There is no requirement to run the same OS on all devices, let alone the fact that it is not physically possible. All you need to do is to establish a common language. You can run any OS on any device, or no OS, or Windows, or UNIX, or RT-11, or CP/M.
As an analogy, you do not need to be a genetic relative of someone to talk to him. The only requirement is that both are speaking the same language.
I have Win10 technical preview running this very moment. It is marginally better than Win8 but suffers from a hit by the same ugly stick. This series of desktop Windows is a dead end, as it is oriented only for PCs, and PCs themselves are a dead end. Win8/10 can also run on tablets, primarily as WinRT, but that offers no benefit to anyone whatsoever, except that porting of the stuff to other platforms cannot be done by anyone except MS.
CP/M? I used have to program my computer...an old C64...