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A 14,400 baud dial-up modem made by USRobotics (1994)

A modem (comes from: modulator demodulator) is a piece of computer hardware. It is used to communicate between distant computers. Two modems, one on each computer, are required to make a connection, and each modem can send and receive data to and from the other modem.

• Modulation is changing the digital data from a computer to analog data (audio tones or sounds) to be sent over telephone lines.
• Demodulation is changing the analog data which is received over the telephone lines to digital data to be used by the computer.