what is modem and it really do ?

Modem is a device which is basically used in work of connection to LAN connection where it works as a converter. It is a converter which converts the analog signal to digital before receiving signals in your computer and also works as a digital to analog converter when you are sending signals to any other server which is connected to your LAN cable. now a days modem can do more than this single job which means that now modem is also used for creating multiple connection which means from a single connection more than one user can access data of each other. work of multiconnection is of hub or switch but now a days it can be also done by this modem.                

You can see here that after modem pols are carrying cables which has analog signal but in between modem and computer there are digital signals which are in form of zero and one,.

Below are few basic diagrams which shows the connection of modem to the computer--

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