Main functional components of a DVD drive. Main functional units and operating principle. External and internal storage

• 
  the general structure of the device is determined;
• 
  the main relationships of elements are determined;
• 
  the nature of the influence of the absence of necessary connections (or the appearance of unauthorized connections) on the general behavior of the device as a whole is clarified;
• 
  the location of the fault is localized within the individual chip responsible for this relationship;
• 
  the signals at the chip pins are checked for compliance with the manufacturer’s specifications;
• 
  the faulty element is replaced.

To consider the most typical malfunctions of CD/DVD drives, let us turn to the structure of this rather complex device, shown in the figure:

In accordance with this structure, three main groups of its “diseases” can be distinguished:

• 
  mechanical failures;
• 
  malfunction of the optical system;
• 
  malfunction of electronic components.

Mechanical failures account for 80...85% total number malfunctions. They can also be divided into several main groups:

• 
  lack of lubrication of rubbing parts;
• 
  accumulation of dust and dirt on the moving parts of the disk transport mechanism;
• 
  clogging of friction surfaces;
• 
  violations of regulations;
• 
  mechanical breakdowns of transport mechanism parts.

The accumulation of dust and dirt on the moving parts, especially on the edges of the moving slide of the carriage, makes it almost impossible to lock the mechanism, and as a result the drive constantly ejects the disc.

Rice. 2. Typical places where dirt and dust accumulate on the optical disc carriage

Clogging of the friction surfaces leads either to the carriage mechanism stopping in intermediate positions or to the disc slipping during rotation. Both make the drive impossible to use. Failure to regulate the transport mechanism also leads to a similar result.

The mechanical faults listed above mainly concern simple mechanisms of relatively cheap drives. Expensive models, as a rule, have complex mechanisms, and for them the main type of mechanical failure is the breakdown of mechanism parts. Most often this happens because the user, instead of using the control buttons, pushes the carriage with the disk into the drive with his hand. The consequences of such actions can be the most unpleasant. If it is enough to clean, wipe, lubricate a dirty and unkempt mechanism and it again performs its functions properly, then haste and excessive efforts lead to quite expensive and time-consuming repairs of the drive.

The second type of common malfunctions includes malfunctions of the optical-electronic information reading system. Despite small sizes, this system is a very complex and precise optical device. Just look at block diagram(Fig. 3) to agree with this. In terms of frequency of occurrence during the first one and a half to two years of operation, optical system failures account for 10...15% of the total number of failures. To highlight the main “diseases” of optics and their characteristic manifestations, let’s consider its composition:

• 
  servo disk rotation control system;
• 
  Servo positioning system for laser reading device;
• 
  servo autofocus system;
• 
  radial tracking servo system;
• 
  reading system;
• 
  control circuit laser diode.

• 
  start and acceleration of disk rotation;
• 
  steady state of rotation;
• 
  braking interval to a complete stop;
• 
  remove the disc using the carriage tray and take it out of the drive.

Rice. 3. Structure of connections of the optical-electronic information reading system

The servo system for positioning the information reading head ensures a smooth approach of the head to a given recording track with an error not exceeding half the track width in the search modes for the required piece of information and normal playback. The reading head, and with it the laser beam, moves across the disk field by the head motor. Engine operation is controlled by forward and reverse motion signals from the control processor, as well as signals generated by the radial error processor. Characteristic signs of a malfunction are both erratic movement of the head along the guides and its immobility.

The radial tracking servo system ensures that the laser beam remains on the track and provides optimal conditions for reading information. The system operates based on the three light spot method. The essence of the method is to divide the main laser beam using a diffraction grating into three separate beams that have a slight divergence. The central light spot is used for reading information and for operating the autofocus system. Two side beams are located in front and behind the main beam with a slight offset to the right and left. The mismatch signal of these beams from the positioning sensors affects the tracking drive, causing, if necessary, correction of the position of the central beam.

The performance of the radial tracking system can be monitored by changes in the error signal supplied to the tracking drive.

