"All of us who are in this game are busy learning
how to run these big machines," said Dr. Mike Levine, a scientific
director at the Pittsburgh Supercomputing Center and a physics
professor at Carnegie Mellon University. A project like Green Destiny
is "a good way to get people's attention," he said, "but it is only the
first step in solving the problem."
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Green Destiny belongs to a class of makeshift
supercomputers called Beowulf clusters. Named for the monster-slaying
hero in the eighth-century Old English epic, the machines are made by
stringing together off-the-shelf PC's into networks, generally
communicating via Ethernet — the same technology used in home and
office networking. What results is supercomputing for the masses — or,
in any case, for those whose operating budgets are in the range of tens
or hundreds of thousands of dollars rather than the hundreds of
millions required for Q.
Dr. Feng's team, which also includes Dr. Michael
S. Warren and Eric H. Weigle, began with a similar approach. But while
traditional Beowulfs are built from Pentium chips and other ordinary
processors, Green Destiny uses a special low-power variety intended for
laptop computers.
A chip's computing power is ordinarily derived
from complex circuits packed with millions of invisibly tiny
transistors. The simpler Transmeta
chips eliminate much of this energy-demanding hardware by performing
important functions using software instead — instructions coded in the
chip's memory. Each chip is mounted along with other components on a
small chassis, called a blade. Stack the blades into a tower and you
have a Bladed Beowulf, in which the focus is on efficiency rather than
raw unadulterated power.
The method has its limitations. A computer's power
depends not just on the speed of its processors but on how fast they
can cooperate with one another. Linked by high-speed fiber-optical
cable, Q's many subsections, or nodes, exchange data at a rate as high
as 6.3 gigabits a second. Green Destiny's nodes are limited to
100-megabit Ethernet.
The tightly knit communication used by Q is
crucial for the intense computations involved in modeling nuclear
tests. A weapons simulation recently run on the Accelerated Strategic
Computing Initiative's ASCI White supercomputer at Lawrence Livermore
National Laboratory in California took four months of continuous
calculating time — the equivalent of operating a high-end personal
computer 24 hours a day for more than 750 years.
Dr. Feng has looked into upgrading Green Destiny
to gigabit Ethernet, which seems destined to become the marketplace
standard. But with current technology that would require more energy
consumption, erasing the machine's primary advantage.
For now, a more direct competitor may be the
traditional Beowulfs with their clusters of higher-powered chips.
Though they are cheaper and faster, they consume more energy, take up
more space, and are more prone to failure. In the long run, Dr. Feng
suggests, an efficient machine like Green Destiny might actually
perform longer chains of sustained calculations.
At some point, in any case, the current style of
supercomputing is bound to falter, succumbing to its own heat. Then,
Dr. Feng hopes, something like the Bladed Beowulfs may serve as "the
foundation for the supercomputer of 2010."
Meanwhile, the computational arms race shows no
signs of slowing down. Half of the computing floor at the Metropolis
Center has been left empty for expansion. And ground was broken this
spring at Lawrence Livermore for a new Terascale Simulation Facility.
It is designed to hold two 100-teraops machines.
