dynamic Range), the better the presentation of the original.

For CD, the sampling frequency is used 44.1 kHz and a 16-bit dynamic range. This means obtaining 44,100 counts per second and the amplitude of the signal at the moment of each reference is described by a 16-bit number, which gives 65,536 possible values. This sampling frequency provides frequency response as sufficient for sounds with a height of 20 kHz. However, some "audiophiles" (Audiophiles) believe that this is not enough to transmit psychoacoustic effects that arise outside the perception of human hearing. The sound is recorded on two tracks to achieve stereo effect.

Uncomplicated calculations show (44 100 samples per second * 2 bytes * 2 channels) that one second sound is described by 176,400 bytes with an appropriate data rate of 176.4 kb / s. A single-speed CD-ROM drive transmits data at such a speed, but part of the data stream contains information to correct errors, which reduces the effective data transfer rate to 150 kb / s. The CD can store 74 minutes of the encoded stereo sound data, which, taking into account the service losses for detecting and correcting errors, gives the standard capacity of a 680 MB compact disk. The table contains all the considered parameters.

Rotational speed

Permanent linear speed

The first generation of single-speed CD-ROM drives relied on the design of the players of sound CDs. Technology used to rotate disk permanent linear speed (Constant Linear Velocity - CLV), i.e. The disk rotated the same as the sound CD, which ensured the transfer rate of 150 kb / s. The data track should be held under the reading head with the same speed on the inner and external parts of the disk. For this you have to change the speed of rotation of the disk depending on the position of the head. The closer to the disk center, the more faster the disk rotates to ensure a permanent data stream. The speed of rotation of the disk in the players of the sound CD is from 210 to 540 rpm.

Since there are more sectors on the external edge of the disk than in the center, the CLV technology uses a servo-motor that slows the speed of rotation of the disk when switching to external tracks to maintain a constant data transfer rate from the laser reading head. The internal buffer memory of the drive controls the speed of rotation using a quartz generator for clocking data at the buffer output at a certain speed and maintain the buffer filled by 50% when data is read into it. If the data is read too quickly, a 50% filling threshold exceeds and a command of slowing the speed of rotation of the spindle engine.

If sound CDs need to read with a constant speed, then such a requirement for CD-ROM disks is not necessarily. Essentially, the faster the data is read, the better. As CD-ROM technology improves, the speed has been constantly increased and in 1998 there appeared drives with a 32-fold data transfer rate of 4.8 MB / s.

For example, a four-speed drive that uses CLV technology must rotate the disk at a speed of about 2120 rpm when reading internal tracks and 800 rpm when reading external tracks. The variable rotation speed is also required when reading audio data, which are always read at a constant speed (150 Kb / s) regardless of the speed of transmission data. The most important factors in the drive rotation speed drives are the quality of the spindle motor rotating, and the program that controls the operation of the drive, as well as the positioning system, which should quickly and accurately move the read head to the desired position to access the data. Simple increase in speed of rotation is not enough.

Another factor is the level of using the time of the central processor: with increasing speed of rotation and, therefore, the data transfer rates increase, and the time that the processor must spend on data processing from the CD-ROM drive. If at the same time the processor time requires other tasks, the CD-ROM drive is available less data processing capabilities and the data transfer rate will decrease. A properly designed CD-ROM drive must minimize the processor use time at specified speed of rotation and data rate. It is clear that the internal performance of the fast drive should be greater than that of slow.

CD-ROM drives always provide the data buffer capacitance. Of course, a buffer with a capacity of 1 MB is definitely better buffer with a capacity of 128 KB from the point of view of data transfer rate. However, without a good drive program management program, a slight increase in productivity almost does not justify the costs of additional buffer memory.

Permanent angular speed

The CLV technology remained the dominant CD-ROM drive technology until Pioneer, who released the first four-speed drive, was not released in 1996 ten-high-speed DR-U10X drive. This drive worked not only in mode with a conventional constant linear speed, but in mode with constant angular speed (Constant Angular Velocity - CAV). In this mode, the drive transmits data from variable speed, and the spindle engine rotates at a constant speed as hDD.

Overall performance has a strong influence access time (Access Time). As the CLV-drive speed increases, the access time is often deteriorating, as it is more difficult to ensure sharp changes in the speed of rotation of the spindle motor required to maintain a constant and high data rate due to the inertia of the disc itself. The CAV-drive maintains a constant rotation speed, which increases the data transfer rate and reduces the search time when the head moves to the outer edge. If the access time in the first CLV drives was 500 ms, then in modern CAV drives it decreased to 100 ms.

