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Chapter 5Output Devices and Media

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The Basics of Output

Output is processed data, usually text, graphics, or sound, that can be used immediately by people, or stored in computer-usable form for later use.

There are many types of computer output. Those used directly by people fall in two general categories: hard copy and soft copy.

Hard copy is a permanent version of output, typically recorded on a tangible medium such as paper or microfiche/microfilm.

Soft copy is a temporary version of output, typically displayed on a computer screen.

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Output-Oriented Hardware

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Monitors

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Monitors

Monitors are peripheral devices that contain viewing, or display, screens.

Many monitors use a cathode ray tube (CRT) as the display screen.

A monitor is often paired with an input device, such as a keyboard, to form a unit called a video display terminal (VDT).

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Resolution

The clarity, or sharpness, of images displayed on the monitor is a function of its resolution.

Resolution is increased by increasing pixel density and decreasing dot pitch.

Refresh rate also affects image clarity. As each pixel is illuminated, it lights up - and immediately begins to fade. To minimize this fade, and the resultant flickering that may be seen by the user, each pixel must be illuminated regularly.

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Cathode Ray Tube Monitors

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Monochrome Monitors

Monochrome monitors display pixels in a single color on a screen with a contrasting background.

The most common color combinations are dark/light green, dark/light amber, and black/white.

Although limited to one color, monochrome monitors can usually display shades of that color, called gray-scaling.

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Color Monitors

Color monitors display characters and graphics using a combination of red, green, and blue, and therefore are called RGB monitors.

A color monitor is able to display anywhere from eight to hundreds of thousands of colors at one time.

Color monitors are especially useful for displaying graphics.

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Some Color Graphics Standards

Color Graphics Adapter (CGA) standard - provides low-resolution, 4-color graphics.

Enhanced Graphics Adapter (EGA) standard - provides up to 16 colors at higher resolution.

Video Graphics Array (VGA) standard - can handle up to 256 colors, with a moderate increase in resolution.

Super Video Graphics Array (SVGA) standard - provides even more colors, and increased resolution.

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Flat-Panel Monitors

Portable and notebook computers require small, lightweight, low-powered monitors. Flat-panel monitors meet these criteria, and can be used to display text and graphics in either monochrome or color.

The two most commonly used flat-panel display technologies are liquid crystal and gas plasma.

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Types of Flat-Panel Monitors

A liquid crystal display (LCD) screen is made of two sheets of polarizing material sandwiched together with a liquid crystal solution between them. The liquid crystals “twist” when an electrical current is applied.

A gas plasma display screen is made of a sandwich of two sheets of transparent material filled with an inert gas (such as neon) that glows when an electrical current is applied.

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Monitor Ergonomics

The science of studying the interaction of humans and office equipment is called ergonomics.

There has been concern that electromagnetic emissions from computer monitors, particularly those in the 5 Hz to 400 KHz range, might cause cancer or affect pregnancies.

Another cause for concern has been physical maladies such as carpal tunnel syndrome.

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Workstation Ergonomics

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Printers

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Printers

Printers are the most common type of hard copy output devices.

One way to classify printers is by whether they are impact or nonimpact.

Impact printers create images on paper by striking an inked ribbon against the paper, depositing the ink on the paper.

Nonimpact printers use heat, electricity, or laser technology to create the image on paper.

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Impact Printers

These printers create images on the paper by physically striking an inked ribbon to deposit its ink on the paper.

An important advantage of impact printers is their ability to produce multiple (carbon) copies of documents and forms in one printing.

Some impact printers, called character printers, print a single character at a time, while line printers print an entire line at once.

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Dot-Matrix Printers

Dot-matrix printers create characters in the form of small dots arranged in matrix format.

Dot-matrix printers offer a number of advantages, including:· Are reasonably economical· May be reasonably fast· Can print graphics

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Dot-Matrix Printers (continued)

There are also some disadvantages associated with dot-matrix printers, including:· Reduced quality of output.· They may be rather noisy.· They are slower than line or page

printers

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Solid Font Printers

Solid font printers form an entire character in one print stroke.

A font is a complete set of characters in a consistent and unique typeface.

A common solid font printer used with personal computers is the daisywheel printer.

Chain printers and band printers are most often used as high-speed printers attached to larger computers.

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Daisywheel Printers

Daisywheel printers use a spoke metal or plastic disk (shaped something like a daisy) with printed characters along its perimeter.

Noted for their high-quality printing, daisywheel printers used to be quite popular with personal computer users for word processing.

The “wheel” is removable and replaceable.

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Line Printers

Chain and band high-speed impact printers are called line printers because they appear to print an entire line at a time.

Chain printers use a set of metal characters on a rotating chain to print an entire line of up to 132 characters almost simultaneously.

Band printers use a rotating band with characters embossed on the band.

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Line Printers

Chain Printer --->

<--- Band Printer

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Nonimpact Printers

Nonimpact printers use heat, electricity, or laser technology to produce an output image. Most are dot-matrix printers.

The advantages they offer over impact dot-matrix printers include:· They are faster.· They are quieter.· The quality of print is higher.

The two primary nonimpact printer technologies are laser and ink-jet.

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Laser Printers

Laser printers represent the latest and fastest growing segment in the printer market. The primary reason for their popularity is their ability to produce text and graphic images with clear, crisp quality.

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Laser Printer Technology

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Ink-Jet Printers

Ink-jet printers spray tiny drops of ink through one or more nozzles onto the paper to create images in dot-matrix form.

The ink is forced out of the nozzles onto the paper through the use of either thermal or mechanical means.

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Thermal Transfer Printers

Thermal transfer printers heat cyan, magenta, yellow, and black wax onto the page.

These printers contain heating devices that, when used with chemically treated paper, form high-quality images.

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Dye Sublimation Printers

Dye sublimation printers produce continuous-tone images by vaporizing colored inks onto specially treated, heat-sensitive paper.

The quality of output of dye sublimation printers rivals that of color photos.

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Output Spools and Buffers

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Spools and Buffers

Spooling software allows data to be stored temporarily on a magnetic storage medium, usually a disk, until the printer is ready to print it.

Buffers, like the CPU’s RAM, are temporary holding areas inside the output device that attempt to compensate for the difference in CPU and output device speeds.

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Spools and Buffers

Use of Spooling Devices

Use of Buffer Memory

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Other Output Devices and Media

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Plotters

Plotters are hard copy devices for producing graphic images on paper.

Flatbed plotters hold the paper motionless on a flat bed while an arm that holds a drawing pen moves around in all directions to create the image.

Drum plotters lay the paper across a drum that rotates forward and backward as an arm holding the drawing pin moves perpendicular to the drum’s motion to create the image.

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Presentation Graphics

Photographic slide devices make it possible to produce 35-millimeter slides of data that can be used with a slide projector and screen.

Screen image projectors rest on the top of an overhead projector, connect to the computer, and duplicate the screen image exactly as it would appear on the monitor.

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Voice Output

Voice output systems convert data into digitized voice messages that are sent to the user.

A special application in which a computer converts electronic signal data into sound is called music synthesis. A music synthesizer can produce high-quality musical sounds.

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Computer Output Microform (COM)

To save space, large organizations, libraries, etc., use computer output microform for miniaturizing and saving documents. The two common forms of microform are microfilm and microfiche.

Microfilm is a continuous roll of acetate film, similar to movie film.

Microfiche are 4- x 6-inch sheets of film, often called “fiche.”