Today I Learned

While I agree, they're doing it to make the account look legitimate for later use.

I think they do this to make accounts look legit when they are astroturfing later.

OG

Well you're not half wrong, at least the LUMI supercomputer, current nr. 9, runs Cray SUSE Linux Enterprise Server with minimal kernel daemons to reduce OS jitter on the compute nodes.

The hardware is generally more mundane on that front, and even the 'exotic' ones are most readily accommodated by Linux (almost all x86 based, with a handful of POWER, ARM, and one that is allegedly DEC Alpha derived).

Generally speaking, a Top500 is a bunch of x86 servers usually nowadays with some GPUs in them connected by ethernet or infiniband.

You are right, and yes, they could run Windows, but it'd be pretty silly.

All the applications they run were written with a pure POSIX mindset, the jobs are run headless, and the legacy of much of the application code dates back to before even Windows NT was a thing.

In the late 2000s, Microsoft actually made a concerted push to try to get into the market, and it was just a laughable failure (they brought nothing to the table, had reduced ecosystem compatibility, and tried to charge more all in the process.

FreeBSD is unlikely to squeeze performance out of these. Particularly disadvantaged because the high speed networking vendors favored in many of these ignore FreeBSD (Windows is at best an afterthought), only Linux is thoroughly supported.

Broadly speaking, FreeBSD was left behind in part because of copyleft and in part by doing too good a job of packaging.

In the 90s, if a company made a go of a commercial operating system sourced from a community, they either went FreeBSD and effectively forked it and kept their variant closed source and didn't contribute upstream, or went Linux and were generally forced to upstream changes by copyleft.

Part of it may be due to the fact that a Linux installation is not from a single upstream, but assembled from various disparate projects by a 'distribution'. There's no canonical set of kernel+GUI+compilers+utilities for Linux, but FreeBSD owns a much more prescriptive project. I think that's gotten a bit looser over time, but back in the 90s FreeBSD was a one-stop-shop, batteries included project that included everything the OS needed maintained under a single authority. Linux needed distributions and that created room for entities like RedHat and SUSE to make their mark.

So ultimately, when those traditionally commercial Unix shops started seeing x86 hardware with a commercially supported Unix-alike, they could pull the trigger. FreeBSD was a tougher pitch since they hadn't attracted something like a RedHat/SUSE that also opted into open source model of business engagement.

Looking at the performance of these applications on these systems, it's hard to imagine an OS doing better. Moving data is generally as close to zero copy as a use case can get, these systems tend to run essentially a single application at a time, so the cpu and io scheduling hardly matter. The community used to sweat 'jitter' but at this point those background tasks are such a rounding error in the overall system performance they aren't worth even thinking about anymore.