What is a NIC?

A Network Interface Card (NIC), also called a Network Adapter, is used to connect a computer to the cabling used in a local area network (LAN). Typically, the NIC attaches to the computer�s expansion bus via an ISA slot (8-bit or 16-bit) or a PCI slot (32-bit). The NIC has one or more external ports with which to attach the network cable.

The primary function of a NIC is to allow the computer to communicate on the network. It does this by transmitting/receiving and controlling traffic with other computers or devices on the network. When transmitting, the NIC converts data from parallel to serial, encodes and compresses it, and then places it on the wire in the form of an electrical or optical signal. The process is reversed on the receiving end. The NIC translates the electrical signal it receives off the wire into bits that can be read by the computer.

Each NIC has a unique identifying MAC address hard-coded onto the card. In addition, a NIC must have a network adapter driver that enables it to communicate with the network protocols. (The network adapter driver is discussed under the section 'Network Driver Standards: NDIS and ODI.') A NIC is specific to a particular type of LAN architecture (e.g., Ethernet, Token Ring, or Fiber-Optic). It is possible to install more than one NIC in the same computer.

Most NICs connect directly to a computer�s system bus via a 32-bit PCI slot or an 8-bit or 16-bit ISA slot for older computers.

A NIC operates at the Physical layer, the lowest layer of the OSI model.