When in the early 80s of the last century, Sony and Philips released sound CDs(Compact Disc - CD), no one could have imagined what a valuable information carrier they would become in the near future. The durability, random access capabilities, and high sound quality of CDs have attracted widespread attention and widespread adoption. 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 CD-ROMs large capacity. 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 an important role in the following aspects of a computing system:

• Support software : The 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 disk.

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 the traditional manufacturing process, 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 to ensure that the laser beam was focused on the surface of the disk and directed precisely at 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 just directed at the surface of the disk, but is emitted semiconductor device and passes through a diffraction grating, which forms 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 ways storing “samples” as numbers. The process of converting an analog signal to a digital one is 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 bit rates is high-quality digital video recorded at a correspondingly high bit rate. 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 to the sound card, and a 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 old interface IDE 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. On a PC with two IDE hard 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. The latest Fast Wide SCSI specification 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 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.

In general, the SCSI interface provides greater PC expansion potential and provides better performance, but it is significantly more expensive than the IDE interface. The modern preference for internal EIDE drives is more convenient and cheaper than technical excellence, so the SCSI interface is chosen only for external CD-ROM drives.

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. Processor load depends on several factors, including the PIO mode used, the IDE/PCI bridge design in the computer, the capacity and design of the CD-ROM drive buffer, and the 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 a digital signal encoded by tracks of tiny pits on the surface of the disc. 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, which reduces vibration and improves 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 operating 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 drive. 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

Orange Book defines CD-R discs ecordable 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 conforming to ISO 9660 format.
• 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). The structure is recorded on this track ISO file 9660 and applied CD-I program, as well as the VideoCD Information Area, which contains general information about the VideoCD disc. 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 after 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. The CD-I application program is required and 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 does a CD-ROM drive work?

The operating principle of a CD-ROM drive is similar to that of conventional floppy disk drives. Surface optical disk(CD-ROM) moves relative to the laser head with a constant linear speed, and the angular speed varies depending on the radial position of the head. The laser beam is directed onto the track and focused using a coil. The beam penetrates the protective layer of plastic and hits the reflective layer of aluminum on the surface of the disk. When the beam hits the protrusion, it is reflected onto the detector and passes through a prism, which deflects it onto a photosensitive diode. If the beam hits the pit, it is scattered, and only a small part of the radiation is reflected back and reaches the photosensitive diode. On the diode, light pulses are converted into electrical ones: bright radiation is converted into zeros, weak radiation into ones. Thus, pits are perceived by the drive as logical zeros, and a smooth surface as logical ones.

CD-ROM drive performance

The performance of a CD-ROM is usually determined by its speed characteristics during continuous data transfer over a certain period of time and the average data access time, measured in KB/s and ms, respectively. There are one-, two-, three-, four-, five-, six - and eight-speed drives that provide data reading at speeds of 150, 300, 450, 600, 750, 900, 1200 Kb/s, respectively. Currently, two- and four-speed drives are common. In general, 4x speed drives have more high performance, but assessing the net benefit of a 4x-speed drive over a 2x-speed drive can be tricky. First of all, it depends on what operating system and what type of application you are working with. At high intensity repeated access to a CD-ROM and reading a small amount of data (when working with databases), the “pulse” speed of reading information becomes great importance. For example, according to InfoWorld magazine, 4x-speed drives (compared to 2x-speed drives) perform on average twice as fast during database access. In the case of simple data copying, the gain ranges from 10 to 30%. However, the greatest benefit is obtained when working with full-length video.

To increase the performance of disk drives, they are equipped with buffer memory (standard cache sizes: 64, 128, 256, 512, 1024 KB). The drive buffer is a memory for short-term storage of data after it is read from the CD-ROM, but before it is sent to the controller board and then to the CPU. This buffering allows the disk device to transfer data to the processor in small chunks, rather than taking up its time by slowly sending a constant stream of data. For example, the MPC Level 2 standard requires that a 2x speed CD-ROM drive consume no more than 60% of the CPU resources.

Important characteristic drive is the level of buffer fill, which affects the quality of playback of animated images and videos. This value is defined as the ratio of the number of data blocks transferred to the buffer from the drive and stored in it until the start of their output to the system bus, to the total number of blocks that the buffer is capable of holding. Too much fill may cause delays in output from the buffer to the bus; On the other hand, a buffer that is too low will require more attention from the processor. Both of these situations lead to jumps and stuttering during playback.

