"Mass media" refers to technology that is designed to reach a large number of people. It is the principal mode of communication for the great majority of the general populace. Newspapers, magazines, radio, television, and the Internet are the most prevalent outlets for mass media. Other methods include postal services, telephones, and some types of electronic media. Television is an optical image transmitted via antennas or cables to receivers connected to them. The received signal is then projected on a screen for viewing by the audience. Television signals are transmitted at high frequencies, which allows for visual images to be displayed on a screen with little interference from outside noise sources. Television signals can also carry audio information as well as video. Radio is the transmission of sound recordings (gramophone records) as opposed to live performances (theatre or opera). Computer files containing data are converted into sequences of ones and zeros by a process called "encoding," which in turn are transmitted over a network to be reconstructed by another computer system called a "decoder." The decoder converts the binary code back into words or pictures which are then presented on the screen or heard by the listener. Computer networks are groups of computers connected together so they can share resources simultaneously. They allow multiple users to access the same database or use the same software program by connecting to the program through a central server. Modern networks may connect various devices including phones, printers, and televisions.