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Supercomputers are astonishing feats of engineering, boasting mind-blowing processing power and the ability to calculate the answer to life, the universe and everything. But to some they are supervillains rather than superheroes. For decades governments around the world funded supercomputers with military applications in mind, and some of the most powerful machines ever made were put to work modelling missile trajectories and simulating nuclear war.

Today's supercomputers still do some of that, but they're increasingly being used with the very best intentions: to model the effects of climate change, to find better ways of using energy, to investigate new materials, design new kinds of vehicles and to predict natural disasters.

Take IBM's Watson: after a brief career winning game shows, it's taken a more serious job identifying the most effective treatments for a common brain cancer known as glioblastoma. The system has also been used to identify appropriate treatments for patients with lung cancer.

Watson is an impressive machine, but as supercomputers go it's actually quite modest: its 2,880 processor cores and 16TB of RAM sounds great until you discover that Tianhe-2, aka Milky Way 2, has more than three million cores and 1,375 tebibytes of RAM. That's enough to run Crysis 3 with everything turned up to eleven - so what does it and its fellow supercomputers do all day? Allow us to introduce the world's ten most powerful computers and the high points of their CVs.

China

Reckon your quad-core PC is pretty powerful? The National Super Computer Center in Guangzhou, China, has a machine with a staggering 3,120,000 cores delivering 33.86 petaFLOPs. The machine was developed by China's National University of Defense Technology (NUDT) and as you might expect the defence side of things is shrouded in secrecy, but Chinese media reports say it'll also be used to predict earthquakes, for climate modelling and to help China's car industry. That latter claim has baffled many observers: automobile engineering professor Bian Mingyaun of Tsinghua University told the South China Morning Post that using a supercomputer to design cars was "like running after a chicken with an axe quite unnecessary."

Japan

Fujitsu's K Computer is another former number one: in 2011 it was the first computer to top 10 petaFLOPs. It's installed at the RIKEN Advanced Institute for Computational Science in Kobe, Japan, where it runs a variety of applications for tasks including disaster prevention, medical science and climate modelling. That requires a lot of power: at full pelt the K Computer uses the same amount of energy of nearly 10,000 suburban homes.

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In depth: 10 supercomputers that are saving the world in super-fast time