Monitoring and control of the vertical movement of the focusing lens is carried out under the influence of servofocus. This system ensures precise focusing of the laser beam while working on the working surface of the disk. After loading and starting the CD, focus adjustment begins maximum level output signal of the photodetector matrix and the minimum level of the error signal of the fine focusing and focus zero passage detectors. At the moment the disc starts, the CD-ROM control processor generates correction signals that provide multiple (double or triple) movement of the focal lens necessary to accurately focus the beam on the disc track. When focus is found, a signal is generated that allows information to be read. If after two or three attempts this signal does not appear, the control processor turns off all systems and the disk stops. Thus, the performance of the focusing system can be judged both by the characteristic movements of the focal lens at the moment the disk starts, and by the signal that starts the disk acceleration mode when the focus of the laser beam is found.

The information reading system contains a photodetector matrix and differential signal amplifiers. The normal operation of this system can be judged by the presence of high-frequency signals at its output when the disk rotates.

The laser diode control system provides the rated excitation current of the diode in the disk starting and information reading modes. A sign of normal operation of the system is the presence of an RF signal with an amplitude of about 1 V at the output of the reading system.

In addition to functional malfunctions of the optical system, very often it fails due to dust accumulated on the focal lens (Fig. 4). In this case, in order to bring the CD-ROM into working condition, it is enough to wipe the lens with a soft flannel. Under no circumstances should solvents be used for cleaning! The focal lenses of most CD-ROMs are made of organic plastic, and solvent will permanently damage their surface.

Rice. 4. CD/DVD drive optics: a) dusty lens, b) clean lens

The third group of malfunctions includes all damage to the electronic components of the drive. Despite the rather small (relative to the total number of drive defects) percentage of cases of electronic failure - 5...10%, troubleshooting electronic circuits is the most labor-intensive part of the repair.

Systems for recording, reading and subsequent processing of information determine the general functional diagram of a CD/DVD drive, shown in Fig. 5. In addition to the systems discussed above, it includes a clock generator that provides clock signals to all CD-ROM nodes, and an EFM demodulator that converts 14-bit code messages from the disk into 8-bit serial code. Next, the information enters the digital data processor, which, together with the processor system management is the heart of the entire device. This is where data deinterleaving and error correction occurs. The task of data interleaving when recording information is to “stretch” each byte of information over several recording frames. Moreover, even if there is a loss of even a few frames of information as a result mechanical damage disk surface, the result of deinterleaving data will be the presence of small errors in individual bytes. Such errors are corrected by an error correction circuit.

Rice. 5. Functional diagram of CD-ROM

Depending on the error correction strategy chosen for a particular CD-ROM model and, accordingly, the complexity of the processor and the device as a whole, in practice, a particular CD-ROM can either correct one or two minor errors in the information frame (which corresponds to cheap models), or in several stages restore, with a probability of 99.99%, serious and long-term destruction of information. As a rule, expensive CD-ROM models are equipped with such error correctors. This is the answer to the frequently asked question: “Why is this disk readable on a friend’s machine, but my PC doesn’t even see it?”

From the output of the digital data processor, the corrected digital information is supplied via a communication interface to the PC input, where it is further processed. If reading is done from an audio disc, the information goes to a digital filter, from it to a digital-to-analog converter and then, through analog correction and amplification circuits, to the audio outputs.

Thus, even after a superficial examination of the functional diagram of the CD-ROM device, we can conclude that this device is quite complex electronic system, which means that without a properly chosen troubleshooting strategy, it is extremely difficult to find a specific “culprit”.

It is not difficult to find a fault when it announces itself (as, for example, in Fig. 6). But unfortunately, in the vast majority of cases, a faulty microcircuit appearance no different from the correct one.

Rice. 6. Faulty chip on CD-ROM board

In Fig. 7 shows an algorithm for troubleshooting and detection, which is used by EPOS specialists to troubleshoot CD-ROM devices of almost any type. In practice, this algorithm invariably gives a positive result.

Basic functional units and operating principle.

TOPIC 3.3 CD drives

The following CD (optical) media are available:

¾ CD-ROM - read-only device

¾ CD-R – read and write once

¾ CD-RW – for reading and multiple writing

¾ Magneto-optical drives

Drives: CD-R, CD-RW, CD-ROM, DVD-R, DVD-RW

The operating principle of all optical storage devices is based on laser technology: The laser beam is used to both read and write information. CD-ROM drives.

