Design and main components of the cd rom drive. Open Library - an open library of educational information. Optical disc structure

In mass commercial production, CDs are made by stamping or pressing, rather than laser burning as many believe (see picture below). Although a laser can be used to etch data onto a glass master disc coated with a photosensitive material, burning the discs directly when producing hundreds or thousands of copies would be impractical to say the least.

Below are the main stages of CD production.

Application of a photoresistor layer. A round plate of polished glass, 240 mm in diameter and 6 mm thick, is coated with a layer of photoresistor approximately 150 microns thick and then fired at 80°C (176°F) for 30 minutes.

1. Laser recording. A Laser Beam Recorder (LBR) sends pulses of blue or violet light that illuminate and soften certain areas of the photoresistor layer of the glass master disk.

2. Formation of a master disk. The treated glass disk is immersed in a solution of sodium hydroxide (caustic soda), which dissolves the areas exposed to the laser, thereby forming depressions in the photoresistor layer.

3. Electrolytic molding. Using a process called electroforming, a previously prepared master disc is coated with a layer of nickel alloy. As a result, a metal master disk is created, called the parent disk.

4. Partitioning the master disk. The metal matrix is then separated from the glass master disk. It is a metal master disk, which can already be used for the production of small batches of disks, since the matrix wears out very quickly. Splitting the master disc often leads to damage to the glass base, so several more negative copies of the disc (called mother copies) are created using electroforming. Negative copies of the master disc are subsequently used to create a working matrix used in the process of mass replication of compact discs. This allows a large number of discs to be stamped without repeating the process of forming a glass master disc.

5. Disc stamping. A metal working die is used in a casting machine to form the pattern of data (pits and plates) in a molten polycarbonate mass of about 18 grams at a temperature of 350°C (or 662°F). In this case, the pressure force reaches approximately 20,000 pounds per square inch. Typically, modern thermal stamping presses take no more than three seconds to produce each disc.

6. Metallization. To create a reflective surface, a thin (0.05–0.1 micron) layer of aluminum is applied to the stamped disk by sputtering.

7. Protective coating. To protect the aluminum film from oxidation, a thin (6–7 microns) layer of acrylic varnish is applied to the metallized disk using a centrifuge, which hardens under the influence of ultraviolet rays.

8. Final product. Finally, label text or some image is applied to the surface of the disc using screen printing, which also dries under the influence of ultraviolet rays. The manufacturing process for data CD-ROMs and music CDs is almost the same CD-ROM. Compact Disc Read-Only Memory, read: “sidi-rom”) - a type of CD with read-only data recorded on them ( read-only memory - read-only memory). CD-ROM is a modified version of CD-DA (disk for storing audio recordings), allowing you to store other digital data on it (physically it is no different from the first one, only the format of the recorded data has been changed). Later, versions were developed with the ability to both write once (CD-R) and rewrite multiple times (CD-RW) information on a disk. A further development of CD-ROM disks became DVD-ROM disks. CD-ROM disks are a popular and cheapest means for distributing software, computer games, multimedia and other data. CD-ROM (and later DVD-ROM) has become the main medium for transferring information between computers, displacing the floppy disk from this role (now it is giving way to more promising solid-state media). The CD-ROM recording format also provides for recording on one disk information of mixed content - both computer data (files, software, readable only on a computer) and audio recordings (played on a regular audio CD player), videos, texts and pictures. Such disks, depending on the order in which the data is presented, are called advanced.

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

28. Operating principle of inkjet printing with electrostatic control. Advantages and disadvantages.

Continuous ink printer. The liquid is shaken with a vibrator to prevent sediment. The drop is directed either onto the paper or continues to circulate further (depending on the control signals). The liquid is supplied under pressure, crushed into droplets, which are charged and controlled by electrodes.

Advantages: No connectors or cables; Quiet operation; High print quality; Continuous ink supply; No heating.

Flaws: Low data transfer speed; Need to install a printer; Low printing speed

29. SATA interface. Architecture, characteristics. ATA (English) Serial ATA) - serial interface for data exchange with information storage devices. SATA is a development of the parallel ATA (IDE) interface, which after the appearance of SATA was renamed PATA (Parallel ATA). SATA devices use two connectors: 7-pin (data bus connection) and 15-pin (power connection). The SATA standard provides the ability to use a standard 4-pin Molex connector instead of a 15-pin power connector.

Using both types of power connectors at the same time may damage the device. The SATA interface has two data transfer channels, from controller to device and from device to controller. LVDS technology is used to transmit the signal; the wires of each pair are shielded twisted pairs.

There is also a 13-pin combined SATA connector used in servers, mobile and portable devices for thin storage. It consists of a combined connector of a 7-pin connector for connecting the data bus and a 6-pin connector for connecting the device’s power supply. To connect to these devices in servers, a special adapter can be used.

30. Plasma panels. Operating principle, characteristics. A gas discharge screen (the English tracing paper “plasma panel” is also widely used) is an information display device, a monitor based on the phenomenon of phosphor glow under the influence of ultraviolet rays that occur during an electrical discharge in an ionized gas, in other words, in plasma. The operation of a plasma panel consists of three stages: initialization, during which the position of the charges of the medium is ordered and prepared for the next stage (addressing). In this case, there is no voltage at the addressing electrode, and an initialization pulse having a stepped form is applied to the scanning electrode relative to the backlight electrode. At the first stage of this pulse, the arrangement of the ionic gas medium is ordered, at the second stage there is a discharge in the gas, and at the third the ordering is completed. Addressing, during which the pixel is prepared for illumination. A positive pulse (+75 V) is supplied to the addressing bus, and a negative pulse (-75 V) is supplied to the scanning bus. On the backlight bus, the voltage is set equal to +150 V. backlight, during which a positive pulse is applied to the scanning bus, and a negative pulse equal to 190 V is applied to the backlight bus. The sum of the ion potentials on each bus and additional pulses leads to exceeding the threshold potential and a discharge in the gas environment. After the discharge, the ions are redistributed at the scanning and illumination buses. Changing the polarity of the pulses leads to a repeated discharge in the plasma. Thus, by changing the polarity of the pulses, the cell is discharged multiple times. One cycle of “initialization - addressing - illumination” forms one image subfield. By adding several subfields, you can provide an image of a given brightness and contrast. In the standard version, each frame of the plasma panel is formed by adding eight subfields. Thus, when high-frequency voltage is applied to the electrodes, gas ionization or plasma formation occurs. A capacitive high-frequency discharge occurs in the plasma, which leads to ultraviolet radiation, which causes the phosphor to glow: red, green or blue. This glow passing through the front glass plate enters the viewer's eye. Characteristics: resolution, aspect ratio, lumen contrast, Connectors and ports.

