Microsoft has let consumers start trying out its upcoming touch-based Windows 8 operating system, which aims to power a new wave of computer tablets and traditional PCs designed to counter Apple's big gains in the market through its Macs and iPads.
The test "beta" version of the revamped system was introduced at the Mobile World Congress in Barcelona, the world's largest mobile phone trade show, and borrows some of the look of Microsoft's Windows Phone 7 software for Windows 8.
Windows 8 does not have the traditional "Start" menu, and applications are spread across a mosaic of tiles in a design Microsoft calls "Metro" - seen as an attempt by the company as a scramble to preserve its market share.
Executives said it powers up on PCs in eight seconds, much faster than the previous version.
The tiles, which resemble road signs, can be navigated with a finger swipe on the screen or with a keyboard and mouse. But those testing out the new operating system will not be able to try out the finger swiping unless they already have systems enabled for touch use, and the system is not expected to make its official debut until September or October.
Microsoft executives in Barcelona showed off how users can use their fingertips to swipe in and out of applications, and tilt upright computer screens to a flat position so they can be used as two-person gaming boards or big drawing tablets. A slim laptop had a hinge allowing it to be turned inside out so it could be used as a tablet instead.
"It's beautiful, it's modern, it's fast, it's fluid," said Steven Sinofsky, president of Microsoft's Windows division. "Windows 8 is a generational change in the windows operating system."
Microsoft is also opening an internet Windows Store where users can download applications for the operating system. Applications are free for those testing out the beta version, but would include both free and paid versions after the operating system is released.
The test version was downloaded by people from more than 70 countries as Microsoft gave its presentation about Windows 8, but the company did not immediately disclose the number of downloads.
If Windows 8 is a hit, it could help struggling PC makers, including Hewlett-Packard and Dell. Besides giving businesses and consumers a reason to consider new PC purchases, Windows 8 is expected to spawn a new breed of hybrid machines that will be part tablet computer and part laptop like the device that Mr Sinofsky demonstrated.
If Windows 8 is a flop, however, it will increase the pressure on Microsoft CEO Steve Ballmer. His 12-year reign has been marred by the company's troubles adapting to an internet-driven upheaval. As Microsoft has stumbled, faster-innovating companies such as Apple and Google have elbowed their way into a position to steer the direction of computing for the next decade.