The PC monitor is the most important device for displaying textual and graphical information. Monitors are available in color and monochrome. They can work in two modes: text or graphics.

Digital (TTL) monitors

The term TTL (Transistor Transistor Logic - transistor-transistor logic) refers to the standard series digital microcircuits used in electronic engineering. And as always, when it comes to digital technology, it is read that the signals have only two states: logical 1 and logical 0 ("yes" and "no").

Monochrome monitors

When it comes to TTL monitors, they most often mean monochrome monitors, the control signals of which are generated by MDA or Hercules graphic cards. Already from the very concept of monochrome it is clear that a point on the screen can only be light or dark. At best, the points can also differ in their brightness. Hercules-monitor is capable of displaying an image only in the form of light and dark dots with a resolution of 728x348 and can work in conjunction with the entire system only with a video card. Other monitors produce an image (similar to TVs) as a result of a high image frame rate with minimal flicker. This principle is not implemented in the monitor type Hercules. A TTL monitor can also be distinguished from an analog monitor by the number of pins on the connector for connecting to a PC. The Hercules monitor has a 9-pin D-type plug (male). However, be careful: the RGB monitor described below also has the same connector.

RGB-monitors

Digital RGB monitors (Red/Green/Blue - red/green/blue) are mainly designed to connect to the EGA standard card. Such devices also support monochrome mode with a resolution that allows you to display 16 colors. RGB monitors have a lower resolution than Hercules monitors. These monitors can be recognized by their characteristic color coding on the front panel.

Analog monitors

In this case, we will talk about monitors that work with video cards of the VGA standard and higher. They are capable of supporting VGA resolution of 640x480 pixels and higher.

The name "analog" does not mean resolution capabilities, but, unlike TTL monitors, a way to transfer information about the represented colors from the video card to the monitor. When working in True Color mode, there must be an appropriate number of lines to convey a palette of colors with 24 degrees of depth. Therefore, on digital monitors no such information is transmitted. This is the only small area of ​​the PC where the analog principle of information processing has remained to this day. Analog signal transmission takes place in the form of voltages of various levels. VGA monitors can work not only in color, but also in monochrome mode. In the latter case, the colors and their shades are replaced by shades of gray.

The principle of image formation in monitors based on a cathode ray tube (all of the above) is not much different from the principle of operation of a TV. The beam of electrons emitted by the electron gun (cathode) hits a screen covered with a phosphor and causes it to glow.

LCD displays (LCD)

In the late 80s, the first notebook (laptop) PC models were introduced. The main factor that led to the reduction in their weight was, first of all, the use of liquid crystal displays (Liquid Crystal Display, LCD) as an information display device. The screen of such a display consists of two glass plates, between which there is a mass containing liquid crystals, which can change their optical structure and properties depending on the applied to them. electric charge. This means that the crystal changes its orientation under the influence of an electric field, thereby the crystals reflect light in different ways and make it possible to display information. Since the resistance is relatively high, the crystals can only move at a certain speed. This property was clearly manifested when moving the mouse cursor over the LCD screen of the first displays. When moving quickly, the cursor simply disappeared. Liquid crystals received an electrical impulse, but did not have time to react when the cursor had already moved to another place. To reduce blurring and increase image contrast, liquid crystal displays made using DSTN (Dual-scan Super-Twisted Nematic) technology have been developed. Toshiba has developed a thin film transistor active matrix liquid crystal display, the so-called TFT (Thin Film Translator) technology. In a TFT display, unlike a DSTN display, there is no slowdown. A variation of DSTN technology was MLA (Multiline Addressing) technology. One of the disadvantages of such displays may be familiar to you from wrist watch, calculators, etc. that work with LCD indicators. If you look at the screen at an angle, you can only see the silvery surface. The image and sharpness of LCD screens depend on the viewing angle. Good quality image is achieved at an observation angle of 90°. Liquid crystals do not themselves glow, so these monitors need a backlight or external light.

Gas plasma monitors

For gas plasma monitors there are no such restrictions as for LCD displays. They also have two glass plates, between which there are not crystals, but a gas mixture, which is highlighted in the appropriate places under the action of electrical impulses. The disadvantage of such monitors is the impossibility of their use in portable computers with battery and battery power due to the high current consumption.

