5 of the world's fastest supercomputers

The positions haven't shifted, but there were plenty of changes atop the list released Monday of the world's 500 fastest supercomputers.

K Computer, which became the world's fastest supercomputer by a factor of three five months ago, has been upgraded and is now four times speedier than the next-fastest. It is more powerful than the next seven supercomputers combined.

The supercomputer is capable of 10.51 Petaflops. That means it can do 10.51 quadrillion -- that's a million billion -- calculations per second. Hence the supercomputer's name: The letter "K" is short for the Japanese word "kei," which symbolizes 10 quadrillion.

For comparison's sake, the fastest commercially available Intel processor (the Core i7) is capable of about 109 gigaflops, or about 109 billion calculations per second. That means K Computer is more than 96,000 times faster than your PC.

The K Computer is a truly massive supercomputer: it comprises 864 computer racks. Still, it remains surprisingly energy efficient -- one of the most efficient on the list.

K Computer is used at the Riken Institute for Physical and Chemical Research in Kobe, Japan. The Riken Institute shares its computing power for researchers' projects around the world.

The Top 500 list is revised each June and November by researchers at the National Energy Research Scientific Computing Center, the University of Tennessee in Knoxville and the University of Mannheim in Germany. In the latest edition, unveiled Monday, the top 10 fastest supercomputers were unchanged since the last list came out in June. That's the first time that's happened since the list began in 1993.

NEXT: No. 2: Tianhe-1A