List of Various Computer Output Devices
What are various output devices? Explain
The output devices are the instruments between the user and the computer system. These devices are used to output the processed data i.e. information from the CPU. The most common output devices are printers, plotters etc.
There are two basic categories of computer produced output
1. Output for immediate use by people.
2. Output that is stored in computer usable form for later use by the computer.
Output can be hardcopy or softcopy :
The information is stored on the tangible medium. Soft copy generally refers to the computer screen. Output hardware is categorized according to whether it produces hard copy or soft copy. The principal hard copy output devices are printers and plotters. The principal soft copy devices are cathode ray tubes, video screens, flat screens, and voice output systems.
Hard copy output devices :
The widely used hard copy output devices are printers and plotters. A printer is capable of printing character, symbol and sometimes graphics on paper. Printers are categorized on the basis of whether or not the image produced is formed by physical contact of the print mechanism with the paper. Impact printers do have contact, non impact printers do not. A plotter is used for creating graphics because it can produce specialized and free from drawings on paper. Plotters are categorized according to whether or not they use pens, how the paper is placed in them, which of their part move. To suit different users, different types of printers and plotters are available with different characteristics and capabilities – cost, quality and speed.
1. Impact Printers: An impact printer makes contact with the paper. It usually forms the print image by pressing an inked rubber against the paper with a hammer like mechanism… in one type of (letter quality) impact printer – the hammers presses images of fully formed characters against the ribbon just like a type writer. The printer mechanism in another type of impact printer called dot matrix printer is made of separate pin like hammers that strike the ribbon against the paper in computer determined pattern of dots. Both the printers are used with micro computers systems.
a. Letter quality printers: Also called as character printers or serial printers as they print one character at a time, produce a very high quality print images, because the entire character is formed with a single impact.
The three principal letter quality printers are
b. Dot matrix printers: Also called as serial printers developed with two objectives greater speed and more flexibility. It has a print head composed of a series of little print hammers that look like the heads of pins. This print hammers strike the ribbon individually as the print mechanism moves across the entire print line in both directions. The color printer uses black ribbon with color strips. The speed of dot matrix printer ranges from 240 to 4800 words per minute. They make less noise and produces good quality print out.
c. High speed printers: These are developed to satisfy the high volume output requirements of most large computer installations, which cannot be satisfied by dot matrix or letter quality printers. These line printers are so called because they print a whole line of character practically at once, come in several varieties including drum printers, belt printers and chain printers. The speed of this printer is measured in lines per minutes. Advantage of this type of printer is it produces an extremely large volume of hard copy output and disadvantage is it is noisy and poor image quality.
2. Non impact printers: Printers that do not strike characters against ribbon or paper when they print on non impact printers.
The main categories are (1) Inkjet Printer (2) Thermal Printer (3) Laser Printer.
a. Inkjet Printer: The dots are formed by tiny droplets of ink. These printers can almost match the speed of dot matrix printer. Color Inkjet Printers are also used to produce high quality color prints.
b. Thermal Printer: It is designed to heat the surface of the chemically treated paper so that a dot is produced based on the reaction of the chemical to the heat. No ribbon or ink is involved. They require special and expensive paper.
c. Laser Printer: The process resembles the operation of a photocopy machine. A laser beam is directed across the surface of a light sensitive drum and fired as needed to record an image in the form of a pattern of tiny dots. The images are then transferred to the paper, a page at a time in the same fashion as a copy machine, using special toner.
3. Plotters: A plotter is specialized output device designed to produce high quality graphics in variety of colors. There are two basic types of plotters, which use pens and that do not. Drum plotters and flat bed plotters both use pens. Electrostatic plotters do not use pen.
In a drum plotter, the paper is mounted on the surface of a drum. The drum revolves and the plotter pens are horizontally positioned over the target area. When the paper has rotated to the correct point, the pens are dropped to the surface and moved left and right under program control, across the paper as the drum revolves. When the image is complete, the pens are raised from the surface. Flat bed plotters are designed, so that the paper is flat and one or more pens move horizontally and vertically across the paper.
Electro static paper uses electro static charges to create images out of very small dots on specially treated paper. The paper is run through a developer to allow the image to appear. Electrostatic papers are faster than pen plotters and produce images of very high resolution.
4. Computer output micro film/micro fiche systems
The principal advantages of this technology are:
Soft copy output devices : Two main types of video screens are
1. Cathode Ray Tube: It is the most popular soft copy output device used with terminals connected to large computer systems and as a monitor for micro computer system. This type of video display screens are used to view the data entry and computer output.
Two types of monitors are present :
1. Alpha numeric monitors: Displays letters, numbers and special characters such as $,*,?. They display 80 characters per line. With 24 lines visible at one time.
2. Graphic monitor: Displays both alpha numeric data and graphic. Graphics monitor can be divided into groups that display one-two and three dimensional graphics. The CRT’s screen displays is made up of small picture elements called pixels. The smaller the pixels (the more points that can be illuminated on the screen) the better the image clarity or resolution. Most screens are capable of displaying 80 characters of data horizontally and 25 lines vertically. The video display units can also be divided in to monochrome-capable of displaying a single color image. Multichrome-capable of displaying multicolored images. Disadvantages: Large size, high power consumption, occasional flickering of images.
2. Flat Screen Technology: It is useful for laptop computers. It has higher resolution, low power consumption with same graphics capabilities of the traditional CRT.
Three types:
1. Liquid crystal display.
2. Electro luminescent display.
3. Gas Plasma display.
When a small amount of current is applied to both wires, a chemical reaction turns the chemical a dark color, there by blocking light. The principal advantages of LCD are –
1. Low power consumption.
2. Low cost
3. Small size.
Disadvantages:
1. They do not exit light. Image has very little contrasts.
2. The optimum viewing angle is very narrow.
3. LCDs have no color capability.
4. The resolution is not as good as that of CRT.
The combined voltage from a row and column cause the screen to glow at that point.
EL display provides a very high image resolution and excellent graphic capability, also generates its own light. The major limitation is cost.
Advantages:
1. The images are much better than on a standard CRT.
2. The resolution is excellent.
3. Glaring problem is not significant.
4. Screens do not flicker.
Disadvantages:
1. Only single color is available.
2. The technology is expensive.
3. It uses lot of power.
4. It does not show sharp contrast.
3. Voice Output Systems:
Voice output systems are relatively new and can be used in some situations where traditional display screen soft copy output is inappropriate. It is certainly more helpful to hear a warning that you are speeding than to take your eyes off the road to check a display. Two different approaches to voice output have evolved speech coding and speech synthesis. Speech coding on human speech, is reservoir of sound to draw from, the building the words and phrases to be output. Sounds are coded and stored on disk to be retrieved and translated back as sounds. Speech coding is used in automobiles, toys and games. Speech synthesis relies on the use of set of basic speech sounds that are created electronically without the use of human voice. One of the major applications of speech synthesis is providing reading machines for the blind.