Chapter 7 - Data Communications

Abstract

This chapter discusses data communications in computer systems. A user sitting at a terminal wishes to communicate with a computer system over conventional telephone lines. Computers transmit bits of digital data, and telephone lines transmit analog data, or continuous waveforms. The digital data typed by a computer user must be transformed into analog data for transmission over a phone line. This is the function of a modem. The converted data is then transmitted in analog form over the telephone network to the main computer site, where another modem converts the analog data back to digital form. Ordinarily a modem is connected to a data communications controller, a device that receives signals from the transmission line, converts them into computerized form, and passes them on to the central computer system. The data communications controller handles many of the chores associated with managing data communications and, thus, frees the central computer system so that it may work on performing useful computations.