What can be a carrier of information? That on which everything that we need to remember can be preserved, for human memory is short-lived. Our ancestors left important data on the ground, and on stone, and on wood, and on clay until paper appeared. It turned out to be a material that meets the most important requirements for a data carrier. It was light, durable, easy to record and compact.
These requirements are met by modern storage media - optical(these are CDs or laserdiscs). True, at the transitional stage (since the beginning of the 20th century), between paper and disks, magnetic tape helped us a lot. But her days are over. To date, the most convenient and reliable receptacle and storage of information are disks.
And how to put the information on the disk? The concept of "recording a cassette" has been known to us for more than a dozen years. We are also talking about disks. Only this process has become much easier and cheaper.
Today we will talk about optical storage media: device, recording technology, main differences.
CD-R became the very first recordable optical media. They had the ability to record only once. The data were stored when the working layer was heated by a laser, causing its chemical reaction (at t? = 250°C). At this point, dark spots are formed in places of heating. That's where the concept of "burn" came from. DVD-R discs are burned in a similar way.
The situation is slightly different with CD, DVD and Blu-ray discs that have an overwrite function. Such dark dots do not form on their surface, because. the working layer is not a dye, but a special alloy, which is heated by a laser up to 600°C. Then, the areas of the disk surface that fell under the laser beam become darker and more reflective.
At the moment, in addition to CD discs, which can be considered pioneers in a number of optical media, discs such as DVD and Blu-ray have appeared. These types of discs are different from each other. For example, capacity. A Blu-ray disc can hold data up to 25 GB, a DVD disc can hold up to 5 GB, and a CD disc can hold up to 700 MB in total. The next difference is the way data is read and written to Blu-ray drives. The blue laser is responsible for this process, the wavelength of which is one and a half times less than that of the red laser of CD or DVD drives. That is why on the surface of Blu-ray discs, equal in area to discs of other types, you can record information many times larger.
laser disc formats
The three types of laser discs listed above can also be classified according to their formats:
1. CD-R, CD-RW discs are the same in size (up to 700; sometimes 800 MB, but such discs are not readable by all devices). The only difference is that CD-R is a one-time recordable disc, while CD-RW is reusable.
2. DVD-R, DVD+R, and DVD-RW format discs differ only in the ability to rewrite DVD-RW discs multiple times, but otherwise the parameters are the same. 4.7 GB is the size of a standard DVD and 1.4 GB is the size of an 8 cm DVD.
3. DVD-R DL, DVD+R DL are double-layer discs that can hold 8.5 GB of information.
4. Formats BD-R - Blu-ray discs are single-layer, 25 GB and BD-R DL - Blu-ray discs are double-layer, 2 times larger.
5. Formats BD-RE, BD-RE DL Blu-ray discs - rewritable, up to 1000 times.
Discs with "+" and "-" signs are a relic of format disputes. Initially, it was believed that "+" (for example, DVD + R) is the leader for the computer industry, and "-" (DVD-R) is the quality standard for consumer electronics. Now almost all equipment easily recognizes discs of both formats. None of them have clear advantages over each other. The materials for their production are also identical.
what are optical discs
The disc itself, which is used at home to record information, is no different in size from commercially produced discs. The structure of all optical media is multilayer.
- The basis of each is the substrate. It is made of polycarbonate, a material resistant to various external environmental influences. This material is transparent and colorless.
- Next comes the working layer. For recordable and rewritable discs, it differs in its composition. For the former, it is an organic dye, for the latter, a special alloy that changes the phase state.
- Then comes the reflective layer. It serves to reflect the laser beam, and may include aluminum, gold or silver.
- Fourth - protective layer. The protective layer, which is a hard varnish, covers only CDs and Blu-ray discs.
- The last layer is the label. This is the name of the top layer of varnish that can quickly absorb moisture. It is thanks to him that all the ink that falls on the surface of the disc during the printing process dries quickly.
the process of transferring information to disk
Now a drop of scientific theory. All optical storage media have a spiral track running from the very center to the edge of the disk. It is along this track that the laser beam records information. The spots formed during the "burning" of the laser beam are called "pits". Areas of the surface that remain untouched are called "lands". In binary language, 0 is pit and 1 is land. When the disc starts playing, the laser reads all the information from it.
"Pits" and "lands" have different reflectivity, therefore, the drive easily distinguishes all dark and light areas of the disk. And this is the very sequence of ones and zeros inherent in all physical files. Gradually, it became possible to increase the accuracy of focusing due to the development of technologies that have achieved a reduction in the wavelength of a laser beam. Now a much larger amount of information can be placed on the same area of the disk as before. the distance between the laser and the working layer directly depends on the wavelength. Shorter wave means shorter distance.
disc burning methods
- Recording a disc in domestic conditions occurs with the help of a laser beam. It is also called "burning" or "cutting".
Recording in the industrial production of discs is called stamping. In this way, discs with recording of music, movies, computer games are produced in large quantities. All the information that gets on the disk during stamping is a lot of tiny depressions. Something similar happened when gramophone records were made.
organization of the recording process on optical media
Stage 1. Media type recognition. We loaded the disc and wait until the recorder gives out information about the appropriate recording speed and the most optimal power of the laser beam.
Stage 2. The recording management program queries the recorder about the type of media being used, the amount of free space, and the speed at which the disc should be burned.
Stage 3. We indicate all the necessary data requested by the program, and make a list of files that require writing to disk.
Stage 4. The program transfers all the data to the recorder and monitors the entire “burning” process.
Stage 5 The recorder sets the power of the laser beam and starts the recording process.
Even with media of the same format, the quality of the recording can be drastically different. In order for the recording quality to be high, you should pay attention to the speed specified in the recording. There is a "golden rule" - fewer errors at lower speed and vice versa. The recorder itself, namely, its model, also plays a significant role.
signature on optical discs
It is advisable to immediately sign the disk on which some information appeared, in order to avoid confusion. This can be done in different ways:
- printing text on blanks, the surface of which is varnished and allows you to print texts and images using an MFP with a special tray.
