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March 5, 2001

Computing Pioneer Challenges the Clock

By JOHN MARKOFF

Thor Swift for The New York Times
Jo C. Ebergen, left, and Ivan Sutherland of Sun Microsystems are pursuing an approach to computer chip design that is based on asynchronous logic. On such a chip, the digital circuits are switched on and off by pieces of data, not impulses from a vibrating crystal.


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MOUNTAIN 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."


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