Microsoft is recommending either Windows 7 Home Premium or Professional for most of its customers, it said.

Windows 7 Home Premium is for the average user and Windows 7 Professional -- replacing Windows Vista Business -- is for small businesses and people who work at home but have to operate in an IT-managed or business environment with security and productivity concerns, the company said.

Windows 7 Starter is a limited-functionality version of the OS that will be available worldwide but only as a pre-install by OEMs (original equipment manufacturers). This expansion of its availability -- Vista Starter was only available in emerging markets -- led one blogger to surmise that Windows 7 Starter is the version Microsoft will push for the netbook market.

"This version will only be sold through PC makers to users," wrote Paul Thurrott on the popular , which has a list of SKUs and the differences in functionality. "This suggests that netbook makers will choose this version, even in the US."

Windows 7 Enterprise is Microsoft's SKU for its enterprise customers, while PC enthusiasts that "want it all," according to Microsoft, should purchase Windows 7 Ultimate.