The network card is a printed circuit board that plugs into the bus of both user machines (clients) and servers in a local area network (LAN). The adapters are wired to a network hub, switch or router, typically using twisted wire pair cables. In the case of a single home computer, the network adapter is often wired to a router, which is connected to or includes a DSL or cable modem for Internet access.
Also commonly called a "network interface card" (NIC), the network adapter controls the transmission and receiving of data at the data link level.
A "network ready" or "LAN ready" computer means that it has an RJ-45 port for a cable to an Ethernet network. In the past, Token Ring and LocalTalk networks were widely used, but Ethernet became the standard for LANs.
Almost all new desktop and laptop computers come with Ethernet circuits directly on the motherboard, and laptops also have built-in Wi-Fi for wireless connectivity. 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, network adapters connect via a USB port or PC Card (Card Bus) slot.