Linux

Yes, in the linux stat. The otheros option on the early PS3 allowed you to boot linux, which is what most, of not all, of the clusters used.

I wonder if the numbers are still this good if you consider more supercomputers.

Great question. My guess is not terribly different.

"Top 500 Supercomputers" is arguably a self-referential term. I've seen the term "super-computer" defined whether it was among the 500 fastest computer in the world, on the day it went live.

As new super-computers come online, workloads from older ones tend to migrate to the new ones.

So there usually aren't a huge number of currently operating supercomputers outside of the top 500.

When a super-computer falls toward the bottom of the top 500, there's a good chance it is getting turned off soon.

That said, I'm referring here only to the super-computers that spend a lot of time advertising their existence.

I suspect there's a decent number out there today that prefer not to be listed. But I have no reason to think those don't also run Linux.

I can't imagine Supercomputers to use a mainstream operating system such as Ubuntu. But clearly people even put Windows on it, so I shouldn't be surprised...