Network Interface Cards (NIC)
A NIC (network interface card) is designed to communicate over a computer network. It
allows users to connect to each other either by using cables or wirelessly if the NIC is a
wireless NIC (WiFi/WNIC). Every entity on a network, a PC, printer, router, etc., that
needs to communicate with other devices must have a NIC if it is to communicate over the
network. On older computers, the NIC is probably an expansion card, usually PCI or PCI
express. High performance cards can cost less that $30. NIC functionality is now often
integrated into the motherboard chipset or implemented with a dedicated Ethernet chip on
A similar situation is true for laptop computers. At one time, a PCMCIA network card
would be used in a laptop computer for the NIC just as the PCI card was used in desktop
computer, but now, NIC functionality is often integrated with the motherboard.
Ethernet is the dominant standard for cable connections for wired computer networks. An
Ethernet connector looks similar to a telephone connector, only larger. This connector is
called "RJ45". Ethernet cables are either a shielded or unshielded cable of four twisted
pairs of 24 AWG connectors, specified at 100 ohm impedance. Maximum cable length for CATX
cables is 100 meters.
Early versions of Ethernet cables were CAT3 or CAT4 (CAT being short for category).
These versions were not long lived. CAT5 and CAT5e are currently the most commonly used
cables (bandwidth of 100 MHz, 100 Mbps), with CAT6 (bandwidth of 250 MHz, 1 Gbps)
available and the configuration of the near-future. A CAT7 cable (bandwidth of 600 MHz)
specification is in development, and should be available in a few years.
Each Ethernet NIC has a unique serial number called a "media access code" (MAC address)
that is used to identify the NIC and associated computer on the network. No two NIC will
have the same address, because the NIC manufacturers must purchase blocks of addresses
from the Institute of Electrical and Electronics Engineers (IEEE).
NIC cards are capable of different speeds. Speeds of up to one gigabit per second
(Gbps) are now available. Two NIC can communicate if they differ in speed ratings, but
they will communicate at the rate of the slower NIC.
On a very simple network, NIC can be used to link personal computers (PC). If the
computers are connected directly to one another, the network is a "peer-to-peer" (P2P,
also called an "ad hoc") network. If computers are connected directly to one another, a
"cross-over" Ethernet cable is needed (also called a "Null-Modem cable"). This cable is
not "straight-through" like standard Ethernet, but crosses the send and receive connectors,
so that send line from computer A connects to the receive line of computer B.
For networks of a few computers, a "hub" can be used, with all of the computers
connected to the hub. Any message sent from any PC will be seen by all of the computers,
but only the computer with the correct MAC address will receive the message. P2P networks
are useful for many purposes. File and printer sharing are the most common applications.