The main characteristics of monitors:

Vertical (frame) and horizontal (linear) scanning frequency

Screen resolution, i.e. the number of dots (pixels) reflected on the screen

Screen diagonal, i.e. the distance between the lower right and upper left corners

Monitor grain size, i.e. phosphor dot size on the inner surface of the screen

The type of cathode ray tube that determines the quality of the phosphor coating

The speed of switching from text to graphics mode, i.e. permission change

Availability and quality of anti-reflective coating (the screen takes on a blue tint)

Radiation level (it is advisable to purchase a protective screen along with the monitor)

The monitor is a device for visual display of information. The signals that the monitor receives (numbers, symbols, graphic information, and timing signals) are generated by the video card. Thus, the monitor and video card are a kind of tandem, which for optimal performance must be configured accordingly. In order to work effectively, both components must be optimally matched to each other. Currently there are more than 30 modifications various types video cards that differ in design, parameters and standards. Naturally, it is not possible to describe the whole variety of these types. In this regard, it was decided to classify video cards according to accepted standards. Perhaps, with such a division, standards will be considered that no longer play a significant role in the RS and are obsolete, but they are worth mentioning for the sake of completeness.

Designations:

MDA - Monochrome Display Adapter monochrome display)

CGA - Color Graphics Adapter (color graphics adapter)

HGC - Hercules Graphics Card ( graphics card Hercules)

EGA - Enhanced Graphics Adapter (advanced graphics adapter)

VGA - Video Graphics Adapter (video graphics adapter)

SVGA - Super Video Graphics Adapter (super video graphics adapter)

Currently MDA, CGA, Hercules and EGA monitors are not used, because they do not have the proper resolution, which leads to rapid eye fatigue. Moreover, they are unable to software download Cyrillic fonts (Russian letters). Recently, SVGA monitors have become the most widely used.

Printer

The printer (or printing device) is designed to display information on paper. All printers can also output pictures and graphics, color or black and white images. There are several thousand printer models that can be used with the IBM PC. Consider the main types.

Dot matrix (dot) printers

Needle printer (Dot-matrix-Printer, aka matrix) for a long time was the standard output device for the PC. In the recent past, when inkjet printers were still unsatisfactory, and the price of laser printers was quite high, dot printers were widely used. They are still frequently used today. The advantages of these printers are determined, first of all, by the speed of printing and their versatility, which lies in the ability to work with any paper, as well as the low cost of printing. When choosing a printer, you should always proceed from the tasks that will be assigned to it. If you need a printer that has to print various forms all day without interruption, or print speed is more important than quality, then it is cheaper to use a needle printer. If you want to receive on paper quality image, then use an inkjet or laser printer, but this, of course, will increase the cost per sheet significantly. Needle printers have a significant advantage - the ability to print multiple copies of a carbon paper document at once. And the disadvantage of such printers is the noise they produce during operation. The principle by which a needle printer prints characters on paper is very simple. A needle printer generates characters with several needles located in the printer head. The paper feed mechanism is simple: the paper is pulled in by a shaft, and an ink ribbon is placed between the paper and the printer head. When the needle strikes this tape, a painted trace is left on the paper. The needles located inside the head are usually activated by an electromagnetic method. The head moves along a horizontal rail and is controlled by a stepper motor. There are heads: 9*9 needles, 9*18, 18*18, 24*37. Needles are arranged in one or two rows. With the help of a multi-color ink ribbon, the possibility of color printing is realized.

By studying this topic, you will learn:

On the classification and purpose of output devices;
- main characteristics of monitors;
- main types of printers and their characteristics;
- main types of plotters and their characteristics,
- what is the purpose of audio output devices.

Classification of output devices

The information entered into the computer is converted with the help of programs into a certain end result that a person needs. However, in the computer, this processing result is stored in binary code and completely incomprehensible to humans. To convert binary codes into a human-readable form, special hardware is needed, which are called output devices.

Output devices - hardware for converting a computer (machine) representation of information into a form understandable to a person.

For the normal operation of the output device, as well as the input device, a control unit (controller, or adapter), special connectors and electrical cables are required, and it is imperative - control program(driver). Only when these conditions are met, the output device provides the necessary form for representing output results in the form of text, image, sound, etc. The variety of output devices is determined by various physical principles that underlie their work.