Design features CD-ROM drives

As you know, most drives are external and built-in (internal). CD drives are no exception in this sense. Most CD-ROM drives currently offered are built-in. External storage costs noticeably more. This is easy to explain, since in this case the drive has its own housing and power supply. The form factor of a modern embedded CD-ROM drive is determined by two parameters: half-height (HH) and a horizontal size of 5.25 inches.

The front panel of each drive provides access to the CD loading mechanism. One of the most common is the CD-ROM loading mechanism using a caddy. The caddy is a clear plastic container into which the disc is placed before loading directly into the drive. Another way is to load using a tray mechanism. The tray mechanism is similar to a tray that moves out of the drive after pressing the “Eject“ button. A disk is installed on it, after which the “tray” is pushed into the drive manually. There are varieties of tray mechanism, for example pop-up. In this case, loading the disc on the “tray” occurs semi-automatically, after lightly touching it.

In addition, on the front panel of the drive there are:

device operation indicator (busy);

jack for connecting headphones or a stereo system (for listening to audio CD);

sound volume control (for audio CD).

The caddy system also has a hole that allows you to remove a CD even in emergency situation, for example, if the “Eject” button does not work.

Device and technology of CD-ROM production

All CD-ROMs have the same physical manufacturing format and a capacity of 650 MB. Disc with a diameter of 120 mm, a thickness of 1.2 mm and a central hole with a diameter of 15 mm. The central area around the 6mm wide hole is called the clamping area. It is immediately followed by a lead in area containing the table of contents of the disc. Next is a 33 mm wide area intended for data storage and physically representing a single track. The final area is the lead out area, 1 mm wide. The outer rim of the disc is 3 mm wide.

The data storage area can logically contain from 1 to 99 tracks, but disparate information cannot be mixed on one track. Digital information is stored on a CD-ROM in the form of pits alternating along the spiral, deposited on the surface of polycarbon plastic. The pit is perceived by the laser beam as a logical zero, and the smooth surface as a logical one.

CD-ROM is produced by stamping. A plastic base is made from a glass matrix, after which a layer of aluminum is applied on top of the plastic to reflect the laser beam, which is covered with a protective layer of varnish. In CD-R, to increase the reflectivity of the laser beam, a layer of gold is applied to the plastic, which is coated with a dye, then a protective layer of varnish is applied to the dye.

Information is recorded on a CD-ROM at the time of its manufacture, i.e. stamping. Information is recorded on a CD-R using a CD recorder. The laser beam burns a bell-shaped hole on the “plate”, which gives an advantage over a conventional CD-ROM, since in such a hole the laser beam is scattered more strongly and less of the radiation hits the receiver. However, after recording information on a CD-R, it becomes a regular CD.

Connecting CD-ROM drives. Digital interfaces

Currently, the most common are SCSI and IDE interfaces. In addition to these interfaces, there are a lot of other standards from specific manufacturers, such as Sony, Panasonic, Mitsumi, Matsushita, but their role is very small. SCSI and IDE interfaces have improved versions. For SCSI these are SCSI-2 and Fast SCSI-2, for IDE - the EIDE interface. The latter supports two parallel channels and, in terms of characteristics, occupies an intermediate position between SCSI and IDE. The SCSI interface is faster in terms of the potential speed of data exchange with the disk, but in reality this does not provide an advantage, since even CD-ROM drives with four times the speed cannot transmit data faster than 700 KB/s. However, given that the general concept of computing is gradually shifting towards a multitasking environment, when access to both the hard disk and a CD-ROM device is required simultaneously, the use of the SCSI interface may be more preferable in the future.

Connecting CD-ROM drives

Today, 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 embedded devices. The CD-ROM drive is connected to the I/O board via the IDE interface along with the hard drive according to the master/slave principle. However, in this case, the speed of data exchange with the hard drive is reduced. One way to solve this problem is to connect CD-ROM devices to different channels of the same EIDE interface or to two different IDE controllers. If the CD-ROM has a SCSI interface, then it is connected to the SCSI controller accordingly. Another approach is to use 32-bit CD-ROM drive drivers instead of the currently used 16-bit ones. It is also possible to connect CD-ROM drives via the sound card controller. It should also not be forgotten that modern motherboards can contain built-in SCSI and IDE controllers, which eliminates the need for additional fee I/O for connecting CD-ROM drives.

