Device What is does
 Gateways: Convert information from one format to another.
  • The proper technical term for a DSL, FiOS, or Cable "modem" is a gateway because with DSL and cable, the data remains in a digital format from the customer's network to the ISP and internet.     
  • Since the digital data is not converted to an analog data, the device is technically not a modem.
  • However, since calling a DSL/cable gateway a modem is a term many people easily understand, it the 2 terms are used interchangeably.
  • Typcially, routers today will perform the functionality of both a router and a switch - that is, the router will have multiple ethernet ports that devices can plug into.
  • In a similar vein, combination "modem/routers" are actually typically performing the roles of a gateway, a router, and a switch.
 Modem: Stands for modulate demodulate.

They allow devices to communicate with other remote devices by converting digital data into analog data and transmitting it over an analog telephone line.
 Routers: Are responsible for sending data from one network to another.
 Switches: They use the MAC address of a device to send data only to the port the destination device is plugged into.
 Hubs: Unlike switches, hubs broadcast data to all ports, which is inefficient.