Virginia Tech's Center for High-End Computing System (CHECS) is famous for building a 1100-node, G5-based supercomputing cluster in 2003 called System X. At the time it was built, it ranked as the third fastest supercomputer in the world with a sustained performance of just over 12 teraflops. The CHECS is building a new cluster, this time using 324 Mac Pro towers, that will have a theoretical computing capacity of 29 teraflops.

The new system will not replace System X, according to CHECS Director Dr. Srinidhi Varadarajan. "Unlike System X, which is a production machine for computational science and engineering researchers, the new system is intended to be pure computer science research system," he told Ars. The system will be used to study two main areas: power-aware software systems that can adjust performance automatically to maximize efficiency, and distributed shared memory systems that can run existing threaded code on high-performance clusters "as if they were scaled up versions of multi-core desktops."

System X uses 1100 Xserves with dual-2.3GHz, 64-bit G5 processors—2,200 cores total—connected with a standard data rate InfiniBand switching network with 20 Gbps bandwidth. In comparison, the new, presently-unnamed system is comprised of 324 dual-quad core 2.8GHz Xeon processors for a total of 2,592 cores. The system is also connected by a quad-data rate InfiniBand network, which provides 80 Gbps total bandwidth, a 300 percent increase. Thought the hardware should give some blazing performance, it probably won't reach 29 Tflops when benchmarked. "I would be vastly surprised if it sustained 29 teraflops on Linpack," said Varadarajan. "The new cluster will provide us with a large scale development and performance tuning platform for both these activities," however.

Varadarajan and his team chose Mac Pros for a few reasons. For one, Xserves are power dense, which requires a lot of cooling to prevent thermal hot spots. "System X has a hybrid liquid-air cooling system in a dedicated facility, which enables significantly better cooling without hot spots. This machine is however, housed in a conventional air cooled room," Varadarajan told us. Also, the Mac Pro has a large number of power and temperature sensors built in, which is necessary for the power/performance research and tuning, as well as an additional full-height PCI Express 2.0 slot for use in other research projects. And, despite common wisdom to the contrary, the Mac Pros beat other systems on price. "The Mac Pros are highly competitive even against building a white box off the cheapest prices," he added.

Upgrading System X with current, Xeon-based Xserves would result in an 8800-core monster that could push as much as 100 Tflops—at least in theory— coming close to Top 10 territory. "The top 10 is a highly mobile target; I expect it will look quite a bit different over the next two iterations," said Varadarajan. But a replacement for System X is still in the early planning stages; the needs of university researchers and funding constraints mean there is no guarantee that any replacement would use Xserves.

Dr. Varadarajan expects it will be several weeks before the system comes online, when tuning and benchmarking can begin. Once there are tangible numbers on the system's performance, we'll have a better idea how Mac Pros can fare in cluster-type systems. The new system should prove to be a formidable competitor, especially among academic systems.