31. Electronic book reading devices. Operating principle, characteristics.

The base (substrate) of the screen is a glass (for E-ink Vizplex, Pearl, Karta, Triton models) or plastic (for E-ink Mobius or E-ink Flex models) plate, a little less than half a millimeter thick. There are lower electrodes on it, above which there is a layer of special transparent microcapsules. The diameter of each microcapule is approximately equal to the diameter of a human hair. A microcapsule is the smallest possible point on an e-ink screen.

Vizplex e-ink display

Above the microcapsules are upper transparent electrodes attached to the upper protective plate of the screen. This plate is made of transparent plastic. Along the contour of the display, the substrate and the top plate are sealed with sealant.

Inside each microcapsule there are special microgranules - tiny particles of powder of different colors. In black and white screens they come in two colors - black and white. In color screens, microgranules of other colors are also used. Manufacturers do not report their quantity or color. The main feature of white microgranules is the ability to be attracted to the electrode when a negative potential is applied to it, and black ones - when a positive potential is applied.

When a microcapsule of white microgranules floats to the surface, its upper surface is painted white; when black microcapsules float, it turns black. If the proportion of white and black microgranules near the surface is equal, the color of such a capsule will be gray. Modern e-ink displays of the Vizplex, Pearl, Karta, E-ink Mobius models can reproduce 16 shades of color from white to black.

After the voltage is removed from the electrodes, the microgranules in the microcapsule remain in the same position that they took under the influence of the electric field. That is, the e-ink screen itself consumes energy only when the image on it changes.

32. IEEE1394 interface. Architecture, characteristics.

IEEE 1394 (FireWire, i-Link) is a high-speed serial bus designed for exchanging digital information between a computer and other electronic devices.

The cable consists of 2 twisted pairs - A and B, soldered as A to B, and on the other side of the cable as B to A. An optional power conductor is also possible.

The device can have up to 4 ports (connectors). There can be up to 64 devices in one topology. The maximum path length in the topology is 16. The topology is tree-like, closed loops are not allowed.

When a device is connected or disconnected, the bus is reset, after which the devices independently select the main thing from themselves, trying to shift this “dominance” to their neighbor. After identifying the main device, the logical direction of each cable segment becomes clear - to the main one or from the main one. After this, numbers can be distributed to devices. After the numbers are distributed, calls to the devices can be executed.

During the distribution of numbers, packet traffic flows on the bus, each of which contains the number of ports on the device, as well as the orientation of each port - not connected/to the main one/from the main one, as well as the maximum speed of each connection (2 ports and a piece of cable). The 1394 controller receives these packets, after which the driver stack builds a map of the topology (connections between devices) and speeds (worst case speed along the path from the controller to the device).

Bus operations are divided into asynchronous and isochronous.

Asynchronous operations are writing/reading a 32-bit word, a block of words, as well as atomic operations. Asynchronous operations use 24-bit addresses within each device and 16-bit device numbers (bus bridging support). Some addresses are reserved for the most important control registers of devices. Asynchronous operations support two-phase execution - a request, an intermediate response, then a final response later.

Isochronous operations are the transmission of data packets in a rhythm strictly timed to the 8 KHz rhythm, set by the bus master by initiating “write to the current time register” transactions. Instead of addresses, isochronous traffic uses channel numbers from 0 to 31. There are no acknowledgments; isochronous operations are one-way broadcasts.

Isochronous operations require the allocation of isochronous resources - channel number and bandwidth. This is done by an atomic asynchronous transaction to certain standard addresses of one of the bus devices, selected as the “isochronous resource manager”.

In addition to the cable implementation of the bus, the standard also describes the on-board implementation (implementations are unknown).

33. Technologies for manufacturing LCD screens. Active and passive matrix. Interfaces for connection.

Active and passive matrix. Interfaces for connection. LCD matrix technologies: All matrices can be divided into active and passive. Passive matrices They consist of individual cells combined into a rectangular grid to which control voltage is applied. The electrical capacity of each cell requires a certain amount of time to recharge, resulting in the image being displayed for a long time. Slow LCDs are used to prevent flickering. Active matrix. In active matrices, as well as in passive matrices, there is one electrode per cell. But, each pixel of the screen has an additional amplifier, which reduces the switching time of the voltage on the electrode; moreover, thanks to the transistor attached to each cell, the matrix remembers the state of all elements of the screen, and resets it only when a refresh command is received. Such a matrix operates on the principle of random access memory. This is currently the most common type of LCD matrix. This technology is based on combining two different technologies into one. TN Technology: When the transistor is in the off state and does not create an electric field, the LCD molecules are in their normal state and are aligned to change the polarization angle of the color passing through them by 90 degrees. This occurs due to the fact that the molecules are in a twisted state relative to each other in a spiral. When the transistor generates an electric field, all LC molecules line up in lines parallel to the polarization angle.

34. Touch capacitive-resistive screens. Operating principle, advantages and disadvantages.

The principle of operation of such displays is simple, and to some extent it is similar to a matrix one. In this case, the conductors are replaced with special infrared rays. Around this screen there is a frame in which there are built-in emitters, as well as receivers. If you tap on the screen, some beams will overlap and they cannot reach their own destination, namely the receiver. As a result, the controller calculates the contact location. Such screens can transmit light, they are durable, since there is no sensitive coating and there is no mechanical touch at all. However, such displays currently do not meet high accuracy and are afraid of any contamination. But the diagonal of the frame of such a display can reach 150 inches.

Projective capacitive technology.

The device consists of two glass substrates on which two layers of electrodes are applied, separated by a dielectric and forming a lattice using alternating voltage. And at the point of contact the change in capacitance is recorded.

Advantages: operability at low temperatures, high light transmission, supports multi touch technology.

Disadvantage: Requires a conductive object.

35. Operating principle of the modem. Characteristics.

The modem provides conversion of signal digits into alternating current frequency range - this is the process of modulation, as well as reverse conversion demodulation.

