Dealers of Lightning (39 page)
On May
22, 1973, he drafted his first memo describing the concept
for
PARC's
patent attorneys. Subject: "The
ETHER Network." Soon
after that, he met David Boggs for the first time.
Meanwhile,
Boggs had found his own separate way to
PARC—
escorted, as had been so many others, by
Alan Kay.
Like
all of Stanford's grad students in electrical engineering,
Boggs
had
been
sentenced to snooze through a weekly one-hour
seminar
in
the department's largest lecture hall featuring a talk from some person
prominent in industry. The point was to inoculate
the
ripening
"double-E s" with the excitement of engineering in the real world.
For
the most part, however, the sessions merged into a single soporific ten-
week drone.
That is, until Kay showed up shortly before Christmas 1972. He started
speaking
in
general terms about the interesting work taking place at the
research center Xerox had opened up across the street from the campus.
Then he put up a series of slides of a machine he and his colleagues had
built to mimic the PDP-10. Boggs shook off his torpor and sat upright.
High-performance computing was his field. He understood that any
group that could build a PDP-10 from scratch was something special.
When the seminar ended at five and everyone was free to leave, he
bolted down front and subjected Kay to close questioning.
The latter, who was always on the lookout for potential recruits with
what he called "special stars in their eyes," noticed the telltale stellar glow
in Boggs s. Knowing that Novas were starting to arrive at the rate of two
or three a week for the POLOS team and that they needed someone to
assemble them to make sure nothing was dead on arrival, he forwarded
Boggs’s resume to Bill English, who hired him to work part-time through
the end of the Stanford school year. Boggs was duly anointed keeper of
the test stand, which was a steel rack erected in the basement of Building
34. It held a perfectly functional Nova, the cover removed and the parts
arranged to be easily accessible in case they needed to be swapped with
those of a balky machine to determine which piece was causing the
glitch. To the rest of the lab Boggs seemed rather a solitary figure in his
basement lair. But he was available for kibitzing the day Bob Metcalfe
stumbled by, hauling his bale of yellow co-ax.
Metcalfe had sketched Ethernet out in a series of memos with a fair
amount of input from Thacker and Lampson—"inventing the network in
real time, working out bits and pieces of the idea," as Boggs later recalled.
But until then he had made no effort to determine if the parts would
work together in the real world as well as they did on paper. The most
critical question concerned the cable—the passive ether itself. An electrical pulse, Metcalfe understood, becomes attenuated, or stretched, as it
travels along a wire. The longer the distance, the worse the resulting dilution and the more difficult for a receiver to recapture the original data. As
he and Boggs soldered the test apparatus together, he explained that this
was the reason he needed to fire pulses down the cable and read what
came out at the other end.
"I have to know how bad it is," he said.
After that day they did not encounter each other for a couple of
months, until Metcalfe reappeared in the basement one afternoon, this
time holding a small piece of hardware he had designed to connect the
POLOS Novas to the ARPANET.
"Can I smoke test this on your rack?" he asked Boggs. (The allusion
was to a procedure that works exactly as it sounds: You shoot a voltage
surge through a circuit to test whether some hidden fault will make it
burst into flame.)
They spent a week or two testing the circuit together for a few hours
each day. Debugging a complex electronic device being almost as powerful
a bonding experience as, say, serving on a submarine in wartime, Metcalfe
learned a lot about his partner: That he was a digital whiz, accomplished
at wielding the oscilloscope, and, most interesting, underemployed in his
POLOS work. Presently the pair showed up at Bill English's office door,
figuratively holding paintbrushes and a bucket of whitewash. "Metcalfe
wants me to work on something with him for a while," Boggs said. "Is that
okay with you?"
Having secured English's acquiescence they walked on down the hall
to Metcalfe's office, where Metcalfe raked together a thick wad of
memos comprising the Ethernet invention record he had assembled
for Xerox's patent department. "Go read this," he said.
"That," Boggs recalled, "was pretty much the last time SSL got any
work out of me. For the next twelve months at least I spent every
working day with Metcalfe."
They slept when they were exhausted and the rest of the time they
worked, as unconscious of alarm clocks or the sun as casino players on a
roll. "There was no chip on the Ethernet board that both of us didn't
know about," Metcalfe recalled. "There was no line of my microcode that
Boggs did not understand. We worked on the whole thing together, every
minute, every piece of it." Boggs was placed on the payroll full-time for
the summer and stayed even after the school year resumed, placing his
Stanford Ph.D. studies on hold. He did not finish his doctorate for
another nine years.
