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GCN Home > 07/19/04 issue

System X designers beat the odds

By Joab Jackson, GCN Staff

Srinidhi Varadarajan, an assistant professor of computer science at Virginia Polytechnic Institute and State University, helped make supercomputing history last year.

The $10 million Mac OS X supercomputer he designed, nicknamed System X, outperformed systems costing hundreds of millions more.

His secret ingredient: 1,100 off-the-shelf Apple Power Mac dual-processor G5s. The design raised eyebrows, because Apple Computer Inc. had never considered itself a maker of supercomputing components.

System X is currently ranked by Top500.org as the third most powerful computer in the world. Virginia Tech uses it for systems modeling, computational chemistry, biochemistry, nanoscale electronics and other research problems. The G5s meanwhile have been replaced by Apple Xserve units, which require less cooling and electricity.

Varadarajan received a bachelor’s degree in electronics and communications engineering from the Regional Engineering College of Warangal, India, and a Ph.D. in computer science from the State University of New York at Stony Brook. The National Science Foundation has given him a Faculty Early Career Development award.

GCN associate editor Joab Jackson interviewed Varadarajan at his Blacksburg, Va., office by phone.

GCN: You often speak at conferences about the increasing difficulty of testing new supercomputing technologies. Why is it harder when there are so many more supercomputers today?

VARADARAJAN: The large supercomputing facilities at the Energy Department, NASA and National Science Foundation centers must be perfectly stable as a production resource.

If you want to improve performance or try new programming models or memory management techniques, the machine will necessarily become unstable. If it crashes, you are in trouble. And you need to test on very-large-scale systems.

Simulation alone is not sufficient.

In the late 1980s and early 1990s, we had access to machines where we could do testing, but then they disappeared.

The scalability problems you see with systems of 2,000 processors are considerably different from those you see with 32 processors.

When you are writing an algorithm today, you have to rely more on intuition with no experimental evidence to back it up. You don’t know if the implementation is really scalable or not. So System X is intended to operate with both kinds of code.