1983

Ethernet

Chuck Thacker (b. 1943), Butler Lampson (b. 1943), Robert Metcalfe (b. 1946), David Boggs (b. 1950)

To connect multiple computers that need to communicate with each other, what you need is a LAN, or Local Area Network. But how will the computers connect together? This was actually an open question for engineers, and they tried out a number of network topologies in the marketplace: various star networks, ring networks, and bus networks. The technology that won out is called Ethernet. It was first developed by engineers at Xerox PARC—including Chuck Thacker, Butler Lampson, Robert Metcalfe, and David Boggs—and patented in 1975, then standardized in 1983. In the 1980s it used coaxial cable to implement an inexpensive bus topology.

A bus topology means that every computer communicates on the same single wire. One question in this arrangement is “who gets to talk now?” In the Ethernet approach, a computer that wants to send a packet first looks at the bus to see if it is clear. If it is, it starts sending its packet. It listens as it sends, and if it sees that its packet is getting corrupted, it knows that a collision occurred—two computers started sending their packets at the same time. So it stops sending and waits a random amount of time before trying again. Why random? Because if both computers immediately start resending, they would simply collide again.

It sounds like collisions would happen all the time, especially if a lot of computers share the same bus. But the system works surprisingly well even though there is no central control.

Because Ethernet cards and cable were inexpensive and easy to install, and also available from many companies, Ethernet took off. Today just about every LAN uses Ethernet and most laptops come with an Ethernet port because the hardware is so cheap.

The original Ethernet specification ran at ten megabits per second. One gigabit per second is now common at the consumer level.

Ethernet is another one of those technologies that we take for granted because engineers make it work so well. Every computer that connects into a LAN with a wire uses it.

SEE ALSO ENIAC—The First Digital Computer (1946), ARPANET (1969).

Blue Ethernet network plug connected to the back of the desktop PC.