A modem is a device that converts digital signals from the computer into analog signals that can be transmitted over the telephone channel.
The modem allows you to connect two remote computers using the telephone line so that they can exchange information with each other. The modem is one of the most widespread methods for interconnecting computers due to its simplicity and low cost.
The great coverage of the conventional telephone network allows the almost immediate connection of two computers if a modem is used. The modem is for all these reasons the most popular method of access to the Internet by private users and also by many companies.
The information handled by the computer is digital, that is, it is made up of a discrete set of two values, 1 and 0. However, due to the physical limitations of the transmission lines, it is not possible to send digital information through a telephone circuit. .
In order to be able to use telephone lines (and in general any transmission line) to send information between digital computers, an information transformation process is necessary. During this process the information is adapted to be transported by the communication channel. This process is known as modulation-demodulation and it is the one that is carried out in the modem.