Re: I wonder what OS Dropbox's servers run on. And AWS...
"In any case, even Microsoft has admitted that Azure does NOT run on Windows, so if Microsoft isn't doing it, why would anyone else ?"
Azure runs on Hyper-V Server - a dedicated hypervisor layer similar to VMware ESXi. Hyper-V currently has about 30% of the commercial hypervisor market, and is completely free for the fully featured version. Windows is not required, but Hyper-V can be installed as part of a Windows OS if preferred.
(As compared to Linux virtualisation where as far as am aware, you can only run a hypervisor as a bolt on to the full Linux OS)