- using a recorder, with the support of special technologies that apply text and a single-color image to a special surface. The cost of such disks can be 2 times higher than the cost of simple disks;
- a signature made independently by hand (with a special marker);
- LabelTag technology - the text is applied directly to the disk work surface. The inscription may not always be well read;
- labels printed separately on any of the printers. Their use is not welcome, because. they can damage the surface of the disc, come off at the time of its playback.
duration of storage of optical storage media
On the labels of new discs, you can see a period that indicates how long you can save data on this medium. Sometimes this figure corresponds to 30 years. In reality, such a period is practically impossible. During its existence, the disk can be subjected to various influences and damage. If it was recorded at home, then its shelf life is reduced even more. Only ideal storage conditions will keep all the data on the disks safe and sound.
All the variety of optical discs currently used in computers and household equipment can be divided into two main groups: CDs (Compact Disk) and DVDs (Digital Versatile Disk/Digital Video Disk). CDs and DVDs have the same physical dimensions (diameter 120/80 mm), but differ in data recording density and characteristics of the optical heads used for reading data. CDs and DVDs are divided into three categories based on functionality:
Not writeable (read-only);
Write-once and read-multiple;
With the possibility of rewriting.
The principle of operation of all currently existing optical drives is based on the use of a laser beam to write and read information in digital form. During recording, the laser beam leaves a trace on the active layer of the optical carrier, which can then be read using the same laser beam, but at a lower power than during recording.
CD drives use a 780 nm infrared laser and a 0.45 numerical aperture optical system to read data. (Numerical aperture - from lat. apertura- hole - equal to 0.5 n sinα, where n is the refractive index of the medium in which the object is located, α is the angle between the extreme rays of the conical light flux entering the optical system.) Capacity of standard CDs used for data storage , is 650 or 700 MB. CDs recorded in the AudioCD format (which was developed for consumer audio devices) can hold up to 80 minutes of stereo recording.
To read data into DVD-actuators are used 
a red laser with a wavelength of 650 nm and an optical system with a numerical aperture of 0.6. The capacity of standard DVDs is 4.7 GB or more.
CD-ROM (Compact Disk Read Only Memory) - non-rewritable laser-optical discs, or ROM CDs. The CD is made using a very powerful infrared laser that burns 0.8 micron holes into a special glass control disc. At the same time, depressions are formed on the surface - depressions (eng. pit) - and even spaces - platforms (eng. land). The writing starts at some distance from the hole in the center and moves towards the edge in a spiral. A template is made on this control disk with protrusions in those places where the laser burned holes. Liquid resin (polycarbonate) is introduced into the template, and thus a CD is obtained with the same set of holes as in a glass disc. A very thin layer of aluminum is applied to the resin, which is covered with a protective varnish. CD-ROMs are written by the manufacturer and are used to distribute large amounts of read-only information. At the same time, the user does not have the opportunity to either erase or write information to such a disk.
CD-Rs are made from polycarbonate blanks, which are also used in the production of CDs. However, the structure has some differences. A spiral track is preliminarily applied to the disc, and there is a dye layer between the polycarbonate layer and the reflector. At the initial stage, the dye layer is transparent, which allows the laser light to pass through it and be reflected from the reflector layer. When information is written, the laser power increases and when the beam reaches the dye, the dye heats up, as a result, the chemical bond is destroyed. This change in molecular structure creates a dark spot. When reading, the photodetector captures the difference between dark spots and transparent areas. This difference is perceived as the difference between depressions and platforms. As a dye, metal nitrogen, cyanine, phthalocyanine or the most promising formazan, a mixture of cyanine and phthalocyanine, are used. The reflective layer is the thinnest film of gold or silver.
CD-RW allow you to repeatedly record information on discs with a reflective surface, under which a layer of the Ag-In-Sb-Te (silver-indium-antimony-tellurium) type with a variable state phase is deposited. This alloy has two states: crystalline and amorphous, which have different reflectivity. The CD burner is equipped with a laser with three power options. At the highest power, the laser melts the alloy from a crystalline state (high reflectivity) to an amorphous state (low reflectivity) to form a depression. At an average power, the alloy melts and returns back to its natural crystalline state, while the cavity again turns into a platform. At low power, the laser reads information, determining the state of the material (no state transition occurs).
DVD is the same compact disc made on the basis of polycarbonate with cavities and pads. However, there are several differences. The DVD has a smaller cavity (0.4 microns instead of 0.8 as usual), tighter helix (0.74 microns instead of 1.6), uses a shorter red laser beam (650 nm instead of 780 nm). Together, these improvements resulted in a sevenfold increase in disk capacity (4.7 GB).
Currently there are 4 formats DVD:
1. Single-sided single-layer (4.7 GB).
2. Single-sided double-layer (8.5 GB).
3. Double-sided single-layer (9.4 GB).
4. Double-sided double-layer (17 GB).
With two-layer technology, a translucent reflective layer is placed on the lower reflective layer. Depending on where the laser is focused, it is reflected either from one layer or another. To ensure reliable reading of information, the pits and areas of the lower layer must be slightly larger in size, so the capacitance of the lower layer is slightly less than that of the upper layer.
DVDs have the following features:
Significantly larger capacity compared to CD;
CD compatible;
High speed data exchange with DVD drive;
High reliability of data storage.
It is worth noting that the emergence of new technologies Blu-ray and HD-DVD allows you to place on the disc information several times more than on a regular DVD. These technologies are based on the use of a blue laser with a wavelength of 405 nm. The HD-DVD format records 15 GB of information on one layer and 30 GB on two layers. Blu-ray, respectively, stores 25 and 50 GB.
Magneto-optical disks
The principle of operation of a magneto-optical drive (Magneto Optical) is based on the use of two technologies - laser and magnetic.
The fundamental structure of all types of magneto-optical disks is the same, the only difference can be that some disks have one working surface, while others have two. The principal structure of a one-sided disk is shown in Figure 2.17.
The surface of a magneto-optical storage device (MOD) is covered with an alloy whose properties change both under the influence of heat and under the influence of a magnetic field. If the disk is heated above a certain temperature, then it becomes possible to change the magnetic polarization by means of a small magnetic field. This is the basis for reading and writing MOD technologies.
So, when recording, the laser beam heats the section of the disk where the recording should be made to the so-called "Curie point" (for most of the alloys used, this state occurs at a temperature of about 200 ° C).
At the Curie point, the magnetic permeability drops, and a change in the magnetic state of the particles can be produced by a relatively small magnetic field. The field sets all bit cells to the same state. This erases all information on the disk.
Then the direction of the magnetic field is reversed, and the laser is turned on only at those moments when it is necessary to change the orientation of the particles in the bit cell (bit value). Then the alloy is cooled, and its particles solidify in a new position.
