During the development of Windows Server 2008, I was told by project manager Alex Hinrichs that Microsoft had completely changed the way it developed Windows. Thanks to the componentization of the underlying OS, it was no longer necessary to "fork" the Windows build tree so that different parts of the product team could develop their own parts of the OS in isolation. These teams would utilize "virtual build labs" where they checked in their code, tested it, and ensured that it was ready before pushing it into the main build, or winmain.
Forking is bad because changes made on all branches have to be folded back into the main "trunk" build at some point, and that can be time consuming and error-prone. But apparently, the Windows client team has gone back to the old way of doing things. While no one outside of the company can really say why they've done so, we can guess--and yes, it's just a guess--that it has to do with timing: Microsoft is barreling towards a late 2009 release for its next OS, Windows 7, and it needs to ensure that it hits its ship targets. So recently, the team forked its build tree to accommodate separate RC (release candidate) and RTM (release to manufacturing) branches. The RC branch follows the existing 70xx build numbers, while the RTM branch has jumped to 71xx. These builds are kept in lockstep, so that build 7106, shown here, corresponds to RC build 7076.
There are rumors, too, that a new UI is coming and it may make sense for Microsoft to hold on to that UI for the RTM builds, so that it has one last surprise to offer up to its eager fans. Indeed, the smartest thing Microsoft has done with Windows 7, in many ways, is keep the drama high by playing things close to the vest. That said, our first RTM-level build, build 7106, doesn't really offer anything in the way of revelation. (A newer build, 7107, has also leaked recently, and we can expect more to come in the days ahead.)
