In this chapter, you learn what is output and what are output devices. Display devices are introduced, including CRT monitors, flat-panel displays, video cards, and high-definition television. You explore monitor quality and monitor ergonomics. Various types of printers are presented, such as impact printers, nonimpact printers, portable printers, plotters and large-format printers, and special-purpose printers. You find out about audio output and other output devices, including data projectors, facsimile machines, and multifunction devices. Finally, you become acquainted with terminals and output devices for physically challenged users.
Output is data that has been processed into a useful form called information. Four types of output are text, graphics, audio, and video. Text consists of characters (letters, numbers, punctuation marks, or any other symbol requiring one byte of computer storage space) that are used to create words, sentences, and paragraphs. Graphics are digital representations of nontext information such as drawings, charts, photographs, and animation (a series of still images in rapid sequence that gives the illusion of motion). Audio is music, speech, or any other sound. Video consists of images played back at speeds to provide the appearance of full motion. An output device is any computer component capable of conveying information to a user.
Back to Top
A display device is an output device that visually conveys text, graphics, and video information. Information shown on a display device is called soft copy because the information exists electronically and is displayed for a temporary period of time. Display devices include CRT monitors, LCD monitors and displays, gas plasma monitors, and televisions. A CRT monitor is a monitor that is similar to a standard television set because it contains a cathode ray tube. A cathode ray tube (CRT ) is a large, sealed, glass tube. The front of the tube is a screen coated with phosphor material that glows as an electron beam moves back and forth, which produces an image on the screen. LCD monitors and LCD displays use liquid crystal to present information on the screen. A liquid crystal display (LCD ) has liquid crystals between two sheets of material. When an electric current passes through the crystals, they twist, causing some light waves to be blocked and allowing others to pass through, which creates the images.
Similar to an LCD display, a gas plasma monitor is a flat-panel display. A gas plasma monitor, however, substitutes a layer of gas for the liquid crystal material. When voltage is applied, the gas releases ultraviolet light that causes pixels on the screen to glow and form an image. An NTSC converter converts a computer’s digital signal into an analog signal that a standard television set can display. High-definition television (HDTV ) is a type of television set that works with digital broadcasting signals and supports a wider screen and higher resolution than a standard television set.
Back to Top
The quality of a CRT monitor depends largely on its resolution, dot pitch, and refresh rate. The quality of an LCD monitor or display depends primarily on its resolution.
A CRT monitor’s screen is coated with tiny dots of phosphor material, called pixels. that glow when electrically charged to produce an image. Resolution. which describes the sharpness and clearness of that image, is related directly to the number of pixels a monitor can display. The greater the number of pixels the display uses, the better the quality of the image. Dot pitch. a measure of image clarity, is the distance between each pixel on a display. The smaller the distance between pixels (dot pitch), the sharper the image. Refresh rate is the speed that a monitor redraws images on the screen. Refresh rate should be fast enough to maintain a constant, flicker-free image.
The resolution of an LCD monitor or display generally is proportional to the size of the monitor or display. That is, the resolution increases for larger monitors and devices.
Back to Top
The goal of ergonomics is to incorporate comfort, efficiency, and safety into the design of items in the workplace. Features that address monitor ergonomic issues include controls to adjust the brightness, contrast, positioning, and height and width of images. Newer monitors have digital controls that allow you to fine-tune the display. Many monitors also have a tilt and swivel base so the angle of the screen can be altered to minimize neck strain and glare. Monitors produce a small amount of electromagnetic radiation (EMR ), which is a magnetic field that travels at the speed of light. High-quality monitors should comply with MPR II. a standard that defines acceptable levels of EMR for a monitor.
A printer is an output device that produces text and graphics on a physical medium such as paper or transparency film. Printed information is called hard copy because the information exists physically and is a more permanent from of output. Printers can be grouped in two categories: impact and nonimpact.
Impact printers form characters and graphics by striking a mechanism against an ink ribbon that physically contacts the paper. A dot-matrix printer is an impact printer that prints images when tiny wire pins on a print head mechanism strike an inked ribbon. A line printer is an impact printer that prints an entire line at one time. Two popular types of line printers are band printers and shuttle-matrix printers.
Nonimpact printers form characters and graphics without actually striking the paper. An ink-jet printer is a nonimpact printer that sprays drops of ink onto a piece of paper. A laser printer is a nonimpact printer that creates images using a laser beam and powdered ink, called toner. A thermal printer is a nonimpact printer that generates images by pushing electrically heated pins against heat-sensitive paper. Although the print quality of standard thermal printers generally is low, two special types of thermal printers, thermal wax-transfer printers and dye-sublimation printers. have a much higher print quality.
Some printers are used for special purposes. A photo printer is a color printer that can produce photo lab quality pictures as well as printing everyday documents. A label printer is a small printer that prints on an adhesive type material that can be placed on a variety of items. A portable printer is a small, lightweight printer that allows a mobile user to print from a notebook or handheld computer while traveling. Plotters are sophisticated printers used to produce high-quality drawings such as blueprints, maps, and circuit diagrams. A large-format printer. which operates like an ink-jet printer but on a larger scale, creates photo-realistic quality color prints.
Back to Top
An audio output device produces music, speech, or other sounds. Two commonly used audio output devices are speakers and headsets. Most personal computers have an internal speaker that outputs low-quality sound. Many users add high-quality stereo speakers or purchase PCs with larger speakers built into the sides of the monitor. A woofer can be added to boost low bass sounds. A headset plugged into a port on the sound card allows only the user to hear sound from the computer.
Back to Top
A data projector takes the image on a computer screen and projects it onto a large screen so that an audience of people can see the image. Two smaller, lower priced data projectors are an LCD projector. which uses liquid crystal display technology, and a digital light processing (DLP ) projector. which uses tiny mirrors. A facsimile (fax ) machine transmits and receives documents over telephone lines. A fax modem is a communication device that allows you to send (and sometimes receive) electronic documents as faxes. A multifunction device (MFD ) is a single piece of equipment that looks like a copy machine but provides the functionality of a printer, scanner, copy machine, and sometimes a fax machine.
Back to Top
A terminal is a device that performs both input and output because it consists of a keyboard (input), a monitor (output), and a video card. A dumb terminal has no processing power and cannot function as an independent device. Dumb terminals connect to a host computer that performs the processing and then sends the output back to the dumb terminal. An intelligent terminal has memory and a processor that has the capability of performing some functions independent of the host computer. Some special-purpose terminals perform specific tasks and contain features designed for a particular industry. A point-of-sale (POS ) terminal is a special-purpose terminal used to record purchases at the point where a consumer buys a product or service. An automatic teller machine (ATM ) is a self-service, special-purpose terminal used to access your bank account.
Back to Top
For users with mobility, hearing, or vision disabilities, many different types of output devices are available. For example, hearing-impaired users can instruct programs to display words instead of sound. With the Windows operating system, physically challenged users can set options to make programs easier to use. Visually impaired users can change the size or color of text to make words easier to read. Blind users can use speech output, where the computer reads information that displays on the screen. A Braille printer outputs information in Braille onto paper.
Back to Top