Following are the client versions of Windows 7. Except for Starter, all versions are available in 32- and 64-bit versions. See Windows 7
Windows 7 Starter
A 32-bit version for PCs outside the U.S. No support for Aero interface and limited user customization.
Windows 7 Home Basic
Similar to Windows 7 Home Premium, but available only in emerging markets outside the U.S. Not all Aero functions are provided.
Windows 7 Home Premium
Supports full Aero interface, Media Center and multitouch. See Windows Media Center
Windows 7 Professional
Adds Remote Desktop, backup utility, XP Mode for running earlier Windows applications and support for domain-based company networks. Counterpart to the Business version in Windows Vista. See Windows XP Mode
Windows 7 Enterprise
Same as Professional plus BitLocker encryption, support for multiple languages and Unix applications. Available only through enterprise licensing.
Windows 7 Ultimate
For PC enthusiasts. Combines Professional and Enterprise versions.