They use constantly recharging batteries to prevent momentary power outages from shutting down your network servers or clients.
Switches are basically multiple bridges in a single device.
If a user sends a message to someone in his own segment, it stays within the local segment. Only those packets intended for users on other segments are passed onto the backbone. A switch forwards data packets only to the appropriate port for the intended recipient, based on information in each packet header. To insulate the transmission from the other ports, the switch establishes a temporary connection between the source and destination, and then terminates the connection when the conversation is done. Jane Tipton at the Berkley Hotel calls Bill Johnson in another room, and the operator or phone switch connects the two of them on a dedicated line.