An output device is a part of computer hardware equipment, used to communicate the results of data processing which are carried out by an information processing system (such as a computer), to the outside world. Output devices carry the results of various operations performed by the user. Some of the devices, which are used to display the processed result or output are as follows:
A monitor (also called a visual display unit) is an electronic visual device used to display the output. The rectangular area of the monitor, its refresh rate and dot pitch, all directly affect the resolution of the display.
Resolution refers to the clarity of screen and is measured by the number of individual tiny coloured dots (knows as pixels), scattered on the screen. Resolution indicates the number of dots per inch. The smaller the dot pitch is, the better the resolution will be.
Types of Monitors
The popular type of monitors are as follows:
(i) CRT (Cathode Ray Tube)
The CRT works in the same way as a television. It contains an electron gun at the back of the glass tube.
This gun fires electrons in a group of phosphor dots, which is coated inside the screen. When the electrons strike the phosphor dots they glow to give the colours.
(ii) LCD (Liquid Crystal Display)
These screens are used in laptops and notebook sized PCs. A special type of liquid is sandwiched between two plates. It is a thin, flat and light weight screen made up of any number of colours or mono-chrome pixels arranged in front of a light source.
Some of the major features of LCD monitors are:
• Long life
• Light weight
• Better screen privacy
• Less eyestrain
• Reduced radiation
(iii) LED (Liquid/Light Emitting Diode)
LED is an electronic device that emits light when electric current is passed through it.
LEDs usually produces red light, but today’s LEDs can produce RGB (Red, Green and Blue) light and white light as well.
(iv) 3-D Monitor
3-D Monitor is a television that conveys depth perception to the viewer. 3-D describes an image that provides the perception of length. When 3-D images are made interactive, user feels involved with the scene and this experience is called virtual reality.
TFT (Thin Film Transistor)
TFT and Active-Matrix LCD (AMLCD) is a liquid Crystal Display (LCD). With active-matrix displays, each pixel is controlled by one to four transistors that can make the screen faster, brighter, more colourful than passive-matrix and capable of being viewed at different angles. Because of this improved technology, active-matrix screens are often more expensive but have better quality than a passive-matrix display.
A printer is an output device, which produces a hard copy of documents that are stored in an electronic, form on physical print media such as paper or transparencies. So printers are the primary output devices used to prepare permanent documents. The speed of a printer is normally rated either by Pages Per Minute (PPM) or by Characters Per Second (CPS).
Printers can be classified into two broad categories:
(i) Impact Printers
(ii) Non-Impact Printers.
(i) Impact Printers
Impact printers rely on a forcible impact to transfer ink to the print media; similar to the action of a typewriter. There is a mechanical contact between the paper and the print head.
Impact printer’s varieties includes:
(a) Line Printer
These are impact shaped character printers which are capable of printing an entire line at once instead of one or more character at a time. Print quality of line printer is not high.
(b) Drum printer
It is an old line printer technology that is used to form character images around a cylindrical drum as its printing mechanism. When the desired character for the selected position is rotated around the hammer line, the hammer hit the paper from behind and push it into the ribbon and onto the character.
(c) Daisy wheel printer- It can print one character at a time. In daisy wheel printer, round disk extends a portion of the wheel making contact with ink ribbon that makes contact with paper for creating the character. This procedure is repeated for each key when it is pressed. These printers are fitted with unchangeable print heads called daisy wheels. To print each character, the wheel is rotated and the appropriate stroke is struck against an inked ribbon. Daisy wheel printers cannot produce high quality print graphics. The speed of daisy wheel printer is about 100 cps.
(d) Dot matrix printer -The term dot matrix refers to the process of placing dots to form an image. It uses print heads to shoot ink or strike an ink ribbon to place hundreds to thousands of little dots to form text or images. It prints one character at a time. The speed of dot matrix printer lies between 200 to 600 cps.
The quality of the image is determined by the dots per inch. These printers are slow, noisy and are not commonly used for personal computers. They can print multi-layer forms, which neither inkjet nor laser printers can print. It can print special characters and graphics. Dot matrix printer do not have fixed character fonts.
(ii) Non-impact Printers
Non-impact printers are much quieter than impact printers as their printing heads do not strike the paper. Most non-impact printers produce dot-matrix patterns. There is no mechanical contact between the paper and the print head. These printers are comparatively faster and produce high quality output. They can be used for printing text and graphics both in black and white and coloured versions.
The main types of non-impact printers are as follows:
(a) Electrographic printers- Electrographic or electro- photographic printers are very fast printers and they fall under the category of page printers.
They can produce documents at a speed of over 20000 lines per minute i.e. more than 250 pages per minute. The electrographic technology has developed from the paper copier technology.
(b) Thermal printer- Thermally printed paper tends to darken over time due to exposure to sunlight or heat. The print quality produced is poor. Thermal printers are widely used in battery powered equipment such as portable calculators.
(c) Electrostatic printer- Electrostatic printers are generally used for large format printing. They are favoured by large printing shops because of their ability to print fast and lower printing costs.
(d) Laser Printer- Laser printers work on the principle of electro-photography and use a beam of laser light like a photocopier. The powered ink (i.e. toner) is transferred to paper to form a text/image pattern and then fixed by heat or pressure. When used to print a bulk of papers, the laser printer produces the cheapest cost per printout.
(e) Inkjet Printer An inkjet printer fires extremely small droplets of ink onto the paper to create impression of text or image. The print head of inkjet printers, known as print cartridge, contains tiny nozzles (50 or more) through which different coloured inks can be sprayed onto the paper to form the characters or graphic images. Colour inkjet printers provide an inexpensive way to print fully coloured documents.
It is an output device similar to a printer that uses a pen, pencil, marker or other writing tools to make a design.
Plotters are generally used to generate the map of building and shopping malls. A plotter is a computer printing device for printing vector graphics. In the past, plotters were widely used in applications such as Computer Aided Design (CAD) and other print jobs. Though they have generally been replaced with wide-format conventional printers.
There are two basic types of plotters those that use pens and those that do not. Drum plotters and flatbed plotters use pens but electrostatic plotters do not use the same.
(i) Drum plotter- A drum plotter contains a long cylinder and a pen carriage. The output paper is placed over the drum. The pen is mounted horizontally on the carriage. Both the pen and drum move under the computer’s control to produce the desired drawing.
(ii) Flatbed plotter- A flatbed plotter consists of a stationary horizontal flat surface on which paper or any other medium is fixed. The pen is mounted on a carriage that can move along the horizontal and vertical axis.
(iii) Electrostatic plotter- It marks the paper with electrostatic charges and runs it through a developing system to create an image. They produce high-quality images and are used by graphic and commercial artists.
Speaker is an output device that receives sound in the form of electric current from the sound card and converts it into sound format. Speakers are used for listening to music.
Computer speakers (multimedia speakers) are the speakers, which are attached internally or externally to a computer system.
Headphones are a pair of small loudspeakers or less commonly a single speaker, held close to a user’s ears and connected to a signal source such as an audio amplifier, radio, CD player or portable media player.
They are also known as stereo phones, headsets or cans.
It is an output device, which is used to project information from a computer onto a large screen, so it can be viewed by a large group of people simultaneously.
Projectors are widely used for classroom training or conference halls with a large audience. It provides a temporary output display.
Speech synthesizer is used to produce sound from a text and can be implemented in software and hardware. A text-to-speech system converts normal language text into speech.