OUNTAIN VIEW, Calif.,
Feb. 28 — Ivan Sutherland has declared the corridor where he and
his team of six Sun Microsystems chip designers work to be a "clock-free
zone."
The clock is the microelectronic crystal that beats at the
heart of every microprocessor chip, orchestrating the
synchronous dance of electrons that course through the hundreds
of millions of wires and transistors of a modern computer.
Such crystals, which tick up to 1.5 billion times each second
in the fastest of today's desktop personal computers, dictate
the timing of every circuit in every one of the chips that add,
subtract, divide, multiply and move the ones and zeros that are
the basic stuff of the information age.
But in the age of the digital metronome, Mr. Sutherland is a
heretic.
The team has been engaged in a decade-long crusade, pursuing
a radically different approach to the design of circuits that
are the building blocks of today's computers.
Its approach, which uses a technique known as asynchronous
logic, differs from conventional computer circuit design in that
the switching on and off of digital circuits is controlled
individually by specific pieces of data rather than by a
tyrannical clock that forces all of the millions of the circuits
on a chip to march in unison.
Mr. Sutherland says that after a decade of work his group has
made breakthroughs that will soon make asynchronous computer
designs possible on a significant scale. In four papers
scheduled to be presented at a technical conference in Salt Lake
City beginning on March 11, his team will lay out an idea that
he says will lead to a paradigm shift in modern computer
design.
Clockless computing, according to its small band of
proponents, would offer greater computational speed and lower
power consumption, as well as making it possible to design new
chips more quickly.
There are few believers in the approach in the mainstream of
the computer world, which is not convinced that such a wholesale
change of the way the industry designs and manufactures chips is
practical. But Mr. Sutherland's crusade is noteworthy, in part
because of who he is.
He is credited with inventing the field of interactive
computer graphics, forerunner of contemporary capabilities like
computer-aided design and virtual reality. In 1963, his Ph.D.
thesis described a light pen used to create engineering drawings
directly on the cathode-ray tube of a computer display.
Four years later, he developed the head- mounted display that
led directly to the idea of three-dimensional virtual reality
visors and helmets. Then in 1968 he was a co- founder of
Evans & Sutherland, which became the world's premier
computer graphics company, selling graphics systems used by
engineers and flight simulators used for training pilots. It
still makes graphical systems, and Mr. Sutherland is on the
board.
He joined Sun Microsystems a decade ago when it formed a
corporate research laboratory. He came with the intention of
finding new ways to speed up computing, and built a small team
with the goal of pioneering a set of technologies to make
asynchronous logic a viable option for computer designers.
"This is a fundamental point," he said. "The clock paradigm
is running out of steam."
The tiny community of asynchronous logic proponents is made
up of small academic and corporate research teams like Mr.
Sutherland's and several small start-up companies. They say that
today's conventional chip design process will soon reach its
practical limits as processors achieve greater and greater
speeds. Among other drawbacks, the current approach often leaves
designers grappling with timing glitches that are maddeningly
difficult to debug.
"You solve a problem at one point in a chip, and it creates
problems in other places that are almost impossible to find,"
said Wesley Clark, a computer designer and industry pioneer who
has consulted with Mr. Sutherland's team at Sun Microsystems
Laboratories. "It adds acre-engineer years to the design
problem," he said, referring to the need of chip companies to
add another "acre" of engineers to solve a problem.
Some researchers have been intrigued by the possibilities of
the asynchronous approach to computing since the 1950's and
60's, when the concept was pioneered by John von Neumann at the
Institute for Advanced Study in Princeton, N.J., and by David
Muller at the University of Illinois.
But it has been a largely quixotic quest, and today there are
only a handful of examples of asynchronous designs that
work.
For example, Royal Philips Electronics has built a pager
using asynchronous electronics, taking advantage of the fact
that the circuits produce far less radio interference than do
clock-driven circuits. This makes it possible to operate a radio
receiver that is directly next to the electronic circuit,
greatly increasing the unit's operating efficiency.
Philips has also actively pursued research into asynchronous
logic. Two small start-ups, Asynchronous Digital Design
in Pasadena, Calif., and Theseus Logic in Orlando, Fla.,
are developing asynchronous chips for low-end consumer markets
and high-performance computing systems.
Additionally, some longtime computer designers are beginning
to use asynchronous logic to solve thorny problems. Chuck Seitz,
an influential designer of parallel supercomputers at the
California Institute of Technology, is now chief executive of
Myricom, a maker of interconnection systems used to
create clusters of I.B.M.,
Silicon Graphics and
Hewlett-Packard computers.
Myricom is now using asynchronous circuitry where conventional
clocked-circuitry would be unworkable because of the varying
clock speeds of the disparate machines.
He notes that in a complicated modern computer chip as much
as 15 percent of the circuitry is devoted to distributing the
clock signal and as much as 20 percent of the power is consumed
by the clock.
"Ivan has done excellent work," said Mr. Seitz, who has read
the papers prepared by the Sun research group. Still, he notes
that the conventional design techniques used by circuit
designers today will be hard to dislodge in favor of an unproven
approach.
Moreover, some of the nation's best computer designers are
outright skeptics about asynchronous logic. Gordon Bell, the
designer of Digital Equipment's VAX computer architecture in the
early 1970's, said that he was doubtful whether asynchronous
logic would ever achieve a following outside of the research
community.
Mr. Bell, who is now a senior researcher at Microsoft, said he had tried to
persuade Mr. Sutherland to enter into a wager over whether
asynchronous designs would be widely adopted but that the two
men had not yet agreed on the terms of the bet.
"I wonder if he's found some new magic potion," Mr. Bell
said.
Mr. Sutherland, in fact, says a new magic is precisely what
he has found. He draws an analogy to the first steel bridges,
which were built like stone bridges, with arches. It took some
time, he said, for designers to recognize the possibilities of
the suspension bridge — a form impossible to create with stone
alone but which was perfectly suited to the properties of
steel.
The same is true with asynchronous logic, he said. His
research shows that it will be possible to double the switching
speed of conventional clock-based circuits, he said, and he is
confident that Sun in particular will soon begin to take
advantage of that speed. "A 2X increase in speed makes a big
difference," he said, "particularly if this is the only way to
get that fast."
