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.

Pens

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

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 speakers.

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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