Among the output devices, several classes can be distinguished according to the form of information presentation (Figure 20.1): monitors, printers, plotters, audio output devices.

Rice. 20.1. Classification of output devices

Monitors

general characteristics

The monitor is designed to display symbolic and graphical information.

Monitors can be made on the basis of cathode ray tubes or in the form of liquid crystal panels.

At laptop computers monitors are made in the form of liquid crystal panels. The compact size of liquid crystal monitors, which are flat screens, as well as the absence of harmful factors affecting human health, make this type of monitor more and more popular for desktop computers.

The main characteristics of monitors implemented on the basis of a cathode ray tube are:

screen resolution,
- distance between dots on the screen,
- screen diagonal length.

Screen resolution

Any image on the screen is represented by a set of dots called pixels (from the English Picture "s ELement - an element of the picture). The number of dots horizontally and vertically of the screen determines the resolution of the monitor. The standard mode of operation of a modern monitor supports a resolution of 800x600, 1024x768 pixels and others modes The higher the resolution of the monitor, the better the image.

In text mode, only characters known to the computer are displayed on the screen, and in graphic mode, any image consisting of dots is displayed. To represent any character in text mode, use fixed amount pixels, such as 8x8 or 8x14.

Monitors are black and white (monochrome) and color. Color images are obtained by mixing three basic colors: red, green, blue. Primary colors are created by three electron beams, each of which is responsible for its own color. All the variety of shades is explained by the summation of basic colors in various proportions.

Remember the drawing lesson when you had to mix paints to get the desired shade. So, to get a turquoise color, it is enough to mix green and blue paints, and Crimson obtained by adding blue to red.

Distance between dots on the screen

The clarity of the image on the monitor is determined by the distance between the dots on the screen, or the step size ("grain size"). The value of this parameter ranges from 0.22 to 0.43 mm. The smaller this value, the better the image quality.

Screen diagonal length

This parameter is measured in inches and ranges from 9" to 41". The choice of monitor size depends on the area of ​​use of the personal computer. For educational and domestic purposes, the most popular monitors are 14 and 15 inches. Working with specialized graphics packages requires the use of larger diagonal monitors, such as 17 inches. In computer-aided design systems, where it is necessary to simultaneously display a large amount of graphic information, it is desirable to use monitors with a diagonal of 21 inches or more for efficient operation.

The resolution of the screen is largely determined by the ratio of the diagonal length and the step size (table 20.1). For example, with a diagonal size of 14 inches and a pitch of 0.28 mm, the monitor will operate optimally at a resolution of 800 by 600 pixels.

Table 20.1. Relationship between diagonal, pitch and screen resolution

video card

The actual operating modes of the monitor depend on the type of video card that provides control and interaction of the monitor with a personal computer. The video card, or video adapter, is installed on system board in the system unit of the computer and comes with a set of driver programs. A monitor, a video adapter and a set of driver software form the video system of a personal computer.

To provide the ability to connect a TV or VCR to a computer, the computer is equipped with a video converter. The TV converter allows you to display a computer image on a TV screen or record on a VCR. PC converters perform the reverse conversion, in which the image from the TV screen is displayed on the monitor.

All monitors are subject to mandatory health safety testing. Therefore, when buying them, you need to require a safety certificate confirming the quality of the purchased monitor and the low level of radiation (Low Radiation).

Printers

general characteristics

Printers are designed to print results on paper. In this case, the machine representation of information is converted into symbols (letters, numbers, signs). Any character is printed as a set of dots. Image formation is carried out by the head of the printing device. Each line is printed in two directions: the print head moves from left to right and from right to left. The transition to the output of the next line is carried out using a special mechanism for pulling paper between the printer rollers. Functionality modern printers allow you to display various text, drawings, graphics not only on paper, but also on a special film, for example, to create slides.

to one system unit you can connect from one to three printers of any type.

According to the method of generating output information printers are divided into:

Sequential, when the document is formed character by character;
- lowercase, when the entire line is formed at once;
- page, when the image of the whole page is formed.

By the number of colors used when printing a document distinguish between black and white and color printers.

By printing method printers are impact and non-impact.

