Supercomputers today have thousands of processors, can perform trillions of calculations per second and have hundreds and hundreds of gigabytes of memory capacity. TOP500.org maintains a list of the fastest 500 supercomputers in the world. Here are the countries with the most supercomputers on the list:

United States has 257 of the fastest supercomputers.
United Kingdom has 53.
Germany 46
France 34
Japan 22
China 12
Sweden 9
Russia 9

Computers this powerful are used to simulate global weather phenomena, simulate protein folding, sequence genes, play chess, predict traffic patterns.