Modulation is the process of changing one or more parameters of the output signal according to the law of the input signal. In this case, the input signal is, as a rule, digital and is assigned to modulating. The output signal is usually analog and is often called a modulated signal.

Modem classification:

1. By type of channel used

2. By speed

3. By area of application

4. By execution

5. By means of control

Main types of modulation:

1. Phase. With phase modulation, signals of the same amplitude and frequency, but different in phase, correspond to a logical one or zero. The phase of the carrier changes abruptly when the next discrete signal passes, in contrast to the previous one.

2. Amplitude modulation. With amplitude modulation, only the amplitude of the carrier changes

3. Frequency modulation. For logical one and logical zero, sinusoids of two different frequencies are selected.

36. Methods of modulating signals for transmission over communication channels.

Signal modulation methods:

How does a modem manage to transmit a sequence of binary bits over telephone lines?

Lines intended for speech transmission have a limited bandwidth: in fact, no more than 3 kHz. This means that signals with a frequency exceeding 3 kHz cannot be transmitted through such a line. There is also a lower limit to the operating frequency range of a telephone line - several tens of hertz.

To transmit data over telephone lines, you can use old, proven methods of modulating analog signals, perhaps known to you from an institute radio engineering course. A so-called carrier signal is transmitted over the telephone line, the frequency of which does not exceed the bandwidth of the line. It is accompanied by an information signal, which slightly changes the characteristics of the carrier signal (amplitude, frequency and phase). At the receiving end, they are separated from each other by an operation called detection.

Amplitude modulation

Amplitude modulation is based on changing the amplitude of the carrier signal by the transmitted signal. It is still used in radio broadcasting on medium and long waves.

A sinusoidal signal with a frequency of, for example, 1 kHz is transmitted over a telephone line: one corresponds to a signal with a large amplitude, and zero corresponds to a small one.

Such a signal can be transmitted over telephone lines, however, its form (carrying information about the transmitted data) is subject to distortion due to interference on the line. As a result, this method is used only for data transmission at very low speeds - on the order of several tens of bits/s.

Frequency modulation

Frequency modulation is used for radio broadcasting in the ultrashort wave range. When detecting a frequency modulated signal, the signal amplitude is small, so most interference does not affect the signal quality. If you want to feel this, compare the quality of radio transmissions in the long-wave LW range (which uses amplitude modulation) and in the ultra-short-wave FM range with frequency modulation.

To use frequency modulation to transmit binary data, a zero value is encoded with a tone with a frequency of, for example, 1 kHz, and a one value with a tone with a frequency of 2 kHz.

Frequency modulation provides better protection against interference than amplitude modulation, but the transmission speed of this method still does not exceed 1,200 bps. The limiting factor is the narrow bandwidth of telephone communication lines.

Phase modulation

Several better results were achieved after using the so-called phase modulation. In this case, the signal frequency remains constant, and modulation is performed using the phase shift of the signal (Fig. 2-8). Bandwidth is not critical, so this method provides a data transfer rate of about 4,800 bps.

Quadrature amplitude-phase modulation

However, the speed of 4,800 bps is completely insufficient. In order to squeeze out everything that it is capable of from a narrowband telephone channel, quadrature amplitude-phase modulation was “invented,” which is, in fact, a combination of amplitude and phase modulation: each transmitted value is associated with a certain combination of signal amplitude and phase shift.

Here, the digital value v1 is assigned to the signal amplitude a1 and phase f1. At any given moment in time, one of the discrete values, determined by a specific amplitude and phase, is transmitted through the analog channel. Since both amplitude and phase can take on positive and negative values, the points of all possible transmitted digital values are located in all four quadrants of the coordinate plane shown in Fig. 2-9. Perhaps that is why this type of modulation is called quadrature amplitude-phase modulation.

One way or another, with the use of quadrature amplitude-phase modulation, modems became capable of transmitting data at a relatively high speed - up to 33,600 bps. As for further increasing speed, it would seem that all possibilities have already been exhausted. However, no, another reserve was found.

37. Main structural components of HDD. Main characteristics of HDD.

Main components of HDD drives

The main design elements include disks, read/write heads, head drive mechanism, disk drive motor, printed circuit board with control circuits, cables and connectors, and configuration elements (jumpers, switches).

Discs are available in the following sizes: 5.25"; 3.5"; 1.8"; 1"; Compact Flash Type II, PC Card Type II.

Disc coating

1. Oxide layer – a polymer coating filled with iron oxide.

2. Thin-film layer – cobalt alloy, by sputtering or galvanization.

3. Double antiferromagnetic (AFC) - consists of 2 layers separated by a thin film of ruthenium and thicker magnetic layers.

Read/write heads.

Each head is pressed against the disk using a spring and all heads are pressed simultaneously. The gap is 0.4 µin or 10nm.

Head drive mechanism

1. Stepper motor – an electric motor whose rotor rotates the block of heads to a certain angle.

2. Moving coil motor. The moving coil is fixed to the head block and is located in the field of a permanent magnet. Moving the coil displaces the head block from the influence of the flowing current.

A moving coil motor uses a servo drive system. For a moving coil motor, the following mechanisms are distinguished:

a) Linear - a block of heads moving along the radius of the disk together with a lever.

b) Rotary - head arms are attached to the moving coil, which rotate through an azimuth angle.

Servo

Ways to build a feedback loop:

I. With an auxiliary wedge - information is recorded in the high sector of each cylinder in front of the index mark (read 1 time per revolution).

II. With built-in codes - an improved version of the auxiliary wedge. Information is recorded at the beginning of each cylinder and sector.

III. Specialized disk – information is recorded on the working surface of a dedicated disk. Servo head Only in read mode. Information is read constantly.

Purpose: Correction of head position, written in Gray code. when moving from 1 number to the next, only 1 binary code changes.

A laser sight is used to accurately position the head, and the distance is determined by the interference method. Temperature calibration is used for tracking - all heads are alternately transferred from 0 to any cylinder. Corrections are recorded in the drive memory. During calibration, all exchanges and processes stop. Many drives have AIV support. Calibration starts after data exchange. Disc sweeping automatically moves the head to a randomly selected track.

Air filters

Recirculation filters in the HAD unit to clean the internal atmosphere.

The barometric filter is designed to equalize the pressure inside and outside the unit to maintain the air gap and working surface.

Sea level (-300m to 3000m)

When temperature changes occur, acclimatization is necessary. (+4 acclimatization required for 14 hours).