The most important characteristics of printers are:

The width of the printer carriage, which determines the maximum possible document format: A4 or A3;
- print speed, which determines the number of characters or pages printed by the printer per second or minute;
- resolution of the printer, which determines the print quality as the number of dots per inch - dpi (dots per inch) when outputting a character.

According to the method of obtaining an image on paper, the method of applying the coloring material (toner) printers are: matrix, inkjet, laser, thermal, lettering. Consider the main types of printers.

Dot matrix printers

Dot matrix printers relate to impact printers, since the image is formed using a set of needles (matrix) that strike the paper through an ink ribbon placed in a special case - a cartridge.

As a result, an imprint of the image of the displayed character remains on the paper.

The movement of each needle to obtain the required image is controlled by an electromagnet located in the head of a dot matrix printer.

The more needles in the head, the higher the print quality.

Dot matrix printers come in 9-, 18- and 24-pin sizes.

Inkjet printers

Inkjet printers are non-impact printers because the print head does not touch the paper. Thanks to this, their work is almost silent.

To obtain an image, special ink is used, and instead of a print head, a cartridge is installed, similar to an inverted ink tank, in which thin jets of ink are ejected from holes (nozzles). Their smallest droplets are deflected under the action of control electromagnets and, having reached the paper, create the required image. The number of nozzles ranges from 12 to 64. The more nozzles, the better the print quality. Inkjet printers provide images with a quality close to printing, which determines the wide scope of use of inkjet printers for creating various documents.

The print speed of inkjet printers is much faster than dot matrix printers. Unfortunately, the cost of printing with inkjet printers is also significantly higher. When working with an inkjet printer, we must not forget that ink tends to spread when in contact with water. Therefore use given type printers can only be used in dry rooms. For the same reason, the inkjet printer uses only high quality smooth paper.

Laser printers

Laser printers use laser ray.

Using a lens system, a thin laser beam forms an electronic image on a photosensitive drum.

To the charged areas of the electronic image are attracted particles of dye powder (toner), which is then transferred to paper.

Laser printers provide high quality prints and significant output speeds - from a few pages per minute in color to more than a dozen pages per minute in black and white.

These properties of a laser printer determine its use as a network printer, which provides modes of collective access. Laser printers are widely used in publishing.

Plotters

Plotters, otherwise known as plotters, designed to display graphic information, creating diagrams, complex architectural drawings, artistic and illustrative graphics, maps, three-dimensional images. Plotters are used for the production of high-quality color documentation and are indispensable for artists, designers, decorators, engineers, and planners.

The size of output documents on the plotter is larger than the size of documents that can be created using the printer. The maximum printable length is usually limited by the length of the paper roll, not by the design of the plotter.

The image on paper is formed by the print head. Point by point, the image is applied to paper (tracing paper, film), hence the name of the plotter - plotter (from English to plot - to draw a drawing).

The main characteristics of the plotters are:

Image drawing speed, measured in millimeters per second;
- output speed, determined by the number of conditional sheets printed per minute;
- resolution, measured, like a printer, in dpi (dots per inch).

By design, plotters are divided into tablet and drum plotters. In flatbed plotters, the paper is stationary and the print head moves in two directions. In drums, the head moves along one of the coordinates, and the paper moves along the other with the help of the clamping system.

According to the principle of operation, plotters are divided into pen, inkjet, electrostatic, thermal transfer, pencil.

Pen plotters use regular pens to produce images. To obtain a color image, several pens of different colors are used.

Inkjet plotters form an image similar to inkjet printers by spraying droplets of ink onto the paper. The higher quality of color printing compared to pen plotters determines the widespread use of inkjet plotters in various areas human activities, including computer-aided design, engineering design.

Electrostatic plotters create an image using an electrical charge as the paper is pulled through. Electrostatic plotters are very expensive and are used when high quality output is required.

Thermal transfer plotters create a two-color image using heat-sensitive paper and electrically heated needles.

Pencil plotters use a regular stylus to form an image. They are the cheapest and work with cheap consumables.

Audio output devices

It is difficult to imagine a modern computer silent, without the ability to hear various sounds - signals, music, human speech. To do this g, speakers or headphones are connected to the computer, which convert the data into binary representation into sound.

