It is releasing the test code this week to the 15,000 or so people who have been beta testing SP1 already, and will also make it available on Thursday to those in the MSDN and TechNet developer programs.
"We feel really good and we look forward to receiving feedback from our larger set of testers," said David Zipkin, a senior product manager on the Windows Client team.
Microsoft also said on its Vista blog on Wednesday that it will make available a "blocker" that will allow customers who have Vista and use Windows Update to block SP1 upon its final release to allow for further testing. Microsoft offered a similar option with Windows XP Service Pack 2.
Service Pack 1 is mainly designed as a collection of bug fixes and performance improvements rather than an attempt to add new features. Among the changes that are more feature-related is the ability to use BitLocker encryption on multiple hard drive volumes as well as changes to the desktop search feature which were made to satisfy antitrust concerns from Google.