Router and modem

A modem allows your computer/devices to connect to the internet. It provides your connection through your service provider (ISP). A router takes that connection and shares it between different computers/devices. So that you can have everything connected at the same time. Some combination units are out there that have both the modem and the router in one.

there is another device with same purpose ie switch its like a router a router used in old days now days we use switch insted if a router...the main difference is that a switch contains the memory address (ip address) of every computer.so the communication is too fast.

I think the difference between modem and router is how they pass the data that they receive. Router is used to pass data between computers, because computer system talk in IP language, all router have to do is passing the messages to the right computers, while modem is used to pass data from computer system through a different system (such as phone network or GSM network). because the way phone talk to each other is different from the way computer talk, the data is first 'translated' so they can travel through the phone system, at the other end of the phone system the modem do the opposite, which is to translate it back to the language that computer system can understand.