Telephone lines that are used in a conventional phone system are designed to transmit human speech with analog signals. Analog signals vary continuously, like waves, along their length. Computers store and process data in digital format and communicate both internally and with each other in binary digits
When two computers communicate with each other over a conventional phone line, a modem translates the binary information from the computer at the sending end to an analog signal that can pass over the phone line. At the receiving end, another modem translates the analog signal back to binary information that can be used by the computer. The conversion from binary to analog information is called modulation, and the conversion back from analog to binary is called demodulation. The word modem, short for modulator/demodulator, is the name for the device that performs these conversions.
Both standard modems and fax modems perform this conversion. There are also ISDN, DSL, and cable modems that provide digital communication. These modems do not convert digital and analog signals. They enable computers to transmit digital information directly without the conversion. When you communicate over analog telephone lines, you need standard modems.
The speed at which modems transmit data is called the throughput. This is measured in bits per second (bps)
The conversion between digital and analog data is governed by proprietary and international standards, called modem protocols. Improving protocols have allowed faster data throughput rates. Besides using the available bandwidth more effectively, protocols have incorporated data compression to speed the throughput and error control for greater reliability. The protocols for modems operating at 56 kilobits per second (Kbps) are now designed to support receiving data from an Internet service provider connected to a digital line, but send with the standard digital-to-analog conversion.
Windows supports many different modems. For a comprehensive list of hardware supported by Windows operating systems, see Compatible Hardware and Software in Help and Support Center. Microsoft has tested these modems with Network Connections. If you have a modem that is not on this list, it might still work perfectly well with Windows, especially if the manufacturer provides an installation disk or .inf file for Windows. Some modems are compatible with a supported modem and can be installed by choosing the supported information. Check the documentation provided with the modem for details. You may also find installation files or other useful information at the manufacturer's Web site.