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

This situation persisted before the development of a new generation digital signal processors (Digital Signal Processor - DSP), which could provide 16-fold data transfer speeds, and in the fall of 1997, Hitachi has released the first CD-ROM drive using only CAV technology (FULL CAV). It overlooked many problems of PARTIAL CAV drives, in particular, the need to control the position of the head and change the rotation speed to maintain a constant data transfer rate and maintain approximately the permanent access time. In a new drive, it was not required to expect to calm the speed of rotation of the spindle engine between transitions.

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

However, when the disc is rotated at such a high speed, there have been problems of excessive noise and vibrations often as a whistling sound caused by the release of air from the hull of the drive. Since the CD-ROM drive is clamped in the center, the strongest vibration occurs on the outer edge of the disk, i.e. Where the data rate is maximum. Since only in a small number CD-ROM, the data is stored at the outer edge, most of the high-speed drives in practice rarely ensure the theoretical maximum data transfer rate.

Applications

Soon there was a question about which applications use the advantages of high-speed CD-ROM drives. Most multimedia disks were optimized for the use of 2-speed and, at best, 4-speed drives. If the video is recorded so as to play in real time at a 300 kb / s data transmission rate, then you do not need to exceed the two-time speed. Sometimes a faster drive could quickly read the information in the buffer cache, from which it was then reproduced, freeing the drive for another work, but this reception was rarely applied.

The reading of huge images from the PHOTOCD discs is the perfect application of the high-speed CD-ROM drive, but the need to unpack images during reading from the disk requires only a 4-fold data transfer rate. Actually the only application in which high data transfer is really necessary is to copy serial data to a hard disk, i.e., in other words, installing software applications.

CD-ROM fast drives are truly fast only when transmitting sequential data, but not random access. Ideal use for high long data transfer rates is a high-quality digital video recorded with an appropriate high speed. MPEG-2 video, implemented in digital universal disks (Digital Versatile Disc - DVD) requires a transmission rate of about 580 kb / s, and the MPEG-1 standard according to the White Book for VideoCD requires the speed of only 170 kb / s. Thus, the standard CD-ROM capacity of 660 MB will be read in just 20 minutes, so high-quality video will have practical interest only on DVDs with significantly greater capacity.

Interfaces

CD-ROM drives there are three main connections: power, sound output to sound card and data interface.

Now in most CD-ROM drives, the IDE data interface is used, which theoretically can be connected to the IDE controller existing in almost every PC. The original hard disk with the IDE interface was designed to the AT bus and the old IDE interface allowed to connect two hard drive - lead (master) and slave (Slave). Subsequently, the ATAPI specification allowed one of them to become the drive IDE CD-ROM DRIVE. The EIDE interface took another step forward, adding the second IDE channel for two more devices that could be hard drives, CD-ROM drives and tape drives.

Working with one of these devices should be completed before accessing any other device. Connecting the CD-ROM drive to the same channel to which the hard disk is connected, reduce the PC performance, since the slower CD-ROM drive will block access to the hard disk. In a PC with two hard drives IDE, the CD-ROM drive must be isolate, connecting it to the secondary IDE channel, and hard drives should be connected as a lead and driven to the primary channel. Hard drives will compete with each other, but without the participation of the Slow CD-ROM drive. The disadvantage of the EIDE interface consists in limiting the number of connected devices. Four and all devices must be mounted as internal, so the possibility of expansion can be limited to the size of the PC body.

The SCSI-2 standard allows connecting to one host adapter to 12 devices that can be internal and external. 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 requires a relatively long time, so while one device uses the bus, any other device can position the heads for the production of read and write operations. The newest Fast Wide SCSI Specification supports the maximum data rate of 20 MB / s compared with the EIDE speed 13 MB / s, and due to the presence of the built-in "intelligence" SCSI devices require less attention to the processor compared to IDE devices.

The advantages of the SCSI interface compared to the IDE are also manifested when using RS resources, in particular, IRQ interrupt requests lines. Due to a large number additional cards And the devices modern RS impose increased requirements for using IRQ, leaving little space for further expansion. For the initial EIDE interface, the IRQ 14 line is usually allocated, and for secondary IRQ 15, so four devices are added due to two interrupt lines. The SCSI interface is less relevant to resources, since regardless of the number of devices on the bus requires only one IRQ line for the host adapter.

In general, the SCSI interface provides greater potential for expanding PC and provides better performance, but it is significantly more expensive than the IDE interface. Modern preference in internal EIDE drives is more convenient and cheap than technical perfection, so the SCSI interface is selected only for CD-ROM external drives.

Comparison DMA and PIO mode

Traditionally, CD-ROM drives for data transfer was used Programmable I / O (PROGRAMMABLE INPUT / OUTPUT - PIO), not direct memory access (Direct Memory Access - DMA). It was justified in the first developments, because the hardware implementation was easier and approached for devices at a low data transfer rate. The disadvantage This method is that the data transfer controls the processor. As the data transmission rate increases in the CD-ROM drives, the load on the processor has increased, and therefore 24- and 32-speed drives have fully occupied the processor in PIO mode. The load on the processor depends on several factors, in particular, from the PIO mode used, the IDE / PCI bridge circuit in a computer, capacitance, and the CD-ROM drive buffer circuit and the CD-ROM drive drivers.