When reading, a low power laser beam is used. The reflected light hits a photosensitive element, which determines the direction of polarization. Depending on this direction, the photosensitive element sends a binary one or a binary zero to the magneto-optical drive controller.
Magneto-optical drives are built-in and external. In addition to conventional disk drives, the so-called optical libraries with automatic disk change are widely used, the capacity of which can be hundreds of gigabytes and even several terabytes. The disk change time is a few seconds, and the access time and data transfer speed are the same as conventional disk drives.
Flash drives
Information carriers based on flash memory chips are now widely used in digital cameras, mobile phones, and computers.
Flash memory is a special type of non-volatile, rewritable semiconductor memory. A flash memory cell consists of a single transistor of a special architecture that can store multiple bits. The bulk of media based on flash technology is the so-called flash cards, which are the main storage media for modern portable technology. The second direction, which is now rapidly developing, is a flash memory with a USB interface for direct connection to a computer. The advantage of flash memory over hard drives, CD-ROMs, and DVDs is that there are no moving parts, so flash is more compact and provides faster access. Information written to flash memory can be stored for a very long time (from 20 to 100 years) and is able to withstand significant mechanical loads (5-10 times higher than the maximum allowable for conventional hard drives). The disadvantage, in comparison with hard drives, is the relatively small volume, as well as the limitation on the number of rewriting cycles (from 10,000 to 1,000,000 for different types).
Computer flash drives in the form of a key fob with a USB port are used as removable storage media and have a capacity of 16, 32, 64, 128, 256, 512 MB, 1 GB, 2 GB, 4 GB, 8 GB, which, of course, is not the limit, so how technology is constantly improving.
Input devices
Input devices convert information from peripheral devices into digital form. The following devices are used to enter information: keyboard, manipulators, scanners, digitizers (digital tablets), touch screens, speech input tools, digital cameras, etc.
Keyboard
The keyboard is the main means of entering information into a PC. It is a matrix of keys combined into a single whole, and an electronic unit for converting keystrokes into a binary code. Each key on the keyboard corresponds to a seven-digit scan code (scan code). When a key is pressed, the keyboard hardware generates a one-byte press code, and when released, respectively, a one-byte release code. The click code is the same as the scan code. The release code differs from the scan code by the presence of one in the most significant bit of the byte. If the key remains pressed for more than 0.5 s, then press codes are automatically generated at a frequency of 10 times per second. Automatic code generation stops when the key is released or another key is pressed. So, when a key “sticks”, in order to eliminate the consequences, it is enough to press any other key. Principle 
keyboard action is shown in Figure 2.19. When a key is pressed, the signal is registered by the keyboard controller and initiates a hardware interrupt, the processor stops working and performs the scan code analysis procedure. The interrupt is processed by a special program that is part of the read-only memory (ROM). Any keyboard has 4 groups of keys:
Typewriter keys for entering uppercase and lowercase letters, numbers and special characters;
Service keys that change the meaning of pressing the rest and perform other actions to control keyboard input (Alt, Ctrl, Shift, Tab, Backspace, Enter, Caps Lock, Num Lock, Print Screen, etc.);
Function keys (F1-F12), the meaning of pressing which depends on the software product;
The keys of the dual-mode small numeric keypad, providing fast and convenient entry of digital information, as well as cursor control and switching keyboard modes.
Manipulators
Manipulators are devices designed to control the cursor (pointer) on the monitor screen.
Manipulators make the user's work more convenient, especially in programs with a graphical interface. Manipulators include: mouse, joystick, light pen, trackball, etc.
The mouse is a device for specifying the desired points on the display screen by moving it on a flat surface. The coordinates of the mouse location are transmitted to the computer and cause the mouse cursor (pointer) to move accordingly. In accordance with the principle of operation, opto-mechanical and optical mice are distinguished.
The principle of operation of an opto-mechanical mouse (Fig. 2.20) is to convert the movement of the mouse into electrical impulses generated using an optocoupler - LEDs (light sources) and photodiodes (light receivers). When you move the mouse, the rotation of the ball through the rollers is transferred to the disks with "slots". The rotation of the disc causes the light flux between the LED and the photodiode to be blocked, which leads to the appearance of electrical impulses. The pulse frequency corresponds to the mouse movement speed.
Currently, optical mice are widely used. All modern optical mice constructively contain a miniature video camera, which uses a CMOS sensor as a photosensitive element. (An image sensor containing a light-sensitive layer of silicon in which photons are converted into electrons. CMOS - Complementary Metal Oxide Semiconductor - CMOS - Complementary Metal Oxide Semiconductor Structure) A light source, usually red, is located opposite the sensor to illuminate the surface under the mouse Light-emitting diode. When the mouse is moved, the sensor processes the surface images and sends them as signals to a specialized DSP (Digital Signal Processing) processor, which analyzes changes in the received images and determines the direction of mouse movement accordingly. However, optical mice cannot be used on glass or mirror surfaces.
There are also wireless mice in which, using the built-in transmitter, information is transmitted by infrared rays or radio signals. These signals are recorded by a special receiver and fed into the computer. When using infrared, the mouse must be within line of sight of the receiver. If the radio band is used, then this condition is not mandatory.
The latest development in the field of mouse manipulators is the use of laser technology. When you move the mouse, the laser beam, reflected from the surface, hits the sensor, which translates the detected changes in the surface into the movement of the cursor on the monitor screen. The use of a laser beam allows the mouse to be made more sensitive than a conventional optical mouse, as well as to use it on any surface. At the same time, the laser is invisible and safe for humans.
The quality of a particular mouse model is determined by the resolution of the mouse, which is measured in dpi (dot per inch - the number of dots per inch), although there is another unit cpi (count per inch - the number of counts per inch). Typically, mouse resolution, depending on the model, ranges from 300 to 900 dpi. The higher the resolution, the more accurately the mouse cursor is positioned. Structurally, mice are made in the form of a plastic box with buttons, as a rule, with two - the main one and the additional one.
Another manipulator in which the cursor is moved by manually rotating a ball protruding above a flat surface is a trackball (Fig. 2.22, a). The principle of operation is the same as that of an opto-mechanical mouse. The trackball is essentially the same mouse, only turned upside down.
