Computer has various peripheral devices such as: modem, vision systems, speech recognition and voice response devices, terminal etc. These parts make a computer very important and attractive instrument in our daily life. Using various peripheral devices of computer we can do many essential tasks easily.

Terminal: 

A terminal is a popular input/output device. Terminals are used for two-way communications with a CPU or with other terminals a few feet or thousands of miles away. With the aid of a terminal, a user can access computers around the world. Terminals, also called workstations, allow a user to interact with a computer. It uses a keyboard to enter data and a cathode ray tube (CRT) screen, or monitor, for displaying data. Because data must be keyed into these devices one character at a time, the possibility of error is high and the data transmission rate is very low; thus limiting the use of terminals to small-volume input and inquiries only. Some of the functions that can be performed using terminals are described below.

Messaging: The communication of information from one terminal to one or more remote terminals.

Data Collection: Data are received by terminals and recorded on secondary storage media for subsequent processing. This eliminates needs to record the information on a source document and then to key the information from the source document into a computer.

Inquiry or transaction processing: Data stored in central data files can be accessed from remote terminals for updating or to determine answers to inquiries about information stored in these files. The system employed by most airlines to maintain and update flight information is an example of such a function.

Remote job processing: Programs can be received from remote terminals directly to a CPU for processing. After execution, the result can be transmitted back to the terminal or to other terminals for output.

Graphic display and design: Data ban be displayed in graphic form, and can also be manipulated and manipulated and modified. Interactive graphic displays, from simple vides games displayed on a television set to sophisticated computerized systems, provide complex designs and three-dimensional displays.

Terminals are available with features to suite the multitude of applications to which they are applied. In general three broad types of terminals are: dumb, smart and intelligent.

Speech Recognition and Voice Response Devices:

Speech recognition devices were introduced in the early 1970s. Typically, these systems contain a database of stored voice patterns. The database of voice patterns in generally stored in a recognition unit or in secondary storage. A microphone, attached to the keyboard or recognition unit, records the spoken word patters. A build-in microprocessor then compares words with the stored patterns and transmits the result of the comparison to a computer for processing. A sentence must be spoken as a serried of Speech recognition devices are generally used in situations where access to a switch is not possible or where a user’s hands are otherwise occupied.

Because voice patterns vary greatly from person to person, most speech recognition services are speaker-dependent and must be fine-tuned to each operation. This is generally accomplished by having the operator speaks each of the words or digits to be stored in the recognition unit dictionary several times. An average of the spoken voice patterns is taken and stored as the standard for future voice communications.

Speaker-independent systems are less common and have a very restricted vocabulary: generally then digits and “yes” or “no” response. Despite their restricted vocabulary, speaker-independent systems are widely usable since they do not have to be fine-turned but can be understood by anyone. Clearly, speaker-independent systems are more desirable than speaker-dependent systems. Expense, large database requirements and the limitations or current technology have made the development of voice recognition systems slow. Manufactures are beginning to offer sophisticated speech recognition devices for the popular microcomputer.

One of the strongest impacts made on the use of voice response has come from the manufacturers of microcomputers. The pricing and availability of voice response units are economically feasible for even the smallest concern. Voice response is no longer an isolated discipline but another among the multitude of computer output techniques.

Vision Systems:

This system utilizes a digitizer, camera, computer, and a technique termed as image processing. Image processing is concerned with digitizing and storing of computer-processed images and with pattern recognition.

Familiar examples of computer-processed images are: computer generated digitized portraits at amusement parks, computer-produced special effects in movies, digitized images of Jupiter and Saturn beamed from image processors of spacecraft to earth etc. All these examples have one thing is common, that is to digitize an image. In a visual system, all images that must be recognized or interpreted are digitized and stored in a database. Only after the database has been established, the visual system can be applied to pattern recognition. Pattern recognition, the process of interpreting images, begins when the system digitizes the image of the object to be interpreted. The digitized image is then compared to those in the database to determine a probable match. As it is unlikely that a perfect match will be achieved, there is always a small possibility or error.

Modem:

A modem is the bridge between digital and analog signals. It converts digital data into analog signals by varying or modulation an electrical wave, a process known as modulation. Modulation is carried out for sending digital data thorough analog telephone system. On the receiving end of a phone connection, a modem does just the opposite. It demodulates the analog signals back into digital code. The two terms MOdulate and DEModulate give the modem its name. Modem communications involve three elements of personal computing: serial ports, modem commands, and communications software.