Data transmission using DMA is always more efficient and takes only a few percent of the processor time. Here, a special controller manages data transfer directly to system Memory and from the processor only the initial memory allocation is required and the minimum acknowledgment (Handshaking). In this case, performance depends on the device, and not from the system. DMA devices must provide one and the same performance regardless of the system to which they are connected. DMA has long been a standard tool of most SCSI systems, but only recently it has become widely used for IDE interfaces and devices.

TrueSE technology

To allow users to execute applications directly from a CD without transmitting to a hard disk, Zen Research, when developing Truys technology, has taken an original approach to improving the performance of CD-ROM drives - to improve the data transfer rate and access time, and not just rotate the disk faster. In the usual CD-ROM, one focused laser beam is used to read a digital signal encoded by the tracks of tiny peits on the disk surface. In the method of Zen Research apply Specialized large integrated circuit (Application-Specific Integrated Circuit - ASIC) To illuminate multiple tracks, simultaneously detecting them and parallel reading from tracks. ASIC has analog interface elements, such as a digital phase adjustment of frequency (Digital Phase-Locked Loop - DPLL), digital signal processor, Servo-motor controller, parallel data converter to serial and ATAPI interface. If necessary, you can connect an external scheme of the SCSI or IEEE 1394 interface.

The split laser beam used in conjunction with the matrix of multiple rays detectors lights and detects several tracks. An ordinary laser beam is passed through a diffraction grid that splits it into seven discrete rays (such storage facilities are called multipath - MultiBeam) illuminating seven tracks. Seven rays are served through the mirror on the lens and then on 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 matrix when the central beam is on the track and focused. Reflected rays are returned by the same path and sent a mirror on the detectors matrix. The multipath detector has seven detectors leveled with reflective tracks. Conventional detectors are provided for focusing and tracking.

Despite the fact that the mechanical elements of the CD-ROM drive are somewhat changed (the rotation of the disk and the reading head movement remained the same), the disk carrier format complies with the CD or DVD standard, and a normal approach is used to search for and tracking. Truex technology can be used in CLV and CAV drives, but Zen Research is focused on CLV to ensure a constant data transfer rate for the entire disk. In any case, a higher transmission rate is achieved at a lower drive speed, which reduces the vibration and increases reliability.

Kenwood Technologies has released the first 40-high-speed TRUEX CD-ROM drive in August 1998, and in half a year he developed a 52-speed drive. Depending on the working medium and the quality of the media, the Kenwood 52x TruEx CD-ROM drive provides 6.75 - 7.8 MB / s (45x - 52x) throughout the disc. For comparison, we indicate that the usual 48-speed CD-ROM drive provides the rate of 19x on the inner tracks and reaches the speed of 48x only on the external tracks. At the same time, its rotation speed is more than twice as high as Kenwood Technologies drive.

CD-ROM standards

To deal with the CDs themselves and in which they can read them, you must first get acquainted with disk formats. Usually standards on CD are produced in the form of books with color covers and the standard itself is called the color of the cover. All CD-ROM drives are compatible with the yellow book standards (Yellow Book) and Red Book (Red Book), and also have built-in Digital Analog Converters (Digital-to-Analog Converter - DAC), which allows you to listen to the audio discs of the red book through headphones or sound output.

Red Book (Red Book)

The Red Book is the most common standard CD and describes the physical properties of the CD and digital sound encoding. It determines:

• Specification of sound for 16-bit pulse-code modulation (Pulse Code Modulation - PCM).
• Disk specification, including its physical parameters.
• Optical styles and parameters.
• Deviations and frequency of block errors.
• Modulation system and error correction.
• Control system and display.

Each music fragment recorded on the CD satisfies the standard of the Red Book. It mainly allows for the sound for 74 minutes and partitioning information on tracks (Tracks - tracks). Later, adding to the Red Book describes the CD Graphics option using subcode channels from R to W. Adding describes various applications of subcode channels, including schedule and MIDI.

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

• Disk specification, which is a copy of the red book.
• Modulation system and error correction (from a red book).
• Optical styles and parameters (from a red book).
• Management and display system (from the Red Book).
• The structure of digital data that describes the sector structure, ECC and EDC for CD-ROM disk.

CD-ROM XA

As a separate yellow book expansion, the CD-ROM XA specification contains the following:

• Disk format, including channel q and sector structure when using mode sectors 2.
• The data search structure based on ISO 9660 format, including file alternation, which is not available for data mode 2.
• Sound coding using levels in and using ADPCM modulation.
• Video coding, i.e. Fixed images.