The storage media on a CD-ROM disc is an embossed backing. Recording information is a process of forming a relief on a substrate by burning miniature strokes with a laser beam. The reading is carried out by registering the reflection of the laser beam. Signal from stroke 1, from surface without stroke 0.

CD-ROM drives

Boot device

Optical-mechanical block

Drive control and autonomous control systems

· Universal decoder

Interface block

An electromechanical drive rotates a disk placed in the loading device. A semiconductor laser generates a low-power infrared beam that hits a separation prism, is reflected from a mirror, and is focused on the surface of the disk. The beam moves to the desired track as follows: first, the motor, following a command from the built-in microprocessor, moves a movable carriage with a reflecting mirror and the desired track. The reflected beam is focused by the lens, reflected from the mirror, hits the separation prism, and directs the beam to the second focusing lens, then the beam hits the photosensor, converts light energy into electrical impulses. Signals from the photosensor are sent to a universal decoder, which is necessary to convert pulses into digital information understandable to a computer; it is a processor.

Autonomous tracking system for disc surface and data recording tracks provide high accuracy of information reading. The signal from the photosensor in the form of pulses enters the autonomous control system, where tracking error signals are detected. These signals from the amplifier enter the autonomous control system: focus, autonomous control system for the power of the emitted laser, the speed of rotation of the disk, radial feed, the power of the laser radiation, the linear speed of rotation of the disk.

DVD drives

DVD discs are designed as single-sided or double-sided.

Unlike CD in DVD discs The distance between recording tracks is smaller and the size of recording strokes is reduced. As a result, the capacity is increased. The number of images stored in DVD format is comparable to the quality of professional studio video recordings, and the sound quality is not inferior to that of a studio.

Write-once and write-once drives

For one-time recording use CD-R discs, which are a disk whose registration layer is made of a material that darkens when heated. The dark and light areas of a CD-R are similar to the streaks and smooth surfaces of a CD-ROM.

CD-RW are rewritable discs, the recording layer of which is made of organic compounds that can change their phase state from amorphous to crystalline under the influence of a laser beam.

When heated by a laser beam above a certain critical temperature, the material of the recording layer goes into an amorphous state and remains in it after cooling. When heated to a temperature significantly below critical, it restores its original state (crystalline).

Laser beam Laser beam

Reflective layer Recording layer

CD-ROM Protective varnish layer

Section 4. INFORMATION DISPLAY DEVICES

• 
  magnetic disks;
• 
  read/write heads;
• 
  head drive mechanism;
• 
  disk drive motor;
• 
  printed circuit board with electronic control circuit.

The hermetic block is filled with air under pressure of one atmosphere. In the covers of the hermetic blocks of some hard drives there is a special hole, sealed with a filter film, which serves to equalize the pressure inside and outside the block, as well as to absorb dust.

^ Figure 5 - Basic design elements of a hard drive drive
The overall dimensions of hard drives are standardized according to a parameter called form factor (Form-Factor). For example, all HDDs with a 3.5" form factor have standard case dimensions of 41.6x101x146 mm.

^ Magnetic disk substrates The first hard drives were made of aluminum alloy with the addition of magnesium. Modern models use a composite material of glass and ceramics with a low thermal expansion coefficient as the main material for disk plates, which makes them less susceptible to temperature changes and more durable. Magnetic disks are available in the following sizes: 3.5"; 5.25"; 2.5"; 1.8".

^ The discs are covered with a magnetic substance - the working layer. It can be either oxide or thin film based.

Read/write heads provided for each side of the disc. When the drive is turned off, the heads touch the disk. When the disks unwind, the aerodynamic air pressure on the heads increases, which leads to their separation from the working surfaces of the disks. The closer the head is to the disk surface, the higher the amplitude of the reproduced signal.

^ Head drive mechanism ensures the movement of the heads from the center of the disks to the edges and actually determines the reliability of the drive, its temperature stability and vibration resistance. All existing head drive mechanisms are divided into two main types: with a stepper motor and a moving coil.

^ Drive motor causes the disk pack to rotate, the speed of which, depending on the model, is in the range of 3600 - 7200 rpm (i.e. the heads move at a relative speed of 60 - 80 km/h). The rotation speed of some hard drives reaches 15,000 rpm. HDD rotates continuously even when it is not accessed, so the hard drive should only be installed vertically or horizontally.

