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The term modem is a contraction of "modulate and demodulate." In the context of information technology, to modulate means to turn a computer's output of binary digits (bits, zeroes and ones) into some sort of an analog wave that can travel across a medium. In the case of copper wire, this takes the form of a wave of electrical current. In the case of fiber optic cable, this takes the form of a wave of light. To demodulate is to convert this wave back into digital bits that a computer can input. In the case of traditional modems, it may be helpful to simply think of this device as converting zeroes and ones into sound waves, which then travel over the phone line to another modem, where the sounds are converted back into zeroes and ones. Today, the fastest modems for analog telephone lines (sometimes called POTS, "plain old telephone service") are rated at 56,000 bits (56 kilobits) per second. However, FCC regulations are such that no modem can operate faster than around 52,000 bps. Moreover, anytime there is any degree of noise or distortion on the telephone line, this causes the modem to drop down to a slower speed. Thus, even with a very good phone line, the typical home computer user is only likely to reach speeds of around 45,000 bps (45 Kbps). Although such modems approach what was the cutting-edge speed of the ARPANET in 1969, this form of connection is fairly low bandwidth by today's standards. Moreover, users of traditional modems over telephone lines are subject to sudden disconnections for any of a variety of reasons. For these reasons, and because other technologies have become more affordable, many consumers are turning to what are called broadband connections to their ISPs. (Question: why are 56 Kbps modems sometimes described as being capable of 57,600 bps rather than 56,000 bps? Answer: because in the binary computer context, one K is equal to 1024, not 1000, as in the decimal metric system.) |
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If you encounter technical errors, contact rit@calvin.edu. |
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