Write about Modems and its Types

Modems

A special device called modem (modulator/demodulator) is used to carry out the process of modulation and demodulation. Hence when an analog facility is used for data communication between two digital devices, two modems are required, one near each device. Digital signal generated at sender computer’s end is converted to analog form by modulator of the modem placed near it. The analog signal is transmitted through telephone line and is converted to digital form by demodulator of the modem placed near receiver computer. The receiver computer processes the data, and then the modem near it modulated the processed data to analog form. The nalaog data is returned via telephone line to the sender computer end,where analog signals are dedmodulated to digital form first by the modem there, and then digital data is passed on to the sender computer.  Higher the modem’s transmission speed, better it is because it can communicated faster. Transmission speeds of earlier modems were 300, 1200 or 2400 bps. Modems available now can operate at 9600, 14400 or 28800 bps. Modems are of two kinds:

1. Internal
2. External

1. Internal modem is an optional add- on circuit board that plugs into one of the computer’s expansion slots. It gets its power from computer’s expansion bus. Iti s manufactured and supplied by comouter mannufacturers.
2. External Modem is a separate box containing circuitry and logic to modulate data signals. It has its own power supply, in/oof switch, and front panel LCDs to indicate its status. External modems are slightly more expensive than internal modems. An external modem is connected to a computer via serial port.