Normally, computers have built-in modems and have an RJ-11 connector to plug a phone line, but they can also be added using a modem expansion card. With the help of a modem card, a computer can send an analogue signal that carries the digital information, and decode the signal to produce the digital data. Now, modems can use satellites, television cables and power lines to transmit data signals. They provide faster transmission of data and a great range of channels. They are classified based on the data that can be transferred in a set amount of time, generally bits per second (bps) or bytes per second (B/s).