Spindle motor.

Designed to rotate the disk and is located on the 1st axis with 12 Volt voltage. In addition to ball bearings, highly plastic lubricant is used.

Control board

The hermetic block contains a controller, noise pre-amplifiers, switches, and signal conditioners.

Main elements of the controller block:

1. Control microcontroller - an 8 or 16-bit destination controller ensures interaction of all storage units and communication with the external interface.

2. Buffer memory up to 10 MB. used for caching and recording corrections.

3. Spindle motor control unit.

4. Positioning control unit. Generates pulses to move from cylinder to cylinder.

5. Head switch for generating write current and transmitted readout amplifier.

6. Read/write channel – these are circuits that extract synchronization pulses from the signal and generate write signals.

7. Servo Director – allocates servo codes.

8. HDC hard drive controller. Performs basic functions related to reading and writing data.

Cables and connectors

Interface: 40, 50, 80 pin.

The power connector is standard, the connector is for grounding.

USB, Fire Wire, Fiber Channel, and LPT ports are used for external device storage.

Main characteristics of HDD:

Formatted capacity represents the amount of useful information stored - that is, the sum of the data fields of all available sectors. Unformatted capacity is the maximum number of bits recorded on all tracks of a disk, including service information (sector headers, control codes of data fields). The ratio of formatted and unformatted capacities is determined by the track format.

The spindle speed, measured in revolutions per minute, allows us to indirectly judge productivity (internal speed).

The interface determines how the drive is connected.

Buffer memory capacity, caching capabilities (read, write, multi-segment, adaptability).

Internal organization parameters:

The number of physical disks or surfaces used to store data. Modern drives with a small height have a small (1-2) number of disks to lighten the head block. More drives (and height) are common among older drives and modern high-capacity drives.

The number of physical read-write heads, naturally, coincides with the number of working surfaces. Note that the number of heads (and working surfaces) may be less than twice the number of disks - usually there are models of this kind in each family. This is done to recycle disks in which one of the surfaces turns out to have a manufacturing defect, or based on other technological considerations.

The physical number of cylinders has increased from several hundred, characteristic of the first hard drives, to tens of thousands.

The sector size is usually 512 bytes.

The number of zones and the number of sectors on the track in the outer zones.

The location of servo marks or servo heads can be on a dedicated surface, on working surfaces, or a hybrid

The encoding-decoding method can be MFM, RLL, PRML.

The reliability of the device and the reliability of data storage are characterized by the following parameters:

The expected time to failure, measured in hundreds of thousands of hours, is, of course, an average for a given product.

More valuable to the user is the warranty period, during which the manufacturer (or supplier) provides repair or replacement of a failed device.

The probability of uncorrectable read errors for modern hard drives is on the order of one error per 1014 bits read.

The probability of correctable errors is of the order of one in 10 bits read.

The probability of search errors characterizes the quality of the servo system. Modern hard drives are characterized by the probability of one error per 108 search operations. These errors (if their number is small) are quite harmless, since the presence of the cylinder number in the header of each sector does not allow you to “miss” when performing read or write operations. Repeating the search operation only slightly reduces the average access time.

38. The concept of a 3D conveyor. The concept of “three-dimensional graphics”.

3D conveyor

All three-dimensional objects are defined using a mathematical model - it is this model that is the “starting point” in the sequence of obtaining an image on the screen, called a 3D Pipeline.

The conveyor consists of the following stages:

1. Determining the state of objects (Situation modeling) - this part of the program is not directly related to computer graphics, it models the world that will be displayed in the future. For example, in the case of Quake, these are the rules of the game and the physical laws of the player’s movement, the artificial intelligence of monsters, etc.

2. Determination of geometric models corresponding to the current state (Geometry generation) - this part of the pipeline creates a geometric representation of the current moment of our small “virtual world”.

3. Breaking down geometric models into primitives (Tesselation) - this is the first truly hardware-dependent stage. It creates the appearance of objects in the form of a set of certain primitives, of course, based on information from the previous step of the pipeline. The most common primitive in our time is the triangle, and most modern programs and accelerators work with triangles. Any flat polygon can always be divided into triangles, and it is with three points that a plane in space can be uniquely defined.

4. Binding of textures and lighting (Texture and light definition) - at this stage it is determined how geometric primitives (triangles) will be illuminated, as well as which and how textures will be applied to them in the future (Textures: images that convey the appearance of the object’s material, i.e. non-geometric visual information. A good example of texture is sand on a completely flat beach). Typically, at this stage, information is calculated only for the vertices of the primitive.

5. View geometric transformations (Projection) - here new coordinates are determined for all vertices of primitives based on the position of the observer and the direction of his view. The scene is, as it were, projected onto the surface of the monitor, turning into two-dimensional, although information about the distance from the observer to the vertices is stored for subsequent processing.

6. Rejecting invisible primitives (Culling) - at this stage, completely invisible ones (those remaining behind or to the side of the visibility zone) are excluded from the list of primitives.

7. Setup - here information about primitives (vertex coordinates, texture mapping, lighting, etc.) is converted into a form suitable for the next stage. (For example: coordinates of screen buffer points or textures - into fixed-size integers that the hardware works with).

8. Filling of primitives (Fill) - at this stage, in fact, a picture is built in the frame buffer (memory allocated for the resulting image) based on information about the primitives generated by the previous stage of the pipeline, and other data. Such as textures, fog and transparency tables, etc. As a rule, at this stage, for each point of the painted primitive, its visibility is determined, for example, using a depth buffer (Z-buffer) and, if it is not obscured by a point closer to the observer ( another primitive), its color is calculated. The color is determined based on the lighting and texture mapping information previously defined for the vertices of this primitive. Most of the characteristics of the accelerator that can be gleaned from its description relate specifically to this stage, since basically it is this stage of the pipeline that is accelerated in hardware (in the case of inexpensive and affordable boards).

9. Final processing (Post processing) - processing the entire resulting image as a single whole with some two-dimensional effects.

Some stages of the conveyor can be rearranged, split into parts, or combined. Secondly, they may be absent altogether (rarely) or new ones may appear (often). And thirdly, the result of each of them can be sent back (bypassing other stages). For example, the picture obtained at the last stage can be used as a new texture for the 8th, thus realizing the effect of reflective surfaces (mirrors).

