What is a Network Interface Card?

A Network Interface Card (NIC) is a device that allows computers to be joined together in a network, typically a Local Area Network (LAN). Networked computers communicate with each other using a particular protocol or agreed-upon language for transmitting data packets between the different machines or "nodes." The network interface card acts as an interpreter, allowing the machine to both send and receive data on a LAN. Information Technology (IT) specialists often use these cards to setup wired or wireless networks.

One of the most common languages or protocols used with a LAN is Ethernet. There are also other, lesser-used protocols such as Token Ring. When building a LAN, a network interface card is installed in each computer on the network and each one must use the same architecture. For example, all the cards must be Ethernet cards, Token Ring cards, or an alternate technology.

An Ethernet network interface card is installed in an available slot inside the computer, typically on the motherboard. The NIC assigns a unique Media Access Control (MAC) address to the machine, which is used to direct traffic between the computers on a network. Network cards also change data from a parallel format, used by computers, to a serial format necessary in data transfers; and then back again for received information.

A card's back plate features a port that fits a data cable, such as an Ethernet cable, which runs from each NIC to a central hub or switch. The hub acts like a relay, passing information between computers using their MAC addresses and allowing them to share resources like printers and scanners. In a wired network, a cable physically connects each computer to each other or to a hub.

A network interface card does not have to be hard-wired with physical cable. Wireless cards are installed like their wired counterparts, but rather than a port for a cable, the card features a small antenna. The NIC communicates with a central wireless switch or hub via radio waves. Wireless LANs are often convenient, but may have some restrictions depending on the material a building is made from. For example, lead in walls can block wireless signals between the network interface card and a hub or switch.

When buying components for a LAN, it is important to make sure the NICs and hub or switch have the same capabilities. The entire network should be either wired or wireless, unless components are specifically chosen that have both functionalities. In addition, newer versions of hardware often support more features and greater data speeds than older equipment. It is important to make sure a central switch or hub is just as good as the individual cards used in a network.

Computer users can also connect LANs located in different areas of a city, region, or country, through Asynchronous Transfer Mode (ATM) and the creation of a Wide Area Network (WAN). LANs are built with a network interface card in each computer, but ATM uses Internet connections to link multiple LANs to an online switch, making each one part of a network. This type of WAN is referred to as an "Internetwork," as the larger WAN consists of individual nodes that are each a smaller LAN.