Super-computers have become massively parallel, with hundreds or even thousands of CPUs. Legacy software providers typically set license terms according to the number of CPUs, and software license fees could get prohibitively expensive.
Yes, Linux can be easily customized. But, if you are building a massively parallel with nodes of 2-16 CPUs, you really don't need much customization: the kernel already has everything you need. You might need to develop or tweak a device driver for your interconnect, but that's easy to do, and possible on legacy OS's as well.
you are right-
I work with several HPC labs- years ago they
wanted to go to a supported “UNIX” from DEC’s
Tru64 unix to HPUX or whatever -in some cases
such as DEC, they could get the software for a minimal
fee- but then it was on proprietary hardware-
Well, from Berkley to MIT- (with the help of taxpayer
money)- the big centers started porting to open source
and forcing hardware manufacturers to make their hardware with Linux drivers- it is all about lowering
the cost- at first it was pretty buggy- but for the
most part it runs now.
BTW- several years ago Microsoft GAVE quite a few centers $100’s thousands to buy windows hardware and run
Microsoft code- I know of a center who took them up on it- no one EVER did a project on that Microsoft cluster.
They mentioned licensing, but did just glance over it. It’s no wonder there is a move to Linux, try building a super-scalar online application with a DB on the back-end... Licensing on Oracle/SQL will kill your ROI.