OUTPUT DEVICES
In this Lecture 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, non-impact 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.
Define the four categories of output
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 non-text 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.
Identify the different types of display devices
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 analogue
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.
Describe factors that affect the quality of a display device
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.
Identify monitor ergonomic issues
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.
Explain the differences among various types of printers
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 non-impact.
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.
Non-impact printers form characters and graphics without actually
striking the paper.
An ink-jet printer is a non-impact printer that sprays drops of ink onto a
piece of paper.
A laser printer is a non-impact printer that creates images using a laser
beam and powdered ink, called toner.
A thermal printer is a non-impact 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 colour 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 travelling.
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 colour prints.
Describe the uses of speakers and headsets
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.
Identify the purpose of data projectors, fax machines, and
multifunction devices
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.
