Re: Scientific Linux?
As others have commented, I suspect it is Linux on the clusters and desktops for physicists and Microsoft available for admin and perhaps for physicists as well for reasons of user choice.
History links for Fermi Linux/Scientific Linux for anyone interested...
Connieh Sieh's slides from some conference or other. Slide 5 will give you a bit of deja vu.
TD;LR Redhat linux transitioned to a paid model around 2003. What I remember reading somewhere else but is not mentioned on the slide is that the paid model was per core licencing. CERN (and other HEP sites) use rather a lot of cores....
Despite a discount from Redhat, the economics of the situation suggested hiring a few people and doing a recompile from source. Connie was already doing Fermi Linux based on Red Hat sources at that point.
The logic of Reghat's acquisition of CentOS now suggests distributing CentOS and providing a local repository...
Springdale is an independently compiled RHEL clone with active and fairly responsive support from a couple of IT staff at Princeton University. They do have an RHEL 8.0 recompile out for 64 bit and there is a netinstall boot image (I've not tried it, alpha, not supported &c)