Today, we are going to talk about switch. Switch is a networking device that connects end-device(i.e. computer and server) and networking device(router, wireless access-point). Switch is a Layer Two device. When you say Layer Two device, it resides at the Data Link Layer for ISO Model reference and Network Interface for TCP/IP Model reference.
Switch is the modern Layer Two device that is commonly used in almost in a Network Infrastructure today because of its capability to forward data in a high speed level which is up to Gigabit speed. Switch commonly have 24ports, 36ports, or 48ports for Ethernet connection.
Cisco Catalyst Switch 2950 Courtesy: http://www.esellerpro.com