+ Linux is leveraged in next-gen supercomputers ... +

IBM and the United States stole the top slot last November when the BlueGene/L system running Linux topped 70 teraflops (trillions of calculations) per second on the Linpack Benchmark and displaced Japan's Earth Simulator as king of ultra high performance computing (HPC). The Earth Simulator runs a customized flavor of Unix, and is capable of 35.86 teraflops. Since taking the lead, IBM has cemented its position by nearly doubling the performance of BlueGene/L, which kept the top spot on the June 2005 Top 500 list with a Linpack performance of 136.8 teraflops...

http://www.top500.org/