Windows CE is the smallest and arguably the most interesting of the Microsoft Windows operating systems. Windows CE was designed from the ground up to be a small ROM-based operating system with a Win32 subset API. Windows CE extends the Windows API into the markets and machines that can't support the larger footprints of the Windows XP kernel.

The now-defunct Windows 95/98/Me line was a great operating system for users who needed backward compatibility with MS-DOS and Windows 2.x and 3.x programs. Although it had shortcomings, Windows Me succeeded amazingly well at this difficult task. The Windows NT/2000/XP line, on the other hand, is written for the enterprise. It sacrifices compatibility and size to achieve its high level of reliability and robustness. Windows XP Home Edition is a version of Windows XP built for the home user that does strive for compatibility, but this is secondary to its primary goal of stability.

Windows CE isn't backward compatible with MS-DOS or Windows. Nor is it an all-powerful operating system designed for enterprise computing. Instead, Windows CE is a lightweight, multithreaded operating system with an optional graphical user interface. Its strength lies in its small size, its Win32 subset API, and its multiplatform support.

Windows CE also forms the foundation for the initial version of the .NET Compact Framework, a version of the .NET runtime for mobile and embedded devices. The Compact Framework provides the same powerful .NET runtime environment with a smaller class library so that it fits in small battery-powered devices.