Switch

A network switch or switching hub is a computer networking device that connects network segments.
The term commonly refers to a network bridge that processes and routes data at the data link layer (layer 2) of the OSI model. Switches that additionally process data at the network layer (layer 3 and above) are often referred to as Layer 3 switches or multilayer switches.
The term network switch does not generally encompass unintelligent or passive network devices such as hubs and repeaters
Function
The network switch, packet switch (or just switch) plays an integral part in most Ethernet local area networks (LANs). Mid-to-large sized LANs contain a number of linked managed switches. Small office/home office (SOHO) applications typically use a single switch, or an all-purpose converged device such as a gateway to access small office/home broadband services such as DSL or cable internet. In most of these cases, the end-user device contains a router and components that interface to the particular physical broadband technology, as in Linksys 8-port and 48-port devices. User devices may also include a telephone interface for VoIP.
A standard 10/100 Ethernet switch operates at the data-link layer of the OSI model to create a different collision domain for each switch port. If you have 4 computers (e.g., A, B, C, and D) on 4 switch ports, then A and B can transfer data back and forth, while C and D also do so simultaneously, and the two "conversations" will not interfere with one another. In the case of a "hub," they would all share the bandwidth and run in Half duplex, resulting in collisions, which would then necessitate retransmissions. Using a switch is called microsegmentation. This allows you to have dedicated bandwidth on point-to-point connections with every computer and to therefore run in Full duplex with no collisions