Input:
Getting Data from the User to the Computer
Some
input data can go directly to the computer for processing. Input in this
category includes bar codes, speech that enters the computer through a
microphone, and data entered by means of a device that converts motions to
on-screen action. Some input data, however, goes through a good deal of
intermediate handling, such as when it is copied from a source document and
translated to a medium that a machine can read, such as a magnetic disk. In
either case the task is to gather data to be processed by the computer
‹sometimes called raw data and convert it into some form the computer can
understand.
Keyboard
A
keyboard is usually part of a personal computer or part of a terminal that is
connected to a computer somewhere else. Not all keyboards are traditional,
however. A fast-food franchise like McDonald's, for example, uses keyboards
whose keys represent items such as large fries or a Big Mac. Even less
traditional in the United States are keyboards that are used to enter Chinese
characters.
Mouse
A mouse
is an input device with a ball on its underside that is rolled on a flat
surface, usually the desk on which the computer sits. The rolling movement
causes a corresponding movement on the screen. Moving the mouse allows you to
reposition the pointer, or cursor, an indicator on the screen that shows where
the next interaction with the computer can take place. The cursor can also be
moved by pressing various keyboard keys. You can communicate commands to the
computer by pressing a button on top of the mouse. In particular, a mouse
button is often used to click on an icon, a pictorial symbol on a screen; the
icon represents a computer activity-a command to the computer-so clicking the
icon invokes the command.
Trackball
A
variation on the mouse is the trackball. You may have used a trackball to play
a video game. The trackball is like an upside-down mouse-you roll the ball
directly with your hand. The popularity of the trackball surged with the advent
of laptop computers, when traveling users found them- selves without a flat
surface on which to roll the traditional mouse.
Abbreviated MICR, magnetic-ink character recognition is a method of
machine-reading characters made of magnetized particles. The most common
example of magnetic characters is the array of numbers across the bottom of
your personal check.
Most magnetic-ink characters are preprinted on your check. If you compare a
check you wrote that has been cashed and cleared by the bank with those that
are still unused in your checkbook, you will note that the amount of the cashed
check has been reproduced in magnetic characters in the lower-right corner.
These characters were added by a person at the bank by using a MICR inscriber.
Scanner
An
inexpensive way to get entire documents, pictures, and anything on a flat
Surface into a computer is by using a scanner. Scanners use optical
recognition systems that have a light beam to scan input data to convert it
into electrical signals, which are sent to the computer for processing. Optical
recognition is by far the most common type of source input, appearing in a
variety of ways: optical marks, optical characters, bar codes, handwritten
characters, and images. Scanners use Optical Character Recognition software,
described below, to translate text on scanned documents into text that is
suitable for word processors and other computer applications.
Output:
Information for the User
As we have seen, computer output takes the form of screen or printer output.
Other forms of output include voice, microfilm, and various forms of graphics
output.
A computer system often is designed to produce several kinds of output. An
example is a travel agency that uses a computer system. If a customer asks
about airline connections to Toronto, Calgary, and Vancouver, say, the travel
agent will probably make a few queries to the system to receive on-screen output
indicating availability on the various flights. After the reservations have
been confirmed, the agent can ask for printed output that includes the tickets,
the traveler's itinerary, and the invoice. The agency may also keep the
customer records on microfilm. In addition, agency management may periodically
receive printed reports and charts, such as monthly summaries of sales figures
or pie charts of regional costs. We begin with the most common form of output,
computer screens.
Computer Screen Technology
A user's
first interaction with a computer screen may be the screen response to the
user's input. When data is entered, it appears on the screen. Furthermore, the
computer response to that data-the output-also appears on the screen. Computer
screens come in many varieties, but the most common kind is the cathode ray
tube (CRT). Most CRT screens use a technology called raster-scan technology.
The backing of the screen display has a phosphorous coating, which will glow
whenever it is hit by a beam of electrons. But the light does not stay lit very
long, so the image must be refreshed often. If the screen is not refreshed
often enough, the fading screen image appears to flicker. A scan rate-the
number of times the screen is refreshed-of 60 times per second is usually
adequate to retain a clear screen image. As the user, you tell the computer
what image you want on the screen, by typing, say, the letter M, and the
computer sends the appropriate image to be beamed on the screen. This is
essentially the same process used to produce television images.
A computer display screen that can be used for graphics is divided into dots
that are called addressable, because they can be addressed individually by the
graphics software. Each dot can be illuminated individually on the screen. Each
dot is potentially a picture element, or pixel. The resolution of the screen,
its clarity, is directly related to the number of pixels on the screen: The
more pixels, the higher the resolution. Some computers come with built-in graphics
capability. Others need a device, called a graphics card or graphics adapter
board, that has to be added.
There have been several color screen standards, relating particularly to
resolution. The first color display was CGA (color graphics adapter), which had
low resolution by today's standards (320x200 pixels). This was followed by the
sharper EGA (enhanced graphics adapter), featuring 640x350 pixels. Today, VGA
and SVGA are common standards. VGA (video graphics array) has 640x480 pixels.
