MODEM Device

        In a data communication 
system , workstations and other 
remote input and output devices
are linked with one or more 
processors to capture input data 
and receive output information .
connecting equipment and software,
sometimes referred to as interface
elements, are used to bridge the 
different operation environments
of these input and output devices
and processor . 
   A modem is a modulation and 
demodulation devices that converts
the discrete stream of digital on 
or off electric pulses used by the
computers into the type of 
continuously variable analog wave 
patterns used to transmit the human
voice over many existing telephone 
lines. A modem is needed to modulate or convert the digital signals and the pulses whereas older telephone lines are used to transmit data.
     Actual data transfer takes place from digital to analog to digital . The data are in the binary digits atr the beginning and at the end . If the distance of such communication  increase the digital pulses may not reach the destination . 
     As a general concept, a pair of modem are require for the data communication . Each modem is connected to a computer and a telephone from keyboard is accepted by a computer and the data is transmitted to another computer via telephone line.