Modem stands for Modulation and Demodulation. It is an electronic device. It converts digital signals into analog signals and vice versa. It is used to send and receive data between two computers through telephone line. Both computers must have modems.

Data is communicated through telephone line in the form of analog signals. The sender computer sends data to receiver computer as follows:

The modem of sender computer converts digital signals into analog signals and sends to the receiver computer through telephone line. The process of converting the digital signals into analog signals is called modulation.
The modem of receiver computer receives data from telephone line in the form of analog signals. It converts these signals into digital signals and enter insides the computer. The process of converting the analog signals into digital form is called demodulation.

The main features of modem are:

Speed
Self Testing
Voice over Data

1- Speed
    The rate at which a modem converts the digital signals into analog form (and vice versa) and transmits over communication media is called modem speed. The speed of modem is measured in bits per second (bps). Today, the modems can send data at 56 kbps over the standard telephone lines.

2- Self Testing
    Modem has the capability to check the analog as well as digital connection automatically. It can also check its internal circuits.

3- Voice over Data
    Modem also allows voice conversation while data is being transmitted. For voice conversation, modems at both ends must have this features.

Modem - 3 Main Features of Modem