Microsoft is going to lauch four version aka Windows 8, Windows 8 Pro, Windows 8 Enterprise, and Windows 8 RT.
Windows 8 is for Desktops/Laptops & Tablets powered by x86 processors for bot 32 bit & 64 bit. Windows 8 will include updated Windows explorer, task manager, multi-monitor support and ability to switch languages on the fly, which was previously available only in Enterprise and Ultimate editions of Windows 7.
Windows 8 Pro is mainly designed for technical professionals. It includes all the features in Windows 8 plus features for encryption, virtualization, PC management and domain connectivity.
Windows 8 Enterprise, includes all the features of Windows 8 Pro plus additional features for IT organizations that enable PC management and deployment, advanced security, virtualization, new mobility scenarios.
Windows 8 RT will only be available as a preinstalled OS on tablets and other mobile devices. "Windows RT will include touch-optimized desktop versions of the new Microsoft Word, Excel, PowerPoint, and OneNote.
In terms of upgrades, users of Windows 7 Starter, Home Basic, and Home Premium will be eligible to upgrade to Windows 8 or Windows 8 Pro. Windows 7 Professional and Ultimate users will only be eligible to upgrade to Windows 8 Pro.
By comparison, Windows 7 was available in six editions, Starter, Home Basic, Home Premium, Professional, Ultimate, and Enterprise.