Internet users need a modem to connect to the Internet because signals that comes from telephone and cable lines are analog, and computers can only process digital information. The modem takes the analog signal from the connection line and converts it into digital information that the computer can read.
Internet providers offer connection to the Internet through phone or cable lines. Although high-speed DSL and cable connections are much faster than the dial-up connections of the past, the information that runs through these two types of lines is still analog.
Computers, tablets and smartphones are digital devices, so they need modems to convert the signal into a digital format. In some places, digital lines called ISDN lines are available, but these still involve a variety of different digital signal types. IDSN modems help moderate these signals so that computers can get a clear connection. Modems also convert digital data from computers into analog signals that can feed back into analog connections.
Many smartphone, tablet and eReader users can also access the Internet through 3G and 4G mobile connections. Computer users can connect to mobile Internet connections using USB sticks, and a few laptops also allow mobile SIM card connections. Cell phone providers offer plans that allow users to access mobile Internet connections. Users do not need modems to access the Internet via a mobile connection.