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A '''network card''', '''network adapter''', '''LAN Adapter''' or '''NIC''' (network interface card) is a piece of [[computer hardware]] designed to allow computers to communicate over a [[computer network]]. It is both an [[OSI model|OSI layer]] 1 ([[physical layer]]) and layer 2 ([[data link layer]]) device, as it provides physical access to a networking medium and provides a low-level addressing system through the use of [[MAC address]]es. It allows users to connect to each other either by using cables or wirelessly.

Although other network technologies exist, [[Ethernet]] has achieved near-ubiquity since the mid-1990s. Every Ethernet network card has a unique 48-bit serial number called a [[MAC address]], which is stored in [[Read-only memory|ROM]] carried on the card. Every computer on an Ethernet network must have a card with a unique MAC address. No two cards ever manufactured share the same address. This is accomplished by the [[Institute of Electrical and Electronics Engineers]] ([[IEEE]]), which is responsible for assigning unique MAC addresses to the vendors of network interface controllers.

Whereas network cards used to be [[expansion card]]s that plug into a computer bus, the low cost and ubiquity of the Ethernet standard means that most newer computers have a network interface built into the [[motherboard]]. These either have Ethernet capabilities integrated into the motherboard chipset, or implemented via a low cost dedicated Ethernet chip, connected through the [[Peripheral Component Interconnect|PCI]] (or the  newer [[PCI express]] bus). A separate network card is not required unless multiple interfaces are needed or some other type of network is used. Newer motherboards may even have dual network (Ethernet) interfaces built-in.

The card implements the electronic circuitry required to communicate using a specific [[physical layer]] and [[data link layer]] standard such as [[Ethernet]] or [[token ring]].  This provides a base for a full network [[protocol stack]], allowing communication among small groups of computers on the same [[LAN]] and large-scale network communications through routable protocols, such as [[Internet Protocol|IP]].

There are four techniques used to transfer data, the NIC may use one or more of these techniques.

*Polling is where the [[microprocessor]] examines the status of the [[peripheral]] under program control.
*Programmed [[I/O]] is where the [[microprocessor]] alerts the designated [[peripheral]] by applying its address to the system's [[address bus]].
*Interrupt-driven [[I/O]] is where the [[peripheral]] alerts the [[microprocessor]] that it's ready to transfer data.
*DMA is where the intelligent [[peripheral]] assumes control of the [[system bus]] to access memory directly. This removes load from the CPU but requires a separate processor on the card.

A network card typically has a [[twisted pair]], [[BNC connector|BNC]], or [[Attachment Unit Interface|AUI]]  socket where the network cable is connected, and a few [[Light-emitting diode|LED]]s to inform the user of whether the network is active, and whether or not there is data being transmitted on it.  Network Cards are typically available in 10/100/1000 [[Megabit per second|Mbit/s]] varieties. This means they can support a transfer rate of 10, 100 or 1000 Megabits per second.

[[Category:Hardware]]
[[Category:Networking]]