Network Interface Controller

A network interface controller (also known as a network interface card, network adapter, LAN adapter and by similar terms) is a computer hardware component that connects a computer to a computer network.

Early network interface controllers were commonly implemented on expansion cards 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.

Purpose of the Network Interface Controller

The network interface controller implements the electronic circuitry required to communicate using a specific physical layer and data link layer standard such as Ethernet, Wi-Fi, 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 IP.

Although other network technologies exist (e.g. token ring), Ethernet has achieved near-ubiquity since the mid-1990s.

Every Ethernet network interface controller has a unique 48-bit serial number called a MAC address, which is stored in read-only memory. Every computer on an Ethernet network must have at least one controller. Normally it is safe to assume that no two network controllers will share the same address, because controller vendors purchase blocks of addresses from the Institute of Electrical and Electronics Engineers (IEEE) and assign a unique address to each controller at the time of manufacture.

The NIC allows computers to communicate over a computer network. It is both an 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 addresses. It allows users to connect to each other either by using cables or wirelessly.

Implementation

Whereas network controllers used to operate on expansion cards that plugged 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. Newer server motherboards may even have dual network interfaces built-in. The Ethernet capabilities are either integrated into the motherboard chipset or implemented via a low-cost dedicated Ethernet chip, connected through the PCI (or the newer PCI express) bus. A separate network card is not required unless additional interfaces are needed or some other type of network is used.

The NIC may use one or more of four techniques to transfer data:

• Polling is where the CPU 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.[dubious – discuss]
• Interrupt-driven I/O is where the peripheral alerts the microprocessor that it is ready to transfer data.
• Direct memory access is where an 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.

An Ethernet network controller typically has an 8P8C socket where the network cable is connected. Older NICs also supplied BNC, or AUI connections. A few LEDs inform the user of whether the network is active, and whether or not data transmission occurs. Ethernet network controllers typically support 10 Mbit/s Ethernet, 100 Mbit/s Ethernet, and 1000 Mbit/s Ethernet varieties. Such controllers are designated 10/100/1000 - this means they can support a notional maximum transfer rate of 10, 100 or 1000 Megabits per second.

Some products feature NIC partitioning (NPAR).

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