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Ethernet is a type of cabling commonly used in high-speed wired computer networks. You'll find Ethernet cabling in local-area networks (LANs). It's also commonly used with broadband Internet, connecting the cable modem or DSL modem to a wired router or a wireless router, for example. To use Ethernet with your computer, it will need an Ethernet card, which is an expansion card that provides an Ethernet jack and the hardware and software needed to transmit over the Ethernet network.
If you look at the connector on the end of an Ethernet cable, called an RJ45 or an 8P8C modular connector, you'll notice that the RJ45 looks a lot like a telephone line connector, but the Ethernet connector is larger and wider. An Ethernet cable has male RJ45 connectors on both ends, and the cables can be anywhere from a few feet to hundreds of feet long (or one to 70 meters).
Ethernet cabling uses a twisted-pair wiring configuration in which the manufacturer twists pairs of wires together. This twisting helps reduce electromagnetic interference (EMI) bleeding into individual wires. Most of the time, the twisted pairs involve wires from the same pins — pins 1 and 2, 3 and 6, 4 and 5, and 7 and 8 — although a few other pairings are possible, depending on the manufacturer. If you look inside an Ethernet cable, you might see that the sheaths covering the wires for these matching pairs are color-coded.
With the Ethernet cabling standard, you can have two wiring configurations. First, the cable can be wired straight across, with pin 1 at one connector directly wired to pin 1 at the other connector. In this configuration, each of the eight pins is wired directly to each other. Second, the cable can be wired so that some pins are receivers on one end and transmitters on the other end of the Ethernet cable.
You'll sometimes see Ethernet referred to as IEEE 802.3, but that designation refers to the standard by which Ethernet works. Sometimes, Ethernet is called 10BASE-T, 100BASE-TX, or 1000BASE-T, depending on the maximum speed of a particular cable.
Xerox developed Ethernet in the early 1970s, achieving a patent in 1975, and initially appearing as a standard in use in 1980. The earliest Ethernet ran at speeds of 3 megabits per second (Mbps), but upon release of the standard, it ran at 10 Mbps. Later, high-speed Ethernet operated at 100 Mbps. Within recent years, Ethernet cabling began operating at 1000 Mbps, equal to 1 Gbps. If an Ethernet cable can support a high-speed transmission, it also can work backwards to support slower speeds, which allows users to mix Ethernet cards, routers, and modems that only support slower speeds.