Voice output devices, if appropriate software is installed on the computer, can produce sounds similar to human speech. We find examples of the use of speech output in modern supermarkets at the exit control to confirm the purchase, in telephone devices, in automotive equipment. These devices are also widely used in education when teaching foreign languages.

Control questions and tasks

1. What are output devices for?

2. List the main characteristics of the monitor.

3. How do you understand the term "screen resolution"?

4. What does the word "pixel" mean?

5. What is a personal computer video system?

6. List the main printing technologies.

7. What is the basic principle of a dot matrix printer?

8. What is the basic working principle inkjet printer?

9. Give a comparative assessment of inkjet and laser printers.

10. Describe the principle of operation of plotters and their types.

11. What is the application of audio output devices?

Monitor

The monitor is a device for visual display of all kinds of information, which is connected to the PC video card.

There are monochrome and color monitors, alphanumeric and graphic monitors, monitors on cathode ray tube and LCD monitors.

Cathode Ray Monitors ($CRT$)

The image is created using a beam of electrons, which are released by an electron gun. A high electrical voltage accelerates the electron beam, which falls on the inner surface of the screen, coated with a phosphor (a substance that glows under the influence of the electron beam). The beam control system drives it line by line across the entire screen (creates a raster) and regulates its intensity (the brightness of the glow of the phosphor dot).

$CRT$-monitor emits electromagnetic and x-ray waves, high static electrical potential, which have an adverse effect on human health.

Figure 1. Cathode Beam Monitor

Liquid crystal monitors ($LCD$) based on liquid crystals

Liquid crystal monitors (LCDs) are made from a liquid substance that has some of the properties of crystalline bodies. When exposed electrical voltage liquid crystal molecules can change their orientation and change the properties of the light beam that passes through them.

The advantage of liquid-crystal monitors over $CRT$-monitors is the absence of electromagnetic radiation harmful to humans and compactness.

The digital image is stored in the video memory, which is located on the video card. The image is displayed on the monitor screen after reading the contents of the video memory and displaying it on the screen.

The stability of the image on the monitor screen depends on the frequency of image reading. The image refresh rate of modern monitors is $75$ or more per second, which makes the image flicker imperceptible.

Figure 2. LCD Monitor

Printer

Definition 2

Printer - peripheral device, designed to output numerical, textual and graphic information on paper. According to the principle of operation, a laser, inkjet and dot matrix printer are distinguished.

Provides near-silent printing, which is formed by the effects of xerography. The entire page is printed at once, which ensures high printing speed (up to $30$ pages per minute). High print quality laser printers provided by the high resolution of the printer.

Figure 3. Laser printer

Provides virtually silent printing high speed(up to several pages per minute). In inkjet printers, an ink printhead prints, ejecting ink under pressure from tiny holes onto the paper. The print head, moving along the paper, leaves a line of characters or an image strip. The print quality of an inkjet printer depends on the resolution, which can reach photographic quality.

Figure 4. Inkjet printer

It is an impact printer that forms characters with the help of several needles located in the printer head. The paper is pulled in by a rotating shaft, and an ink ribbon passes between the paper and the printer head.

On the printhead of a dot matrix printer is a vertical column of small rods (usually $9$ or $24$) that are "pushed" out of the head by the magnetic field and hit the paper (through the ink ribbon). The print head, moving, leaves a line of characters on paper.

The print speed of dot matrix printers is slow, they produce a lot of noise and the print quality is not high.

Figure 5 Matrix printer

Plotter (plotter)

Definition 3

A device designed for complex and wide-format graphic objects (posters, drawings, electrical and electronic circuits etc.) under PC control.

The image is applied with a pen. It is used to obtain complex design drawings, architectural plans, geographic and meteorological maps, business schemes.

Figure 6. Plotter

Projector

Definition 4

Multimedia projector(multimedia projector) - a stand-alone device that provides transmission (projection) to big screen information from an external source, which can be a computer (laptop), VCR, DVD player, camcorder, document camera, TV tuner, etc.

$LCD$ projectors. The image is formed using a translucent liquid crystal matrix, of which $3LCD$ models have three (one for each of the three primary colors). $LCD$-technology is relatively inexpensive, therefore it is often used in models of various classes and purposes.

