Output devices are also peripheral devices that enable a computer to communicate information to humans or other machines. Output devices receive date from a computer and transform them into a usable Output can be categorized as soft-copy or hard-copy.
Soft-Copy (Output Devices).
Normally, the output is produced on the screen of the computer system, users prefer to preview output on screens.
Monitors (CRT) Cathode Ray Tube).
The most popular soft-copy output device is the monitor. A monitor is a television-like a device that displays data or information like other output devices, monitors come in many styles and price ranges.
Monitor quality is often discussed in terms of resolution, a measure of the number of picture elements, or pixels for short, that the display screen that can be controlled individually. The more pixels, the clearer, and sharper the image. A 640 x 480-pixel screen contains 640 horizontal pixels and 480 vertical pixels.
Types of Monitors.
A monochrome (single color) monitor is used where output consists mainly of text and numbers, although with the appropriate circuitry, some monochrome monitors can display graphics. A monochrome monitor usually displays either green, amber, or white characters on a Black screen. A typical text resolution in monochrome monitors is 640 x 350 pixels, and graphics resolution is 720 x 348 pixels.
To produce an image on a cathode-ray tube (CRT), an electron beam moves across a phosphor coated screen. intensifying the strength of the beam, the phosphor coating lights in certain places, forming the characters. the most common type of CRT has a display screen of 25 lines of 80 characters each. other sizes are available, including those used in desktop publishing applications. Such screens can display two full 8 ½ x 11-inch pages at their normal size.
A color monitor.
A color monitor is often preferred for output containing graphics. Three colors of phosphor dots form a pixel on color monitors. These colors blend to make other colors by varying the intensity of the electron beam focused on the phosphor dots.
Two types of color monitors are commonly used composite and red-blue (RGB). A composite color monitor used only one electron gun to control the intensity of the three phosphor dots in each pixel. In an RGB three electron guns, one for each dot in a pixel, control the intensity of the phosphor dots. An RGB monitor produces a much sharper picture because the three electron guns allow finer control over the intensities of the phosphor dots.
Flat-Panel Display sometimes is called (FPD). This kind of display is found on all portable computers and it is also new for desktop computers. FPD uses Liquid-crystal display(LCD) OR light-emitting diode (LED) technology to give better look to a traditional monitor.
Printers (Hardcopy output devices).
The printer is counted in most useable in output devices. Printers can print text as well as graphics on papers. Various types of printers are available in terms of quality, speed, and cost. The print available from hard-copy output device.
There are two types of mechanisms available.
Impact printers also called noisy printers print by hammering or pin striking on ink ribbon which leaves as the impression of the characters on the paper this printer can produce carbon copies because of striking capability paper used in these printers could be single sheets or continuous sheets impact printers are also divided into Character-at-a-time printers.
- Character-at-a-time printers.
- Line –at-a-time printers.
Character At-A-Time Printer.
This mechanism is similar to ordinary typewriters speed of these printers is measured in characters per second (cps ) they are available in two sizes 80 column and 132 column printers having one printing head beside monochromes color printers are also available in this category this character –at-a-time printers are divided into daisy wheel and dot matrix printers.
Daisy wheel printers.
Modern electronic typewriters are using daisy wheels the wheel looks like a daisy the character image is printed on the paper and produce letter-quality there were several disadvantages like no graphic printing slow speed and only one type of writing.
Dot matrix printers.
Dot matrix printers use print heads containing pins from 9 to 24 back and forth movement of the head prints te data bi-directional printing is also possible the 24 pins dot matrix called letter quality (LQ) printer produces more dots giving crisper characters 9 pins dot matrix printers result is not good dot matrix printers are more popular with computer users speed ranges from 100to 800 characters per second color dot matrix printer are also in use printers have built in buffers to store the data thus freeing computer to process other jobs.
At-a-time printers are not suitable because of their slow speed so high-speed line prints are used they have a special mechanism that prints a whole line at once it can typically print in the range of 400 LPM to 8000 LPM they are normally 132 column printers having 132 printing heads these line printers could be of following types.
Lt has a complete character set engraved around the circumference of each print position of the drum one complete round is required to print the whole line.
The chain rotates until all of the required print positions on the line have been filled then the page moves to print the next line.
Band printers operate the same way as chain printers work.
These are quieter printers means they do not produce noise while printing they can not produce the carbon copies the output of these non-impact printers is far better than impact non-impact printers are categorized into flowing categories.
The original models of these printers were character matrix printers and had only limited success in recent years improved designs have resulted in very successful page printers which have been competing favorably with daisy wheel printers.
Thermal transfer printers.
Thermal –transfer printers is an inexpensive alternative to the ink-jet printer it uses heat to transfer ink to paper a thermal –transfer printers produces near –letter quality characters some thermal printers use special heat sensitive paper which is turned black at the places where the hot pins strike fax machine is the example of the type of thermal printer.
Electrostatic printers are fast high – resolution used where complex images are needed such as in mapping integrated circuit design satellite imaging and remote sensing they are very expensive color printers.
laser printers are used where the best quality output is the main consideration they produce high-quality text and graphics a laser beam is directed at a mirror the beam into a drum leaving negative charge on the drum then positively charged toner (ink) sticks to the drum laser printers are also called page printers and their speed is measured in pages per minute ( ppm) commercial laser printer are much faster the speed ranges from 4 to 600 pages per minute these are available at affordable prices with relatively low maintenance cost.
A plotter is a specific output device intended to produce high quality graphics in a variety of colors plotters are particularly valuable for making maps and architectural drawings although.
A flatbed plotter is designed so that paper lies flat on a table like surface the size of the bed determines the maximum size of the sheet if paper under computer control between one and four color pens move across the paper and the paper moves beneath the pens.
A drum plotter works like a flatbed plotter except that the paper is output over a drum enabling continuous output that is useful for example to track earthquake activity, bar graphs and pie charts created with a plotter can enhance business presentations plotters are based on different technologies following plotters are available in the market
Speaker is also kind of output devices which is connected to a computer and generate sound. The sound is produced by a computer through a sound card.