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Modem overview

Updated: January 21, 2005

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

Modem overview

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 machines perform this conversion. When you communicate over analog telephone lines, you use standard modems. There are also ISDN and cable modems that provide digital communication. They enable computers to transmit digital information directly without the conversion over special lines. The most recent developments with the fastest transmissions are broadband technologies such as cable or DSL (Digital Subscriber Line) that transmit over cable or phone lines as waves similar to radio or television.

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 data that is received from an Internet service provider that is connected to a digital line but that sends data with the standard digital-to-analog conversion.

The Microsoft® Windows Server 2003 family supports many different modems. If you are looking for a new modem that is compatible with Windows, see the compatibility information in Support resources. Microsoft has tested these modems with Network Connections. If you have a modem that is not on this list, it may 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 may 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.

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