39. Projectors. Operating principle. Characteristics.

A multimedia projector is a self-contained optical device that creates a flat image on a large screen by projecting information onto the screen fed into the projector. The source of output information for modern multimedia projectors can be almost anything, including video players, computers, external hard drives, flash drives, smartphones, tablets and other electronics. Today, there are many models on the market, from budget ones costing 10 thousand rubles to expensive premium devices costing several thousand dollars.

Types of projectors

Characteristics:

1 The size of the matrix, as well as its physical size

3.Technology (DLP, LCD)

4. Interface (fiwi ,Ethernet

5.projector weight

Multimedia projectors can be divided into several categories:

Professional solutions for the entertainment industry, cinemas, large presentations. These are expensive, high-tech devices, large in size.

Projectors for business and education are high-performance devices designed to withstand high loads and constant operation.

Multimedia projectors for the home - used to create home theaters, for games and entertainment. These are the most inexpensive devices available to most buyers, but at the same time satisfying all the necessary quality requirements.

40. Video capture device. Operating principle. Characteristics.

Video capture is the process of converting analog video into digital form and then storing it on a digital storage medium. The most typical example of video capture is the digitization of television broadcasts or VHS tapes on a specially equipped PC. Video decoder: receiving the signal, digitizing it, digital decoding into YUV format and transmitting the signal to the video controller. Video controller: converts the signal to RGB, organizes storage in a memory buffer, sends data to the DAC, forms a live TV movie after reverse analog conversion of the digital captured image, transmits the VGA signal from the video adapter. Video blaster functions: 1. Reception of low frequency signals.2. Displaying the received video in a window.3. Freeze frame.4. Frame reduction in graphic standards (TIF, PCX, IGA, GIF).Characteristics of video blasters.1. Low-frequency video signal format.1. How are luminance and chrominance signals separated? Comb and bandpass filters are used for separation. If RGB representation is used, then there is no modulation and encoding.2. Digitization depth – the number of bits per sample.

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 writing multiple times

¾ Magneto-optical drives

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

The operating principle of all optical information storage devices is based on laser technology: a laser beam is used both to 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 emitted laser power, disk rotation speed, radial feed, laser emission power, linear disk rotation speed.

DVD drives

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

Unlike CDs, DVDs have smaller spacing between recording tracks and smaller recording stroke sizes. 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, CD-R discs are used, which are a disc whose recording 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

Laboratory work No. 4

Topic: Disk drive (drive)

Goal: To know the insides of the drive, how it works, DVD discs.

Explanation of the work.

CD-ROM drive device.

A CD-ROM drive is a complex electronic-optical-mechanical device for reading information from laser disks. A typical drive consists of an electronics board (sometimes two or even three boards - a spindle control circuit and an opto-receiver amplifier separately), a spindle assembly, an optical read head with a drive for its movement and disk loading mechanics.

A typical drive consists of an electronics board, a spindle motor, an optical readhead system, and a disk loading system. The electronics board contains all the drive control circuits, the interface with the computer controller, the interface connectors and the audio signal output. Most drives use a single electronics board, but some models have separate circuits on small auxiliary boards.

Spindle assembly (the motor and the spindle itself with the disk holder) are used to rotate the disk. Typically the disk rotates at a constant linear speed, which means that the spindle changes speed depending on the radius of the track from which the optical head is currently reading information. As the head moves from the outer radius of the disk to the inner radius, the disk must quickly increase its rotational speed by approximately doubling, so good dynamic response is required from the spindle motor. The motor is used for both acceleration and deceleration of the disk.

The spindle itself is fixed to the axis of the spindle motor (or in its own bearings), to which the disk is pressed after loading. The surface of the spindle is sometimes covered with rubber or soft plastic to prevent the disc from slipping, although in more advanced designs only the upper clamp is rubberized to increase the accuracy of the disc being installed on the spindle. The disk is pressed against the spindle using the upper clamp located on the other side of the disk. In some designs, the spindle and clamp contain permanent magnets, the attractive force of which forces the clamp through the disk to the spindle. Other designs use coil or flat springs for this purpose.

Optical head system consists of the head itself and its movement system. The head contains a laser emitter based on an infrared laser LED, a focusing system, a photodetector and a pre-amplifier. Focusing system It is a movable lens driven by an electromagnetic voice coil system, similar to the movable loudspeaker system. Changes in the magnetic field strength cause the lens to move and the laser beam to refocus. Thanks to its low inertia, such a system effectively tracks the vertical runout of the disk even at significant rotation speeds.

Head movement system has its own drive motor, which drives the carriage with the optical head using a gear or worm gear. To eliminate backlash, a connection with an initial voltage is used: with a worm gear - spring-loaded balls, with a gear - pairs of gears spring-loaded in opposite directions. The motor used is usually a stepper motor, and much less often a brushed DC motor.

Disc loading system There are three options: using a special cassette for the disk (caddy), inserted into the receiving niche of the drive (similar to how a 3" floppy disk is inserted into the drive), using a retractable tray (tray), on which the disk itself is placed, and using a retractable mechanism. Systems with Tray usually contain a special motor that allows the tray to extend, although there are designs (for example, Sony CDU31) without a special drive, systems with a retracting mechanism are usually used in compact CD-Changers for 4-5 discs. and necessarily contain a motor for drawing in and ejecting disks through a narrow charging slot.

On the front panel The drive usually contains an Eject button for loading/unloading a disc, a drive access indicator, and a headphone jack with an electronic or mechanical volume control. A number of models have added a Play/Next button to start playing audio discs and switch between audio tracks.

Most drives also have a small hole on the front panel designed for emergency removal of the disk in cases where this cannot be done in the usual way - for example, if the tray drive or the entire CD-ROM fails, if there is a power failure, etc. You usually need to insert a pin or a straightened paper clip into the hole and gently press - this unlocks the tray or disk case, and it can be pulled out manually (although there are drives, for example Hitachi, in which you need to insert a small screwdriver into such a hole and rotate it located behind the front drive panel axle with slot).

How a DVD drive works

What does it consist of?

1. All you can see without opening its case is the tray, which plays the role of a sliding tray where you insert the disk so that the drive can begin working with it later.

2. Hidden in its vast part is a motor that forces the tray to move out of its garage (body) and then return to its original place, regardless of whether it is empty or with contents - a disk.

3. A motor, thanks to which the disk rotates around its axis to the speed declared by the manufacturer. For example, if it is a regular disk type - CD, the reading speed can reach 52X and higher.

