Second time in 24 years U.S. has been thrown out of the top flight of world's most powerful supercomputers. Thanks to an upgrade to a Swiss supercomputer has bumped the US Department of Energy's (DoE) Cray XK7 to number four on the prestigious TOP500, a list that rates the supercomputers across the globe.

The only other time when US fell out of the top three in this list was in 1996. Currently, two Chinese supercomputers occupy the first two positions in TOP500 list.

The U.S. system has been overpowered by Switzerland's Piz Daint machine, which is installed at the country's national supercomputer centre. The supercomputer Piz Daint is named after a peak in the Grison region of Switzerland.

The upgrade to the Swiss supercomputer has boosted its performance to 19.8 petaflops, which is twice more than the previous 9.8 petaflops. On the other hand, the American DoE supercomputer in question, located at the Oak Ridge National Laboratory in Tennessee, has a capacity of 17.6 petaflops. (1 petaflop is equal to one thousand trillion operations per second)

Although US has slipped down to the fourth position from the erstwhile third, most of the supercomputers in the list belong to North America and now, Oak Ridge National Laboratory looks all set to re-enter the top three spot later this year, when its Summit supercomputer comes online. This one is expected to have a peak performance of more than 100 petaflops.

However, the Chinese supercomputers are way more powerful than both the U.S and Swiss machines.

China's Tianhe-2 (Milky Way-2) machine, which stands at the second position currently, has a throughput of 33.9 petaflops and the top spot owner Sunway TaihuLight machine at China's supercomputing centre in Wuxi has a massive 93 petaflops capacity.

Japan is currently working on building a supercomputer, the AI Bridging Cloud; its number-crunching ability will go beyond the Sunway machine. Once completed, the AI Bridging Cloud is expected to have a peak performance of 130 petaflops.

These kinds of number-crunching supercomputers are generally used to carry out super difficult tasks, such as, incredibly detailed simulations, weather forecasts and tackling problems in physics, computational science, and geophysics.