7. Network Interface cards (NIC)

Network cards are needed if the computer does not have a built-in network chip on the motherboard.  A NIC allows data packets to travel back and forth between computer and network.

Each network card / chip has a unique 48 bit identification code called its MAC address (short for 'Media Access Control). If the network card senses that the destination address within the data packet matches its MAC address, it allows the packet through, otherwise it just ignores it.

The MAC address is also very handy if a network manager want to only allow certain authorised machines to connect to the network. For instance the school may own a number of laptops for use by students, each one has its own MAC address, if any other laptop tries to plug in, it is just ignored.

Wireless Network card

This works in the same way as a standard Ethernet card, but it has the added complication of using wireless data packets.

or it may take the form of a 'dongle' that attaches to an USB port.

Most laptops today have the wireless circuitry built in the motherboard and so does not need any additional devices to connect to a network.