Only such CD-ROM XA formats are used as CD-I BRIDGE formats for Photo CD VideoCD Plus Sony PlayStation System.

Green Book (Green Book)

The green book describes the CD-interactive (CD-I), the player and the operating system and contains the following:

• CD-I disk format (track and sector structure).
• The data search structure based on the ISO 9660 format.
• Sound data using levels A, B and C modulation ADPCM.
• Real-time encoding fixed video images, decoder and visual effects.
• Compact Disc Real Time Operating System (CD-RTOS).
• Basic (minimum) system specification.
• Extension for video films (MPEG cartridge and software).

CD-I can store 19 hours of sound, 7500 fixed images and 72 minutes of full-screen full-resistant video (MPEG) in standard CD format. Now CD-I discs are outdated.

Orange Book (Orange Book)

Orange book Defines CD-Recordable discs with multi-sesses (multisession) feature. Part I determines the magneto-optical rewritable CD-Mo discs (Magneto Optical); Part II defines once recorded CD-WO discs (Write Once); Part III determines the rewritable CD-RW (RWRITABLE) discs. All three parts contain the following sections:

• Disc specification for unappointed and recorded disks.
• Pre-Groove modulation.
• Data organization, including binding.
• Multi-step and hybrid discs.
• Recommendations for measuring the reflectivity, power management, etc.

White Book (White Book)

• Disk format, including the use of tracks, information Area VideoCD, segment playback area, audio / video track and CD-DA tracks.
• The data search structure satisfies the ISO 9660 format.
• MPEG Coding Audio / Video Tracks.
• Coding a playback segment element for video sequences, fixed form 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 and playback management sequences.

Up to 70 minutes of full-resistant video are encoded in the MPEG-1 standard with data compression. The white book is also called Digital Video (DV). The VideoCD disk contains one data track recorded in CD-ROM XA MODE 2 mode 2. It is always the first disk track (Track 1). On this tracks, the structure of the ISO 9660 file and applied cD-I programAs well as VideoCD Information Area, which contains general information about VideoCD disk. After the data track, the video is recorded on one or more subsequent paths during the same session. These tracks are also recorded in Mode 2 mode. Form 2. Session closes after recording all tracks.

Blue Book (Blue Book)

The Blue Book defines the specification of Enhanced Music CD for multi-session extruded disks (i.e. unlocked discs) containing sound and data sessions. Discs can be played by any player of sound CDs and on PC. The blue book contains the following:

• Disc specification and data format, including two sessions (sound and data).
• Directory Structure (ISO 9660), including directories for CD Extra, Images and data. The format of CD Plus information files is also defined, image file formats and other file codes and formats.
• MPEG fixed image data format.

CDs corresponding to the specifications of the blue book are also called CD-Extra or CD-Plus. They contain a mixture of data and sound recorded in separate sessions to prevent data tracks and possible damage to high-quality home stereo systems.

CD-I Bridge

The CD-I Bridge is the specification of the Philips and Sony companies for disks designed to play on the CD-I players and in the PC. It contains the following:

• The disk format that defines the CD-I BRIDGE disks as satisfying the CD-ROM XA specifications.
• Data Search Structure in accordance with ISO 9660. The CD-I application is required, which is stored in the CDI directory.
• Encoding audio data that includes ADPCM and MPEG.
• Coding video data for compatibility with CD-I and CD-ROM XA.
• Massion disk structure, including sectors addressing and volume space.
• Data for CD-I, since all CD-I players should read the 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:

• Total disk format, including software layout, index table, volume descriptor, data area, skew of a Q-channel subcode, CD-DA clips and a microcontroller reading sectors.
• Data search structures, including directories structure, file info.pcd and system of the sectors readable by the microcontroller.
• Encoding image data, including image encoding and image packages.
• ADPCM files for simultaneously play sound and images.

A lot of information on CD-ROM drives is contained on the site. http://www.cd-info.com/.

