A printed circuit board that plugs into the bus of both user machines (clients) and servers in a local area network (LAN). Also commonly called a "network interface card" (NIC) or "LAN card," the network adapter transmits data onto the network and receives data from the network. It works at the data link protocol level (see OSI model).
It's Ethernet
Today, Ethernet is the local area network standard, whereas in the past, Token Ring and Apple's LocalTalk networks were widely used. Therefore, most network adapters are "Ethernet adapters." A "network ready" or "LAN ready" computer means that it has an RJ-45 port for a cable to an Ethernet network, and virtually all new desktop and laptop computers have this capability. See Ethernet.
The adapters are wired to a network hub, switch or router, using twisted wire pair cables (see twisted pair). Even though a single computer may not be part of a network, the network adapter and RJ-45 port are used to connect to the Internet via cable or DSL (see broadband router).
In the network hub, switch or router, the counterpart network adapter circuitry is built into each port. In high-end routers such as those used in the Internet backbones, the network adapter circuitry for each port is housed on "line cards" that plug into the unit.
Retrofitting Old Equipment
All new desktop and laptop computers have Ethernet circuits on the motherboard, and laptops also have built-in Wi-Fi; the wireless version of Ethernet (see Wi-Fi). To retrofit older desktops, network adapters can be plugged into the PCI bus, or USB-based adapters can be plugged into a USB port, eliminating the need to open the case. For older laptops, wired and wireless network adapters can be connected via a USB port or PC Card slot (see wireless adapter). See LAN, Ethernet, wireless LAN, data link protocol, OSI model, auto negotiate and teaming NICs.
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