^ Printed circuit board with electronic circuit controls and other drive components (front panel, configuration elements and mounting parts) are removable. Electronic circuits for controlling the motor and head drive and a circuit for exchanging data with the controller are mounted on the printed circuit board. Sometimes the controller is installed directly on this board.
Questions for self-control:

1. 
   Floppy disk drives. Design, operating principle, main components, specifications FDD;
2. 
   Logical structure of floppy disks;
3. 
   Hard drives magnetic disks. Design and operating principle of HDD, form factors, types;
4. 
   Main characteristics and operating modes of hard disk drives. Controllers and HDD connection;
5. 
   Modern models drives;
6. 
   Logical structure of the hard drive;
7. 
   Formatting hard drives;
8. 
   Utilities servicing hard magnetic disks.

Topic 4.2 CD-R (RW) drives. DVD-R (RW)
The student must:
have an idea:

• 
  about the purpose of CD-R (RW) drives. DVD-R (RW)

know:

• 
  operating principle and main components of a CD-ROM drive;
• 
  CD-ROM drive performance characteristics;
• 
  operating principle and main components of a DVD drive;

be able to:

• 
  connect CD and DVD drives;

CD-R, (RW), DVD-R (RW) drives: operating principle, design and main components, technical characteristics.

Guidelines
CD-ROM drives

CD-ROM is a compact disc (CD) designed to digitally store information previously recorded on it and read it using a special device called a CD-ROM driver - a drive for reading CDs.

The CD manufacturing process includes several stages.

At the first stage, an information file is created for subsequent recording on the medium. At the second stage, using a laser beam, information is recorded onto a medium, which is a fiberglass disk coated with a photoresist material. Information is recorded in the form of a sequence of spirally arranged indentations (strokes), as shown in Figure 6. The depth of each pit stroke (pit) is 0.12 µm, the width (in the direction perpendicular to the plane of the drawing) is 0.8 - 3.0 µm. They are arranged along a helical track with a spacing of 1.6 µm between adjacent turns, corresponding to a density of 16,000 TPI (625 TPI). The length of the streaks along the recording track ranges from 0.83 to 3.1 µm.

^ Figure 6 - Geometric characteristics of a compact disc (a) and its cross section (b)
At the next stage, the photoresist layer is developed and the disk is metallized. A disc made using this technology is called a master disc. To replicate CDs, several working copies are made from the master disc using electroplating. Working copies are coated with a more durable metal layer (for example, nickel) than the master disk, and can be used as matrices for duplicating CDs up to 10 thousand pieces. from each matrix. Replication is carried out by hot stamping, after which the information side of the disc base, made of polycarbonate, is vacuum metallized with a layer of aluminum and the disc is coated with a layer of varnish. Disks made by hot stamping, in accordance with the passport data, provide up to 10,000 cycles of error-free data reading. The thickness of the CD is 1.2 mm, diameter - 120 mm.

The CD-ROM drive contains the following main functional units:

• 
  boot device;
• 
  optical-mechanical unit;
• 
  drive control and automatic control systems;
• 
  universal decoder and interface unit.

^ Figure 9 - Design of the optical-mechanical CD-ROM drive unit
Automatic tracking systems for the disk surface and data recording tracks ensure high accuracy of information reading. The signal from the photosensor in the form of a sequence of pulses enters the amplifier of the automatic control system, where tracking error signals are isolated. These signals enter automatic control systems: focus, radial feed, laser radiation power, linear speed of disk rotation.

A universal decoder is a processor for processing signals read from a CD. It consists of two decoders, a random access memory device and a decoder control controller. The use of double decoding makes it possible to recover lost information up to 500 bytes. The random access memory serves as a buffer memory, and the controller controls the error correction modes.

The interface unit consists of a digital-to-analog converter, a low-pass filter and an interface for communication with a computer. When playing audio information, the DAC converts the encoded information into an analog signal, which is fed to an amplifier with an active filter low frequencies and further on sound card, which is connected to headphones or speakers.

^ The following are performance characteristics that you should consider when selecting a CD-ROM for your specific application.