CD-ROM drives

Principle of operation of the CD-ROM drive

The principle of operation of the drive resembles the principle of operation of conventional drives for flexible disks. Surface optical disk (CD-ROM) moves relative to the laser head with a constant linear velocity, and the angular speed varies depending on the radial position of the head. The laser beam is directed to the track, focusing with the coil. The beam penetrates through the protective layer of plastic and falls on the reflective layer of aluminum on the surface of the disk. If it comes to the protrusion, it is reflected in the detector and passes through the prism deviating it to the photosensitive diode. If the beam falls into the fossa, it dissipates and only a small part of the radiation is reflected back and reaches a free-sensitive diode. On the diode, the light pulses are converted into electrical, bright radiation is converted into zeros of a weak one - in units. Thus, the holes are perceived by a drive as logical zeros, and a smooth surface as logical units

CD-ROM drive capacity

CD-ROM performance is usually determined by its high-speed characteristics with continuous data transmission for a certain period of time and average access to data measured in Krib / C and MS. There are single, two, three-, four-, five, six and eight-speed drives, providing data reading at a speed of 150, 300, 450, 600, 750, 900, 1200 kb / s, respectively. Currently, two- and four-speed drives are rapid. In general, the four-time drives have a higher performance, but it is not so easy to estimate the net advantage of the drive with a four-time speed compared to a double-speed drive. First of all, it depends on what operating system And with what type of application is underway. With a high intensity of recurring access to CD-ROM and reading a small amount of data (for example, when working with databases), the "pulse" information reading speed is gained importance. For example, according to InfoWorld log, the capacity of the four-time drives, compared with double-speed drives, in the case of an operation of access to the database, on average, halved. In case of simply copying data, the winnings ranges from 10 to 30%. However, the greatest advantage will be done when working with full-length video.
To increase the productivity of the drives, they are equipped with buffer memory (standard cache volumes: 64, 128, 256, 512, 1024 KB). Drive buffer is a memory for short-term data storageAfter reading them from CD-ROM, but before shipment in the controller fee, and then in the CPU. Such buffering makes it possible to transmit data to the processor in small portions, and not to take it time to slowly shipping a constant data stream. For example, according to the requirements of the MPC level 2, the CD-ROM drive double speed should occupy no more than 60% of the CPU resources.
An important characteristic of the drive is the degree of buffer filling, which affects the quality of the playback of animation images and video. This value is defined as the ratio of the number of data blocks transmitted to the buffer from the drive and stored in it until the beginning of their issuance on system bus, To the total number of blocks that can accommodate the buffer. Too much filling can lead to delays when issuing from buffer on a tire; With an arc side, a buffer with a too low degree of filling will require more attention from the processor. Both of these situations lead to jumps and breakdown images during playback.

Design features of CD-ROM drives

As you know, most drives are external and embedded (internal). CD drives in this sense are no exception. Most CD-ROM drives offered are embedded. External storage It is more expensive worth it. This is easily explained, since in this case the drive has its own body and power supply. The form factor of the modern CD-ROM drive is determined by two parameters: half height (Half-High, HH) and a horizontal size of 5.25 inches.
On the front panel of each drive, there is access to the CD loading mechanism. One of the most common is the CD-ROM loading mechanism using Caddy. Caddy is a plastic transparent container in which a CD is contained before loading directly into the drive. Another way is to load using the Tray mechanism. The tray mechanism is really similar to the tray, which is extended from the drive usually after pressing the EJECT button. A CD is installed on it, after which the "tray" in the drive is moved to the manual. There are varieties of the tray mechanism, such as POP-UP. In this case, the loading of the disk on the "tray" occurs semi-automatic, after easily touch.
On the front of the drive panel, in addition, there are: Device Indicator (BUSY), a jack for connecting headphones or stereo systems (for listening to audio discs), sound volume control (also for audioCD). For the CADDY system, a hole is also provided, with which you can remove the CD even in an emergency, for example, if the EJECT button does not even work.

CD-ROM Device and Technology
CD-ROM device

All CD-ROM have the same physical manufacturing format and capacity of 650 MB. Disk with a diameter of 120 mm, thickness of 1.2 mm and central hole diameter 15 mm. The central region around the opening of a width of 6 mm is called the mounting area (Clamping Area). It immediately follows the header area (LEAD in Area) containing the table of contents of the disk (Table of Content). Next is the area of \u200b\u200b33 mm wide, intended for storing data and physically representing a single track. The final is the terminal area (LEAD OUT) 1 mm width. External rim disk 3 mm wide.
The storage area logically contains from 1 to 99 tracks, but heterogeneous information cannot be mixed on one track. Digital information is stored on the CD-ROM in the form of a spiral alternating spiral, applied to the surface of the poly carbon plastic. A hole is perceived by a laser beam as a logical zero, and a smooth surface as a logical unit.
CD-ROM is manufactured by stamping. A plastic base is made from a glass matrix, after that, the layer of aluminum is applied on top of the plastic for reflection of the laser beam, which in turn is covered with a protective layer of varnish. In CD-R, to increase the reflection of the laser beam on the plastic, a layer of gold is applied, which is covered with dye, then a protective layer of varnish is applied to the dye.
Unlike CD-R, the record of information on the CD-ROM is performed at the time of its production. Stamping. On CD-R information is recorded using a CD of the Recorder. The laser beam burns on the "plate" hole of the bell-shaped form, which gives an advantage over the usual CD-ROM, since in such a hole the laser beam is stronger and the smaller portion of radiation falls into the receiver. However, after recording information on CD-R, it actually becomes an ordinary compact disc.

