Pretty good for free stuff.
SEE HEREWhile a Windows-based cluster claimed the #10 slot last November, that machine fell to #13...and is now listed as being driven by SUSE Linux. So Windows' highest performing platform is now at #15, an AMD Opteron-based, 30,720-core cluster built by Dawning for China's Shanghai supercomputer center, with an Rmax score of 180,600. Only five of the Top 500 supercomputers currently use Windows HPC, compared to 472 which run some variant of Linux.