This new preliminary version, called Release Preview, can be downloaded at http://preview.windows.com and its interface is available in 14 languages, Microsoft on Thursday.

Microsoft also announced that starting on June 2, it will offer a Windows Upgrade program in 131 markets so that consumers who buy participating Windows 7 PCs through Jan. 31 of next year will be able to purchase an upgrade to Windows 8 Pro for an estimated retail price of US$14.99 during the promotion period. Microsoft will later announce details of a similar program aimed at consumers who have already bought Windows 7 PCs.

The previous Windows 8 test version, called Consumer Preview, was released in February and downloaded more than 1 million times within its first 24 hours of availability. At this point, Windows 8 is the most tested Microsoft operating system ever, according to the company.

As with any other major Windows revamp, much is riding on Windows 8, which has been designed with tablet devices in mind. As iPad and Android tablets sell by the millions, Windows is a minor player in this market, putting Microsoft at a disadvantage not only among consumers but also among corporate buyers.

There is much expectation among industry analysts and market observers related to how well -- or not -- Windows 8 will do once it's released in general availability. Microsoft hasn't given a date for its shipment, but the consensus is that it will probably be available before the end of this year.