Microsoft plans to reveal more details about its forthcoming Longhorn OS upgrade during its Professional Developers Conference (PDC) next month – but will keep details of its seemingly Apple-inspired user interface (Aero) secret.

Aero may get some attention during chief software architect Bill Gates' opening keynote speech, but isn't finished yet and is unlikely to appear in a pre-beta iteration of Longhorn that's to be given to developers attending the event, sources said.

Video footage leaked in May 2003 clearly showed an OS X-like genie effect, in which a window would ripple in a curtain-closing-like effect across the screen as it closed.

Attendees will learn more about Avalon, the OS engine that underpins Longhorn's UI. Microsoft calls it: "A brand new client platform for building smart, connected, media-rich applications in Longhorn." Developers at the show will be told how to take advantage of Avalon in their applications.

Avalon means the next Windows OS will support new styles of user interfaces and elements. Developers will be able to create Windows client applications that use the type of navigation features found on the Web to browse information, reflecting Apple's move to a more user-centric Finder in OS X.

Yukon find it

WinFS (Windows Future Storage, code-name Yukon) will be discussed. This is a service that sits on top of the existing Windows file system and is meant to make it simpler and more intuitive for users to find files on computers running Longhorn.

Microsoft describes WinFS as an: "Entirely new user experience and model around the storage of user's data." For example, Outlook address book data today is restricted to that email client. With WinFS, that data could be made available to all applications on a PC. Mac OS X already integrates an Address Book feature, which shares its data with enabled applications.

WinFS will require that applications be rewritten to exploit such capabilities. Microsoft plans to release application upgrades when Longhorn ships.

Much work remains to be done on WinFS. It works, and developers can start developing applications for it, but it is slow, fragile and many features are missing, a source familiar with the development said.

‘Big bet’

Microsoft is working hard to finish the PDC version of Longhorn. The goal is to meet "zero bug bounce," a stage where development catches up to testing and there are no active bugs, at least for the moment. The operating system will be "about half done" when the PDC rolls around, the source said. A Longhorn beta is planned for 2004.

Gates has called Longhorn "a big bet" for Microsoft, warning its release to be "a bit scary" because Microsoft is making fundamental changes to its OS.

The PDC promises a feast of code names: including Longhorn, Aero, Avalon and Yukon. Other code-named products and technologies on the agenda are Indigo and Whidbey.

Indigo is Microsoft's new framework and programming model for building connected applications and Web services. Whidbey is the next version of Microsoft's developer tool, Visual Studio .Net.

The company’s secrecy around many of the PDC topics has helped build expectations for a show packed with new technology.

PDC will also almost certainly fan the flames of speculation about Longhorn's release. Sources claim Microsoft has set August 15, 2005, as an internal due date. However, last July Gates and Microsoft CEO Steve Ballmer declined to comment on a date.

PDC runs from October 26-30.