A joystick is a device that is usually used in game consoles and game computers (Fig. 2.22, b). It is a lever, the movement of which leads to the movement of the cursor on the screen. The lever has one or more buttons. In this case, the cursor takes the form of some moving object.
A light pen can be used to indicate a point on a display screen or to form images. The tip of the light pen contains a photocell that reacts to the light signal transmitted by the screen at the point where the pen is touched. Since the monitor screen consists of many dots (pixels), when the button is pressed on the pen, a signal is transmitted to the PC, according to which the coordinates of the electron beam are calculated at the time of its registration. Another area of application for a light pen is its use with a digitizer. Digitizer (digitizer) is a device designed to enter graphic information. When the pen is moved over the tablet, its coordinates are fixed in the computer's memory, i.e. in this case, the light pen performs a "writing" function.
Touch screens
A touch screen is a screen combined with touch devices that allows you to enter information into a computer with the touch of a finger.
In general, when working with a touch device, the user touches a cursor (the surface of this device), a letter, a number, or another displayed figure on the screen with a finger. Regardless of the physical nature of the principles underlying the functioning of a sensor device, a rectangular coordinate system is associated with its surface, which allows you to fix the touch of a finger and transmit a signal to a computer. According to the principle of operation, the following sensor technologies are distinguished : resistive, capacitive, infrared and technology based on surface acoustic waves (SWA).
resistive technology. Resistive technology is based on the method of measuring the electrical resistance of a part of the system at the moment of touch. The resistive screen has a high resolution (300 dots/inch), a long resource (10 million touches), a short response time (about 10 ms) and a low cost. But besides the pluses, there are also minuses, for example, such as a 20% loss 
light flux.
capacitive technology. The sensing element of a capacitive touch screen is glass with a thin, transparent, conductive coating on its surface. When touching the screen image capacitive; connection between the finger and the screen, which causes a current pulse to the point of contact (Fig. 2.24). Another capacitive NFI technology (Dynapro) (Fig. 2.25) is based on the use of an electromagnetic wave. NFI uses a special touch-sensitive electronic circuit that can detect a conductive object - a finger or a conductive input pen - through a layer of glass, as well as through gloves or other 
potential obstacles (moisture, gel, paint, etc.).
Surfactant technology(surface acoustic waves). In the corners of such a screen, a special set of elements made of piezoelectric material is placed, to which an electrical signal with a frequency of 5 MHz is applied. (Piezoelectric materials are substances that have a piezoelectric effect, that is, the appearance of an electric field under the influence of elastic deformations is a direct piezoelectric effect.) This signal is converted into an ultrasonic acoustic wave directed along the surface of the screen. Even a light touch on the screen at any point causes active absorption of waves, due to which the pattern of ultrasound propagation over its surface changes somewhat.
Infrared technology. Along the borders of the touch screen, special radiating elements are installed that generate light waves of the infrared range, light waves of the infrared range propagate along the surface of the screen, forming a kind of coordinate grid on its working surface.
If one of the infrared rays is blocked by a foreign object that has fallen into the zone of action of the rays, the beam stops arriving at the receiving element, which is immediately fixed by the microprocessor. It is worth noting that the infrared touch screen does not care what kind of object is placed in its workspace: pressing can be done with a finger, a fountain pen, a pointer, and even a gloved hand. Touch screens can be hinged and built-in (Fig. 2.28).
Over the past few years, touch screens have proven to be the most convenient way for human-machine interaction. Application touch screens has a number of advantages that are not available with any other devices. So, information systems made on the basis of touch kiosks help in obtaining the necessary or interesting information in exhibition halls, railway stations, government, banking, financial and medical institutions, etc. 
Scanners
A scanner is a device that allows you to transfer graphic information placed on a paper to a computer. 
magic or film.
These can be texts, drawings, diagrams, graphs, photographs, etc. The scanner, like a copier, creates a copy of the image of a paper document, but not on paper, but in electronic form.
The principle of operation of the scanner is as follows. The copied image is illuminated by a light source (usually a fluorescent lamp). In this case, a beam of light examines (scans) each section of the original. A beam of light reflected from a paper sheet through a reducing lens enters a charge-coupled device (CCD). (A device that accumulates an electronic charge when a light flux hits it. The charge level depends on the duration and intensity of illumination. In the English literature, the definition is CCD - Couple-Charget Device) A reduced image of the copied object is formed on the surface of the CCD by scanning. 
The CCD converts the optical image into electrical signals. A CCD is a matrix that contains a large number of semiconductor elements that are sensitive to light radiation.
In black-and-white scanners, several shades of gray are formed at the output of each CCD element using an analog-to-digital converter.
Color scanners use the RGB color model. The scanned image is illuminated through a rotating RGB filter or successively lit three colored lamps - red, green, blue. The signal corresponding to each primary color is processed separately. To do this, there are parallel lines of sensors, each of which perceives its own color. The number of transmitted colors ranges from 256 to 65,536 and even 16.7 million. The resolution of scanners is measured in the number of distinguishable dots per inch of an image. In this case, two values are indicated, for example 600 × 1200 dpi. The first is the number of horizontal dots, which is determined by the CCD matrix. The second is the number of vertical motor steps per inch. The first, the minimum value, should be taken into account.
According to their design, scanners are hand-held, flatbed, drum, projection, etc. Fig. 2.30).
Information output devices
Output devices are devices that output information processed by a computer for perception by the user or for use by other automatic devices.
The output information can be displayed on the monitor screen, printed on paper, reproduced in the form of sounds, transmitted in the form of any signals.
Monitors and video adapters
A monitor (display) is a device designed to display textual and graphic information for the purpose of its visual perception by the user.
The monitor is the main peripheral device and serves to display information entered using the keyboard or other input devices (scanner, digitizer, etc.). The monitor is connected to the computer via a video adapter. The following types of monitors are currently in use:
Based on a cathode ray tube (CRT);
- 
liquid crystal;
Plasma (gas-discharge).
The difference between these monitors lies in the different physical principles of imaging.
CRT-based monitors are no different from conventional TVs in terms of the principle of operation. When forming an image, the video data is converted into a continuous stream of electrons, which are “fired” by the cathode carcasses of the kinescope. The resulting electron beams are passed through a special guide grid, which ensures that the electrons hit exactly the right point, and then reach the luminescent layer. When bombarded with electrons, the phosphor emits light.
There are several types of cathode ray tubes, which differ from each other in the arrangement of the guide grating and the phosphor layer.