Data Transfer Rate - DTK - Maximum speed, with which data is sent from the storage medium to RAM computer. High speed CD-ROM drive data transfer is necessary primarily for synchronizing picture and sound. If the transmission speed is insufficient, video frames may be dropped and audio may be distorted.

The quality of reading is characterized by the error rate (Eror Rate) and represents the probability of receiving a distorted information bit when reading it.

^ Average Access Time (AT) is the time (in milliseconds) it takes the drive to find the desired data on the media.

Buffer capacity is the amount of random access memory in a CD-ROM drive used to increase the speed of access to data recorded on the media. Buffer memory (cache memory) is a memory chip installed on the drive board for storing read data.

^ Mean time between failures is the average time in hours that characterizes the failure-free operation of a CD-ROM drive.

In the process of development of optical disk drives, a number of basic formats for recording information on CDs have been developed.

^ CD-DA (Digital Audio) format - digital audio compact disc with a playing time of 74 minutes.

The ISO 9660 format is the most common standard for the logical organization of data.

Format High Sierra(HSG) proposed in 1995. and allows data written to disk in ISO 9660 format to be read by all types of drives, which has led to widespread replication of programs on CD and contributed to the creation of CDs targeting various operating systems.

The Photo-CD format was developed in 1990-1992. and is intended for recording on CD, storing and playing static video information in the form of high-quality photographic images. A Photo-CD format disc holds from 100 to 800 photographic images of the corresponding resolutions - 2048 x 3072 and 256 x 384, and also stores audio information.

Any CD-ROM disc containing text and graphic data, audio or video information is classified as multimedia. Multimedia CDs exist in various formats for various operating systems: DOS, Windows, OS/2, UNIX, Macintosh.

The CD-I (Jntractive) format was developed for a wide range of users as a standard multimedia disc containing various text, graphic, audio and video information. A CD-I format disc allows you to store a video image with sound (stereo) and a playback duration of up to 20 minutes.

The CD-DV (Digital Video) format provides recording and storage of high-quality video with stereo sound for 74 minutes. During storage, compression is provided using the MPEG-1 (Motion Picture Expert Group) method.

^ Reading the disc is possible using a hardware or software MPEG decoder.

The 3DO format was developed for game consoles.

CD-ROM drives can operate with either a standard IDE (E-IDE) interface or a high-speed SCSI interface.

The most popular CD-ROM drives in Russia are products with the brands Panasonic, Craetive, Samsung, Pioneer, Hitachi, Teac, LG.

DVD drives

Solving the problem of increasing the capacity of optical storage media based on improving the production technology of CDs and drives, as well as existing scientific and technical solutions in the field of high-quality digital video, led to the creation of CDs with increased capacity.

The image quality stored in DVD format is comparable to the quality of professional studio video recordings, and the sound quality is also not inferior to studio quality. Audio information in DVD format is read at a speed of 384 KB/s, which makes it possible to organize multi-channel audio.

Such disk capabilities DVD format due to improved parameters of the working surface of the disks. Like CDs, DVDs have a diameter of 120 mm. The DVD drive uses a semiconductor laser with a visible wavelength of 0.63 - 0.65 microns. This reduction in wavelength (compared to 0.78 microns for a conventional CD drive) made it possible to reduce the size of recording lines (pits) by almost half, and the distance between recording tracks - from 1.6 to 0.74 microns. The pits are arranged in a spiral, like on vinyl long-playing records.

DVD-ROM drives come with both a hardware MPEG-2 decoder in the form of an expansion card for PCI buses, and with a software decoder. DVD-R recording and DVD-RW rewriting drives are capable of working with single-layer, single-sided discs with a capacity of up to 4.7 - 5.2 GB at an information writing speed of about 1 MB/s.
Questions for self-control:

1. 
   CD-R, (RW) drives, operating principle, design and main components, technical characteristics;
2. 
   DVD-R (RW): operating principle, design and main components, technical characteristics.

