At last year's Microsoft Professional Developers Conference (PDC), Microsoft presented a preview of what to expect in the next version of Windows, code-named Longhorn. Although Microsoft might not release the new version until 2006, the Longhorn development cycle is well underway. In this Top 10, I present 10 of the most significant new features that Microsoft plans for the next version of Windows. (In case you were wondering, Microsoft named Longhorn after a saloon near Whistler Mountain in British Columbia, Canada.)

10. Windows .NET Framework— Although Microsoft hasn't made a big deal out of it, the inclusion of the .NET Framework with the next version of Windows shouldn't surprise anyone. The .NET Framework will make deploying Microsoft .NET applications throughout the enterprise easier by eliminating the need to separately download and install the .NET Framework.

9. XAML— Pronounced "zamel," XAML stands for Extensible Markup Language. XAML is a declarative markup language that developers can use in Longhorn to create UI objects much like Web site designers use HTML to create Web pages. XAML supports graphics and can be used to connect .NET Common Language Runtime (CLR) objects.

8. Contacts—With Longhorn, your list of contacts is basically built into the OS rather than being maintained by a separate application such as Microsoft Outlook or by a customer relationship management (CRM) application such as FrontRange Solutions' GoldMine. Longhorn provides the elements and controls you need to manage your list of contacts. The contacts feature uses the new WinFS file system, which I discuss later.

7. Notifications—Another big change that's planned for the Longhorn version of Windows is a change in the way Windows handles notifications. Longhorn offers an API for sending notifications to users. The new notifications model puts the user in control of how notifications are delivered. Users can specify when notifications may or may not be delivered and which type of applications a notification can interrupt.

6. Palladium—Longhorn includes the controversial Palladium security standard. Palladium is a security technology that works with Digital Rights Management (DRM) to control which types of applications and documents the system can work with. Microsoft pushes Palladium as a security tool to protect users from viruses and other ill-intentioned code, but the technology's opponents characterize it as Big Brotherism.

5. Aero—The code name for the Longhorn user experience, Aero is a set of guidelines that developers should follow to make the most of Longhorn's new graphical environment. The key components of the Aero interface in Longhorn include transparent windows, a built-in buddy list, and a dockable task pane.

4. WinFX—WinFX is a managed-code API for the Longhorn OS that essentially replaces the old Win32 API set. WinFX integrates .NET managed code with the underlying OS. Those who are already writing .NET applications will be pleased to learn that the WinFX classes are compatible with the .NET Framework.

3. Indigo—A new communications subsystem that's built into Longhorn, Indigo basically integrates Web services into the OS. Indigo is built on top of the .NET Framework and lets you build service-oriented applications. Windows Server 2003 and Windows XP will also support Indigo.

2. Avalon—Not to be confused with the Aero user experience, Avalon is the code name for Longhorn's new graphical architecture. In Avalon, Microsoft has rewritten Longhorn's graphic stack from the ground up. Avalon replaces the old user32.dll file and graphics device interface (GDI) that provided the graphics support for all previous versions of Windows. Like DirectX, Avalon addresses the hardware directly for improved performance and 3-D graphics. Avalon also provides a screen resolution of 120dpi, up from the current standard of 96dpi.

1. WinFS—Although the preceding features are all fairly sizeable changes for the Windows platform, without a doubt the biggest change is the introduction of the WinFS file system. At its core, WinFS uses a version of the Microsoft SQL Server Yukon database engine to enable relational searches of the Windows data store. WinFS doesn't replace NTFS but rather sits on top of it, integrating rich new search capabilities into Windows as well as introducing a new programming model for data retrieval.