The most widely used monitors with the so-called shadow mask. In a kinescope of this type, a thin metal plate is used to position the electron beam, in which many holes are made by perforation (Fig. 2.32, a). The phosphor in such a kinescope is made in the form of colored triads, where each ellipsis - a luminous element of red, green and blue matter - represents one visible pixel.
Another type of kinescopes built using an aperture grating (Fig. 2.32, b) differs from kinescopes with a shadow mask in that it is not a bulky plate that serves to accurately position the electron beam, but a series of steel threads. The phosphor in a kinescope with an aperture grating is applied to the inner surface of the screen in the form of alternating vertical stripes.
In a CRT with a slotted mask, the guide grille is a plate with vertical long slots-slots (Fig. 2.32, c). The phosphor in such kinescopes is applied either in the form of continuous alternating strips, or in the form of elliptical strips, similar in shape to slots in a slit mask.
The considered types of kinescopes have their advantages and disadvantages. Thus, a CRT with a shadow mask, due to some of its design features, has a number of advantages over other types of kinescopes: a dense arrangement of color triplets, which makes it possible to achieve high image clarity, and a well-established production technology. The disadvantage is a decrease in the service life of the monitor - due to the large area, the perforated mask absorbs about 70-85% of all electrons emitted by the cathodes of the electron gun of the kinescope, resulting in a decrease in the range of brightness and contrast. To achieve a high color image, it is necessary to increase the intensity of the electron flow, which does not have the best effect on the service life of the monitor (as a rule, the life cycle of a device based on a CRT with a shadow mask does not exceed 7-8 years). The scope of such monitors is the processing of large arrays of text material, layout, photo retouching, color correction and CAD (automatic design systems).
The main advantages of a CRT with an aperture grating include greater brightness and contrast due to the greater electron throughput to the phosphor and the increased screen coverage area with the phosphor.
Among the shortcomings, one should note the occurrence of image distortions when displaying a large number of short strokes, in other words, when displaying text in small size.
Monitors using slit-mask tubes combine the advantages of the two previous device types without the disadvantages. Bright, vibrant colors, good contrast, clear graphics and text - all this makes them suitable for satisfying the needs of any category of users. Cathode ray tubes are designed and manufactured by a very limited number of companies. All other monitor manufacturers use purchased solutions. Among the most famous development companies are: Hitachi and Samsung - handsets based on a shadow mask; Sony, Mitsubishi and ViewSonic - aperture grille CRT; NEC, Panasonic, LG are devices that use a slit mask.
Liquid crystal monitors (LCD), or LCD monitors (LCD - Liquid Crystal Display) are digital flat-panel monitors. These monitors use a transparent liquid crystal substance that is sandwiched between two glass plates in the form of a thin film. The film is a matrix, in the cells of which crystals are located. Next to each plate is a polarizing filter, the polarization planes of which are mutually perpendicular.
From the course of physics, you know that if you pass light through two plates whose polarization planes coincide, then complete transmission of light is ensured. However, if one of the plates is rotated relative to the other, i.e. change the plane of polarization, the amount of transmitted light will decrease. When the planes of polarization are mutually perpendicular, the passage of light is shocked.
In LCD monitors, the light from the lamp, falling on the first polarizing filter, is polarized in one of the planes, for example, vertical, and then passes through a layer of liquid crystals. If liquid crystals turn the plane of polarization of a light beam by 90°, then it passes through the second polarization filter without hindrance, since the polarization planes coincide. If there is no rotation, then the light beam does not pass. Thus, by applying voltage to the crystals, it is possible to change their orientation, i.e., thereby control the amount of light passing through the filters. In modern LCD monitors, each crystal is controlled by a separate transistor, i.e. TFT (Thin Film Transistor) technology is used - technology of "thin film transistors". The pixel in the LCD monitor is also formed from red, green and blue colors, and different colors are obtained by changing the applied voltage, which leads to the rotation of the crystal and, accordingly, to a change in the brightness of the light flux.
In plasma monitors (PDP - Plasma Display Panel), the image is formed by the emission of light by gas discharges in the pixels of the panel. The picture element (pixel) in a plasma display is much like a conventional fluorescent lamp. The electrically charged gas emits ultraviolet light, which strikes the phosphor and excites it, causing the corresponding cell to glow with visible light. Modern plasma monitors use the so-called plasmavision technology - this is a set of cells, in other words, pixels, which consist of three sub-pixels that transmit colors - red, green and blue.
Structurally, the panel consists of two flat glass plates located at a distance of about 100 microns from each other. Between them is a layer of inert gas (usually a mixture of xenon and neon), which is affected by a strong electric field. The thinnest transparent conductors - electrodes - are applied to the front transparent plate, and mating conductors are applied to the back. The rear wall has microscopic cells filled with phosphors of three primary colors (red, blue and green), three cells for each pixel. The principle of operation of a plasma panel is based on the glow of special phosphors when exposed to ultraviolet radiation that occurs during an electric discharge in a highly rarefied gas environment. With such a discharge, a conductive “cord” is formed between the electrodes with a control voltage, consisting of ionized gas (plasma) molecules. Therefore, panels operating on this principle are called plasma panels. The ionized gas acts on a special fluorescent coating, which, in turn, emits light visible to the human eye.
The quality of a particular monitor can be assessed by the following main parameters:
Resolution;
Screen size;
The number of reproduced colors;
Screen refresh rate.
Monitor resolution. Usually monitors can work in two modes: text and graphic. In text mode, ASCII characters are displayed on the monitor screen. The maximum number of characters that can be displayed on the screen is called the information capacity of the screen. In normal mode, the screen contains 25 lines of 80 characters each, so the information capacity is 2000 characters. In graphics mode, images are displayed on the screen, formed from individual elements - pixels. In graphics mode, resolution is measured by the maximum number of horizontal and vertical pixels on a monitor screen. The resolution depends on both the characteristics of the monitor and the video adapter. The higher these values, the more objects can be placed on the screen, the better the image detail. For example, a resolution of 800 × 600 means that 800 vertical and 600 horizontal lines can be conventionally drawn on the screen (Fig. 2.35). Each pixel of the screen is involved in the formation of the image, therefore, at a resolution of 800×600, the number of addressable cells is 480,000 pixels. For LCD monitors, resolution is determined by the number of cells located across the width and height of the screen. Modern LCD monitors generally have a resolution of 1024x768 or 1280x1024.