4. A motor that allows the structure on which the drive laser is located to move.

5. Board - playing a major role in operation. A kind of computer that receives the master’s commands and forces them to be carried out by the other components listed above, in order to then turn to the master again and send him the result of their actions.

How does it work?

1. The very first thing the drive does after a disk has been placed in it is trying to read data from it. To do this, he uses all of the above components, but the first of them is the tray and its components.

2. Then the design comes into play, which is driven by the motor from point 4, where we describe what the drive consists of. It contains a laser that emits a “beam of light.”

3. The light beam, thanks to a special “guide prism” and its other components, penetrates the surface of the “reflecting mirror”, which, due to the subsequent movement of the structure with the laser, reflects it onto the surface of the inserted disk.

4. When the beam reaches the target, it is reflected again, but from the very surface of the disk. The beam reflected from the disk again appears at the “reflecting mirror”. And here the guiding prism comes into play again, with the help of which the resulting beam penetrates the “photosensitive device” that generates electrical impulses.

5. The final stage can be considered “chewing” the received information by using microcircuits, which in turn send the received data to the computer, or receive it, and, depending on the type of command, get to work.

DVD capacity (layers and sides)

There are currently four main types of DVD discs, classified by the number of sides (single- or double-sided) and layers (single- and double-layer).

· DVD-5 - single-sided single-layer disk with a capacity of 4.7 GB. Consists of two substrates connected to each other. One of them contains a recorded layer, which is called the zero layer, the second is completely empty. Single-layer discs typically use an aluminum coating.

· DVD-9 - single-sided double-layer disk with a capacity of 8.5 GB. Consists of two stamped substrates connected in such a way that both recorded layers are on the same side of the disc; on the other side there is an empty substrate. The outer (zero) stamped layer is covered with a translucent gold film that reflects the laser beam focused on this layer and transmits the beam that is focused on the lower layer. A single variable-focus laser is used to read both layers.

· DVD-10 - double-sided single-layer disk with a capacity of 9.4 GB. Consists of two stamped substrates connected to each other by their back sides. The recorded layer (zero layer on each side) is usually coated with aluminum. Please note that this type of disc is double-sided; The reading laser is located at the bottom of the drive, so to read the second side the disc must be removed and flipped over.

· DVD-18 - double-sided double-layer disk with a capacity of 17.1 GB. Combines two recording layers on each side. The sides of the disc, each formed by two stamped layers, are joined together with their backs facing each other. The outer layers (layer 0 on each side of the disc) are coated with a translucent gold film, the inner layers (layer 1 on each side) are coated with aluminum. The reflectivity of a single-layer disk is 45–85%, and that of a two-layer disk is 18–30%. Various reflective properties are compensated for by an automatic gain control (AGC) circuit.

Control questions:

1. What is a disk drive for?

2. What does a disk drive consist of?

3. How the drive works

4. What drive companies do you know?

5. DVD capacity

Related information.

Schematic and block diagram of CD/DVD reading and writing drives In order to understand how CD/DVD reading and writing occurs, let’s consider the schematic diagram of a CD/DVD reading device. The main drive components include: a laser diode, which emits light with a wavelength of 780 nm; laser beam splitter (interference polarizer); a system of two focusing lenses and a receiver of a laser beam reflected from the disk. To study the principle of operation of the device, consider the block diagram of a CD-Drive. The CD reading drive works as follows: 1. The laser generates a low-power beam, which, passing through a guide prism and a beam splitter, hits the reflecting mirror. 2. The servomotor, following commands from the microprocessor, moves the carriage with the reflecting mirror to the desired track on the CD. 3. The beam, hitting the disk, is reflected from it and, reflected from the mirror, hits the beam separator. The separation cube reflects the beam onto another guide prism. 4. From the prism, the beam enters the photosensor, the signals from which are decoded by the built-in microprocessor and transmitted to the computer in the form of data. Rice. 3.2. Block diagram of a CD Drive Due to the rotation of the disk and the movement of the carriage, vibration occurs in the drive, which leads to errors. Unlike conventional audio discs, where data can be reconstructed by interpolating adjacent values, CD-ROMs use very sophisticated error detection and correction techniques because any bit can be either a one or a zero. When duplicating a DVD, 288 control bytes, called ECC (Error Correction Code), are added to every 2048 information bytes. With this additional information, you can correct some reading errors. Drive speed SPEED OF CD DRIVES One of the main parameters characterizing CD reading and writing drives is their operating speed. The first CD standard (Red Book) defined the minimum speed (denoted as 1x) for reading data from an audio CD for its high-quality playback. It is equal to 150 KB/s, which is 75 data blocks of 2048 information bytes. The standard specifies a continuous read speed of sequential data, and does not take into account the fact that data may be located in different areas of the disk. Due to the fact that data can be read on computer compact discs (Data CDs) at a higher speed, high-speed CD reading drives have been created Speed parameters of CD-ROM drives

Name		Data transfer rate, byte/s
Single speed
Two speed
Three speed
Four speed
Six-speed
Eight speed
Twelve speed
Sixteen speed
Eighteen speed
Twenty-four speed
Thirty-two speed
Thirty-six speed
Forty-speed
Forty-eight-speed
Fifty-two speed

