A modem (modulator/demodulator) was originally a device that took the analog signal of the phone line and converted it into a digital signal that a computer can understand. Now we use the term “modem” to mean any device that receives the raw signal from an Internet service provider and puts out a signal the computer and other devices can use. The input could be a telephone line, digital subscriber line (DSL), satellite or coax feed. Modems usually have one Ethernet port to which a computer can be connected.
A router is a device that allows multiple devices to connect to a network. It will have several Ethernet ports to which one device per port is attached. For instance, in a home network, various desktop computers, laptops, printers, scanners and CD/DVD drives may be connected through an Ethernet cable to the router. The computers can all use the printers and other devices on the network. If sharing is enabled, the computers can access each other.
Once the modem is receiving its signal, and the router is set up with all of the devices, an Ethernet cable connecting the modem to the router allows every computer to now get onto the Internet. The router handles all of the information flowing back and forth through the network so the various signals don’t get confused.
There is software on the router that allows some level of security to the network to be applied. Computers outside of the network can’t get in and some devices within the network may be restricted. You can also monitor what devices are connected to the network.
Combination modem/router devices can be purchased that perform both roles in one piece of hardware. The disadvantage is if one part of the device fails, the whole unit may not be operational until the unit is replaced.
Also available is a wireless router. Instead of using Ethernet cables to connect to devices, a wireless signal is used. Devices with a wireless modem can connect to the router. This is a useful feature as more devices are being made that have no Ethernet connection. Tablet computers, eBook readers and smartphones can all connect to a network through a wireless router.