Figure 7 LCD Projector

$DLP$ projectors. The image is formed by a reflective matrix and a color wheel, which allows one matrix to be used to sequentially display all three primary colors.

Figure 8. DLP projector

$CRT$-projectors. The image is formed using three cathode-ray tubes of basic colors. Now practically not used.

Figure 9. CRT projector

$LED$-projectors. The image is formed using an LED light emitter. Benefits include a long lifespan that is many times longer than that of projectors with a lamp, the ability to create ultra-portable models that can even fit in your pocket.

Figure 10. LED projector

$LDT$-projectors. The models use several laser light generators. The technology allows you to create compact projectors with very high brightness.

Audio output devices

Built-in speaker

Definition 5

Built-in speaker- the simplest device designed to play sound on a PC. The built-in speaker was the main audio playback device until inexpensive sound cards came along.

In modern PCs, the speaker is used to signal errors, in particular during the POST program. Some programs (for example, Skype) always duplicate the ringing signal to the speaker, but do not output the sound of the conversation through it.

64-bit Windows does not support the built-in speaker, which is due to a conflict between the means of rehabilitation and power management of the sound card.

Devices for outputting sound information that are connected to the output of a sound card.

Figure 11. Speakers and headphones

Every day, sitting down at his workplace in the office, a person takes a mouse in one hand and begins to perform his duties. He knows why he needs a keyboard, a printer, a scanner, but he does not even imagine that they have their own official name. All this - and the output of information.

How it works

All devices in a personal computer are controlled by a central processing unit. To ensure interaction with it, output and input devices make requests to - logical element motherboard. It serves to provide communication and processing requests from external devices to the northbridge or CPU if there is no bridge.

In general, computer science deals with the study of the structure of a personal computer. It defines input and output devices as the components of a typical personal computer that provide the user with the computer. But before proceeding with the description of all devices, the basic I / O device deserves special mention. It's also BIOS. This chip is motherboard The personal computer provides an initial check of all connected devices and starts the operating system.

Classification

Personal computer input and output devices can be classified in different ways. The determining factor for this will be their functional responsibilities.

The first item is the main input-output devices. In fact, only one item could be specified here - the keyboard, since without it, not a single user computer will continue to boot. You can completely turn off the monitor and mouse, but the computer will not work without a keyboard. The exception is server computers that work without external devices connected at all. So, the main input / output devices, without which a normal user will not be able to work, are:

• keyboard;
• monitor;
• mouse.

You can also select additional I / O devices:

• printers;
• scanners;
• joystick;
• projector;
• I/O devices also include sound devices.

This is not a complete list of possible devices that interact with the user, it is possible to list them for a very long time. Therefore, let's look at the input / output devices of the computer in more detail.

Monitors

Computer monitors have undergone many changes throughout their history. Starting from the old ones using a cathode ray tube, and ending with modern LCDs.

The monitor or display itself is a device that serves to output to the end user. They can be divided according to several criteria.

1. By type of information.

• Alphanumeric. These displays are designed to display textual information only.
• Graphic. We encounter these monitors every day, sitting down at Personal Computer. They are intended to present information in graphical form, including video.

2. By screen type.

• on the basis of such you may have worked in 2000.
• LCD is a liquid crystal "flat" display, which is now used everywhere. This type of monitor is also used in laptops.
• Plasma.
• Laser - has not yet entered mass production.

Keyboards

What can be said about keyboards? The fantasy of manufacturers in this area has stepped far ahead, and a sense of humor pushes for the most daring experiments.

Among the keyboards, you can also find minimalistic options - without a side additional panel with numbers, and huge gaming keyboards with built-in joysticks, additional buttons and speakers. There are keyboards with an additional USB-connector and pink keyboards with "incomprehensible buttons" for "blondes". There are also silicone keyboards that roll up to make them easier to carry around, or simply fold up three times.

If you are going to buy a keyboard for yourself, just go to a computer store and choose the one that suits your taste.

mouse

Computer mice are such computer input / output devices, without which work is impossible. regular user. If an advanced user can navigate through folders and files, as well as some programs and games exclusively using the keyboard, then an ordinary person is simply not able to do this. Throughout the existence computer mice didn't change that much.

