A modem (of modulator and scrambler) is a device that modulates or transforms an analogical telephone signal to codify a digital information of the computer and also desmodula the same signal to decode the information that is transmitted. It allows the production of signals that can be decoded and be transmitted easily to reproduce digital information and allows that the computer transmits information through the telephone line. Actually, when we spoke of modem we talked about the apparatus that allows the connection to Internet via telephone; generally nowadays these come integrated to the computer, but there are no other options, as we see in the article.
The modems were born from a necessity to connect machines of teletype by traditional telephone lines. Previously the teletypes and telegraphs were connected by rented lines very expensive. In 1940, George Stibitz connected a teletype to an used computer a telephone line of subscription. In 1958, they were begun to produce modems massively, like part of the system of air defense SAGE. Terminals of air bases, sites of radar and control centers to the control posts of SAGE in the United States and Canada were connected. With time, new modems that allowed their use in the homes, companies, etc. became, being vital for the connection to Internet.
The modems allow that from the computer of a home or company data can be sent, since allows that the DS of the computer become analogical signals able to transmit telephone route. That makes the connection to Internet possible, and along with it the possibility also of lowering and of raising information, of sharing it with other computers, of sending and of receiving messages of electronic mail and the possibility of participating in games with people of different places.
Normally two classes of modem are used: internal or external. The interns are an expansion board in which they are including all the elements of the modem. They are possible to be connected by means of three formats, that include Bus ISA, Bus PCI and the AMR. First of them he was used for a long time but today he is obsolete. In the case of the PCI, it is the connector that is used more at present. He allows to directly connect the peripheral devices to the motherboard. The AMR is almost obsolete because it has minor yield. The internal modem has the advantage to be integrated in the computer and to work with the same electrical energy. They are economic but more difficult to install. Its state can be seen by means of programs.
In the case of the external modem, it is a device that comes in its own housing and it is connected externally with the computer. By the same, it occupies an additional space but it is easier to install. The state without needing a program can be known it indicates since by means of lights that indicate it the noticeable one, the transmission, and if it is with line or no. is connected by traditional port COM, using the UART (transceiving asynchronous universal) of the computer. These modems also count on transformer that must be connected.
Other types of modem include the PC Card, that were used for the portable ones. They have card form and they count on the same capacity that other modems. Also are the modems for port USB, connectionless electrical. They exist for telephony fixes and movable telephony. As far as winmódems, they are internal devices with less electronic pieces, than they replace by means of software of the computer. They are very cheap but nonrecommendable.