Topic 4.3 Magneto-optical storage devices. Magnetic disk drives. External storage devices
The student must:
have an idea:

• 
  about the purpose of CD drives;
• 
  on the purpose of magneto-optical storage devices;
• 
  about the purpose of magnetic disk drives;
• 
  on the purpose of external storage devices

know:

• 
  optical and magneto-optical disc formats;
• 
  how the streamer works

be able to:

• 
  write information to optical and magneto-optical disks

CD drives: formats for recording information, the process of manufacturing CDs, drives with single and multiple write. Magneto-optical storage devices: principles of operation, design and main components, technical characteristics. Logical structure and format of magneto-optical disks. Magnetic tape drives. The principle of placing information on magnetic tapes. Design of tape drive mechanisms. Data structure on magnetic tapes. Recording devices for reading information from magnetic tapes. Cartridges with magnetic tapes. Modern models of streamers. External storage devices: flash drives, ZIP drives. Operating principle and main technical characteristics.
Guidelines

Computer science, cybernetics and programming

This is the fundamental difference between CD drives and hard and floppy drives in which the media rotates at a constant angular speed. The need to maintain a constant linear speed is due solely to the fact that when playing audio CDs, data must enter the decoding device at a constant and strictly defined pace, regardless of which turn of the horns they are read from. Mechanical part of CDROM drives The design of CDROM drives is shown in Fig.

Drive designs CD-ROM

CD-ROM drive must be able to handle compact discs, although of a standard size, but produced by different manufacturers, with various unpredictable surface deviations and defects. The device must ensure disk rotation withconstant linear speed, i.e.its rotation frequency must be inversely proportional to the radius of the spiral track, which is monitored by the optical head. When the head moves to the edge of the disk, its rotation speed decreases and vice versa. This is the fundamental difference between CD drives and hard and floppy drives, in which the media rotates withconstant angular velocity.The need to maintain a constant linear speed is due solely to the fact that when playing audio CDs, data must enter the decoding device in a constant and strictly defined pace, regardless of which turn of the horns they are read from. When working with CD-ROM linear speed can be any. The accuracy of tracking a spiral information track on a rotating disk by the optical head of a disk drive is less than one micron in the radial direction. The electronic part of the drive must detect and correct random data reading errors in real time and operate reliably for a long time.

Mechanical part of disk drives CD-ROM

The design of CD drives is shown in Fig.

Rice. Drive design CD-ROM

The basis of the device is a hard frame made of aluminum or stainless steel. As in other types of drives, the frame is the part of the structure to which all the others are attached nodes ( mechanical and electronic). These include:front panel, false panel, volume control 1 and eject button. Receiving devices for media can be of different types and are designed either for installing CDs in special containers ( caddy ), or be retractable trays, so front panels and false panels. and also the methods of their fastening may be different. Despite the fact that recordable (CD-R) and rewritable (CD-RW) drives contain different laser emitters and electronic components, their design is, in principle, the same as that of conventional CD-ROM drives.

The drive's electronic components are mounted on several printed circuit boards. Most often there are two of them: main board, on which the drive control and interface circuits are assembled, andheadphone amplifier board;A socket for connecting them is usually mounted on it. Almost all mechanical components of the drive are combined intodisk and head drive mechanism.They are produced by only a few companies, among which, first of all, we must name the companies Sony, Philips, Toshiba, IBM . Therefore, all the numerous models of CD drives available for sale are assembled on the basis of only a few types of drive mechanisms, which perform about 80% of the functions of these devices. This standardization and, as a consequence, interchangeability is one of the characteristic features of this type of drive.

The design of a typical drive mechanism is shown in the following figure. In its upper part there are devices that ensure the reception, fixation and removal of the CD. The basis of the drive mechanism is block VS-7S, which is a frame to which all other parts are attached. It is installed in a housing on fourrubber supports,protecting the drive mechanism from shocks and vibrations that inevitably occur when the drive is operating as part of the system. However, despite the presence of shock-absorbing suspension, the CD drive is a delicate and very fragile mechanism.Movable unit, loading mechanism chassis And shielding coverconstitute a device that performs mechanical operations for receiving and fixing a compact disc on the rotorspindle motor,as well as its unloading.

Smooth and safe execution of these operations is ensured by several levers. mi and hydraulic dampers. You move moving parts I using drive motors for loading and unloading the disk.

