Networking: the Story of Ethernet
By today's standards the Alto was not a particularly powerful computer. But if several Altos are linked, along with file servers and printers, the result looks suspiciously like the office of the future.
The idea of a local computer network had been discussed before PARC was founded-in 1966, at Stanford University. Larry Tesler, now manager of object-oriented systems at Apple, who had graduated from Stanford, was still hanging around the campus when the university was considering buying an IBM 360 timesharing system.
One of the guys and I proposed that instead they buy 100 PDP-ls and link them together in a network," Tesler said. Some of the advisors thought that was a great idea; a consultant from Yale, Alan Perlis, told them that was what they ought to do, but the IBM-oriented people at Stanford thought it would be safer to buy the timesharing system. They missed the opportunity to invent local networking." So PARC ended up with another first. At the same time that the Alto was being built, Thacker conceived of the Ethernet, a coaxial cable that would link machines in the simplest possible fashion. It was based in part on the Alohanet, a packet radio network developed at the University of Hawaii in the late 1960s.
Thacker made the remark that coaxial cable is nothing but captive ether," said Kay. So that part of it was already set before Robert Metcalfe and David Boggs came on board-that it would be packet-switching and that it would be a collision-type network. But then Metcalfe and Boggs sweated for a year to figure out how to do the damn thing." (Metcalfe later founded 3Com Corp., Mountain View, Calif.; Boggs is now with DEC Western Research in Los Altos, Calif. The two of them hold the basic patents on the Ethernet.)
I've always thought the fact that [David] Boggs was a ham radio operator was important.... [He] knew that you could communicate reliably through an unreliable medium. I've often wondered what would have happened if he hadn't had that background."-Bert Sutherland
I've always thought the fact that Boggs was a ham radio operator was important," Sutherland said. It had a great impact on the way the Ethernet was designed, because the Ethernet fundamentally doesn't work reliably. It's like citizens' band radio, or any of the other kinds of radio communication, which are fundamentally not reliable in the way that we think of the telephone. Because you know it basically doesn't work, you do all the defensive programming-the say again, you were garbled' protocols that were worked out for radio communication. And that makes the resulting network function extremely reliably.
Boggs was a ham and knew that you could communicate reliably through an unreliable medium. I've often wondered what would have happened if he hadn't had that background," Sutherland added.
Once the Ethernet was built, using it was fairly simple: a computer that wanted to send a message would wait and see whether the cable was clear. If it was, the machine would send the information in a packet prefaced with the address of its recipient. If two messages collided, the machines that sent them would each wait for a random interval before trying again.
One innovative use for the network had nothing to do with people sending messages to one another; it involved communication solely between machines. Because the dynamic memory chips were so unreliable in those days, the Alto also ran a memory check when it wasn't doing anything else. Its response to finding a bad chip was remarkable: It would send a message telling which Alto was bad, which slot had the bad board, and which row and column had the bad chips," Thornburg said. The reason I found out about this was that one day the repairman showed up and said, Any time you're ready to power down, I need to fix your Alto,' and I didn't even know anything was wrong."