Connecting CD-ROM drives
Digital interfaces

Currently, the most common is SCSI and IDE interfaces. In addition to these interfaces, there are a lot of other standards of specific manufacturers such as Sony, Panasonic, Mitsumi, Matsushita, but their role is quite small. In turn, both SCSI and IDE interface have improved versions. For SCSI, it is SCSI-2 and FAST SCSI-2, for IDE - EIDE interface. The latter supports two parallel channels and according to the characteristics occupies an intermediate place between SCSI and IDE. The SCSI interface compared to the IDE in principle is more rapid on the potential metabolic rate with a disk, but it really does not advantage, since even CD-ROM drives with four-time speed cannot transmit data faster than 700 KB / s. Nevertheless, if we consider that the overall computing brand gradually shifts towards the multisaded environment, when both the hard disk is needed at the same time as a CD-ROM device, the use of the SCSI interface may be more preferable.

Connecting CD-ROM drives

To date, there are several ways to connect CD-ROM drives. The first method is based on the fact that one IDE interface channel can support two built-in devices. The CD-ROM drive is connected to the I / O board through the IDE interface along with a hard disk on the Master / Slave principle. However, in this case, the rate of data exchange with a hard disk is reduced. One way to solve this problem is to connect the CD-ROM devices to various channels of one EIDE interface or to two different IDE kitrollars. If the CD-ROM has a SCSI interface, then it is connected to the SCSI controller accordingly. Another approach is the use of 32-bit drivers of CD-ROM drivers instead of the 16-bit currently used. There is also the ability to connect CD-ROM drives through a sound card controller. Also, we should not forget that modern motherboards There may be built-in SCSI and IDE controllers, which generally eliminates the need for an additional I / O board to connect CD-ROM drives.

Connect audio channels

Almost every CD-ROM drive has a built-in digital-analog converter (DAC), as well as the output connector for the output of stereo signals. On the external panel of CD-ROM drives (both external and internal), moreover, have a connector for headphones (headphones). If there is an audio information on the CD, the DAC converts it to an analog form and gives a signal to the connector for headphones, as well as on the output audio connectors of the drive, from which in turn, the signal comes to the amplifier and the acoustic system directly or Through a sound card. The advantage of active output is that the audio signal from the CD-ROM is additionally processed by a sound card.
One of the main encountered when working with audio signals is the physical incompatibility of audio connectors for the embedded CD-ROM drive and a sound card. As a rule, the drive, and the sound card have audio connectors with four outputs (two stereo channels and one grounding contact for each of them). Contacts are usually equally equally on both types of devices, however, the problem is that these connectors may have various sizes. Another trouble is associated with the fact that if the DAC is constructively located inside the drive itself, it can be negatively affected by sound playback. In turn, the physical separation of the CD-ROM drive and the DAC with which it works, avoids additional noise.

CD standards

All standards on CDs are more famous for the colors of the libraries in which they are described. In 1980, a series of standards called Red Book related to audio compact disks was adopted. According to this document, the discretization frequency when reading audio signals from the CD-ROM disk should be 44.1 kHz. The amplitude resolution is represented by a 16-bit value. Since the standard defines stereo sound, then not one, and two 16-bit values \u200b\u200bshould be read every second.
The first standard called Yellow Book for CDs with heterogeneous information was adopted in 1985. It was one of the first steps of the computer industry towards the multimedia technology. According to this standard, all discs were divided into two categories: MODE1 and MODE2. The carriers belonging to the first category were recorded with bits of error correction, and the transfer rate useful information At the same time, 150 KB / s. For disks of the second group, it was higher 170 KB / s due to the absence of correction bits.
Mode2 mode in its original form was never implemented. Audio and video information was stored in different parts of the disk, as a result of which the laser beam was forced to constantly "run" from one area of \u200b\u200bthe disk to another. Although the standard identified the error correction process used when reading data from the CD-ROM, it at the same time did not give a sufficient specification relative to the structure of the stored file, which the ISO 9660 standard released in 1988 was more clearly defined.
The Green Book standard adopted in 1986 is dedicated to interactive CD-I CD (CD-interactive). It contains the concept of headers to simplify work with permanently intersecting video and audio information. In the Green Book standard, the idea of \u200b\u200bconstructing MODE2 was formally recycled. The CDs of the MODE2 group were divided into two subgroups: Form1 and Form2. The first, as in the case of the category MODE1 of the Yellow Book standard, determined the error correction process due to additional bits and the speed of information transmission 150 KB / s. The second subgroup allowed to have a read speed of 170 KB / s due to the absence of error correction codes.
Standard XA (Extended Architecture) was developed in 1990 by Philips, Sony and Microsoft and installed the compatibility criteria between CD-ROM CDs, satisfying the Green Book and Yellow Book standards. It defines the method of indexing multimedia-information - graphs, text, raster pictures, sound. The disk that meets the standard XA can be reproduced on an interactive reader cD-I disksCompatible with the Green Book standard, or using a CD-ROM drive, which satisfies the Yellow Book standard, supports the horses and controls the Special Software Driver.
Finally, in 1991, the Orange Book standard appeared dedicated to the CDs with the possibility of repeated recording.

