In late August 2004, Microsoft revealed that it was rethinking its rollout plans for Longhorn, the next Windows client release, and that the company will remove one of the key technologies (WinFS) promised for that release so that it could make a 2006 ship date. Microsoft also announced that it will now make two other important Longhorn technologies—the Avalon presentation layer and the Indigo Web services infrastructure—available to Windows Server 2003 and Windows XP users, significantly improving the chances that companies will adopt those technologies quickly. Here's what you need to know about Microsoft's evolving Longhorn plans.

Houston, We Have a Ship Date
Although much of the IT world has speculated about when Longhorn would ship, Microsoft has never made any public pronouncements about the final release date. The software giant had promised at the Professional Developers Conference (PDC) 2003 that it would ship Longhorn Beta 1 in 2005 and later ship a second beta. Microsoft was to have based the final release on feedback from these betas. With the August 2004 announcement, Microsoft is officially promising that it will make Longhorn "broadly available" in 2006, which means that it will ship the OS as early as possible in 2006.

"For the first time, we're providing guidance and clarity on the target release date of Longhorn," Microsoft Product Manager Greg Sullivan told me recently, "which is something we'd never done before ... The clarification of our roadmap is good for customers, especially enterprise customers. The implication of our use of the language 'broadly available' is that we're targeting the first half of 2006 and are expecting it to happen around mid-2006."

Microsoft will include the Avalon presentation layer and the Indigo Web services infrastructure in Longhorn and will also ship the products separately for Windows 2003 and XP. The company will port the WinFX development libraries related to Avalon and Indigo to Windows 2003 and XP, providing developers with the tools they need to target Avalon and Indigo, regardless of which platform they're using. The reason for this change is that developers told Microsoft that although they were excited about WinFX, Avalon, and Indigo, they couldn't justify spending resources developing for a platform that won't ship until 2006 and likely won't be widely distributed until years later. Now, developers will be able to target Avalon and Indigo technologies more quickly, assured that their efforts will have a wider audience. Microsoft says that it will ship Avalon and Indigo for Windows 2003 and XP simultaneously with the Longhorn release in 2006.

The decision to port Avalon and Indigo to Windows 2003 and XP is good for users because they'll be able to take advantage of rich new applications a few years down the road. However, some people have questioned the need for Longhorn if they can obtain Avalon and Indigo separately. But Longhorn will be a unique release with hundreds of original features and a lot of improvements over today's XP desktop.

What Are Avalon and Indigo?
According to Microsoft, Avalon is a presentation subsystem designed for Longhorn. It provides programmatic rendering and composition capabilities that take advantage of today's fast graphics processors to offload processing from the system microprocessor. Avalon also includes a new declarative programming model that makes developing new types of applications much easier. Specifically, developers can use Avalon to replace the graphics device interface (GDI) and GDI+ subsystems that earlier Windows versions use.

Indigo is a communications subsystem based on the Web services work that Microsoft has put into the Windows .NET Framework. Indigo lets you use Web services for secure, reliable messaging capabilities that are both platform and protocol independent. Perhaps most important, applications that use older communications technologies, such as COM+, Microsoft Message Queue Server (MSMQ), and ASP.NET Web services, will run within an Indigo environment, and Indigo will expose as Web services the messages generated by those legacy subsystems.

No WinFS Until 2007
To meet its projected 2006 release date for Longhorn, Microsoft has culled the WinFS storage engine from this release and will instead release WinFS with Longhorn Server, which is due in 2007. Microsoft also will ship a separate WinFS add-on for Longhorn in 2007 so that desktop users can upgrade to the new storage engine.

Critics point to the removal of WinFS as a sign that Longhorn will be a stripped-down version of its former self. But Longhorn will still include many features that some people mistakenly think depend on WinFS. Instant desktop search is one such feature. Instant desktop search will let users instantly search files, email messages, contacts, and other data repositories for specified information.

In some ways, delaying the release of WinFS until Longhorn Server is available makes more sense than the original plan: WinFS will be a crucial addition for next-generation versions of Active Directory (AD), the Microsoft Exchange Server data store, Microsoft SQL Server, and other server-based technologies. By including WinFS in Longhorn Server, then releasing an add-on for desktop users, Microsoft can more easily deliver an integrated solution that lets users find information where it actually resides—on the server. Note, however, that Windows 2003 and XP won't be getting a WinFS add-on. Microsoft will make that release available only to Longhorn client users.

What's Next?
Other changes under the hood have also affected Longhorn's release. Earlier this year, the core Windows team gave up its plan to make the Windows Server—based Longhorn source code component-based and started over from scratch with the XP Service Pack 2 (SP2) code base. The company is now working to make that code component-based before tacking on any Longhorn-specific features. Meanwhile, various Longhorn feature teams are still working on the older Windows Server—based Longhorn source code. Their work will be integrated into the new source code tree when the XP SP2 component work is complete.

All this development work means that we probably won't see another public preview release of Longhorn any time soon. Microsoft recommends that developers keep working with Longhorn build 4074, which the company released last April at Windows Hardware Engineering Conference (WinHEC) 2004, until it can ship Longhorn Beta 1 sometime in the first half of 2005. Longhorn Beta 2 should ship in late 2005, followed by release candidate (RC) builds and the final release in early 2006.

Recommendations
Although many people view the changes to Microsoft's Longhorn plans as negative, I think that the product was veering dangerously close to not shipping at all. By trimming Longhorn's feature set to a more manageable level and making key Longhorn technologies available to Windows 2003 and XP users, Microsoft has extended an olive branch to both its developer and user communities.

For IT decision makers, the gauntlet has been thrown. You now have the scheduling information you need to make realistic migration plans for both Longhorn Server and the Longhorn client. With this information and Microsoft's widely available product life cycle documents, you should be able to accurately determine when you'll be moving to Longhorn and thus plan and budget accordingly. Still to come, of course, are any Total Cost of Ownership (TCO) benefits—perceived or real—of the Longhorn platform. But my suspicion is that we won't know the answer to that question for another year or more.