Getting Connected: Modems

Telephone lines were designed to transmit the human voice, not electronic data from computers. Modems were invented to convert digital computer signals into a form that allows them to travel over phone lines. Those are the scratchy sounds you hear from a modem's speaker. A modem on the other end of the line understands it and converts the sounds back to digital information that the computer understands.

Buying and using a modem used to be relatively easy. Not too long ago, almost all modems transferred data at a rate of 2400 Bps (bits per second). Today, modems not only run faster, they are also loaded with features like error control and data compression. In addition, modems also act like traffic cops, monitoring and regulating the flow of information. That way one computer doesn't send information until the receiving computer is ready for it. Each of these features--modulation, error control, and data compression--requires a separate kind of protocol. That's what some of the terms you see like V.32, V.32bis, V.42bis and MNP5 refer to.

If you need to replace a modem for an older computer, consider buying an external one, because it is much easier to install and operate. For example, when your modem freezes (not an unusual occurrence), you have to turn it off and on again to get it working properly. With an internal modem, that means restarting your computer--a waste of time. With an external modem it's as easy as flipping a switch.

This table illustrates the relative difference in data transmission speeds for different types of files under the best of circumstances. A modem's speed is measured in bits per second (bps). A 28.8 Kbps modem sends data at 28,800 bits per second. A 56 Kbps modem is twice as fast, sending and receiving data at a rate of up to 56,000 bits per second.

Many things can interfere with the speed of data transfer. These range from excessive noise on the telephone line, the speed of the web server from which you are downloading files, the number of other people trying to access the same file and the overall traffic on the Internet. Until the end of 1995, the conventional wisdom was that 28.8 Kbps was about the fastest speed you could squeeze out of a regular copper telephone line. Today, data transmission for a dial-up connection is typically 56 Kbps.