network interface card (NIC)

Definition of network interface card (NIC) in The Network Encyclopedia.

What is network interface card?

NIC is an adapter card that plugs into the system bus of a computer and allows the computer to send and receive signals on a network. A network interface card (NIC) is also known as a network adapter card or simply a network card.

How It Works

NICs can be legacy components that require manual configuration of interrupt request (IRQ) and base I/O port settings, or they can be plug and play components. NICs are available for any system bus type: Industry Standard Architecture (ISA), Extended Industry Standard Architecture (EISA), Micro Channel Architecture, and Peripheral Component Interconnect (PCI). PCI cards are 32-bit and give the best performance. They are available in various speeds, such as 10 Mbps for Ethernet and 10/100 Mbps for Fast Ethernet. Other cards are available for networking technologies such as Token Ring and Fiber Distributed Data Interface (FDDI).

A computer can communicate with the NIC using several methods, including memory-mapped I/O, direct memory access (DMA), or shared memory. A parallel stream of data is sent to the card and buffered before being packaged into discrete frames for serial transmission over the network. Framing adds headers and trailers to the data, which contains addressing, clocking, and error-checking information. The frames are then converted to electrical voltage pulses that drive an electrical signal over the wire. The receiving NIC processes the signal in the reverse order into a data stream for the receiving computer. Many of these functions are built into the network firmware, while others are governed by the NIC driver software installed on the computer.

NICs can have one or more connectors for cabling to be attached, such as

Network interface card

  • RJ-45 connector for twisted-pair cabling (the most common type)
  • BNC connector for thinnet cabling
  • DB15 connector for connecting drop cables to thicknet cabling

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