Types of a Modem
Types of a Modem
There are two types of modems, namely:
Internal Modem- An internal modem is a modem card that you can plug into an expansion slot on the motherboard. Internal modems do not take up the desk space because they are fixed on the motherboard. These modems use the power supply of the computer and thus are switched on whenever the computer is on. In case of internal modem it is advisable to physically remove the telephone connection from the modem especially during lightening. Lightening causes the internal modem to burn through the connected telephone line. At times, due to this the motherboard may also burn.
External Modem - A serial external modem is connected to the PC through a cable, which is plugged into a serial port on the back of the system unit External modems have their own power cords. Before establishing the connection, you must switch on the modem.
Apart from this classification, the modems are further classified into X2, V90, ISDN, DSL and Cable modems.
The United States Robotics developed a technology called X2 for transmitting data at the speed of 56 Kbps over plain old telephone service (POTS). X2 technology transmits data at the speed of 56 Kbps. This is because the high-speed digital lines connect most phone switching stations. It does not perform the digital-to-analog conversion and directly sends the digital data over the telephone lines.
Today, X2 modems use the V.90 modulation standard. They endow with high-speed Internet access. However, X2 modems have the following limitations:
Data transfer speed is high only when the data is sent to your computer. However, data transmission from your computer to the dial-up server is done using the normal techniques with a maximum speed of 40 Kbps.
When you want to connect to the Internet using the X2 modem, the ISP modem must support the V.90 standard.
Initially, modem standards were built on the assumption that both ends of a modem session have an analog connection to the telephone line. However, V.90 technology was built with an assumption that one end of a modem session has a pure digital connection to the telephone line. Because of the pure digital connection, telephone network acts a digital network.
V.90 technology helps to increase the data transfer speed from the Internet to the computer. It supports data transmission speed of 56 Kbps. This helps to download the Web page with sound and video and other larger files. However, the data transmission speed from the computer to the Internet server is normal. Modems using the V.90 technology are called the V.90 modems.