1. Modem(Modulate and demodulate)
Input/Output device
Converts digital data from computer to analog for transmission over telephone line is modulation
Convert analog from line is converted back to digital by modem for computer at another point is demodulation.
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2. MODEM
Is communication equipment used for long distance data transfer thru telephone line.
Pair of modem is used at both ends

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Types
Internal
Standalone board plugs directly into ISA/PCI slot of PC
Contains its own UART universal synchronuous receiver/transmitter as serial port.
External
Standalone device connected to serial port(com1/2) of system.
Works same as internal , difference is it uses M/B UART to convert serial to parallel and vice versa for bit conversion.
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