A crossover cable might sound like a thing of the past, but it is still in use today in various capacities. It's a cable used to connect two computers together for the purpose of direct communication. Another name for this type of cable is a null modem.
A computer user might want to test the behavior of one computer by connecting it to another, or to connect two computers to avoid having to buy a hub. Computers can also be connected so that two people can compete against each other in a multiplayer game. In each of these instances, a crossover cable can be used to make the connection.
For the first two instances, the computer user will want to make sure that the two computers are in the same workgroup. If they are not, then they will not be able to “see” each other. Once they are members of the same workgroup, the data transfer or monitoring can begin. This is sometimes a requirement for multiplayer gaming as well, so it's best for the user to check the protocols for both the game and the cable to be sure.
Many network cards have the functions inherent to a crossover cable built in. In this case, the user does not need to connect the computers directly as long as both are on the same network, primarily using the same modem or router. The network card does the work that would normally be done by the cable.
Computer users can buy a crossover cable at most computer stores and online computer equipment vendors, although they can also be made from commonly available materials. A number of do-it-yourself websites explain how they are made. People who want to make their own should remember that the signal pins that receive on one end are connected to the pins that transmit on the other. This is different from straight-through cable, in which the pins are connected like to like.
A crossover cable can also be used to connect two Ethernet devices. These devices can be single computers or networks. The principle is the same, but the connection speed and scheme are different, as is the purpose of the connection. In all cases, however, the data send and receive functions are crossed over at both ends of the cable, enabling full data transfer between computers, routers, and even networks.