Nick White, Microsoft Product Manager, in a post on the Windows Vista Team Blog, acknowledged that the Redmond Company is working concomitantly on Vista RC1 and RTM builds. Sven Hallauer, Director of Windows Release Management revealed in an podcast interview the intricacies inherent with the process of incrementing build numbers.

According to Hallauer, Windows Vista's parallel build cycles result in reserved build numbers. In this context, the versions numbered from 5400 to 5699 refer exclusively to Release Candidates of the operating system, while builds numbered starting with 5700 are related to Release to Manufacturing variants. "Sven's team has set aside a specific range of build numbers to incrementally build toward Windows Vista's Release Candidate 1 (RC1) milestone; in this case, build numbers ranging from 5400 through 5699. Likewise, numbers beginning with 57XX have been set aside for the RTM (Release-to-Manufacturing) release," wrote Nick White.

"It helps us to optimize the ability to make the code move forward in a very fast way. That's something that we do at the end of every major milestone, that we branch off," declared Hallauer describing the method for generating the milestone build in a process that dates back to XP.