If WinFX does turn out to be Microsoft's SAA, then Avalon is Longhorn's Presentation Manager. At the end of the 1980s, IBM'S OS/2 was designed to bring a multitasking, graphical user interface to x86-based PCs in the shape of Presentation Manager. The graphical user interface did arrive, but it was called Windows and, after much development time, Presentation Manager was finally put to rest. Avalon is the code name that Microsoft has given to the presentation subsystem in Longhorn. With the decision to delay Longhorn's launch, bits of Avalon will now get rolled into service packs for Windows XP and Windows server 2003.

Anticipating a move for the PC from being the Internet surfing box in the kitchen or spare room for many users to the main home-entertainment system, Microsoft wants applications to look a lot more interesting. This means doing away with dull, grey Windows forms in the users interfaces of many applications and making them look a lot snazzier. In principle, you can build forms on top of movies or 3D shapes. So, with the right graphics backup, Avalon-based applications could look very pretty. The same could be said of Flex, the user-interface technology being built by Macromedia.

Perhaps a bit more useful for corporate use is a rendering system based on vectors instead of bitmaps, making it easier to design application that look the same on various different screen resolutions and zoom levels. If you are thinking of the latter: "Didn't Display Postscript do that on Sun workstation in the late 1980s?Don't Scalable Vector Graphics do that now on the Web? "The answer to both those questions are: yes on both counts.

For developers, the big change is a move to a declarative way of building user interface. It is based on XML, but a different dialect to that being used by the Mozilla groups to define a similar system, called XUL, that is intended to offer cross-platform compatibility. They do broadly the same thing, except XAML, the language that will be used by Avalon programmers, is designed to build application interfaces that run outside of a web browser. XUL is designed to make the web browser the primary host for client applications.

Because it helps do away with the need for a web browser to build client applications that may call down information and services from the web, using Microsoft's.Net protocols, Avalon is very important to the company. Whether it is important to organizations that do a lot of development is another matter.

By making it available to the XP generation of PCs, Microsoft has greatly improved the number of machines that will run Avalon applications. But the lack of cross-platform compatibility will slow down the pace at which many companies can make use of it, even if they want to. The lack of any indication that Microsoft might offer to open up XAML to the standards committees make it difficult to paint Avalon as something that companies should rush to embrace. But, with minimal market share in the browser world, it is no easier to embrace Mozilla's take on this approach to developing client applications. This is a situation where resolutely maintaining the status quo in application development may force some opening up at Redmond.