The first mice worked on the basis of a ball in the base. Moving her to different sides, the ball rotated and controlled by controllers.

Then he was replaced by optical mice based on LEDs. The first generation of optical mice required the obligatory presence of a special mat, on which shading was applied, which contributes to increased light reflectivity of the surface. Moreover, the first mice had personal mats, they could not be replaced with others.

The second generation of optical mice has a more complex device. A mini video camera is installed on the bottom of the mouse, which continuously takes microphotographs of the surface and compares them with each other to determine the displacement of the device.

Mice are newer devices. Among their advantages are low power consumption, reliability, lack of luminescence.

Another version of the mouse is found in the form of an addition to graphics tablet. Such induction mice are quite inconvenient to use, since they cannot be replaced with more comfortable ones that fit the hand, and the increased accuracy is discredited by the small ability to move away from the tablet with it.

Printers

These are printing devices. For all the time of its existence, printers have not changed much. Technologies are developing, laser printers are replacing inkjet printers, however, previous generations continue to live. What is the reason for this? The fact is that for different types of printing are suitable different types printers. They all perform the same function and do not differ much in design. There are the following types of printers:

• matrix;
• jet;
• laser;
• thermal printers.

In the matter of choosing such a device, people usually adhere to personal preferences and habits. However, if you are going to print photos on it, and not only text documents, then laser is more suitable for you due to the increased print quality.

Scanners

An input device for a computer. The peculiarity lies in the fact that scanners enter information into the PC exclusively in graphical form. The development of scanners has stalled solely on changing their sizes. At first they became smaller and more compact, and then they were replaced by huge "combines" - output and input devices that combine a copier, printer and scanner.

Sound

Each of us likes to watch movies, listen to music at home. Speakers, headphones, audio systems and home theater systems, as well as headsets and microphones, all refer to audio output and input devices.

There are many different microphones and speakers, differing in the quality of audio recording or playback, respectively. Probably, anyone can determine for himself how good the sound of a speaker is. When choosing an audio system, it is also recommended to be guided by the design and power to your taste.

Video

To work with video graphics allocate special devices output and input of information - cameras and projectors.

A projector is a device designed to create an image of an object on a large screen. There are the following types of projectors:

• Diascopic. The image appears due to the passage of light rays through a transparent film with a picture.
• Episcopal. Creates an image using the projection of reflected rays.
• epidiascopic creates an image of both transparent and opaque objects on the screen.
• Multimedia the projector is directly related to the topic of the article. This is a device for outputting graphic information from a computer to a large surface.

As for the cameras, there is no need to tell anyone. In most cases, the higher the resolution of the shooting camera, the better the finished picture. With the advent of laptops, USB cameras began to be replaced by built-in laptop monitors.

After reading this article, you learned what output and input devices exist, what types they are divided into, and what types of them are relevant today. If you are going to independently equip your work and play space, as well as independently choose the devices that you want to have at hand at home, then this article should help you with choosing gadgets.

Remember the main rule of the buyer: more expensive does not mean better. In a computer store, when purchasing a printer or headset, you may well overpay for the brand, and then regret your purchase for a long time.

HP printers are an example. Yes, they are considered one of the best, but replacing an empty cartridge or just a small malfunction will cost you a pretty penny solely because of the manufacturer's fame.

When buying a sound system, feel free to check the sound and performance of the speakers. And if you are going to buy a webcam, then test its image, since the resolution declared in the documentation may not always correspond to the existing one.

And the main rule. When purchasing any product, check with the seller for warranty information. For example, for some devices, services require the box in which the unit was shipped. A good example is Asus laptops. In most cases, there is no information anywhere on the store's website that manufacturers require a branded box when contacting a service center.

Be careful and happy shopping!

Monitor

The monitor is a device for visual display of all kinds of information, which is connected to the PC video card.

There are monochrome and color monitors, alphanumeric and graphic monitors, cathode ray tube monitors and liquid crystal monitors.

Cathode Ray Monitors ($CRT$)

The image is created using a beam of electrons, which are released by an electron gun. A high electrical voltage accelerates the electron beam, which falls on the inner surface of the screen, coated with a phosphor (a substance that glows under the influence of the electron beam). The beam control system drives it line by line across the entire screen (creates a raster) and regulates its intensity (the brightness of the glow of the phosphor dot).

