Microsoft Office 2013 (Office 15) was unveiled officially on Monday by CEO Steve Ballmer at a conference in San Francisco. It was revealed it is only compatible with PCs, tablets or laptops which are running either Windows 7 or Windows 8.
Systems which run Vista, XP or older versions of Windows will not be able to run the software. This implies that nearly half of all computers running Windows will need an upgrade to get Office 2013. This is a move by Microsoft to probably entice users to get Windows 8. Though most organizations are probably still working on getting to Windows 7 and Office 2010.