Dynamic Images and WHITE Book Standard

An expert group on standardization (MOVING PICTURE EXPERT GROUP), developed the MPEG-1 standard regarding the compression issues of full-format video (Full-Motion Video). It should be noted that this standard does not define the data storage format. Data in it can be played on the CD-I interactive disc reader, which is equipped with a MPEG-decoder. Another option is to store the full-length video compressed according to the MPEG standard on the CD-ROM device that meets the Yellow Book standard.
The WHITE Book standard has entered some interactive features that allow you to quickly find information on individual frames in direct access mode. The first discs with the WHITE Book standard and called Video-CD appeared in 1994. Currently, some CDs of the VIDEO-CD type can be played on IBM PC and Macintosh computers by unpacking according to MPEG standard, if you install a board, hardware MPEG transforms. However, many CD-ROM patterns do not read the information in continuous mode, which does not allow you to play these discs even after installing the MPEG cards. In addition, the processor should be not lower than 386/25.
All CDs for modern multimedia systems, including interactive compact cD-I discs and VIDEO-CD are recorded in the MODE2 / Form2 standard, i.e. without using correction. The emerging at the same time in the speed of 20 KB / s is used to improve the quality of the video image. In this class of applications, the lack of error correction is not reflected on the quality, which cannot be said about business applications.

PHOTO CD discs and multi-seated

One of the types of CD-ROM with the ability to duplicate information are the so-called Photo CD. A one-time record of information on the disk is called session (Session). Accordingly, the multi-recording is called Multisession. It must be borne in mind that each session requires its table of contents, so the larger number of sessions is used, the less information on the disk. Currently, there are already drives processing multi-session and allowing playing PHOTO CD to play.
The company Kodak has developed devices like Photo CD, allowing to store pictures made on a 35-millimeter film inside up to 100 frames. The idea is that the consumer can scan the pictures obtained using Kodak equipment, and subsequently play on any drive. Really on the disk can store five different versions of the same slide with different resolution of the 24-bit palette.
Using compression (without loss of permissive ability), these five images can be packed in a file of 6 MB. Thus, up to 100 photographs can be stored on a capacity of 600 MB on a CD.
Fast drives are recommended for working with Photo CD, because individual frames can reach the size of up to 18 MB.

Future CD-ROM drives and CD discs

Currently, the CD-ROM capacity is not enough for the multimedia of the native generation products. To increase the CD-ROM capacitance capable of storing a larger amount of data packed according to the MPEG-2 standard, higher read speeds are necessary. Now the new CD-ROM format (HD-CD or High Density CD) is capable of providing a fivefold increase in the volume of CDs without any particular technical tricks. At the same time, the requirements for physical marking of the disk are tougher, namely, the distance between adjacent tracks and the size of the hole is reduced. The wavelength of the reading beam decreases from 780 nm to 635 nm, but the possibility of using all the same cheap lasers working in the Red Spectrum region remains. The data structure also becomes more efficient due to the more advanced logical error correction system, which increases the disk information capacity by 10-15%. The combination of these innovations will allow the volume of information recorded up to 3.7 GB.
The HD-CD technology also introduces the concept of variable speed of reading information from the CD. Instead of entering any short video record, leaving a lot of free space on it, you can record data with less density. This provides for the possibility of dynamic regulation of this process. For example, the record density can be changed for various bit sequences in case of varying complexity of information coding.
According to experts, the process of producing HD-CDs will differ little from the production of ordinary CDs, with the exception of much more complex tolerances. The greatest difficulty is likely to represent the manufacture of high density CD matrix. HD-CD drives will appear this year.
Currently, work is underway on a multi-level CD-ROM. The essence of this technology is the presence of two layers containing recorded data and are one over the other. The laser beam can focus both on the lower and on the top layer. The first version of such systems issued by 3M, accommodates up to 7.8 GB of information at a two-layer recording, although there are no provimes that prevent further increase in the number of layers.
In turn, the main idea of \u200b\u200bfurther increase in the speed of the CD-ROM drives is associated with the use of two laser rays. This can make data the device is much more expensive, so some manufacturers consider it appropriate to improve the CD-ROM drive production technology and the release in the near future relative to cheap models with an 8-fold speed when using one read beam. The presence of high-density discs in combination of existing drives with four-, six- and eight-round speed makes it possible to embed multimedia data to any applications.