Connecting audio channels

Almost every CD-ROM drive has a built-in digital-to-analog converter (DAC), as well as an output jack for outputting stereo signals. In addition, CD-ROM drives (both external and internal) have a headphone jack on the outer panel. If there is audio information on the CD, the DAC converts it into analog form and supplies the signal to the headphone jack, as well as to the audio output jacks of the drive, from which the signal goes to the amplifier and sound system directly or through a sound card. The advantage of the active output is that the audio signal from the CD-ROM is additionally processed by the sound card.

One of the main problems encountered when working with audio signals is the physical incompatibility of audio connectors for the built-in CD-ROM drive and sound card. Typically, both the drive and sound card have four-pin audio jacks (two stereo channels and one ground pin for each). The pin assignments are the same on both types of devices, the problem, however, is that these connectors can have different sizes. Another trouble is that if the DAC is structurally located inside the drive itself, this can negatively affect the quality of sound reproduction. By physically separating the CD-ROM drive from the DAC it works with, additional noise is avoided.

Standards on CD

All CD standards are better known by the colors of the libraries in which they are described. In 1980, a series of Red Book standards related to audio CDs were adopted. According to this document, the sampling frequency when reading audio signals from a CD-ROM disk should be equal to 44.1 KHz. Amplitude resolution is represented as a 16-bit value. Since the standard defines stereo sound, not one, but two 16-bit values ​​must be read every second.

The first standard, called the Yellow Book for CDs with heterogeneous information, was adopted in 1985. This was one of the computer industry's first steps towards multimedia technology. According to this standard, all disks were divided into two categories: Mode1 and Mode2. Media belonging to the first category were recorded with error correction bits, and the transmission speed useful information was 150 KB/s. For disks of the second group it was higher than 170 KB/s due to the absence of correction bits.

Mode2 was never implemented in its original form. Audio and video information was stored in different parts disk, as a result of which the laser beam was forced to constantly “run” from one area of ​​the disk to another. Although the standard defined the error correction process used when reading data from a CD-ROM, it did not provide sufficient specification regarding the structure of the stored file, which was more clearly defined by the 1988 ISO 9660 standard.

The Green Book standard, adopted in 1986, is dedicated to CD-i (CD-interactive). It introduced the concept of titles to simplify work with constantly interspersed video and audio information. In the Green Book standard, the idea of ​​constructing Mode2 was formally reworked. Mode2 disks were divided into two subgroups: Form1 and Form2. The first, as in the case of the Mode1 category of the Yellow Book standard, determined the error correction process due to additional bits and had an information transfer rate of 150 KB/s. The second subgroup allowed a reading speed of 170 KB/s due to the absence of error correction codes.

The XA (Extended architecture) standard was developed in 1990 jointly by Philips, Sony and Microsoft and established compatibility criteria between CD-ROMs that meet the Green Book and Yellow Book standards. It defines the way multimedia information is indexed: graphics, text, raster images, sound. An XA-compliant disc can be played on a Green Book-compliant interactive CD-i disc reader or a Yellow Book-compliant CD-ROM drive that supports XA operations and runs a dedicated driver software.

Finally, in 1991, the Orange Book standard appeared, dedicated to rewritable CDs.

Dynamic images and White Book standard

The Expert Group on Standardization (MPEG - Moving Picture Expert Group) has developed the MPEG-1 standard, which deals with issues of compression of full-motion video (Full-Motion Video). It should be noted that this standard does not define a data storage format. The data in it can be played back on an interactive CD-i disc reader that is equipped with an MPEG decoder. Another option is to store MPEG-compressed full-length video on a Yellow Book CD-ROM device.

The White Book standard, adopted in 1993, introduced some interactive capabilities that allow quick search information on individual frames in direct access mode. The first White Book discs, called Video-CDs, appeared in 1994. Currently, some discs of this type can be played on IBM PCs and Macintosh computers through MPEG decompression if you install a card that performs MPEG conversions in hardware. However, many CD-ROM drives do not read information continuously, which prevents playback of these discs even after installing an MPEG card.

All CDs for modern systems multimedia, including CD-i and Video-CD, are recorded in the Mode2/Form2 standard, i.e. without using correction. The resulting gain in 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 does not affect quality.

