A switch is another internetworking device used to manage bandwidth on a large network. Switches are rapidly becoming one of the most used internetworking devices from connecting even smaller networks because they allow you to have some control over the use of the bandwidth on the network. A switch, which is referred to as a "bridge on steroids" controls how data flows by using the MAC addresses that are placed on each data packet. Remember that this MAC address on the data packet is the same MAC address on the network card of that particular computer.
Switches divide networks into what is known as a Virtual LAN or VLAN. The best thing about a VLAN, which is also a logical grouping of computers on a network into what is described as some sort of communication group, is that the computers really do not have to be in close proximity or even on the same floor. This is because it allows the computers to be grouped by the similarities in the types of users in the VLAN.
Switches use a combination of software and hardware to switch packets between computers and other devices on the network. This software is the switches operating system. And, because switches offer a higher density of connection ports, they can easily replace hubs on the network. This means that each computer on the network can be connected to its own port on the switch. When the computers are directly connected to the switch, the switch can supply each of the computers with a dedicated amount of bandwidth. For example, say users are on a 100Mbps Ethernet network via a switch. Each user can realize a bandwidth of 100Mbps and don't have to compete for the bandwidth the way computers do on a network via a hub because each port on the switch has a dedicated 100Mbps. This is why switches are rapidly replacing hubs. Inexpensive switches are even available to accomodate small networks and home network markets.
Some of the switch hardware can also take advantage of full-duplex access to the network media, which allows for the sending and receiving of data simultaneously. Essentially, this provides access to an Ethernet network that is collision free, when an Ethernet network is pretty much known to have data collisions. A computer existing on a Fast Ethernet network, typically running at 100Mbps, would see a 200Mbps throughput because sending and receiving would occur simultaneously on a full-duplex media.
Since switches are becoming very popular on both the small and large networks, they have all but replaced bridges as the internetworking devices for conserving network bandwidth and expanding LANs into larger corporate internetworks. But, they are also making hubs a device of the past for smaller networks.