Even though Microsoft's much-anticipated Longhorn has been stripped of its unified file system and some of its other key Longhorn technologies will be available for Windows XP and Windows Server 2003, the next Windows release will still be worth the upgrade, according to Microsoft.

"There are a host of new attributes and capabilities that will make Longhorn compelling," said Greg Sullivan, lead product manager at Microsoft.

But Longhorn is no longer the "big bang" update Microsoft had promoted. "We think that this approach is going to make it much more of a stepwise path to Longhorn instead of a big leap," Sullivan said.

Although it is too early for specifics, Sullivan said Longhorn should be a better performing, more stable, and more secure operating system because it will be based on the Windows Server 2003 SP1 (Service Pack 1) code base. Microsoft will also include tools to ease desktop deployment, management and diagnostics, making it simple to spot and fix problems, he said.

Aside from the under-the-hood improvements, Longhorn will offer a new user interface and improved desktop search capabilities, Sullivan said. "In 2006, if I am running Longhorn on my machine and you're running XP with Avalon and Indigo on yours, you're going to look at my machine, and you will want mine," he said.

Avalon and Indigo are, respectively, the graphics and communications subsystems Microsoft developed specifically for Longhorn. Microsoft will now support Avalon and Indigo in Windows XP and Windows Server 2003 as well. As part of this move, Microsoft added support for the Longhorn WinFX application programming model to the older Windows versions.

"Microsoft is trying to establish technologies sooner for people who aren't going to upgrade right away," said David Smith, senior vice president and fellow at Gartner.

Developers adding support for the Longhorn technologies to Windows XP and Windows Server 2003 will be able to use these technologies to target a much larger installed base, instead of just Longhorn systems.