Traditional computer design, he reminded his listeners, was essentially a mathematical exercise. One chose from the standard inventory
of Boolean logic gates—ORs, ANDs, NORs, and so on—and arranged
them to operate sequentially on a stream of bits. This worked fine as
long as the logic elements (mostly transistors) were slow and expensive
and the wires connecting them were relatively fast and cheap, as had
been true throughout the history of digital computing. But it also
meant that the blinding speed of digital computation was something of
an illusion. The logic elements were such data bottlenecks that when
you really examined what was happening inside the system, you could
see that computers were still constrained "to perform individual steps
on individual items of data"—that is, to do only one thing at a time.
The new technology would turn that architecture inside out. As silicon-
based chips got smaller and denser, the microscopic transistors that were
packed on them to make up the logic became faster and cheaper than the
wires linking them. The
wires
became the bottlenecks. Soon the most
important factor limiting the computers efficiency would not be the
sequence of gates, but their geometric arrangement on a flake of silicon
and the rising relative cost of transporting electrons over the minuscule
pathways linking one to another. Computers were about to cease doing
one thing at a time, in favor of doing many things simultaneously. Consequently, their architects would have to abandon the old methods of
designing them simply as linear sequences of logical functions. They
would have to also consider how to get bits from one logical function to
another along the shortest path.
Traditional digital technology required designers to think like factory
planners figuring out how to get raw materials in one end of a building
and finished product out the other. Silicon, however, "forced you to
think like an urban planner," Conway said later. "You had to think hard
about where the roads go." Just
as cities
reaching a certain size suddenly find themselves threatened
by highway
gridlock, she observed,
in
VLSI,
"if you weren't careful you
could end
up having nothing
but
roads
going nowhere." Fortunately
VLSI also
offered a
way
out of that
quandary: Because the logic gates
and other
devices
were now
so
cheap, "it
didn't cost you anything
to have
more of them, if that paid
you
back
by having less highway."
For
engineers who had
reached the top
of their game
the
old way,
VLSI
was full of murky ideas
Many doubted
it was physically possible
even
to fabricate functioning
devices as tiny as
the ones
Mead prophe
sied.
Even
those who thought
VLSI an
interesting idea with great
potential questioned whether
it would
ever supplant the tried-
and-true architectural structures
that had
brought them this
far. In
CSL
the general opinion was
that VLSI was
more than they
needed to
have on their plates. "We didn't
have to
be able to design chips,"
Lampson said—not while the
industrial
designers at
Intel
and other
chip
companies were already
hard at work on
it.
In
any case,
PARC
could hardly
hope to
contribute much to this nebulous science.
At CSL
"they were
already out
front in their own revolution," one researcher later
remarked. "To
them
VLSI was
not really
mainline, it was just this weird sort
of thing
happening somewhere else."
But
for two of Sutherland's laboratory scientists, Lynn
Conway
and
Douglas Fairbairn, Mead's talk scored a direct hit.
Conway
was a rarity at
PARC—
an accomplished designer of advanced
mainframes who chose to give the hardware gurus of the Computer
Science Lab a wide berth. She ranked among
PARC's
senior veterans,
having joined in 1972 from
IBM, where
she had helped design
a
supercomputer at the Yorktown Heights lab, and Memorex,
where
she had
worked as an architect of minicomputers. But at
PARC
she
had
played no
role in developing the Alto or
MAXC.
On the contrary, something about
the intellectual gunplay of
CSL
alarmed her, as did the intimidating
pres
ence
of
Butler Lampson.
"I
always had a hard time dealing with Butler," she recalled.
"He
had
this complete photographic memory of all theory that ever existed about
anything, but sometimes that can be kind of a mental block to being creative. You can be so confrontational and challenging about how smart you
are that you can't always see that somebody else has got this cool idea."
Like Kay, Tesler, and Shoup, Conway found the ambiance more obliging among the Systems Science Lab's lunatic fringe. "Taylor was someone
who could manage the 'neats' and Bert could manage the 'scruffies,'" she
remarked. "In SSL I could survive.
I
could get all excited about an idea
that was half-formed and go tell Bert about it, and he'd get all excited
about it, maybe tell me somebody I should talk to about it. In CSL I'd be
really afraid to present anything until it was perfect, and it would probably get immediately shot down anyway."
Her inaugural assignment at PARC had been something of an acid test
in the implementation of half-formed ideas. The job was to design and
build a combination fax and optical scanning system known as Sierra, the
aim of which was to transmit pages of mixed text and graphics at high
speed via the trick of stripping off the text and sending it in compressed
digital form, leaving only the graphics to be conveyed by conventional
(and slower) fax. The entire page, it was hoped, would therefore transmit
much faster than if faxed as a single coherent image.
Thanks to her big-iron training at IBM and hands-on experience at
Memorex Conway was able to get the machine built in eighteen months,
to everyone's candid surprise. To their disappointment, it emerged as two
gargantuan racks of special-purpose hardware that devoured so much
power one could heat a building with it.
"You could make it, but you wouldn't make any money off it," she
recalled wistfully. "It was such a giant, kludged-up thing with so many
exotic little systems that all it demonstrated was that architects could
envision and build useful systems that would take too much circuitry to
be financially viable."
Sierra would never be feasible as long as it came in such an unwieldy
package. Intel's new 4004, which packed thousands of transistors onto
one chip—a full circuit board's worth of her hard-wired machine reduced
to something you could hold between thumb and index finger—provided
Conway with the first hint of how the circuitry might eventually be re-implemented in a manageable package. The hint of a new class of architectures was somewhere inside there, whispering to her. "The itch," she
said, "was trying to be scratched."
Doug Fairbairn, Mead's second true believer, had arrived at PARC
by way of the Stanford artificial intelligence lab, where he had worked
with Kay and Tesler. "After getting my master's at Stanford I'd gone to
Europe," he recalled. "After six months I came back. I wasn't very
driven to start a career but was thinking, what's my next job? Then I
heard about Xerox and thought, 'If Alan Kay's there, I bet I won't have
to wear a tie to the interview.' And I didn't."
The interview was with Bill English. As usual, English was in desperate
search of engineers to help him and Bill Duvall complete POLOS. Fairbairn spent three years entangled in POLOS hardware implementing the
terminal system, which meant bringing together the TV display, keyboard, and mouse. (The ergonomic design of the latter consumed him
for weeks. "I spent a lot of time on the cord. A normal cord would cause
the mouse to move if you took your hand off. Then I found a wound cord
that stayed put, but constantly unraveled. We ended up spending an
incredible number of hours looking for the right insulated cord.")
Bert Sutherland, who was more willing than Taylor to tolerate independent projects in his lab, but wielded an even more ruthless hatchet
when they did not work out, canceled Sierra and POLOS within weeks of
each other in 1975—the former because of its impracticality, the latter
because it was finally and unmistakably overtaken by the Alto. His two
ace hardware designers were still looking for their next projects when
Mead showed up a few months later. Whether it was their enforced idleness or their experience in building systems whose sheer size had gotten
out of hand, both were captivated by his discussions of how to handle
machine complexity.
"Lynn Conway and I," Fairbairn remembered, "were the ones who
said, 'This VLSI is hot shit.'" They immersed themselves in the new
technology, Fairbairn commuting weekly from Palo Alto to his parents'
home in Los Angeles so he could sit in on Mead's classes at Caltech.