The most important characteristic that determines the resolution and clarity of the image on the screen is the size. 
grains (dot pitch) of the phosphor of the monitor screen. The grain size of modern monitors is between 0.25 and 0.28 mm. Grain refers to the distance between two dots of the same color phosphor. For tubes with a shadow mask, the grain is measured diagonally, for the other two, horizontally. Standard resolutions: 640x480, 800x600, 1024x768, 1600x1200, 1800x1440, etc.
Screen size. The length of the diagonal of the visible area of the image is usually used as a measure. For liquid crystal (LCD) displays, the size of the visible area is the same as the size of the panel. For cathode ray tube (CRT) monitors, the visible area is somewhat smaller. This is due to the design features of the CRT itself. CRT monitors come in 14", 15", 17", 19", and 22" screen sizes. For LCD panels 15, 17, 18, 19, 20 and more inches are used.
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External memory
Optical discs
Optical (laser) disks are currently the most popular storage media. They use the optical principle of recording and reading information using a laser beam.
Information on a laser disc is recorded on one spiral track starting from the center of the disc and containing alternating sections of depressions and protrusions with different reflectivity.
When reading information from optical discs, a laser beam installed in the drive falls on the surface of a rotating disc and is reflected. Since the surface of the optical disk has areas with different reflection coefficients, the reflected beam also changes its intensity (logical 0 or 1). The reflected light pulses are then converted by photocells into electrical impulses.
In the process of recording information on optical discs, various technologies are used: from simple stamping to changing the reflectivity of sections of the disc surface using a powerful laser.
There are two types of optical discs:
CD-disks (CD - Compact Disk, CD), which can be recorded up to 700 MB of information; DVD-disks (DVD - Digital Versatile Disk, digital universal disk), which have a much larger information capacity (4.7 GB), since the optical tracks on them are thinner and more densely placed.
DVDs can be double-layered (capacity 8.5 GB), while both layers have a reflective surface that carries information.
In addition, the information capacity of DVD discs can be further doubled (up to 17 GB) since information can be recorded on both sides.Currently (2006), optical discs (HP DVD and Blu-Ray) have entered the market, the information capacity of which is 3-5 times greater than the information capacity of DVD discs due to the use of a blue laser with a wavelength of 405 nanometers.
Optical drives are divided into three types:
- No write capability- CD-ROM and DVD-ROM
(ROM - Read Only Memory, read-only memory).
CD-ROMs and DVD-ROMs store information that was written to them during the manufacturing process. Writing new information to them is not possible.- Write-once, read-once -
CD-R and DVD±R (R - recordable, recordable).
Information can be written to CD-R and DVD±R discs, but only once. Data is written to the disc by a high-powered laser beam, which destroys the organic dye of the recording layer and changes its reflective properties. By controlling the power of the laser, an alternation of dark and light spots is obtained on the recording layer, which, when read, are interpreted as logical 0 and 1.- With the ability to rewrite- CD-RW and DVD±RW
(RW - Rewritable, rewritable). On CD-RW and DVD±RW discs, information can be written and erased many times.
The recording layer is made of a special alloy that can be brought to two different stable states of aggregation by heating, which are characterized by different degrees of transparency. When recording (erasing), the laser beam heats up a section of the track and puts it into one of these states.
When reading, the laser beam has less power and does not change the state of the recording layer, and alternating sections with different transparency are interpreted as logical 0 and 1.The main characteristics of optical drives:
disk capacity (CD - up to 700 MB, DVD - up to 17 GB) the speed of data transfer from the carrier to the RAM - measured in fractions, multiples of the speed
150 KB/s for CD drives (The first CD drives had this reading speed) and
1.3 MB / s for DVD drives (This was the speed of reading information in the first DVD drives)
Currently, 52x-speed CD drives are widely used - up to 7.8 MB / s.
CD-RW discs are recorded at a lower speed (for example, 32x).
Therefore, CD drives are marked with three numbers "read speed X CD-R write speed X CD-RW write speed" (for example, "52x52x32").
DVD drives are also marked with three numbers (for example, "16x8x6"access time - the time required to search for information on the disk, measured in milliseconds (for CD 80-400ms). If the rules of storage (storage in cases in a vertical position) and operation (without scratches and dirt) are observed, optical media can retain information for decades.
Additional information about disk structure
The disk, created by an industrial method, consists of three layers. An informational pattern is applied to the basis of a disk made of transparent plastic by stamping. For stamping, there is a special matrix-prototype of the future disc, which extrudes tracks on the surface. Next, a reflective metal layer is sprayed onto the base, and then a protective layer of a thin film or special varnish is also sprayed on top. Various drawings and inscriptions are often applied to this layer. Information is read from the working side of the disk through a transparent base.
Recordable and rewritable CDs have an additional layer. For such discs, the base does not have an information pattern, but between the base and the reflective layer there is a recording layer, which can change under the influence of high temperature. When recording, the laser heats up the specified sections of the recording layer, creating an information pattern.
A DVD disc may have two recording layers. If one of them is performed using standard technology, then the other is translucent, applied below the first and has a transparency of about 40%. To read dual-layer discs, complex optical heads with a variable focal length are used. The laser beam, passing through the translucent layer, is first focused on the inner information layer, and upon completion of its reading, it is refocused on the outer layer.
optical disc
Optical disc
a data carrier in the form of a plastic disc designed to record and reproduce sound (CD CD), image (video disc), alphanumeric information (CD-ROM, DVD), etc. using a laser beam. The first optical discs appeared in 1979. Philips created them to record and reproduce sound. An optical disc consists of a rigid, optically transparent base, on which a thin working layer and an additional protective layer are applied. Due to the optical reading method, optical discs are much more durable than gramophone records. A standard CD is 120 mm (4.5 inches) in diameter, 1.2 mm thick, and has a 15 mm center hole. CDs are made of very durable transparent plastic - polycarbonate or PVC. A label is placed on one side of the disc, and the other side has a mirror surface that shimmers with rainbow colors. This is a recording zone, the spiral track of which consists of pits - depressions of various lengths. The distance between two adjacent tracks of the spiral is 1.6 µm, i.e. the recording density is 100 times greater than that of a conventional record. The pits are 0.6–0.8 µm wide and variable in length. It reflects the length of the "1" sequences of the recorded digital signal and can vary from 0.9 to 3.3 µm. Information in the form of pits is protected from mechanical damage on the one hand by the transparent material of the disc, and on the other by a layer of plastic and a label. Compared to mechanical sound recording, it has a number of advantages: a very high recording density and the complete absence of mechanical contact between the carrier and the reader during recording and playback. Music CDs are recorded at the factory. Like phonograph records, they can only be listened to. With the help of a laser beam, signals are recorded on a rotating optical disk in a digital code. As a result of recording, a spiral track is formed on the disc, consisting of miniature depressions and smooth areas. In playback mode, a laser beam focused on a track travels across the surface of a rotating optical disc and reads the recorded information. In this case, the cavities are read as ones, and the areas that evenly reflect light are read as zeros.
