Modem

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A Modem is a piece of computer hardware. It is used to communicate between distant computers. Two modems, one on each computer, are required to make a connection, and each modem can send and receive data to and from the other modem. The term modem stands for modulator - demodulator.

• Modulation is changing the digital data in the personal computer to analog data (audio tones or sounds) so that it can be sent.
• Demodulation is changing the analog data (audio tones) that is received over the telephone lines to digital data to be used by the computer.

Modems are generally classified by the amount of data they can send in a given time, normally measured in bits per second (bit/s, or bps). Pieces of data are sent from one modem to another modem at a set speed or rate. This rate is called the baud rate. One baud is one bit per second.
There are 3 types of modems: internal modems, external modems, and PC card modems. Commonly, modems are used to connect to the Internet through telephone service or cable service. Slow telephone service is called dial-up (maximum 56 kilobaud), faster telephone service is called DSL. DSL data transfer rates are comparable to cable service transfer rates.