Obviously, the higher the read speed, the higher the performance of the entire system. However, it must be taken into account that the speed of the drives also depends on the quality of the disks themselves. When using low-quality CD-ROMs (for example, those whose center of gravity does not coincide with the geometric center of the disk), vibrations occur in the drive, and it is necessary to reduce the rotation speed of the disk. In most cases, such low-quality discs are produced by companies that illegally make copies of software products or music discs (so-called pirates). In this regard, almost all modern disk recording and reading devices have a speed control function. In addition, at high disk rotation speeds, very large loads occur on the disk itself, which sometimes leads to rupture of the disk inside the drive. It should be noted that for everyday work, when the user uses a CD drive to play music, watch videos and play games, a drive with a speed of 8x to 24x is quite sufficient. Of course, when installing an operating system (or other large program), as well as when copying the contents of an entire disk (for example, a movie), the speed characteristics of the drive play a very important role. However, installation of programs is not carried out so often, so a device with speeds from 8x to 24x is quite sufficient for operation. OPERATING SPEED OF DVD DRIVES Modern DVD drives have a slightly slower disc rotation speed compared to CD-ROM devices. However, thanks to the denser data packing on DVDs, the information transfer speed is 9 times the data transfer speed of CD drives. The important thing is that video on DVD players plays at approximately 9x speed (while video programs on CDs are usually rated at 2x or 4x speed). That's why when using a 52-speed CD drive there is no coveted improvement in quality when playing video. By transmitting video data 2.25 to 4.5 times faster, the video shown from a DVD player is of such quality that, in comparison, video from a CD player resembles the flickering image in an old movie theater. Indeed, if you run the same film in VideoCD, VHS or DVD standards, the difference in quality will be noticeable to the eye, and DVD definitely wins. LG Blu-Ray drives LG Electronics released the first Blu-Ray drive in Taiwan (Fig. 3.3). The device writes single-layer BD-R discs at 4x speed, and BD-RE media is written at 2x speed. Rice. 3.3. Drive LG GBW-H10N The GBW-H10N model is available with an ATAPI interface and, in addition to Blu-Ray discs, is compatible with all common optical media formats CD and DVD, including DVD-RAM (recording at 5x speed). The maximum reading speed for DVD-R/RW+R/+RW is 10x, CD-R/RW is read at a speed of 40x. DVD-RW recording is carried out at 6x speed, DVD-R - 12x, DVD+R - 12x, DVD+RW - 8x. CD-R and CD-RW are written at 8x and 10x speeds, respectively. PIONEER The efficiency of Japanese engineers is amazing: before the leading companies had time to determine the future of the Blu-Ray and HD DVD formats, the Pioneer corporation once again lived up to its sonorous name by releasing the world's first internal Blu-Ray recorder with the familiar ATAPI interface. The Pioneer BDR-101A drive supports recording of both BD-R and BD-RE discs (recordable and rewritable, respectively) and BD-ROM. True, the device can only read dual-layer BD-R discs. Drive Pioneer BDR-101A Regular CD-R and CD-RW discs are also supported by this device. The new product is characterized by overall dimensions of 148x42.3x198 mm and a weight of 1.1 kg. The maximum data transfer speed is 72 MB/s. The buffer size for DVDs is 2 MB, and for Blu-Ray discs it is 8 MB. In addition, the device supports technologies that reduce disk vibration and significantly improve the quality of reading/writing information. PLEXTOR Model РХ-В900А, which is an internal AT API drive, will be supplied complete with software for playing videos from Blu-Ray discs on computers running Windows XP or Windows Vista. As the manufacturer promises, the new product will be compatible with 25- and 50-GB disks and will be able to record information onto optical media in the BD-R/RE format at a speed of 2x (about 9 MB per second). As for DVDs, the recording speed for them will be 8x for DVD-R and DVD+RW, 6x for DVD-RW and DVD-ROM, 5x for DVD-RAM and 4x for double-layer DVD+/-R. PlextorPX-BEOOA PHILIPS Drive Philips Drive Philips has announced the release of a new Blu-Ray drive capable of playing and recording Blu-Ray discs up to 50 GB in capacity. In addition to playback, it is capable of recording a 25GB disc in 70 minutes at 2x speed. BENQ BenQ also announced the creation of external devices for playing and recording discs of the new Blu-Ray format (Fig. 3.7). The first drive was the BW 1000. The BW 1000 drive is capable of not only burning Blu-Ray discs, but also CDs and DVDs. The recording speed of new generation discs will be 2x. CD replication will reach 32x (which is not that fast these days); there is no information about the speed of recording on DVD.

Send your good work in the knowledge base is simple. Use the form below

Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.

Posted on http://www.allbest.ru/

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 tasks for which the CD-ROM device is intended include: installing and updating software; searching for information in databases; launching and working with gaming and educational programs; watching videos; listening to music CDs.

The history of the creation of CD-ROMs begins in 1980, when Sony and Philips joined forces to create technology for recording and producing CDs using lasers. Since 1994, CD-ROM drives have become an integral part of the standard PC configuration. The information carrier on a CD is a relief substrate on which a thin layer of light-reflecting material, usually aluminum, is applied. Recording information on a CD is a process of forming a relief on a substrate by “burning” miniature pits with a laser beam. Information is read by registering a laser beam reflected from the substrate relief. The reflective area of the disk surface gives a “zero” signal, and the signal from the stroke gives a “one”.

Data storage on CDs, like on magnetic disks, is organized in binary form.

Compared to hard drives, CDs are much more reliable in transportation. The volume of data located on a CD reaches 700 - 800 MB, and if the operating rules are followed, the CD practically does not wear out.

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 indentations (strokes) located in a spiral, as shown in Fig. 3.7. The depth of each pit stroke (pit) is 0.12 microns, the width (in the direction perpendicular to the plane of the drawing) is 0.8 - 3.0 microns. They are located along a helical track, the distance between adjacent turns of which is 1.6 microns, which corresponds to a density of 16,000 turns/inch.

Rice. 3.7 Geometric characteristics of a compact disc (a) and its cross-section (b) (625 turns/mm). The length of the strokes along the recording track ranges from 0.83 to 3.1 µm

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 is 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.

In Fig. 3.8 shows the design of the optical-mechanical CD ROM drive unit, which operates as follows. An electromechanical drive rotates a disk placed in the loading device.

The optical-mechanical unit ensures that the optical-mechanical reading head moves along the radius of the disk and reads information.

The semiconductor laser generates a low-power infrared beam (typical wavelength 780 nm, radiation power 0.2 - 5.0 mW), which hits the separation prism, is reflected from the mirror and focused by the lens on the surface of the disk. The servo motor, following commands from the built-in microprocessor, moves a movable carriage with a reflective mirror to the desired track on the CD. The beam reflected from the disk is focused by a lens located under the disk, reflected from the mirror and hits a separation prism, which directs the beam to a second focusing lens. Next, the beam hits a photosensor, which converts light energy into electrical impulses. Signals from the photosensor are sent to a universal decoder.

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 sent to an amplifier with an active low-pass filter and then to a sound card that 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-- DTR - the maximum speed at which data is transferred from the storage medium to the computer's RAM. This is the most important characteristic of a CD-ROM drive and is almost always mentioned along with the model name. The disk rotation speed is directly related to the data transfer speed. The first CD-ROM drives transferred data at 150 KB/s, as did Audio CD players. The data transfer speed of the next generations of devices is usually a multiple of this number (150 KB/s). Such drives are called drives with two-, three-, four-fold speed, etc. For example, a 60-speed CD-ROM drive provides information reading at a speed of 9000 KB/s.

