modem

Remote computer terminals communicate with the central mainframe via modems and telephone lines. The controller allocates computer time to the terminals according to predetermined priority rules. The multiplexer allows more than one terminal to use the same communications link at the same time (multiplexing).

The Internet is accessed by users via a modem to the service provider's hub, which handles all connection requests. Once connected, the user can access a whole range of information from many different sources, including the World Wide Web.

Modems are available in various forms: microcomputers may use an plug-in device connected through a communications port, or an internal device, which takes the form of an expansion board inside the computer. Notebook computers use an external modem connected via a special interface card.

Device for transmitting computer data over telephone lines. Such a device is used to convert digital signals produced by computers to analogue signals compatible with the telephone network, and back again.

Modems are used for linking remote terminals to central computers and enable computers to communicate with each other anywhere in the world. In 1997 the fastest standard modems transmitted data at a nominal rate of about 33,600 bps (bits per second), often abbreviated to 33.6K.

56K modems, launched in 1997, achieved higher speeds by using a digital connection to the user's computer, while using a conventional analogue connection in the other direction. ADSL modems can achieve data transmission rates of up to 24Mbit/s downstream and 3.5Mbit/s upstream rate by using digital communications to both the computer and also over the telephone network.