Microsoft on Thursday released the final test version of its next-generation Windows software crafted to power devices ranging from tablets to desktop computers.

"We're thrilled to be at this milestone with the Windows 8 Release Preview," said Windows and Windows Live division president Steven Sinofsky.

The nearly finished Windows 8 software was available for download in 14 languages at preview.windows.com.

Availability of Windows 8 Release Preview marks the final phase of development before the operating system becomes available to makers of computers and other devices.

A "consumer preview" version of Windows 8 was downloaded more than a million times in the 24 hours after its release in February, according to Microsoft.

Microsoft's upcoming Windows 8 series -- featuring an upgraded cloud computing service -- marks a "rebirth" of its operating system, chief executive Steve Ballmer said last week at a gathering in South Korea.

Ballmer described Windows 8 as the "deepest, broadest and most impactful" Windows software ever created by the Redmond, Washington-based tech giant, after the current Windows 7 sold at unprecedented rates to businesses.

"It's really, in some senses, a dawning of the rebirth of MS Windows... It's certainly the most important piece of work we've done," he said in a speech to the Seoul Digital Forum.

Windows 8 allows users readily to store and share personal data among various devices under the "SkyDrive" cloud computing service. Rivals Apple and Google offer such services.

The new Microsoft system will support a wider range of devices, including touch- and stylus-based smartphones and tablet PCs as well as desktop and laptop machines, Ballmer said.

The software giant has been trying to expand its presence in the booming software market for smartphones and tablets, which is currently dominated by Apple and Google.

Ballmer predicted that the cloud computing market would become dominated by a few big players.

Cloud computing refers to the popular trend of using software as a service hosted online at data centers instead of downloading and maintaining programs in personal machines.

Web-based email services such as Gmail are common examples of "cloud" computing.

"The number of core (cloud) platforms, around which software developers will do their innovation, is not ever-broadening," he said.

"It's really a quite smaller and focused number -- Windows, various forms of Linux, the Apple ecosystem."

In three to five years from now, "there will be just a few ecosystems that really can get the critical mass", he said.

Ballmer estimated up to 500 million users will have Windows systems next year, promising the "best economic opportunity" for device makers and app developers.

Microsoft will also soon introduce Skype powered by Windows 8, Ballmer said. His company last year bought the leading Internet video and voice-calling service for $8.5 billion.