Photo-CDs and multisessions

One type of CD-ROM with the ability to add additional information is the so-called Photo-CD. A one-time recording of information to disk is called a session. Recording multiple times is called a multisession. It is necessary to take into account that each session requires its own table of contents, so what large quantity sessions are used, the less information is on the disk. Currently, there are already disk drives that process multisessions and allow you to play Photo-CDs.

Kodak has developed Photo-CD devices that allow you to store up to 100 frames of photographs taken on 35mm film. The idea is that the consumer can scan pictures taken using Kodak equipment and then play them back on any disk drive. In reality, a disk can store five different versions the same slide different resolutions 24-bit palette.

Using compression (without loss of resolution), these five images can be packed into a 6 MB file. Thus, up to 100 photographs can be stored on a 600 MB CD.

The future of CD-ROM and CD drives

Currently, CD-ROM capacity is insufficient for next-generation multimedia products. To increase the capacity of a CD-ROM capable of storing more data packaged according to the MPEG-2 standard, more high speeds reading. The new CD-ROM format currently being developed (HD-CD or High Density CD) is capable of providing a fivefold increase in CD capacity without any special technical tricks. At the same time, the requirements for the physical marking of the disk are becoming more stringent, i.e., the distance between adjacent tracks and the size of the pits are decreasing. The wavelength of the reading beam decreases from 780 nm to 635 nm, but the possibility of using the same cheap lasers operating in the red region of the spectrum remains. The data structure becomes more efficient due to a more advanced logical error correction system, which increases the information capacity of the disk by 10 - 15%. The combination of these innovations will increase the volume of recorded information to 3.7 GB.

HD-CD technology also introduces the concept of variable speed of reading information from a CD. Instead of putting some short video recording on the disk, leaving a lot of free space, it will be possible to record data at a lower density. At the same time, the possibility of dynamic regulation of this process is provided. The recording density, for example, can be changed for different bit sequences in case of varying complexity of information encoding.

According to experts, the HD-CD production process will differ little from the production of conventional CDs, with the exception of much more complex tolerances. The greatest difficulty will probably be the production of the CD matrix high density.

Currently, work is underway on a multi-surface CD-ROM. The essence of this technology is the presence of two layers containing recorded data and located one above the other. The laser beam can be focused on both the bottom and top layers. The first version of such systems, released by 3M, holds up to 7.8 GB of information with two-layer recording, although there are no obstacles preventing a further increase in the number of layers.

Information is written on a CD-ROM disc using an industrial method and cannot be written again. The most widely used are 5-inch CD-ROM drives with a capacity of 670 MB. Their characteristics are completely identical to regular music CDs. Data on the disk is written in the form of a spiral (unlike a hard drive, on which the data is arranged in the form of concentric circles). From a physics point of view, the laser beam determines the digital sequence of ones and zeros recorded on a CD by the shape of microscopic pits (pits) on its spiral. The principle of reading information from an optical disk can be roughly divided into four stages.

1. A weak laser beam is emitted from the laser diode of the CD-ROM drive. Passing through a system of lenses, it focuses on areas of the data spiral of the CD, moving along trajectories set by a servo. The servo drive is used to move the guide lens.

2. The beam makes a reading by reflecting with different intensities from the pit layer of the CD.

3. The reflected beam returns, falling into a group of prisms. There it is refracted and reflected on a photodetector.

4. The photodetector determines the intensity of the light flux and forwards this information to the microprocessor of the disk drive, which completes its analysis, converting it into a digital sequence.

The basis of the CD with a diameter of 12 cm and a thickness of 1.2 mm is made up of a layer of optically pure polycarbonate plastic - this is the back layer. A thin layer of aluminum is applied to it, giving the disk the necessary reflective properties. It is protected from oxidation and mechanical damage by varnishing. The disc label is printed on top of the varnish layer.

The main characteristic of a CD-ROM drive is the data reading speed, which can be increased only in one way - by increasing the disk rotation speed. Since CD-ROM initially adopted a constant linear reading speed (Constant Linear Velocity - CLV), the disk rotation speed is a variable value, inversely proportional to the distance from the read head to the center. For the first generation of devices with a read speed of 150 Kb/s (single-speed, or 1X), it ranges from 200 rpm for the outer part of the disk track to 530 rpm for the inner one. In the next generations, rotation frequencies, and with them the reading speed, simply increased by an integer number of times (two-speed - 2X, four-speed - 4X, etc.).

