Windows 7 is available in 6 different SKUs, but for the most part it boils down to three major editions: Windows 7 Home Premium, Windows 7 Professional, and Window 7 Ultimate / Enterprise.
The Ultimate and Enterprise editions both have the same features, the difference is how Windows 7 is purchased. Ultimate is for the retail (individual user) channel and Enterprise is for volume licensing customers. Enterprise customers with Software Assurance also benefit from the features in the Microsoft Desktop Optimization Pack (MDOP).
Each edition is available for both x86 (32-bit) and x64 (64-bit) platforms.
The following table lists the new features in Windows 7 for each edition (SKU).