Description:
A Network interface card, NIC, or Network card is an electronic component that connects a computer to a computer network,
usually a LAN. It is considered a piece of computer hardware.
Today, most computers are equipped with network cards. Network cards enable a
computer to exchange data with the network. To achieve
the connection, network cards use a suitable protocol, for
example CSMA/CD.
Network cards usually implement the first two layers of the OSI
model, that is the physical layer, and the data link layer. Today,
most network cards use Ethernet. Other
network types are ARCNET, introduced in 1977, LocalTalk or Token Ring.
The network 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 network controller for an IEEE 802 network
such as Ethernet , Wi -Fi, or Token Ring, and every FDDI network
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.


Implementation
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, for IEEE 802 networks and FDDI,
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.
The NIC may use one or more of two techniques to
indicate the availability of packets to transfer:
· Polling is where the CPU examines the status of the peripheral under
program control;
· Interrupt-driven
I/O is where the peripheral alerts the CPU that it is ready to transfer data; and may use one or more of two techniques to
transfer packet data:
· Programmed
input/output is where
the CPU moves the data to or from the designated peripheral to memory;
· 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 more logic
on the card. In addition, a packet buffer on the NIC may not be required and latency can be reduced.
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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