The announcement by Microsoft that Windows 8 and Windows Phone 8 will share a common core should not come as a surprise. This is where the industry as a whole is moving towards, a world where the once-impermeable walls between mobile and non-mobile ecosystems are suddenly shattered, a paradigm shift initiated by consumers (rather than sysadmins or IT directors).
There are a few points worth investigating though. Windows Phone 8 ONLY works on ARM-based processors at the moment (Qualcomm Snapdragon S4 Plus) and the fact that Windows 8 and Windows Phone 8 have common DNA means that ARM, rather than Intel, is in the driving seat as it stands.
The exponential performance growth of mobile processors (which may soon be supplanted by heterogeneous systems combining GPU and CPU) makes it attractive to Microsoft to shift from a single partner (Intel) to one where competition is the norm and Microsoft can call the shots (don't forget that Microsoft also happens to have an architectural license for ARM).
Also of interest is the fact that Microsoft has released two versions of Windows 8; the x86 version and Windows RT, the ARM-based version which is Microsoft's non-legacy OS.
The latter will allow the software giant to migrate away from any legacy-linked issues and from x86 to one where mobile attributes (long battery life, always on, apps, touch friendly) are fundamental to any user experience.
The bottom line is that Windows 9, to be released sometimes in 2015, is likely to be the first major OS from Microsoft that will work both on tethered or untethered devices, from a smartphone to a workstation, with Windows Server taking over from servers, to mainframe and super computers.