$CRT$-monitor emits electromagnetic and x-ray waves, high static electrical potential, which have an adverse effect on human health.

Figure 1. Cathode Beam Monitor

Liquid crystal monitors ($LCD$) based on liquid crystals

Liquid crystal monitors (LCDs) are made from a liquid substance that has some of the properties of crystalline bodies. When exposed to an electrical voltage, liquid crystal molecules can change their orientation and change the properties of the light beam that passes through them.

The advantage of liquid-crystal monitors over $CRT$-monitors is the absence of electromagnetic radiation harmful to humans and compactness.

The digital image is stored in the video memory, which is located on the video card. The image is displayed on the monitor screen after reading the contents of the video memory and displaying it on the screen.

The stability of the image on the monitor screen depends on the frequency of image reading. The image refresh rate of modern monitors is $75$ or more per second, which makes the image flicker imperceptible.

Figure 2. LCD Monitor

Printer

Definition 2

Printer- a peripheral device designed to output numerical, textual and graphic information on paper. According to the principle of operation, a laser, inkjet and dot matrix printer are distinguished.

Provides near-silent printing, which is formed by the effects of xerography. The entire page is printed at once, which ensures high printing speed (up to $30$ pages per minute). The high print quality of laser printers is ensured by the high resolution of the printer.

Figure 3. Laser printer

Provides almost silent printing at a sufficiently high speed (up to several pages per minute). In inkjet printers, an ink printhead prints, ejecting ink under pressure from tiny holes onto the paper. The print head, moving along the paper, leaves a line of characters or an image strip. The print quality of an inkjet printer depends on the resolution, which can reach photographic quality.

Figure 4. Inkjet printer

It is an impact printer that forms characters with the help of several needles located in the printer head. The paper is pulled in by a rotating shaft, and an ink ribbon passes between the paper and the printer head.

On the printhead of a dot matrix printer is a vertical column of small rods (usually $9$ or $24$) that are "pushed" out of the head by the magnetic field and hit the paper (through the ink ribbon). The print head, moving, leaves a line of characters on paper.

The print speed of dot matrix printers is slow, they produce a lot of noise and the print quality is not high.

Figure 5. Dot matrix printer

Plotter (plotter)

Definition 3

A device designed for complex and wide-format graphic objects (posters, drawings, electrical and electronic circuits, etc.) under PC control.

The image is applied with a pen. It is used to obtain complex design drawings, architectural plans, geographic and meteorological maps, business schemes.

Figure 6. Plotter

Projector

Definition 4

Multimedia projector(multimedia projector) - a stand-alone device that provides transmission (projection) on a large screen of information from an external source, which can be a computer (laptop), VCR, DVD player, camcorder, document camera, TV tuner, etc.

$LCD$ projectors. The image is formed using a translucent liquid crystal matrix, of which $3LCD$ models have three (one for each of the three primary colors). $LCD$-technology is relatively inexpensive, therefore it is often used in models of various classes and purposes.

Figure 7 LCD Projector

$DLP$ projectors. The image is formed by a reflective matrix and a color wheel, which allows one matrix to be used to sequentially display all three primary colors.

Figure 8. DLP projector

$CRT$-projectors. The image is formed using three cathode-ray tubes of basic colors. Now practically not used.

Figure 9. CRT projector

$LED$-projectors. The image is formed using an LED light emitter. Benefits include a long lifespan that is many times longer than that of projectors with a lamp, the ability to create ultra-portable models that can even fit in your pocket.

Figure 10. LED projector

$LDT$-projectors. The models use several laser light generators. The technology allows you to create compact projectors with very high brightness.

Audio output devices

Built-in speaker

Definition 5

Built-in speaker- the simplest device designed to play sound on a PC. The built-in speaker was the main audio playback device until inexpensive sound cards came along.

In modern PCs, the speaker is used to signal errors, in particular during the POST program. Some programs (for example, Skype) always duplicate the ringing signal to the speaker, but do not output the sound of the conversation through it.

64-bit Windows does not support the built-in speaker, which is due to a conflict between the means of rehabilitation and power management of the sound card.

Devices for outputting sound information that are connected to the output of a sound card.

Figure 11. Speakers and headphones