Rice. 14.8

Disc and head drive mechanism design

Devices that provide rotation of the media with necessary speed and counts; For the unexpected, they are located under the loading mechanism (Fig. 14.9). Spinde.:; This engine is mounted on the frame of the VS-7S unit and connected toprinted tattoo with diagrams... management. Vibration damping suspensioncontributes to its more uniform rotation. On the. a more critical part of CD drives isoptical head?..which contains gallium aluminum arsenide ( GaAlAs ) laser diode emitter.":

Rice. 14.9 Bottom view of the VS-7S block

(wavelength 780 nm, power radiation about 0.6 mW), photosensor, optical system for automatic beam focusing And precise track tracking mechanism. The optical head can be mixed in two guides: the laser beam hits the surface of the disk through a slot in the frame of the VS-7S unit. The assembly consisting of the optical head and guides is sometimes called sled ( sled ).

In CD-ROM, CD-R and CD-RW drives laser emitters are used different characteristics. But outwardly they are not much different from each other.

The sled must track the position of the turns of the spiral information track on the surface of the disk. Unlike floppy disk drives, in which the magnetic recording/playback heads can be “pointed” to the tracks with reasonable accuracy using a conventional stepper motor, most CD drives use linear moving-coil motors for this purpose, such as are used for moving heads in hard disk drives. The fact is that the positions of the concentric tracks on floppy disks are strictly fixed, which is in good agreement with the operating principle of the stepper motor: its rotor can occupy only a few discrete positions. In addition, the tracks themselves are wide enough, which eliminates the need to fine-tune the position of the heads. The radius of the spiral of a narrow information path CD changes continuously, so the position of the head must be constantly adjusted. This is accomplished by changing the control current in the moving coil of the linear motor. However, some CD drives still use stepper motors with extremely small rotor pitches. Electronic components that ensure movement of the slide in the desired direction are mounted on the main printed circuit board disk drive".

Electronic drive components CD-ROM

In Fig. Figure 14.10 shows a block diagram of a typical disk drive CD-ROM . It can be roughly divided into two parts: the controller subsystem and the drive control subsystem. The controller subsystem interacts with the interface peripheral devices systems, namely with a storage controller. Most of the most complex electronic drive components are related to this subsystem. The controller, the diagram of which is shown in Fig. 14.10, designed to work with the interface SCSI 2 , although most modern disk drives CD-ROM connects to the same interfaces ( Ultra - DMA or E 1 DE ) as hard drives. In both cases, the device is quite “intelligent”, which allows you to simply connect the drive to the system interface (adapter SCSI or drive controller type IDE, EUE or Ultra - DMA ), assign a letter designation to it and get a working system.

The drive control subsystem generates commands for its mechanical part (ensuring the reception and ejection of a CD, adjusting its rotation speed, moving the slide, etc.), and also decodes data (from EFM into normal binary format) and error correction. Analog signals from the exit

"By moving the slide, only rough guidance of the optical head is carried out on the track. Accurate tracking of it and correction of rapid deviations in one direction or another (arising due to imperfections of the media) is carried out optical device the head itself. The weight of the skid is too high For so that they are able to respond to such deviations. ė Note ed. SCSI (Small Computer System Interface) system interface for small computers. ė Editor's note

Rice. 14.10

Block diagram of a typical disk drive CD-ROM (URF radio frequency amplifier, designed to amplify the signal from the photosensor; DAC digital-to-analog converter; low-pass filter low-pass filter)

photosensor are first converted to EFM -signals and then into a stream of binary data and codes CIRC (Cross - InterleavedReed - Solomon Code overlapping Reed-Solomon codes).All operations for focusing the laser beam, tracking the track, controlling the drive of the sled (using feedback), the spindle motor and the mechanism for receiving and ejecting the disk are carried out by the drive control circuit and the servo drive processor.

If you need to understand in more detail the electronic components of CD drives, please note that the one shown in Fig. 14.10, the functional diagram can be considered only as an illustration explaining the general principles of operation of the devices in question. There are few varieties of electronic drive components, but they exist, and this must be taken into account. First of all, this applies to interfaces. As mentioned above, most devices use interfaces Ultra - DMA or EIDE . Some companies produce disk drives SCSI , and only a few manufacturers develop their own interfaces (in most cases they differ only slightly from the standard interfaces SCSI and IDE ). But in any case, try, if possible, to find complete documentation from the manufacturer for the drive you are interested in.