This went on for quite a long time, until the speed of high-end models reached 12X (1800 Kb/s), and mass ones - 8X (1200 Kb/s). For 12-speed models, the speed range is from 2400 to 6360 rpm. It is clear that 6360 rpm is a very high speed for removable media, which is technically difficult to maintain. It is even more difficult to quickly spin up the disk to this speed if the head jumps, for example, from the outer part of the disk to the inner part to read the next piece of information. The unwinding time overlaps with the moving time and should be minimal for quick access. The difficulty increases manifold when trying to increase the speed even further, so 12 times the speed is the limit for CLV mode.

A further increase in reading speed is possible only by abandoning the CLV mode, therefore, in subsequent models of CD-ROM drives, all leading manufacturers, instead of “pure” CLV, began to use to one degree or another the Constant Angular Velocity (CAV) mode, in which the rotation speed is constant (and close to the maximum possible), and the read speed is proportional to the radius. The CAV mode is used either for the entire surface of the disk, or is combined with CLV. The combined mode, when CAV is used for the central part of the disk and CLV for the peripheral part, is called CAV| CLV, Partial CAV or P-CAV.

New models of CD-ROM drives are positioned according to the maximum reading speed as 32-50 speed, which, however, does not give an adequate idea of ​​real performance.

As for the arrangement of information on the disk, it should be taken into account that, firstly, the filling of the disk starts from the center, and, secondly, most disks are not completely filled (on average, only half). That is, the reading speed on the internal part of the disk is decisive for overall performance. For example, the popular CD-TACH test, when assessing speed, takes into account the internal part (0-215 MB) of the disk with a weighting factor of 60%, the middle (1215-430 MB) - 30%, and the external (430-615 MB) - 10%.

High-end CD-ROM drives have a read speed for the internal part of the disk of 12X, mass models - 8-10X. The reading speed of the external part reaches 50X in some models.

The transition from CLV mode to P-CAV and CAV modes did not require special costs from manufacturers, since the maximum speed did not increase and the mechanical part, including the engine, did not undergo significant changes. Therefore, prices for new devices, despite significantly improved parameters, remained at the same, very low level.

And buy better devices with speeds starting from 24x. Despite the slight increase in actual performance, only they support the MultiRead standard, which makes it possible to read rewritable CD-RW discs.

The 24-speed CD-ROMs that appeared on the market in 1997 operated using full CAV technology at a disk rotation speed of 5000 rpm, and their data read speed ranged from 1.8 to 3.6 MB/s. At 50 times the speed of the newest drives, the rotation speed reaches 12 thousand rpm, which is not yet used even in the most modern hard drives. The data flow is 7.2 Mb/s.

However, the noise emitted by the drive at such speeds does not stand up to criticism. It got to the point that some users began to choose 24-32x drives. Maybe a little slower, but quiet. In addition, special programs have appeared that allow you to limit the speed of any drive to no more than the desired one.

CD-ROM drives can have different interfaces. The vast majority connect to the regular IDE output on the motherboard.

Although the process of installing an IDE CD-ROM drive is quite simple, it is worth paying attention to the following points. As you know, any Enhanced IDE adapter has two 40-pin connectors to which two devices are connected: Primary Master and Slave and Secondary Master and Slave. For obvious reasons, Primary Master is always the boot hard drive (C:). So the CD-ROM drive can be either Primary Slave, Secondary Master or Secondary Slave. So, before connecting the power, interface and audio cables on the back wall of the drive, you should set the Master and SLave jumpers accordingly (but it’s still better to connect the CD-ROM to the second IDE, with a separate cable).

Does it make sense to buy 50x drives? Is there really a choice? Firstly, slower drives simply may no longer be on sale, and secondly, by buying a fast drive and using it at a lower speed, you can practically get rid of noise, because when designing fast drives, manufacturers finally began to think about silence and began to build vibration and noise reduction mechanisms into their products. The drive in question uses the second generation of ASUS noise and vibration suppression system. Nowadays, buying a DVD drive only makes sense to watch DVD movies on a monitor. The share of software products released on DVDs is still vanishingly small compared to the market for products on CD-ROMs. In this sense, it is worth adhering to the golden rule - buy when you really need it. Buying equipment for growth is a waste of money. Additionally, DVD-ROM drives are not able to handle CDs as quickly as high-end CD-ROM drives. And the cost of DVD-ROM drives is still much higher than the cost of their CD-ROM counterparts. Summarizing all of the above, we can conclude that a modern high-speed CD-ROM drive with short access time, the ability to reduce speed, silent operation and cool behavior is still quite competitive.