Contactless reading of information from a CD is carried out using an optical head or a laser pickup. The optical head consists of a semiconductor laser, an optical system and a photodetector that converts light into electrical. The readout laser beam is focused on a spiral track with pits located deep in the disk. The head never comes into contact with the disk - it is always at a strictly defined distance from it, which ensures that the track of pits is in the focus of the optical system.
Multimedia technology combines text and graphics with sound and moving images on a personal computer. As storage media in such multimedia computers, optical CD-ROMs (Compact Disk Read Only Memory - that is, read-only CD-ROM) are used. Outwardly, they do not differ from audio CDs used in players and music centers.
The capacity of one CD-ROM reaches 650 MB, in terms of capacity it occupies an intermediate position between floppy disks and a hard magnetic disk (hard drive). The CD drive is used to read CDs. Information on a CD is written only once in industrial conditions, and on a personal computer it can only be read. A variety of games, encyclopedias, art albums, maps, atlases, dictionaries and reference books are published on CD-ROM. All of them are equipped with convenient search engines that allow you to quickly find the material you need. The memory capacity of two CD-ROMs is enough to accommodate an encyclopedia that is larger than the Great Soviet Encyclopedia.
Information optical CDs are designed for single (so-called CD-R) and multiple (so-called CD-RW) recording of information on a personal computer equipped with a special drive. This makes it possible, like a tape recorder, to make recordings on them at home. CD-R discs can only be recorded once, but CD-RW discs can be recorded many times, like on a magnetic disk or tape, you can erase the previous recording and make a new one in its place.
1 - CD; 2 - a translucent coating that protects the information printed on the CD from damage; 3 - reflective coating (the recording medium itself); 4 - protective layer; 5 - focusing; 6 – laser beam; 7 - optical splitter; 8 – photodetector; nine - ; 10 - electric motor rotating the disk
The existing CDs are being replaced by a new media standard - DVD (Digital Versatile Disc or General Purpose Digital Disc). In appearance, they are no different from CDs. Their geometric dimensions are the same. The main difference of a DVD disc is a tenfold higher density of information recording. This is achieved due to the shorter laser wavelength and the smaller spot size of the focused beam, which made it possible to halve the distance between the tracks. The DVD standard is defined in such a way that future models of readers will be developed taking into account the ability to play all previous generations of CDs, that is, in compliance with the principle of "backward compatibility". In 1995 Philips developed the re-recording CD technology. The DVD standard allows for significantly longer video playback times and improved quality compared to existing CD-ROMs. DVD drives are advanced CD-ROM drives.
Encyclopedia "Technology". - M.: Rosman. 2006 .
See what "optical disc" is in other dictionaries:
A data carrier in the form of a plastic or aluminum disk intended for recording and/or reproducing sound (CD), images (Video CD), alphanumeric information, etc. using a laser beam. The recording density of St. 108… … Big Encyclopedic Dictionary
optical disc- A disc containing digital data that can be read using optical technology. [GOST 25868 91] Equipment topics. periphery. processing systems information EN optical disk … Technical Translator's Handbook
OPTICAL DISC, in computer technology, a compact storage device consisting of a disk on which information is written and read using a laser. The most common type is CD ROM. Audio CDs also feature... ... Scientific and technical encyclopedic dictionary
Working with optical discs Optical disc Optical disc image, ISO image Optical drive emulator Software for working with optical disc file systems Recording technologies Recording modes Packet recording Types ... ... Wikipedia
Data carrier in the form of a disk made of a transparent material (glass, plastic, etc.) with metallized microscopy, depressions (pits), which together form spiral or annular ... ... Big encyclopedic polytechnic dictionary
A data carrier intended for recording and/or reproducing information using focused laser radiation. It consists of a rigid (usually optically transparent) base, on which a light-sensitive or reflective layer is applied and ... ... encyclopedic Dictionary
optical disc- 147 optical disc: A disc containing digital data readable by optical technology
1. Introduction
3.1. Technical features of competitors
4. Prospects for the development of optical storage.
5. Comparative analysis of optical drives
5.1 ASUS DRW-1608P
5.2 NEC ND-3540A
6. Safety precautions when working with a PC
6.1 Organization of the workplace
6.2 Safety
Conclusion
List of used literature
1. Introduction
Over the past few years, optical storage has undergone significant changes. Today, the optical drive is an integral part of the PC - which determines the relevance of the chosen topic.
The optical drive has become an integral part of the PC, because. various software products (especially games and databases) began to take up a significant amount of space, and their supply on floppy disks turned out to be excessively expensive and unreliable. Therefore, they began to be supplied on optical discs (the same as regular music), and some games and programs work directly from an optical disc, without requiring copying to a hard drive.
Also, a modern computer is a powerful multimedia center that allows you to play music, watch movies.
The purpose of this thesis is to study optical storage devices. During the study, the following questions will be explored:
¾ The history of the optical drive
¾ The history of the development of optical storage
¾ Prospects for the development of optical storage
¾ Comparative analysis of optical drives
¾ Safety precautions when working with a PC
2. The history of the creation of an optical drive
Optical discs are practically the same age as personal computers. And they even have their parents - vinyl records. The year of arrival of optical discs in modern technology is considered to be 1982. It was then that the two largest companies Philips and Sony took up new developments. Akio Morita, executive director of Sony, who also became famous for authoring the famous Walkman player, believed that such discs should be designed for listening to classical music. And the standard for the duration of the sound was the time of the sound of Beethoven's 9th symphony, which is approximately 73 minutes. It was decided to make the standard playing time equal to 74 minutes 33 seconds. This is how the Red Book standard was born, in which the CD-DA (CD-Digital Audio) disc standard was described. Moreover, its predecessor was the standard of an ordinary vinyl record with a duration of 45 minutes, which has the worst sound quality and performance characteristics of the carrier incomparable with CD. Along with Sony, Philips also took part in the formation of the Red Book standard. Strict requirements were introduced for size, sound quality, data encoding method and the use of a single spiral track.
