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.
"I think we should have been able to achieve 85 [T Flops], but we ran out of time so it was 77 [T Flops]," said Matsuoka of the benchmarks performed on the system. At 85T Flops it would have risen a couple of places in the Top 500 and been ranked fastest in Japan.
There's always next time: A new Top 500 list is due out in June 2009, and Tokyo Institute of Technology is also looking further ahead.
"This is not the end of Tsubame, it's just the beginning of GPU acceleration becoming mainstream," said Matsuoka. "We believe that in the world there will be supercomputers registering several petaflops in the years to come, and we would like to follow suit."
Tsubame 2.0, as he dubbed the next upgrade, should be here within the next two years and will boast a sustained performance of at least a petaflop (a petaflop is 1,000 teraflops), he said. The basic design for the machine is still not finalized but it will continue the heterogeneous computing base of mixing CPUs and GPUs, he said.