Metcalfe, by contrast, resubmitted his doctoral dissertation to Harvard,
fattened up with a properly theoretical digression covering the ALOHAnet. In June 1973 his thesis, entitled "Packet Communication," was
finally accepted ("without enthusiasm," he later groused).
As a working system Ethernet differed from other PARC inventions in
one crucial detail: It was explicitly designed to be imperfect. Metcalfe
labeled the network a "best efforts" system—that is, the computers were
instructed not to rely on everything working perfectly. This ensured that
the system would not crash in the event of a single minor glitch (or even
a torrent), of the sort certain to crop up in a network of bug-prone experimental computers. "I loved it," said Kay, one of its earliest fans. "It was
one of the great finesses of all time, an object lesson in how to make
something work when you don't know how to make it work well."
Ethernet's basic procedure resembled getting somebody's attention in
a crowded library by the most efficient, if crude, method: by shouting.
The ether—that is, the coaxial cable connecting the Altos—was usually
silent. When a machine was ready to transmit a message, it shot a wakeup
bit onto the ether, alerting every other machine that something was about
to happen. Then it sent a packet comprising, consecutively, an eight-bit
destination address (the digital tag of the Alto for which the message was
intended); its own address; the message itself; and a string of verification
bits known as a "checksum." Receiving stations would check the destination address to see if the message was intended for them. If so, they
would copy the whole packet into memory; if not, back to sleep.
Meanwhile, the transmitting station would listen for any sign that its
packet had collided with another machine's. If it detected interference, it
would instantly stop sending, count off a random delay (as would the
transmitter of the conflicting message), and send again. The listen-and-
retransmit process could be repeated as many as fifteen times before the
machines would give up.
As much an enemy of "biggerism" as Thacker, Metcalfe implemented
these complicated electronics on the single circuit board the Alto design
allotted to Ethernet by stripping the system down to its bare essentials.
The original Ethernet board did not even have a timer of its own, relying
instead on the Alto's internal clock for the critical duty of synchronizing
transmissions.
Toward the end of the design phase, however, Boggs insisted on adding
one feature he deemed crucial. This was the "checksum," a bit sequence
that would enable the receiving station to verify that a message had not
been subtly garbled in transmission.
"Sure, David," Metcalfe said. "If you can find room on the board to
fit the checksum logic, you can add it."
This struck Boggs as a little cynical. A checksum system would require
at least eight integrated circuits, or chips. Of the sixty chip positions on the
boards they were using, fifty-nine were already occupied. Then he noticed
that just enough space remained around the margins to wedge in a few
more chips. By the time he was done there was scarcely a millimeter of
unused room. Some chips literally hung off the edge of the board, like
refugees clinging to a packed lifeboat. But Ethernet got its checksum.
With that, Metcalfe and Boggs s invention proved as facile and forgiving as they had hoped. Adding new machines, or "nodes," to the system without interrupting service for even a split second was a cinch:
One punched a tiny hole in the main co-ax and, using a simple piece of
cable TV hardware called a "Jerrold tap," plugged the needle-like end
of a branch cable into it. (This stratagem was suggested by David Liddle, a POLOS engineer and a basketball-playing crony of Metcalfe's,
whose familiarity with Jerrold taps dated from his college job as a cable
TV installer.) The network proved almost infinitely expandable while
remaining emphatically simple, not much more than a cable terminated at both ends that anyone could tap into as easily as a water line.
Yet the Alto's first users were disconcertingly slow to get on the Ethernet bandwagon. Because the network connection was a costly $500
budget option on the first machines, many PARC engineers chose to dispense with it altogether. This was especially true as long as the network
appeared to be useful mainly for sending files between computers—a
superfluous function, since the Altos were equipped with removable
disks that could easily be transferred from one machine to another. "Ethernet was up against 'sneakernet' from the very start," Metcalfe recalled.
All that changed overnight in 1975 with the advent of SLOT, Starkweather's laser printer. The virtues of the combined system called
"EARS"—the Ethernet, the Alto, the research character generator, and SLOT—-were too powerful to ignore. One could now write a memo, letter, article, or dissertation and with the push of a button see it printed in
professional-quality type. ("Before that, you had to have an article
accepted for publication to see your words rendered so beautifully," Liddle mordantly observed much later. "Now it could be complete rubbish,
and still look beautiful.")
