Modem (from modulator-demodulator) is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Modems can be used over any means of transmitting analog signals, from driven diodes to radio. There are basically three different types of modem available for use with desktop PCs. External ones that plug into the serial port of your PC. And internal ones that are installed in either the PCI or ISA slots. These latter can be subdivided into WinModems and full modems. Only the later will run under DOS (see the similar problem with Linux!) It is necessary to use either a SLIP or more usually a PPP driver, which acts as an Ethernet packet driver, if you wish to connect to a remote network via the phone line. The TCP/IP stack is then loaded afterwards. Both the Novell and the Microsoft TCP/IP stacks included a dialer program and SLIP/PPP drivers with the main software. With the introduction of Broadband, Cable and ADSL modems have also appeared, these either fake it as Ethernet devices or will not work under DOS.
Copyright © 2007 Ulrich Hansen, Mainz (Germany), 2010 and 2020 by W.Spiegl. For more information see here. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation. A copy of the license is included in the section entitled "GNU Free Documentation License 1.2".