Re: Good hardware but why not a real operating systems?
Look in the top500 - there are two Windows-based systems in the list; one at the bottom, one below half way.
Windows is utterly unsuitable for this kind of system:
1) Poor-to-no support for high-performance interconnects
2) What's the gui for on a compute node? Sucking resources, that's what.
3) No possibility of vendor optimisations
4) Monolithic kernel
5) Ridiculously high licensing costs
6) Virtually no ability to monitor the internals to find and remove bottlenecks
Contrary to your assertion about 'open source student coders', much of Linux and its ecosystem are the work of highly-paid, highly-motivated and highly-trained developers working at IBM, HP, Cray, Intel, AMD, SGI, Samsung, Google, US and other national labs etc. Oh, and Microsoft too. The difference is that other highly-paid, highly-motivated and highly-trained coders from other organisations can see and critique the changes.
The Cray distribution (and kernel) will be pared down, tuned to their hardware and optimised for the specific application(s) at hand. Bespoke tweaks will be added during the installation phase, to ensure the acceptance criteria are met. During the lifetime of the cluster, there will be dedicated Cray engineers onsite constantly passing information and fixes back and forth to their developers, rather than passing data to Microsoft to (hopefully) get an update at some point in the future.
There are many valid criticisms of Linux (and the open source development model); you have produced none of them.