Generally, a bridge has only two ports and divides a collision domain into two parts. All decisions made by a bridge are based on MAC or Layer 2 addressing and do not affect the logical or Layer 3 addressing. Thus, a bridge will divide a collision domain but has no effect on a logical or broadcast domain. No matter how many bridges are in a network, unless there is a device such as a router that works on Layer 3 addressing, the entire network will share the same logical broadcast address space. A bridge will create more collision domains but will not add broadcast domains.

A switch is essentially a fast, multi-port bridge, which can contain dozens of ports.  Rather than creating two collision domains, each port creates its own collision domain. In a network of twenty nodes, twenty collision domains exist if each node is plugged into its own switch port. If an uplink port is included, one switch creates twenty-one single-node collision domains. A switch dynamically builds and maintains a Content-Addressable Memory (CAM) table, holding all of the necessary MAC information for each port.

Web Links Bridging and Switching Basics http://www.ctr.columbia.edu/~dimitri/teaching/ E6761/Lecture7/ switching_bridging.pdf