A switch is capable of providing the max badnwidth between each device, or something like that.
It's difficult to explain. On a ethernet network with a hub, everyone broadcasts to everyone, so there are tons of wasted packets. You basically have to take the max bandwidth of the hub, and divide it between the # of computers.
I.E. 5 computers on a 100mbit network = 20mbits of bandwidth for each computer.
5 computers on a switch have 100mbit to each other at any one time.
Switches also have the benefit of being able to host 10mbit computers/devices, while maintaining 100mbit connections between other computers.