Output Devices

Output Devices

The output device displays the outcome of processing raw data entered into the computer via an input device. A variety of output devices display output in various formats such as text, photos, physical copies, and audio or video.

Some of the popular output devices are:

  1. Monitor
    • CRT Monitor
    • LCD Monitor
    • LED Monitor
    • Plasma Monitor
  2. Printer
    • Impact Printers
      1. Character Printers
        1. Dot Matrix printers
        2. Daisy Wheel printers
      2. Line printers
        1. Drum printers
        2. Chain printers
    • Non-impact printers
      1. Laser printers
      2. Inkjet printers
  3. Projector

1) Monitor

The output device displays the outcome of processing raw data entered into the computer via an input device. A variety of output devices display output in various formats such as text, photos, physical copies, and audio or video.

The types of monitors are given below.

i) CRT Monitor

CRT monitors are built around cathode ray tubes. They are similar to vacuum tubes in that they generate images in the form of video signals. Cathode ray tubes generate a beam of electrons using electron cannons that strike the inner phosphorescent surface of the screen, resulting in images on the screen. The monitor has millions of red, green, and blue phosphorous dots. When these dots are touched by electron beams, they begin to glow, a process known as cathodoluminescence.

The electron gun assembly, deflection plate assembly, fluorescent screen, glass envelope, and base are the primary components of a CRT display. The face plate is the front (outside surface) of the screen upon which images are formed. It is constructed of fibre optics.

The screen is hit by three electron beams: red, green, and blue. As a result, the colours you see on the screen are a combination of red, blue, and green lights. The magnetic field directs electron beams. Although LCD monitors have mostly supplanted CRT monitors, graphics experts continue to prefer CRT monitors due to their superior colour quality.

ii) LCD Monitor

In comparison to CRT displays, an LCD monitor is a flat panel screen that is compact and lightweight. It is based on liquid crystal display technology, which is utilised in laptops, tablets, and smartphone screens. An LCD screen is made up of two layers of polarised glass with a liquid crystal solution sandwiched between them. An electric current aligns the liquid crystals when light passes through the first layer. The aligned liquid crystals allow changing amounts of light to pass through the second layer, resulting in images on the screen.

The image on the screen is shown on the LCD screen by a matrix of pixels. Old LCDs had passive-matrix panels, which controlled individual pixels by delivering a charge. When images moved quickly on the screen, a few electrical charges could be transferred each second, causing screens to appear fuzzy.

Active-matrix technology is used in modern LCDs, which include thin film transistors (TFTs) and capacitors. Pixels can keep their charge with this technology. As a result, they do not cause screen blur when images move quickly on the screen and are more efficient than passive-matrix displays.

iii) LED monitor

The LED monitor is a more advanced variant of the LCD monitor. It also has a flat panel display and, like LCD monitors, employs liquid crystal display technology. The distinction is in the source of light used to backlight the display. The LED monitor features numerous LED panels, with many LEDs on each panel to backlight the display, whereas LCD monitors use cold cathode fluorescent light to backlight the display. LED displays are used in modern electronic products such as mobile phones, LED TVs, laptops and computer screens, and so on since they not only generate more brightness and light intensity but also require less electricity.

iv) Plasma Monitor

The plasma monitor is another type of flat panel display that uses plasma display technology. It features microscopic cells sandwiched between two glass panels. These cells contain noble gas mixed with a trace of mercury. When a voltage is given to the cells, the gas transforms into plasma and emits ultraviolet light, which displays images on the screen, i.e., the screen is lighted by a tiny amount of plasma, a charged gas. Plasma displays are brighter than liquid crystal displays (LCDs) and have a wider viewing angle.

Plasma monitors provide high resolutions of up to 1920 x 1080, good contrast ratios, a wide viewing angle, a fast refresh rate, and other features.

2) Printer

The processed data is printed on paper by a printer. It allows the user to print images, text, or other data onto paper.

Printers are classified into two sorts based on their printing mechanism: impact printers and non-impact printers.

  • Impact Printers: They are of two types:
    1. Character Printers
      1. Dot Matrix printers
      2. Daisy Wheel printers
    2. Line printers
      1. Drum printers
      2. Chain printers
  • Non-impact printers: They are of two types:
    1. Laser printers
    2. Inkjet printers

Impact Printer

The impact printer uses a hammer or print head to print the character or images onto the paper. The hammer or print head strikes or presses an ink ribbon against the paper to print characters and images.

Impact printers are further divided into two types.

