Microsoft on Monday said it has released a slightly updated test version of Windows Vista, but it is not being made broadly available to the consumers who are trying out the new operating system.

The software maker said the new version, build 5472, should offer better quality and performance. It is being offered only to some of the masses who are testing the Windows update, including certain businesses, technical testers and members of Microsoft's MSDN and TechNet developer programs.

"Microsoft is distributing this in order to provide testers with a more recent build and to encourage application and device driver developers to accelerate development on Windows Vista," the company said in a statement. "This build includes quality and performance improvements based on feedback Microsoft has received on Beta 2 to date."

Among the changes are performance enhancements to the remote-controlled Media Centre interface and adjustments that will mean that people running the operating system in standard mode will have to offer administrator credentials less often.

The next publicly available update to Vista is scheduled to be the first "release candidate" version, which Microsoft has said is coming before the end of September. It released the Beta 2 version of Windows Vista at a hardware conference in May and offered it to any interested testers in June.

The software maker had hoped to have Vista on store shelves and on new PCs in time for this year's holiday season, but it is now shooting for a January release, though many doubt that even that date is attainable.