First, don’t spend your time searching for Windows 9. Microsoft made the decision to skip a version number, claiming that the number nine was simply not big enough to do the new version justice.
Second, Windows 10 will see the implementation of a new, persistent Start menu, which can be resized and filled with Live Tiles depending on user preference.
Third, be assured that compatibility issues will be minimal. Microsoft is conducting extensive testing with more than a million users having tested the OS already.