Modems Modems are used to connect two computers over a phone line. Modem is short for Modulator Demodulator. It's a device that converts data from digital computer signals to analog signals that can be sent over a phone line. This is called modulation. The analog signals are then converted back into digital data by the receiving modem. This is called demodulation. A modem is fed digital information, in the form of ones and zeros, from the CPU. The modem then analyzes this information and converts it to analog signals, that can be sent over a phone line. Another modem then receives these signals, converts them back into digital data, and sends the data to the receiving CPU. At conne