SVGA (super VGA) offers 800x600 pixels or 1024x768 pixels, by far the superior
clarity.
Is bigger
really better? Screen sizes are measured diagonally. Many personal computers
come with a 15 inch screen. A 15 inch screen is fine for most single
applications, but for applications with large graphics, or for having multiple
windows open, it is sometimes inadequate. For a few hundred dollars more, 17
inch can be better. There are even bigger screens that cost substantially more.
Bigger is usually better, but more expensive.
Types of Screens
Cathode
ray tube monitors that display text and graphics are in common use today.
Although most CRTs are color, some screens are monochrome, meaning only one
color, usually green, appears on a dark background. Another type of screen technology
is the liquid crystal display (LCD), a flat display often seen on watches and
calculators. LCD screens are used on laptop computers. Some LCDs are
monochrome, but color screens are popular. Some laptop screens are nearing CRTs
in resolution quality.
Terminals
A screen
may be the monitor of a self-contained personal computer, or it may be part of
a terminal that is one of many terminals attached to a large computer. A
terminal consists of an input device, an output device, and a communications link
to the main computer. Most commonly, a terminal has a keyboard for an input
device and a screen for an output device, although there are many variations on
this theme.
Printers
A printer
is a device that produces printed paper output, known in the computer industry
as hard copy because it is tangible and permanent (unlike soft copy, which is
displayed on a screen). Some printers produce only letters and numbers, whereas
others can also produce graphics.
Letters and numbers are formed by a printer either as solid characters or as
dot-matrix characters. Dot-matrix printers create characters in the same way
that individual lights in a pattern spell out words on a basketball scoreboard.
Dot-matrix printers construct a character by activating a matrix of pins that
produce the shape of the character. A traditional matrix is 5x7-that is, five
dots wide and seven dots high. These printers are sometimes called 9-pin
printers, because they have two extra vertical dots for descenders on the
lowercase letters g, j, p, and y. The 24-pin dot-matrix printer, which uses a
series of overlapping dots, dominates the dot-matrix market. The more dots, the
better the quality of the character produced. Some dot-matrix printers can
produce color images.
There are two ways of printing an image on paper: the impact method and the
non-impact method. Let us take a closer look at the difference.
Impact Printers
The term impact refers to the fact that impact printers use some sort of
physical contact with the paper to produce an image, physically striking paper,
ribbon, and print hammer together. The impact may be produced by a print hammer
character, like that of a typewriter key striking a ribbon against the paper,
or by a print hammer hitting paper and ribbon against a character. A dot-matrix
printer is one example of an impact printer. High- quality impact printers
print only one character at a time.
However, users who are more concerned about high volume than high quality
usually use line printers - impact printers that print an entire line at a
time. Organizations that use mainframe and minicomputers usually have several
line printers. Such organizations are likely to print hearty reports, perhaps
relating to payroll or costs, for internal use. The volume of the report and
the fact that it will not be seen by customers makes the speedy-and less
expensive line printer appropriate. One final note about impact printers: An
impact printer must be used if printing a multiple-copy report so that the
duplicate copies will receive the imprint.
Non-impact Printers
A non-impact printer places an image on a page without physically touching the
page. The major technologies competing in the non-impact market are laser and
ink-jet. Laser printers use a light beam to help transfer images to paper,
producing extremely high-quality results. Laser printers print a page at a time
at impressive speeds. Large organizations use laser printers to produce
high-volume customer-oriented reports. At the personal computer end, low-end
black and white laser printers can now be purchased for a few hundred dollars.
However, color laser jet printers are more expensive.
The rush to laser printers has been influenced by the trend toward desktop
publishing-using a personal computer, a laser printer, and special software to
make professional-looking publications, such as newsletters.
Ink-jet printers, by spraying ink from multiple jet nozzles, can print both
black and white and in several different colors of ink to produce excellent
graphics. As good as they are, color printers are not perfect. The color you
see on your computer screen is not necessarily the color you will see on the
printed output. Nor is it likely to be the color you would see on a four-color
offset printing press. Nevertheless, with low-end printers now under $250, they
may be a bargain for users who want their own color output capability.
There are many advantages to non-impact printers over impact ones, but there
are two major reasons for their growing popularity: They are faster and
quieter. Other advantages of non-impact printers over conventional mechanical
printers are their ability to change typefaces automatically and their ability
to produce high-quality graphics.
Voice Output
We have
already examined voice input in some detail. As you will see in this section,
however, computers are frequently like people in the sense that they find it
easier to talk than to listen. Speech synthesis is the process of enabling
machines to talk to people is much easier than speech recognition. "The
key is in the ignition," your car says to you as you open the car door to
get out. Machine voices are not real human voices. They are the product of
voice synthesizers (also called voice-output devices or audio-response units),
which convert data in main storage to vocalized sounds understandable to
humans.
