Modem technically called the Modulator¬Demodulator. It is an electronic device, which helps transmit programs and data locally or around the world through telephone lines. The main function of a modem (Fig.I-34) is to transform digital signals into analog signals and vice versa. With a modem, : . you can subscribe to a growing number of online and . bulletin board services or can communicate with other computers located elsewhere which have modems attached to them.

A modem may be mounted on a card inside the PC (an internal modem), or it may be a separate piece of equipment that connects to the serial port of the PC via a cable (an external modem). Telephone lines then connect the modem to the telephone service. Modems help in carrying out various functions like electronic mail, online banking, travel, reservations, etc. Some modems contain software that allow documents (files) created on your computer to be sent to fax machines.