Tsubame itself - once you move past the air-conditioners - is split across several rooms in two floors of the building and is largely made up of rack-mounted Sun x4600 systems. There are 655 of these in all, each of which has 16 AMD Opteron CPU cores inside it, and Clearspeed CSX600 accelerator boards.

The graphics chips are contained in 170 Nvidia Tesla S1070 rack-mount units that have been slotted in between the Sun systems. Each of the 1U Nvidia systems has four GPUs inside, each of which has 240 processing cores for a total of 960 cores per system.

The Tesla systems were added to Tsubame over the course of about a week while the computer was operating.

"People thought we were crazy," said Satoshi Matsuoka, director of the Global Scientific Information and Computing Center at the university. "This is a ¥1 billion (US$11 million) supercomputer consuming a megawatt of power, but we proved technically that it was possible."

The result is what university staff call version 1.2 of the Tsubame supercomputer.