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An Ethernet crossover cable connects two computers directly through the Ethernet ports, allowing the computers to pass or share data without having to build a network. The crossover cable eliminates the need for network hardware by connecting the computers' Ethernet terminals directly. An Ethernet crossover cable is wired differently than a standard Ethernet cable, designed to connect to a network router hub or switch. This crossover cable is necessary to connect two computers without the networking hardware.
The biggest advantage of connecting two computers directly is that it takes only seconds and requires no special knowledge or software. Just plug one end of the Ethernet crossover cable into one machine’s networking port, and the other end into the other machine’s port. Once connected, the computers can "see each other's hard drives" and swap data as easily as going from a thumb drive to a hard disk, only faster. This is a great way to share large files or copious amounts of data such as music or digital picture libraries. It is also completely private because data is not broadcast over a network.
A disadvantage of using an Ethernet crossover cable is that the two machines are joined by a physical cable so they must be in fairly close proximity. Another potential disadvantage is that there is no optional built-in security as one has in a network. Once the two computers are directly connected, users can access anything in either machine that is not separately protected through active operating system permissions or encryption. This isn’t an issue when the user owns both systems, but if children, for example, use an Ethernet crossover cable to connect a personal computer to Mom or Dad's computer, financial records or other private folders should be protected from access through encryption or other means.
10BASE-T and 100BASE-TX Ethernet cables use a pair of wires to send and a second pair to receive for a total of four pairs to connect two computers. Hence, each cable end has eight wires and corresponding pinouts. The transmit pair of each device must correspond to the receiving pair on the opposite device. In a network this crossover is accomplished inside the network hardware. In an Ethernet crossover cable, it is done internally in the wire itself. Standard Ethernet cables do not crossover and are sometimes referred to as "straight through" cables.
Crossover cables are available at most electronics outlets and are quite inexpensive. One can also build his or her own Ethernet crossover cable by buying the proper category of spooled cable then attaching RJ45 connectors at either end. Wiring diagrams are available online.