Hubs and switches demystified

Both hubs and switches let you connect multiple computers to a twisted-pair network. Switches are more efficient than hubs, but not just because they are faster. If you really want to know, here's the actual difference between a hub and a switch:

• In a hub, every packet that arrives at the hub on any of its ports is automatically sent out on every other port. The hub has to do this because it is a Physical layer device, so it has no way to keep track of which computer is connected to each port. For example, suppose that Nelson computer is connected to port 1 on an 8-port hub, and Andrea's computer is connected to port 5. If Nelson computer sends a packet of information to Andrea's computer, the hub receives the packet on port 1 and then sends it out on ports 2-8. All the computers connected to the hub get to see the packet so that they can determine whether the packet was intended for them.
• A switch is a Data Link layer device, which means it's able to look into the packets that pass through it to examine a critical piece of Data Link layer information: the MAC address. With this information in hand, a switch can keep track of which computer is connected to each of its ports. So if Nelson computer on port 1 sends a packet to Andrea's computer on port 5, the switch receives the packet on port 1 and then sends the packet out on port 5 only. This process is not only faster, but also improves the security of the system because other computers don't see packets that aren't meant for them.