All About Modems

A brief history of the modem

The word modem originates from its use: the modulation and demodulation of information. A typical modem modulates or changes data using the 1s and 0s of computer language into a signal that can be sent across a phone line and demodulated by a modem on the other end. The basics may stay the same, but the advent of technologies such as DSL, cable modems, and wireless networking continue to transform the modem and its usage.

Modem origins

The speed and volume of data that modems can handle has changed a great deal since the first modems were used in the 1950s. Those modems served NORAD's Semi Automatic Ground Environment (SAGE) air defense system as a means to connect terminals to the SAGE director centers.

This was a typical use for early modems. Terminals would use them to dial in to a central computer system. The modem user would employ a phone handset to dial the required number and then connect the handset to an acoustic coupler, which would convert the audio phone signals to electrical modem signals.

Modem use altered in the late 1970s and early 80s as ownership of personal computers spread. Bulletin board systems (BBS) were a popular way at that time for PC users to communicate with each other. It wasn't the most efficient format. Modems lacked autodial and autoanswer capability, meaning someone had to be present on both ends, and modem speed was only 300 bps, equivalent to about 30 characters per second.

Gaining speed

It wasn't until the Smartmodem was introduced in 1981 that modem users could forego the acoustic coupler and manual dialing. Modem speed increased exponentially through the 90s, from 9600 bps in 1990 to 28.8 Kbps and eventually to 56 Kbps around 1998.

A 56K modem is theoretically near the limit of information that can be passed through the voice bandwidth of a phone line, but because the human voice covers only a small frequency range, today's modem technologies can use the available extra capacity to send and receive information.

Asymmetric digital subscriber line modems, or DSL modems, use the copper wires that are a standard part of phone systems to send data. Because it's asymmetrical, information received via a DSL modem will travel much faster than information sent.

Similar to ADSL, cable modems take advantage of the extra space or bandwidth available in a cable line to send data. An advantage cable modems have over ADSL is that performance is not affected by distance from the cable office. However, cable modems share bandwidth with other users, so speeds can slow during peak usage hours.

I got no strings to hold me down

Wireless modems are something else entirely. Wireless modems connect computers to a wireless local area network, or WLAN, via cellular, satellite, or Wi-Fi protocols. Connection speed will vary depending on the network and protocols. Some will be as slow as dialup, others as fast as broadband.

A few things to investigate when looking at wireless modems are speed, the protocol supported, frequency band, and whether it's full duplex or half duplex. A full duplex wireless modem allows you to send and receive information at the same time.

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