Bridges
Bridges are really just like switches, but there are a few differences which we will mention, but not expand upon. They are as follows:

Bridges are software based, while switches are hardware based because they use an ASICs chip to help them make filtering decisions.
Bridges can only have one spanning-tree instance per bridge, while switches can have many.
Bridges can only have up to 16 ports, while a switch can have hundreds!

桥接是基于软件实现的，交换机是基于硬件实现