Equipment

• Drive ASUS S500/A, firmware v3.4H.
• Cable for connecting the drive to the audio card.
• User instructions (languages ​​include Russian).
• Driver floppy disk.
• Bag with 4 mounting screws.

Key Features

Full specifications can be read on the ASUS website.

Test bench

Look and Feel

I am not an ardent fan of retail packaging due to the fact that products packaged in a colorful box are always more expensive than their bulk counterparts. But in the case of ASUS S500/A, I actually didn’t have much of a choice. The drive is supplied only in retail form. From the box I shook out the audio cable, the bag of screws, the installation floppy disk and the user manual.

Front view

1. Headphone jack;
2. Sound level control;
3. Disk presence indicator;
4. Emergency eject hole;
5. Control buttons (Play/Skip/Speed ​​and Open/Close/Stop).

The presence light is green when there is a disk in the drive and flashes when reading is in progress. The left button, in addition to its main Play/Skip functions, can control speed. If there is a data disk in the drive, then each press of the button changes it in the sequence - 40/32/24/8x. In order to restore maximum speed, you need to open and close the drive tray. Some people bought ASUS disk drives precisely because of this feature.

Back view

1. Nutrition;
2. IDE connector;
3. Configuration jumpers (Master/Slave);
4. Analog output;
5. Digital output;
6. Reserved jumpers.

There were no problems with the installation, except that the drive touched the textolite board of the DIMM module, but this is most likely a problem of the insufficient width of the case, and the dual-processor motherboard is wider than usual. Under DOS mode of Windows 98, the program installed the drivers, updated config.sys and everything worked. The interesting thing is that the drivers from the ancient 4x Hitachi drive worked with ASUS no worse than the original ones. There is nothing surprising here - the ATAPI protocol is used by the system to communicate with CD-ROM drives the same for everyone. I liked the tray. It drives out quickly and clearly with a pleasant sound, there is no looseness or rattling of gears, like many no-name drives. The drive spins the disk with a characteristic turbine whistle. The running noise is quite high. The rated 60 dB is easy to believe. There is almost no vibration. You can feel it only by touching the tray. At speeds of 32x and below, vibration disappears completely. After prolonged use, the drive becomes slightly warm.

CD-R

Clear testing under Windows 98 simply did not work out. According to the graph (white line), at first I thought that the DMA mode was disabled, despite the checkmark in the drive properties. Unchecking the box, however, resulted in even lower results (orange line). The problem turned out to be a disgusting implementation of busmaster drivers. Moreover, Windows Me and Windows 2000 no longer have such problems.

Windows 98, CD Speed ​​99 v0.8b, TDK CD-R80 Reflex, length 79:35,
DMA off (orange), DMA on (white).

Windows 2000 SP2, CD Speed ​​99 v0.8b, TDK CD-R80 Reflex, length 79:35.

Under Windows 2000 the curves took their proper form. The green line is perfect. The yellow line indicates that the rotation speed remains approximately constant throughout the disk. At the end of the disk the speed was higher than 53x, but this is only because the maximum speed is calculated based on a standard 650 Mb disk. On 800 Mb disks the speed will be even higher. True, the S500/A will only be able to read the first 748 Mb of data, as follows from its technical characteristics.

Windows 2000 SP2, CD Speed ​​99 v0.8b, TDK CD-R80 Reflex, length 79:35.
Results in table form.

Average	40.23x
Start	23.73x
End	53.11x
Spin-up Time	5.14 sec
Spin-down Time	6.78 sec
Random Seek	85 ms
Disc Eject Time	1.83 sec
Disc Load Time	1.32 sec
Disc Recognition Time	5.61 sec
Reading type	CAV

CD-ROM

Windows 2000 SP2, CD Speed ​​99 v0.8b, 3D Studio MAX 1.2, length 73:49.