1 Currently rarely installed

PAGE 4

The development of CD drives began with the advent of the first audio CDs in 1982, developed by Sony companies and Philips. The volume of information on the CD was 72 minutes, which is exactly how long one of Bach's popular symphonies lasts, which amounted to 650 megabytes. Soon, in 1985, the first CD ROM drives for PCs appeared, then the main means of transferring information between computers were floppy disks and the volume of 650 megabytes seemed very large.

CD drives ( CDD ) – a necessary attribute of a modern computer.

CD drives work with optical discs information on which is recorded and read using a laser.

 CD - is intended only for storing information previously recorded on it in digital form and reading it using an appropriate device - a drive (storage).

Operating principle of a CD drive

The main functional elements of a CD-ROM drive are: a miniature electric motor, a laser, a system of optical lenses and sensors, and electronic circuit, which performs preliminary processing (reading and decoding information) and drive control.

CD drives work differently than all previously discussed electromagnetic storage media. When recording, a CD is processed by a laser beam (without mechanical contact), burning out the area that stores logical 1, and leaving untouched the area that stores logical 0. As a result, small depressions are formed on the surface of the CD - the so-called pits. ).

Reading information is carried out as follows:

An electric motor rotates the disk. The laser generates a light beam, which is focused by a system of optical lenses on the reflective (metal) surface of the disk. Light reflects differently from the transitions between the main surface and the recesses. The reflected light passes through the lenses to a light intensity sensor, which analyzes and converts it into an electrical binary signal and sends it to the drive electronics for further processing.

Information stored on optical disks, in contrast to information stored on magnetic disks, is practically not subject to the destructive effects of electric and magnetic fields and is much less susceptible to destruction as a result of the natural aging of the media material. In addition, the cost of recording and storing a unit of information on a CD-ROM is significantly less than for magnetic disks.

Optical disc structure

In accordance with accepted standards, the surface of the disk is divided into three areas:

1. Input directory - a ring-shaped area closest to the center of the disc (4 mm wide). Reading information from the disk begins precisely with the input directory, which contains the table of contents, record addresses, number of titles, disk size, disk name;

2. Data area ;

3. Output directory – has an end-of-disk mark.

Types of optical discs:

CD- ROM.

CD- 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 a spiral pattern. R . The abbreviation CD-R (CD-Recordable) denotes a one-time optical recording technology that can be used for archiving data, creating prototype discs for mass production and for small-scale production of publications on CDs, recording audio and video. The purpose of a CD-R device is to record data on

CD- CD-Rs, which can then be read on CD-ROM and CD-RW drives. RW.

Old data can be erased and new data can be written in its place. The capacity of CD-RW media is 650 MB and is equal to the capacity CD-ROM drives

and CD-R. DVD-ROM, DVD-R, DVD-RW.

Similar to the previously discussed types of optical disks, but have a larger capacity.Under developmentHVD 4 (Holografic Versatile Dosc) with a capacity of 1 TB.Technology:

DVD

admits

type

disks

Double-layer discs use a reinforcing layer on which information is recorded. When reading information from the first layer, located deep in the disk, the laser passes through the transparent film of the second layer. When reading information from the second layer, the drive controller sends a signal to focus the laser beam on the second layer and reads from it. With all this, the diameter of the disk is 120 mm and its thickness is 1.2 mm.

As already mentioned, for example, a double-sided, double-layer DVD disc can hold up to 17 GB of information, which is approximately 8 hours of high-quality video, 26 hours of music, or, most clearly, a stack of paper written on both sides 1.4 kilometers high!

FormatsDVD

DVD- 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 a spiral pattern.. can only be single-layer, but it is possible to create double-sided discs. The principle by which DVD-R is recorded is exactly the same as that of CD-R. The reflective layer changes its characteristics under the influence of a high-power laser beam. DVD-R does not bring anything new; technically it is the same CD-R, only designed for thinner tracks. At

DVD+ 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 a spiral pattern. creating DVD-R

The greatest attention is paid to compatibility with existing DVD-ROM drives. Recording laser length 635 Nm + copy protection of recorded discs.CD.DVD.