This CNET-produced chart is based on a larger one from Wikipedia.
Windows 7 Starter is the lightweight version of the new operating system that only. It's not available for upgrade from Windows XP or Windows Vista, and it's fairly hamstrung. Sixty-four-bit isn't available, and the Backup and Restore Center won't work with network-based drives. It also lacks many of the key features that make Windows 7 appealing. Aero is disabled, as is the new theme manager.
Windows Media Center and Windows Media Player aren't included, and so it shouldn't be surprising that none of the more advanced features is baked in, either. XP Mode, which will allow Windows 7 to run XP-only programs, Remote Desktop Host, BitLocker Drive Encryption, and multitouch support are all not available in Windows 7 Starter.
So just what does Starter offer? Users can pin programs to the Taskbar, and the helpful jump lists remain active, too. Snap still functions for quickly resizing program windows, although it doesn't have its slick Aero look. The revamped Windows Search will work, and other under-the-hood improvements--such as better Wi-Fi and device management--are also fully functional. Users can use the in-place Anytime Upgrade option to buy an upgrade from Starter to Home Premium.
Windosw 7 Home Premium is the basic version that should appeal to most casual users, and retails for $119. Most of the big features that Microsoft wants you to know about are included here. Aero Peek for previewing programs and clearing the desktop, Aero Snap for resizing program windows, and the Aero skin with its translucent Taskbar and window borders are all in full effect. Aero Shake is also enabled, which is a quick way to clear the desktop by clicking and holding down on one program window and lightly shaking, hiding all the other open windows.
Theme switching and customization is activated, and the Windows Media Center and Windows Media Player will allow users to stream video directly to their desktops. Multitouch features are enabled, and Home Premium can be used to create a Home Group, which simplifies sharing music, video, and other files between computers that are all members of the same group. It's also available in 64-bit, but can only support up to 16GB of physical RAM. Home Premium can be upgraded using the Anytime Upgrade to either Professional or Ultimate.
Although it sounds full-featured, Home Premium definitely offers less than Windows 7 Pro or Windows 7 Ultimate. Location-aware printing, presentation mode, and XP Mode are not available. Neither is BitLocker, AppLocker, the remote desktop host feature, nor Aero glass via remote. AppLocker is the new feature that allows system administrators to restrict program access from the Group Policy settings. You also can't use the Windows 7 Backup and Restore feature to work with network drives, just like Windows 7 Starter. That feature doesn't come in until the Pro version.
Windosw 7 Professional is the power user edition of the new operating system, retailing for $199.99. In addition to all the features in the Home Premium edition, Pro is designed to be flexible for dual use in the home and small business. It will support up to 192GB of physical RAM in 64-bit mode, it supports legacy Windows XP productivity programs via XP Mode, it can work with two physical processors, and it can back up your data to a networked drive. It still lacks the AppLocker and BitLocker features, it can't handle the pretty but superfluous remote Aero glass support, and it lacks the multilingual interface support pack.
Windows 7 Ultimate, retailing for $219.99, supports those features plus virtual hard-disk booting and a subsystem for Unix applications. Although it's possible to conceive of some home uses for Ultimate, the features that separate it from Windows 7 Pro set it in a class that's almost exclusively for intensive international or network use. For most office or home power users, it's not really recommended.
There are several other versions of Windows 7 available. Windows 7 Home Basic is for emerging markets such as Bangladesh, China, India, and Mexico, and places itself between the Starter edition and the Home Premium edition in terms of features. Aero is partially enabled, for example. Windows 7 Enterprise is identical to the Ultimate edition, but is only available via volume licensing. The Europe-only "E" version was going to come without Internet Explorer, but that has changed to the "N" version that lacks the media player.
If you're planning on buying Windows 7, tell us in the comments below which version you're getting.