Since October 31, 2013, Windows 7 is no longer available in retail (except for the Professional edition preinstalled):
Windows 7 Starter
Windows 7 Starter is the edition of Windows 7 that contains the fewest features. It is only available in a 32-bit version and does not include the Windows Aero theme. The desktop wallpaper and visual styles (Windows 7 Basic) are not user-changeable. Microsoft originally intended to restrict users of this edition to running three simultaneous applications but this limitation was dropped.This edition was available pre-installed on computers, especially netbooks, through system integrators or computer manufacturers using OEM licenses.
Windows 7 Home Basic
Windows 7 Home Basic was available in "emerging markets", in 141 different countries. Some Windows Aero options are excluded along with several new features. Home Basic, along with other editions sold in emerging markets, include geographical activation restriction, which requires users to activate Windows within a certain region or country.
Windows 7 Home Premium
This edition contains features aimed at the home market segment, such as Windows Media Center, Windows Aero and multi-touch support.
Windows 7 Professional
This edition is targeted towards enthusiasts and small-business users. It includes all the features of Windows 7 Home Premium, and adds the ability to participate in a Windows Server domain. Additional features include support for up to 192 GB of Random-access memory (increased from 16 GB), operating as a Remote Desktop server, location aware printing, backup to a network location, Encrypting File System, Presentation Mode, Software Restriction Policies (but not the extra management features of AppLocker) and Windows XP Mode.
Windows 7 Enterprise
This edition targeted the enterprise segment of the market and was sold through volume licensing to companies which have a Software Assurance contract with Microsoft. Additional features include support for Multilingual User Interface(MUI) packages, BitLocker Drive Encryption, and UNIXapplication support. Not available through retail or OEMchannels, this edition is distributed through Microsoft Software Assurance (SA). As a result it includes several SA-only benefits, including a license allowing the operating of diskless nodes (diskless PCs) and activation via VLK.
Windows 7 Ultimate
Windows 7 Ultimate contains the same features as Windows 7 Enterprise, but unlike the Enterprise edition, it was available to home users on an individual license basis. Windows 7 Home Premium and Windows 7 Professional users are able to upgrade to Windows 7 Ultimate for a fee using Windows Anytime Upgrade if they wish to do so. Unlike Windows Vista Ultimate, the Windows 7 Ultimate edition does not include the Windows Ultimate Extras feature or any exclusive features as Microsoft had stated.
All editions will receive Mainstream Support (new features and bug fixes) until January 2015 and Extended Support (security updates) until January 2020.
Windows Aero Glass is Microsoft's 3-D high-end interface for Windows 7. In order to get this interface, you must be running a video card that supports running Aero Glass. Some video cards barely support running Aero Glass and performance suffers and the computer will lag. By simply disabling Aero Glass, you can take a crawling computer and bring new life into it. In any situation, if you want to increase performance, disable Aero Glass.