http://www.top500.org/statistics/list/
As it comes to no surprise, Linux totally dominates on this field.
Operating system Family | Count | System Share (%) | Rmax (GFlops) | Rpeak (GFlops) | Cores |
Linux | 469 | 93.8 | 155667628 | 221440076 | 14109948 |
Unix | 20 | 4 | 4264437 | 5326824 | 200096 |
Mixed | 7 | 1.4 | 1453422 | 1749811 | 528384 |
Windows | 3 | 0.6 | 465600 | 628129 | 46092 |
BSD Based | 1 | 0.2 | 122400 | 131072 | 1280 |