Modulator/Demodulator

(mo-dem)

A device that connects an analog phone line to a digital device (like a computer). In common use, this word has largely progressed from an acronym to a regular word (usually spelled in lower case).

While the phone service is now largely digital, it is not completely so. Thus, there must be some conversion from digital data in your computer to analog (voice-like) data that can be inserted into the phone system and some method of taking that analog data back to digital to feed it into your computer when a reply to a query comes back. That's what a modem does.

There are a variety of modulation techniques for various modem transmission speeds. Over voice lines baud rates range from a snail-like 75 baud to 56,000 baud (56K) and faster. Higher rates usually use some form of data compression and most protocols include some form of error checking. Some modems even keep track of errors and reset the data rate faster and slower as needed for a given transmission. (Note: A baud is a unit of information not necessarily equal to a bit. Data transmission through a modem almost always uses baud.)

More Information

• MODEM Tutorial