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How Modems Work

To establish a dial-up connection to an ISP, you must have a modem installed in or connected to your PC. Most new PCs come with modems built in, and add-on modems for older computers are available at any computer retailer.

Digital to Analog, and Back Again

A modem—internal or external—is so named because it modulates and demodulates transmitted data. (The word modem comes from the mo in modulate and the dem in demodulate.) The modulating process involves taking the digital signal (in binary pulses) from your computer, and then modulating some property of an analog signal (amplitude, frequency, or phase) to transmit the digital data over an analog medium. Demodulation is the same process in reverse, as analog information is demodulated into digital pulses and fed back into a computer. This modulation/demodulation process enables computers (which are digital) to communicate via regular phone lines (which are analog).


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