Windows 2000 SP2, CD Speed ​​99 v0.8b, 3D Studio MAX 1.2, length 73:49.
Results in table form:

Average	38.34x
Start	22.93x
End	50.45x
Spin-up Time	5.66 sec
Spin-down Time	6.37 sec
Random Seek	82ms
Disc Eject Time	1.84 sec
Disc Load Time	1.32 sec
Disc Recognition Time	5.53 sec
Reading type	CAV

Everything is as expected - lower initial and final speeds. The schedule is still impeccable. The maximum speed is 50x with a small margin, as it should be.

CD-RW

Windows 2000 SP2, CD Speed ​​99 v0.8b, That's Write! CD-RW74, length 74:02.

Windows 2000 SP2, CD Speed ​​99 v0.8b, That's Write! CD-RW74, length 74:02.
Results in table form.

Average	10.66x
Start	6.39x
End	14.01x
Spin-up Time	2.80 sec
Spin-down Time	2.95 sec
Random Seek	131ms
Disc Eject Time	2.15 sec
Disc Load Time	1.33 sec
Disc Recognition Time	5.52 sec
Reading type	P-CAV

CD-RW reading speed is limited to 8x. The time it takes to spin up and stop a disc is half that of a CD-ROM and CD-R because the disc doesn't have to spin up to full speed.

It should also be noted that the head positioning time has increased by almost one and a half times, which is again explained by the spindle rotation speed falling by more than three times. So reading CD-RW is not the best strong point drive.

According to CD Speed ​​99, the reading type of CD-RW discs is P-CAV (Partial Constant Angular Velocity). However, the presented graph gives the impression of a typical CAV (Constant Angular Velocity) reading type, without any hint of a plateau at the end of the disk. The speed reaches 14x at the end of the disc only because the drive says one thing (P-CAV) but does something completely different (CAV).

Digital copying of music

When conducting an experiment on extracting audio tracks, I used branded DDT discs - Plastun and Queen - Greatest Hits II. The DDT disk was taken as a disk of normal or slightly shorter than normal length - 43:34. Queen's disc is interesting because it was recorded to capacity. Its length is simply phenomenal - 75:58, which, by the way, is almost two minutes longer than the required 74 minutes of sound. The drive had to show its maximum extraction speed on the Queen disk. CDDAE 99 immediately disappointed me - it turned out that the maximum speed of extracting tracks cannot be more than 20x. Needless to say, in this test the ASUS 50x was much slower than its younger brother ASUS 34x, which does not have this limitation.

I added an additional WinDAC32 test because on the Queen CDDAE 99 disc the results were different from EAC. The problem, apparently, is still in CDDAE, because the results of EAC and WinDAC32 are identical. The speed of extracting audio tracks is quite satisfactory. I think it can be considered as such as long as encoding tracks into .mp3 takes longer than extracting them. On my particular system, the bottleneck is the processor.

CDROM Driver Analyzer

In the reading quality test, I used one of the latest versions of CDROM Drive Analyzer v2.2.0. Older versions lacked the scale to display the speeds of modern drives, and most latest version 2.3.1 showed a transfer at the end of the disk close to 160 Mb/sec, which cannot be true, if only because of the limitations of Ultra DMA/33. As the author himself writes in the documentation for the CDROM Drive Analyzer program, it is intended primarily for testing many drives using one disk. Based on the reading graphs, it is easy to determine the drive that copes with reading errors better than others. Since the purpose of the article is after all ASUS review S500/A, and not comparing it with other drives, I present CDROM Drive Analyzer graphs solely to see what the smooth curves of CD Speed ​​99 can turn into.

CD-R

Windows 2000 SP2, CDROM Drive Analyzer v2.2.0, TDK CD-R80 Reflex, length 79:35.

As you can see, the curve is not at all as smooth as in the CD Speed ​​99 graphs, but nevertheless it grows until the very end of the disk, so there is no reason to worry.

CD-ROM

Windows 2000 SP2, CDROM Drive Analyzer v2.2.0, 3D Studio MAX 1.2, length 73:49.

The same jumps, so the problem here is not in the defective disk, but in the drive itself. Interestingly, in the case of CD-R and CD-ROM discs, the size and number of notches gradually increases towards the end. What would it be?

CD-RW

Windows 2000 SP2, CDROM Drive Analyzer v2.2.0, That's Write! CD-RW74, length 74:02.