  1. Character Printers
  2. Line printers

A) Character Printers

A single character is printed at a time by a character printer, or with a single stroke of the print head or hammer. It does not publish a single line. Character printers include the Dot Matrix printer and the Daisy Wheel printer. These printers are no longer widely used because of their slow speed and the fact that they can only print text. The character printers are classified into two types:

i) Dot Matrix Printer

A Dot Matrix Printer is a type of impact printer. It prints characters and graphics in the form of dot patterns. These patterns are created by striking the ink-soaked ribbon with a print head against the paper. Pins in the print head create a pattern of dots on the paper to form the individual characters. A 24-pin dot matrix printer has more pins than a 9-pin dot matrix printer, hence it generates more dots, resulting in better character printing. The black ribbon can be replaced with colour stripes to provide colour output. Dot Matrix printers can print 200-500 characters per second.

ii) Daisy Wheel Printer

David S. Lee of Diablo Data Systems invented the Daisy Wheel Printer. It is dubbed the Daisy Wheel printer because it consists of a wheel or disc with spokes or extensions that resembles a daisy. Moulded metal characters are attached at the ends of extensions. To print a character, the printer revolves the wheel until the desired character is on the print site, at which point the hammer strikes the disc and the extension strikes the ink ribbon on the paper to form the impression. It cannot print graphics and is frequently noisy and slow, with a speed of 25-50 characters per second. These printers have become outdated as a result of these shortcomings.

B) Line Printers

Line printers, also known as bar printers, print one line at a time. It is a fast impact printer, capable of printing 500 to 3000 lines per minute. Line printers include drum printers and chain printers.

i) Drum Printer

A drum printer is a type of line printer that uses a revolving drum to print characters. On the surface of the drum, there are circular bands of characters. Each band of characters has their own hammer. When you print, the drum rotates, and when the appropriate character comes under the hammer, the hammer smacks the ink ribbon against the paper, causing characters to be printed. The drum spins at breakneck speed, and characters are printed by activating the corresponding hammers. Although not all of the characters are printed at the same time, they are printed at a very fast rate. Furthermore, because it only has a limited amount of characters, it can only print in a specified manner.

ii) Chain Printer

A chain printer is a type of line printer that prints characters by rotating a chain. The characters are engraved on the chain’s surface. The chain rotates horizontally around a series of hammers; one hammer is provided for each print place, so the total number of hammers equals the total number of print spots.

When the appropriate character arrives at the print site, the corresponding hammer knocks the paper against the ribbon and the character on the chain.

They can type between 500 and 3000 lines per minute. Because of the hammering action, they are also noisy.

Non-Impact Printer

Non-impact printers do not produce characters or graphics by striking the ink ribbon with a print head or hammer. They produce characters and images without making any direct physical contact between the paper and the printing apparatus. Because these printers can print an entire page at a time, they are often referred to as page printers. Laser printers and inkjet printers are the most frequent types of non-impact printers:

i) Laser Printer

A laser printer is a non-impact printer that prints characters with a laser beam. The laser beam strikes the drum, which is a photoreceptor and alters the electrical charges on the drum to draw the image. The drum then rolls in toner, which is picked up by the charged picture on the drum. Heat and pressure are then used to print the toner on the paper. After printing, the drum loses its electric charge and the residual toner is collected. Laser printers print with powdered toner rather than liquid ink and generate high-quality print objects with a resolution of 600 dots per inch (dpi) or higher.

ii) Inkjet Printer

The inkjet printer is a type of non-impact printer that uses small, ionised drops of ink to produce images and characters. To spray the ink, the print head features small nozzles. The printer head rotates back and forth, spraying ionised dots of ink on the paper as it passes through the printer. These drops are guided onto the paper by an electric field, which guides the ink onto the correct images and letters.

Ink cartridges are used in inkjet printers. Inkjet printers are colour printers with four cartridges that carry distinct colours: Cyan, Magenta, Yellow, and Black. It can print high-quality photos in a variety of colours. It has the capability of producing print objects with a resolution of at least 300 dots per inch (dpi).

3) Projector

A projector is a type of output device that allows users to display their output onto a large surface, such as a huge screen or a wall. It can be linked to a computer or other comparable devices in order to project its output onto a screen. It magnifies texts, images, and movies using light and lenses. As a result, it is a great output device for giving presentations or teaching a big group of people.

Modern projects (digital projectors) have numerous input sources, such as HDMI connectors for newer equipment and VGA ports for older devices. Some projectors are also designed to enable Wi-Fi and Bluetooth. They can be attached to the ceiling, placed on a stand, and utilised for classroom teaching, presentations, home theatres, and other purposes.

A digital projector can be of two types:

Liquid Crystal Display (LCD) digital projector:

This sort of digital projector is quite popular because it is lightweight and produces clear images. To provide output, an LCD projector employs transmissive technology. It permits the conventional lamp light source to pass through the three coloured liquid crystal light panels. Some colours travel through the panels while others are blocked, resulting in visuals on the screen.

Digital Light Processing (DLP) digital projector:

It has a collection of small mirrors, one for each pixel of the image, and hence produces high-quality images. These projectors are typically utilised in theatres since they provide high-quality video output.

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