Bibliography

1. COMPUNITY N1 (2) 1995
2. Hard and Soft N5, May 1995
3. PC Magazine Russian Edition N6 1994

Probably, some more time ago, such a device, like external drives, it would be a lot of pushing the computer. After all, it is often the fact of the very presence of a CD disk drive inside the PC body automatically made this device "elite": not everyone could afford it.

However, time did not stand in place. Pretty soon drives for laser disks We became commonplace. And then appeared on the scene and external drives.

Exterior drive - what it is

Probably, without any definitions, many are clear that the external drive is a compact device designed to work (read and write) from all kinds of discs that connects to a computer through one of its ports.

The external device is called precisely because it is not inside the system unit, but outside. That is, an external drive can be simply taken and disconnect at any time, connect to another computer or disk drive, pick up on the road or somewhere else.

When the external drive may need

There is a lot of situations when such a drive may be needed, or even at all - without it can not do.

For example, for a netbook. In favor of compactness, netbook manufacturers did not put the drive for laser disks into the case. So the user has lost opportunities to work with such disks. And it would be quite bad if it were not for an external CD drive. It just connects to the device via USB port - and you can start working with laser disks. Therefore, the external drives are most often purchased in a pair with a netbook.

The external drive may also be needed in the event that the main drive on the device has failed. Or if you need to quickly rewrite information from one laser disk to another without pre-transferring data to the hard disk (many at the same time will certainly recall the common two-channel once).

In a word, all sorts of situations, when an external drive for a computer may need, simply not to count.

What are external drives

External drives can be classified differently: depending on the connection port, from the possibility or inability to record, by the method of nutrition, by type of readable discs and on other features.

However, most often external drives are divided into:

• CD drives - those that can read and record only CD-blanks (they are currently practically not found);
• DVD drives - the most common type of disc drives, which "sees" both CD and DVD;
• Blu-ray - respectively, other than CD and DVD, such devices can work with Blu-Ray disks;
• writing and not writing - those that can not only read, but also write information to the disk, or only read (the latter are also practically not used today);
• signable via USB and through an external power supply.

Are there any models for laptops or only for desktop PCs? No, there are no such. External drives are universal, they are equally successfully working on netbooks, and on laptops, and in a pair

Pluses of external drives

Of course, the external drive has several advantages as independent deviceand in front of its built-in "colleague."

• External devices for working with discs can be simply disabled from the computer at any time and, for example, to give a friend. In order to make such a trick with a built-in drive, you will need to disassemble system unit or laptop housing.
• The external drive will help if the main drive broke on the device.
• It will help to work with disks even on those devices where such drives are simply not designable. For example, recently appeared disks external for tablets.
• External drives are compact and easy to connect, it is easy to replace them.

Cons external drives

But, as always, it was not without minus:

• Speed \u200b\u200bis the main weak place of any external drive. No matter how cool, and the USB port is still slower than internal system ports.
• Often an external drive for a laptop requires individual power supply. Moreover, it can be carried out both through USB and through a conventional outlet. The poor-quality food blocks are quickly burning, find the other exactly the same is practically not possible - it is easier to simply buy another drive.
• External drive is more expensive than its built-in fellow.

How to connect external drive

Fortunately, there is nothing complicated in how to connect an external drive. Usually, everything that is required is to insert the USB cord into the appropriate connector on the computer, and the power supply plug is in the outlet.

If necessary, you can still install additional software and drivers. But often it can not be done - the system simply recognizes the device as a new drive and it works well with it using regular means.

How to choose a removable drive

When choosing an external drive, you need to take into account the following points:

• If the computer has a USB port 2.0, then you need to acquire such a drive. The reading and recording process will go much cheerful.
• If there is an opportunity, then you need to prefer a power model from both USB and outlet. If the power supply unit is burning, the device can be fed directly from the computer. In addition, such external drives will allow working in offline mode. For example, on the road with a netbook.
• If possible, the drive must read the majority of common disk formats and record them. In the please of universality, you can neglect other secondary functions, which most often use only a couple of times for all the time and then only from curiosity.
• The appearance of the drive also has a certain role. The beautiful device stylishly looks on the table and will attract a lot of curious looks.
• As for speed, there is no need to purchase the highest-speed. Standard 52 speeds are enough "for the eyes" for all occasions. Especially since the record at high speeds is incorrectly incorrect. Yes, and the motor motor itself can quickly fail if it is abused too often work on increased revs.

Regarding the manufacturer - there are no unequivocal recommendations. In principle, all companies today produce well-free external drives. Each company has both successful and not too models. But frankly bad today will not meet.