And here, finally, something interesting appeared - the graph miraculously straightened out. The notches make themselves felt only at the very end of the disk. It seems that the problem lies in the disk stabilization system, which at read speeds close to 16x and higher is not as effective as we would like. Reading CD-RW is slow but sure.

Damaged disk

Finally, my worst disk had a use. The disk was poorly balanced - extraneous noise was heard from inside some drives when spinning up. Scratches, scuffs, stains and deep gouges? Eat. Among other things, the aluminum working coating is even damaged from the inside. I don’t even want to think about the conditions under which this disc was made. The total amount of disk damage is still not so great as to create a serious problem for any quality drive.

Windows 2000 SP2, CDROM Drive Analyzer v2.2.0, CD #2, length 73:18.

The disc is confidently read. After the middle of the disk, all attempts to restore speed are in vain.

Speed ​​control

What high-speed drive can do without a software speed reduction function? When watching a movie from a CD-ROM disc or playing .mp3 files, it is not at all necessary to keep the drive spindle constantly at maximum speed. Therefore, if the drive does not know any other speeds other than 50x, in practice it can be much slower than another 8x drive, only because it will spin the disk again and again when the user needs a new piece of information. The ASUS S500/A drive is unique in that its speed can be set to any value in the range of 4x - 50x in 1x steps. After quite a long search for a suitable program to control the speed of the drive, I settled on CDSlow

Modern standards and devices for storing information on laser disks. Features of recording information on optical discs.

In 1995, the first optical disc drive appeared in the basic PC configuration - CD-ROM(Compact Disk Read Only Memory, CD-ROM). The device used multilayer CDs with a diameter of 120 mm and a thickness of 1.2 mm, with a disk capacity of 650 - 700 MB.

The CD-ROM drive contains:

– an electric motor that rotates the disk;

– an optical system consisting of a laser emitter, optical lenses and sensors and designed to read information from the surface of the disk;

– a microprocessor that controls the drive mechanics, optical system and decodes the read information into binary code.

Main characteristics of CD-ROM:

– data transfer rate – measured in multiples of the speed of an audio CD player (150 KB/sec) and characterizes the maximum speed at which the drive sends data to RAM computer, for example, a 2-speed CD-ROM (2x CD-ROM) will read data at a speed of 300 KB/sec, a 50-speed (50x) - 7500 KB/sec;

– access time – the time required to search for information on the disk, measured in milliseconds. CD-RW drive

The device is used to record information on CD-R (write once) and CD-RW (CD-ReWritable - rewritable disc) discs.

A CD-RW (CD-ReWritable) disc is used for reusable recording of data, and you can either simply add new information to the free space or completely overwrite the disc with new information (after first clearing the entire disc). The recording speed of modern CD-RW drives is 2x-24x.

DVD-ROM drives and DVD±RW

Capacity DVD the first generation was 4.7 GB, and it received the official name DVD-5, standard DVD-9 involves the use of double-layer discs. Disc standard DVD-9 Capable of storing up to 8.54 GB of data. A further development of the DVD-5 and DVD-9 standards were the standards for double-sided discs DVD-10(9.4 GB) and DVD-18(17.08 GB).

Later, the DVD standard was supplemented with a specification for recordable and rewritable DVD-R discs and DVD-RW.

There are also discs DVD-RAM, which is a single- or double-sided disc placed in a plastic cartridge. To work with them you need a special drive.

The disc format was also developed in 1999 DVD+RW. Differences in the format of information presentation on DVD+RW No. A special feature of the format is that the laser beam’s higher positioning accuracy allows for data correction “on the fly”, rewriting individual bad sectors of the disk in real time, i.e. V DVD+RW a more advanced error correction algorithm has been implemented. On disks DVD+R A special reflective layer with increased reflectivity is used. Blu-Ray and HD drives

In 2002, representatives of nine leading high-tech companies Sony, Matsushita (Panasonic), Samsung, LG, Philips, Thomson, Hitachi, Sharp and Pioneer at a joint press conference announced the creation and promotion of a new high-capacity optical disc format called Blu-ray Disс. According to the announced Blu-Ray Disc specification (or BD-R And BD-RE) is a next-generation rewritable disc with a standard CD/DVD size of 12 cm with a maximum recording capacity per layer and one side of up to 27 GB.