Although the keyboard and mouse are the input devices
with which people work most often, there are a number of other ways to
get data into a computer. Sometimes the tool is simply a matter of choice.
In many cases, however, the usual tools may not be appropriate. For example,
in a dusty factory or warehouse, a keyboard or mouse would become clogged
with dirt fairly quickly. Also, alternative input devices are important
parts of some special-purpose computers.
Pen-based systems use an electronic pen as their primary
input device. You hold the pen in your hand and write or print on a special
pad or directly on the screen. You can also use the pen as a pointing device,
like a mouse, to select commands. It is important to realize here that
the screen is the input device, not the pen. The screen detects pressure,
light, or an electrostatic charge that comes from the pen and then stores
the position of that signal.
Although pen-based systems would seen like a handy way
to get text into the computer for word processing, perfecting the technology
to decipher people’s handwriting with 11 percent reliability is so complex
that pens are not generally used to enter large amount o text. They are
more commonly used for data collection, where the touch of a pen might
select a "yes" or "no" box, or to mark a box next to
a part that must be ordered or a service that has been requested. Another
common use is inputting signatures or messages that are stored and transmitted
as a graphic image, such as a fax. The computer may not be able to decipher
your scrawled note, but if it appears on your coworkers’ screens and they
can read it, that is all that is required. When delivery-service drivers
make deliveries, they often have recipients sign their names on such a
computer-based pad. As handwriting recognition technology becomes more
reliable, pen-based systems will undoubtedly become more common.
Touch screens allow the user to point directly at the
computer display usually to select from a menu of choices on the screen.
Most touch-screen computers used sensors in, or near the computer’s screen
that can detect the touch of a finger.
Touch screens are appropriate in environments where dirt
or weather would render keyboards and pointing devices useless, and where
a simple, intuitive interface is important. They are well suited for simple
applications such as automated teller machines or public information kiosks.
Touch screens have become more common in department stores, drugstores,
and supermarkets, where they are used for all kinds of purposes, from creating
personalized cards, to selling lottery tickets. There are even computerized
screens on slot machines in gambling casinos.
Bar Code Readers
The most widely used input device after the keyboard and
mouse is the flatbed or hand-held bar code reader commonly found in supermarkets
and department stores. These devices convert the bar code, which is a pattern
of printed bars on products, into a product number by emitting a beam of
light – frequently a laser beam – that reflects off the bar code image.
A light-sensitive detector identifies the bar code image by recognizing
special bars at both ends of the image. Once the detector has identified
the bar code, it converts the individual bar patterns into numeric digits.
The special bars at each end of the image are different, so the reader
can tell whether the bar code has been read right-side up or upside down.
After the bar code reader has converted a bar code image into a number,
it feeds that number to the computer, just as though the number had been
typed on a keyboard.
Microphones and Voice Recognition
Now that sound capabilities are a standard part of computers,
microphones are becoming increasingly important as input devices. Sound
is used most often in multimedia, where the presentation can benefit from
narration, music, or sound effects. In software, sounds are used to alert
the user to a problem or to prompt the user for input.
For this type of sound input, a digitized recording is
all that is required. All you need to make such a recording are a microphone
(or some other audio input device, such as a CD player) and a sound card
that translates the electrical signal from the microphone into a digitized
form that the computer can store and process. Sound cards can also translate
digitized sounds back into analog signals that can then be sent to the
Three is also a demand for translating spoke words into
text, much as there is a demand for translating handwriting into text.
Translating voice to text is a capability known as voice recognition (or
speech recognition). With it, you can speak to the computer rather than
having to type, and you can control the computer with simple commands,
such as "shut down" or "print status report."
Voice recognition software takes the smallest individual
sounds in a language, called phonemes, and translates them into text or
commands. Even though English uses only about 40 phonemes, a sound card
can have several different meanings ("two" versus "too,"
for example) making reliable translation difficult. The challenge for voice
recognition software is to deduce a sound’s meaning correctly from its
context and to distinguish meaningful sounds from background noise
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