Network cards let a computer exchange data with a network. To achieve the connection, network cards use a suitable protocol, for example CSMA/CD. Network cards usually implement the first two layers of the OSI model, that is the physical layer, and the data link layer. There are older network protocols such as ARCNET, introduced in 1977, LocalTalk or Token Ring, but today, most network cards use Ethernet.Ethernet cards are available in several different standard packages called form factors that have evolved over the last several generations of PC hardware: