Microsoft has issued Release Candidate 1 (RC1) of its forthcoming Windows Vista operating system. 

The Release Candidates mark the period between beta testing and the final product release.

The latest version is available only to testers in the TechBeta community. The software will be released through Microsoft's MSDN developer network and Technet community for IT staff in the coming days. 

Jim Allchin, co-president of Microsoft's platform and services division, said in an email to TechBeta subscribers that the software giant has made several changes to the user interface since the last beta release.

The RC1 version also offers additional device drivers and improved performance.

"We are not done yet, however, and quality will continue to improve. We will keep plugging away on application compatibility, as well as fit and finish, until the release to manufacturing," Allchin wrote.

He added that the latest version is mature enough for software developers to use for certifying their applications.

Windows Vista is scheduled for availability some time in early 2007.

Amazon started taking advance orders for the operating system earlier this week and disclosed on its website that the software will be available on 30 January. 

The date was later removed from the website and Microsoft has denied that a launch date has been set.