The high data transfer speed of a CD-ROM drive is necessary primarily for synchronizing picture and sound. If the transmission speed is insufficient, video frames may be dropped and audio may be distorted.

However, further increasing the reading speed of CD-ROM drives by more than 72 times is impractical, since with a further increase in the CD rotation speed the required level of reading quality is not ensured. And, besides, a more promising technology has appeared - DVD.

Reading quality is characterized by the error rate (Eror Rate) and represents the probability of receiving a distorted information bit when reading it. This parameter reflects the ability of the CD-ROM device to correct read/write errors. The certified values of this coefficient are 10 -10 -10 -12 . When data is read from a dirty or scratched area of a disk, groups of erroneous bits are recorded. If the error cannot be corrected using the anti-jamming code (used when reading/writing), the data reading speed is reduced and the reading is repeated many times.

Average Access Time (AT) is the time (in milliseconds) it takes the drive to find the data it needs on the media. Obviously, when working on internal areas of the disk, the access time will be less than when reading information from external areas. Therefore, the drive data sheet provides the average access time, defined as the average value when performing several data reads from different parts of the disk. As CD-ROM drives improve, the average access time decreases, but nevertheless this parameter differs significantly from that for hard disk drives (100 - 200 ms for CD-ROMs and 7 - 9 ms for hard disks). This is explained by fundamental differences in designs: hard disk drives use several magnetic heads and the range of their mechanical movement is less than the range of movement of the optical head of a CD-ROM drive.

Buffer memory 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. Thanks to buffer memory, data located in different areas of the disk can be transferred to the computer at a constant speed. The buffer memory capacity of individual CD-ROM drive models is 512 KB.

Mean time between failures is the average time in hours that characterizes the failure-free operation of a CD-ROM drive. The average time between failures of various models of CD-ROM drives is 50-125 thousand hours, or 6-14.5 years of round-the-clock operation, which significantly exceeds the obsolescence of the 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.

The High Sierra (HSG) format was introduced in 1995 and allows data written to ISO 9660 discs to be readable by all types of drives, which has led to the widespread replication of programs on CDs 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 contains from 100 to 800 photographic images of the corresponding resolutions - 2048x3072 and 256x384, 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 (Intractive) 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.

Rice. 3.9 Structure of CD-ROM and CD-R/CD-WR disks

block drive drive disk

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, Creative, Samsung, Pioneer, Hitachi, Teac, LG.

CD-WORM/CD-R write-once and CD-RW write-once drives

CD-WORM (Write Once Read Many) or CD-R (CD-Recordable) drives provide one-time recording of information on a disk and subsequent reading of this information multiple times, while CD-RW (CD-Re Writable -- re-writable) drives allow record multiple times on optical discs.

For one-time recording, discs are used, which are a regular compact disc, the reflective layer of which is usually made of gold or silver film. Between it and the polycarbonate base there is a recording layer (Fig. 3.9), made of organic material that darkens when heated. During the recording process, a laser beam, the wavelength of which, as in reading, is 780 nm, and the intensity is more than 10 times higher, heats individual areas of the recording layer, which darken and scatter the light, forming pit-like areas. However, the reflectivity of the mirror layer and the clarity of the pits of CD-R discs are lower than those of commercially produced CD-ROMs.

In rewritable CD-RW discs, the recording layer is made of organic compounds known as cyanine and phthalocyanine, which tend to change their phase state from amorphous to crystalline and back when exposed to a laser beam. This change in phase state is accompanied by a change in the transparency of the layer. 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, and when heated to a temperature significantly below the critical temperature, it restores its original (crystalline) state. In rewritable discs, the recording layer is usually made of gold, silver, and sometimes aluminum and its alloys.

Existing rewritable CD-RW discs can withstand from several thousand to tens of thousands of rewrite cycles. However, their reflectivity is significantly lower than stamped CD-ROMs and CD-Rs. In this regard, to read CD-RW, as a rule, a special drive with automatic gain control of the photodetector is used. However, there are CD-ROM drive models labeled Multiread that can read CD-RW discs.

The advantage of CD-R/RW discs is that they fade and fail more slowly than conventional discs because the reflective layer of gold and silver is less susceptible to oxidation than the aluminum in most stamped CD-ROM discs. Disadvantages of CD-R/RW discs - the recording layer material of CD-R/RW discs is more sensitive to light and is also susceptible to oxidation and decomposition. In addition, the recording film is in a semi-liquid state and is therefore very sensitive to impacts and deformations of the disk.

Information on a CD-R can be written in several ways.

The most common method of recording a disc in one pass (disk-at-once), when a file from the hard drive is written directly in one session and adding information to the disc is impossible. In contrast, the multi-session recording method (track-at-once) allows you to record individual sections (tracks) and gradually increase the amount of information on the disk.

Like any drives, CD-R and CD-RW are available in two versions: with a standard interface for connecting to an IDE connector (E-IDE) and with a high-speed SCSI interface. External CD-RW drives are available with SCSI and USB interfaces.

The amount of built-in cache memory is important for recording devices, since it is in it that data coming from the hard drive is accumulated. The average cache memory size is 2 - 4 MB. The most popular drives on the Russian market are those with the Panasonic, Sony, Ricoh, Teac, and Yamaha brands. The highest quality and most expensive models are produced by Plextor and Hewlett-Packard. Mitsumi models are popular among inexpensive IDE drives.

Thanks to the further development of CD technologies, the following appeared:

modified CD-R disks with a capacity of up to 870 MB -- 1 GB, produced by Traxdata, Philips and Sony;

Double Density CD standard, proposed by Sony for discs of all modifications (CD, CD-R, CD-RW), which allows increasing the speed of traditional CDs to 1.3 GB, or 150 minutes of audio information;

FMD-ROM disk containing up to 100 working layers, the total capacity of which is at least 140 GB. Each layer of such a disk contains a luminescent substance that emits light under the action of a reading beam. Each layer glows differently, but at the same time is perfectly transparent to laser beams, which allows information to be read simultaneously from several layers.

Posted on Allbest.ru

Design and main components of the cd rom drive. Open Library - an open library of educational information. Optical disc structure

Send your good work in the knowledge base is simple. Use the form below

Similar documents