On CD-DA, the data is presented as follows.
Structurally, the entire disk can be divided into three main parts: lead-in (introductory zone that stores all information about the structure and ownership of the disk), PMA (Program Memory Area - the data itself) and lead-out (output zone, consisting of almost one " zeros" and is essentially an indicator of the end of the disk).
All information is recorded on CD-DA as tracks separated by gaps (pre-gap) equal to 2 seconds. There can be 99 such tracks, and each of them can be divided into 99 fragments. The concept of tracks is somewhat secondary, but well suited to the simplest description of the structure of a disk.
In fact, the information on the disk is presented in the form of blocks-segments, which have a standard size (2352 bytes) and a standard reading speed of 75 blocks per second. That is, if we are talking about a gap of two seconds, then we mean 150 "empty" blocks-segments. The tracks themselves consist of blocks filled with information.
The block segment, in turn, consists of 98 microframes, each of which has a size of 24 bytes (192 bits). 24 bytes may contain a description of the values of six discrete samples of the right and left channels. And the given value of 2352 bytes can be obtained by simply multiplying 98 by 24. So, speaking of this segment size, we are talking only about purely audio information.
3. The history of the development of optical storage
Developed by Philips and Sony, a new specification for storing digital data on CD media became known as the "Yellow Book", and the media itself became known as CD-ROM (Read Only Memory). A block segment of 2352 bytes has been converted. That is, according to the standard, Mode 1 types were provided for storing digital computer data, and Mode 2 - compressed graphic, text and sound data. The block sector of the Mode 1 type stores information on the correction and correction of errors EDC / ECC (Error Detection Code / Error Correction Code) and is the most common. 288 bytes are allocated for correction and error correction in each sector. As a result, 2064 bytes remain for information, 12 of which are allocated for synchronization and 4 bytes for the sector header.
Thus, the basic minimum unit in the CD-DA format is the track, while in the CD-ROM it is the segment.
Device drives on CD-ROM.
After the arrival of two standards, described by the "Red" and "Yellow" books, there was one significant problem: media were strictly tied to the types of drives. That is, the combination of audio and digital data was not implemented at that time. Mixed-format discs have appeared that store both CD-ROM and CD-DA data. Moreover, the first data (CD-ROM) was recorded at the beginning of the disc. This is not very convenient, because audio drives try to read the first track, which can harm the audio equipment, and CD-ROM drives cannot read the program and play audio at the same time.
In November 1985, representatives of the leading CD-ROM manufacturers met to discuss the problem of compatibility and a common type of file system structuring for all media. That is, a standard was required for the file system, the structure of writing and reading, and so on. A document was compiled which was a specification (the name of the specification is HSG) that defines the logical and file formats of CDs. The document was advisory in nature, and although it subsequently determined a lot for the technology industry as a whole, the color of the book was never found for it. The format proposal of the HSG specification was largely based on the representation of the structure of a floppy disk containing a zero track or system track, which stores data about the media type and its file structure with directories, subdirectories and files. The CD is organized a little differently. That is, all data of this type is stored in the service and system areas. The first stores the information necessary for synchronization between the carrier and the drive. The second one has a file structure, and the direct addresses of files in subdirectories are indicated, which reduces the search time.
Three years later (1988) the international standard ISO-9660 was adopted, the main provisions of which were very similar to the HSG representation. This standard described the CD-ROM file system and had three levels. The first level looks like this:
Filenames can be up to 8 characters long;
File names use only uppercase characters, numbers, and the "_" symbol;
Special characters are not allowed in file names - "-,~,=,+";
Directory names cannot have extensions;
Files cannot be fragmented.
The second and third levels of ISO-9660 only facilitate and expand the possibilities of the first. In particular, restrictions on file and directory names have been removed at the second level (for example, it is already allowed to create names with a length of 32 characters), at the third level it is already allowed to fragment files. It is worth noting that ISO-9660 of the first level standardizes mainly the MS-DOS and HFS (Apple Macintosh) file system formats. The second level in these systems is no longer readable.
For the Apple Macintosh, there is a separate standard for the HFS (Hierarchical File System) file system format. This computer platform has its own special file system hierarchy, which is why this standard is in demand. Several file system formats can be written to one disc at the same time.
The specification, developed in 1991, was released as Orange Books. There are two of them. The first standardizes magneto-optical storage devices that can erase and rewrite information. The second book is about write-once drives that can only write to. That is, in the second book we are talking about CD-R (Recordable). Gradually, modern technology began to allow rewriting discs. We are talking about CD-RW (Rewritable) or CD-E (Erasable), which, in fact, are the same. These media and drives most likely fall under the first of the "Orange Books".
In 1993, the "White Book" was published, which standardized a new product - Video CD, developed jointly by JVC, Matsushita, Sony and Philips. This standard is based on the Karaoke video system developed by JVC. The new format allows you to store 72 minutes of video with stereo sound. The compression format is familiar to many - MPEG (Motion Picture Experts Group). The first track is recorded in CD-ROM/XA format, followed by a data block containing compressed video. Based on the acquisitions obtained through the White Book standard, the experts subsequently made significant changes to the Green Book.
At the end of the last century, CD-R drives, which by that time had reached 8X/24X write / read speeds, were supplanted by more versatile CD-RW drives that allow you to write not only write-once discs, but also rewritable ones.
Unlike organic dyes used to form the active layer in CD-R discs, in CD-RW the active layer is a special polycrystalline alloy (silver-indium-antimony-tellurium), which becomes liquid at strong (500-700°C) ) laser heating. During the subsequent rapid cooling of the liquid regions, they remain in an amorphous state; therefore, their reflectivity differs from polycrystalline regions. The return of amorphous regions to the crystalline state is carried out by weaker heating below the melting point, but above the crystallization point (about 200 °C). Above and below the active layer are two dielectric layers (usually silicon dioxide), which remove excess heat from the active layer during the recording process; from above, all this is covered with a reflective layer, and the entire "sandwich" is applied to a polycarbonate base, in which spiral recesses are pressed out, necessary for precise positioning of the head and carrying address and time information.