There are two basic approaches to getting a computer to talk. The first is
synthesis by analysis, in which the device analyzes the input of an actual
human voice speaking words, stores and processes the spoken sounds, and
reproduces them as needed. The process of storing words is similar to the
digitizing process we discussed earlier when considering voice input. In
essence, synthesis by analysis uses the computer as a digital tape recorder.
The second approach to synthesizing speech is synthesis by rule, in which the
device applies a complex set of linguistic rules to create artificial speech.
Synthesis based on the human voice has the advantage of sounding more natural,
but it is limited to the number of words stored in the computer.
Voice output has become common in such places as airline and bus terminals,
banks, and brokerage houses. It is typically used when an inquiry is followed
by a short reply (such as a bank balance or flight time). Many businesses have
found other creative uses for voice output as it applies to the telephone.
Automatic telephone voices ("Hello, this is a computer speaking. . .
" ) take surveys, inform customers that catalog orders are ready to be
picked up, and, perhaps, remind consumers that they have not paid their bills.
Music Output
Personal
computer users have occasionally sent primitive musical messages, feeble tones
that wheezed from the tiny internal speaker. Many users remain at this level,
but a significant change is in progress.
Professional musicians lead the way, using special sound chips that simulate
different instruments. A sound card, installed internally in the computer, and
attached speakers complete the output environment. Now, using appropriate
software, the computer can produce the sound of an orchestra or a rock band.
Those of us who simply enjoy music can have a full sight/sound experience using
multimedia, which we will explore in detail in the next chapter.
Computer Graphics
Let us take a moment to glimpse everyone's favorite, computer graphics. Just
about everyone has seen TV commercials or movies that use computer-produced
animated graphics. Computer graphics can also be found in education, computer
art, science, sports, and more. But perhaps their most prevalent use today is
in business.
Business Graphics
It might
seem wasteful to use color graphics to display what could more inexpensively be
shown to managers as numbers in standard computer printouts. However, colorful
graphics, maps, and charts can help managers compare data more easily, spot
trends, and make decisions more quickly. Also, the use of color helps people
get the picture-literally. Finally, although color graphs and charts have been
used in business for years-usually to make presentations to higher management
or outside clients-the computer allows them to be rendered quickly, before
information becomes outdated. One user refers to business graphics as
"computer- assisted insight."
Video Graphics
Video
graphics can be as creative as an animated cartoon. Although they operate on
the same principle as a moving picture or cartoon-one frame at a time in quick
succession video graphics are produced by computers. Video graphics have made
their biggest splash on television, but many people do not realize they are
watching a computer at work. The next time you watch television, skip the trip
to the kitchen and pay special attention to the commercials. Unless there is a
live human in the advertisement, there is a good chance that the moving objects
you see, such as floating cars and bobbing electric razors, are computer
output. Another fertile ground for video graphics is a television network's
logo and theme. Accompanied by music and swooshing sounds, the network symbol
spins and cavorts and turns itself inside out, all with the finesse that only a
computer could supply.
Computer-Aided Design/Computer-Aided Manufacturing
For more than a decade, computer graphics have also been part and parcel of a
field known by the abbreviation CAD/CAM-short for computer- aided
design/computer-aided manufacturing. In this area computers are used to create
two- and three-dimensional pictures of everything from hand tools to tractors.
CAD/CAM provides a bridge between design (planning what a product will be) and
manufacturing (actually making the planned product). As a manager at Chrysler
said, "Many companies have design data and manufacturing data, and the two
are never the same. At Chrysler, we have only one set of data that everyone
dips into." Keeping data in one place, of course, makes changes easier and
encourages consistency.
Graphics Input Devices
There are
many ways to produce and interact with screen graphics. We have already
described the mouse; the following are some other common devices that allow the
user to interact with screen graphics. A digitizing tablet lets you create your
own images. This device has a special stylus that you can use to draw or trace
images, which are then converted to digital data that can be processed by the
computer.
For direct interaction with your computer screen, the light pen is ideal. It is
versatile enough to modify screen graphics or make a menu selection-that is, to
choose from a list of activity choices on the screen. A light pen has a
light-sensitive cell at one end. When you place the light pen against the
screen, it closes a photoelectric circuit that pinpoints the spot the pen is
touching. This tells the computer where to enter or modify pictures or data on
the screen.
Finally, a well-known graphics input device is the joystick, dear to the hearts
of video game fans. This device allows fingertip control of figures on a CRT
screen.
Graphics Output Devices
Just as
there are many different ways to input graphics to the computer, there are many
different ways to output graphics. Graphics are most commonly output on a
screen or printed paper, as previously discussed. Another popular graphics
output device is the plotter, which can draw hard-copy graphics output in the
form of maps, bar charts, engineering drawings, and even two- or
three-dimensional illustrations. Plotters often come with a set of four pens in
four different colors. Most plotters also offer shading features.
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