Microsoft took a big step into mobile Thursday, unveiling a revamped version of its flagship Windows system and a offering a closer look at Surface, its entry into the hot tablet market.

The new Windows 8 operating system and tablet to go on sale Friday mark a new offensive for the US tech giant seeking to keep pace with Apple and Google amid a dramatic shift away from PCs to mobile devices.

"Windows 8 brings together the best of the PC and the tablet," said Microsoft chief Steve Ballmer.

"What you have seen and heard should leave no doubt that Windows 8 shatters the perception of what a PC really is... It works perfect for work and play and it is alive with your world."

At a New York news event, Microsoft announced that Windows 8 would launch Friday in 37 languages and 140 worldwide markets. It can be downloaded beginning at 12:01 am local time worldwide and will be sold at retail stores.

Analysts say the revamped Windows system provides Microsoft with an opportunity, but that dramatic changes might not be initially welcomed.

"Windows 8 looks like a big, bold, very innovative and very different new operating system," said independent tech analyst Jeff Kagan.

"The problem is that Microsoft is not giving users the chance to get used to the new operating system slowly. Instead they are launching this in an all-or-nothing way."

Rob Enderle of Enderle Group said: "Microsoft has been losing ground to both Google and Apple at an increasing pace and Windows 8 is their strongest response to date. If they miss here there will likely be major changes in Microsoft to adjust to that failure."

Microsoft is also launching a version called Windows RT, designed for tablets and available pre-installed on new devices including its own Surface tablet.

Surface is "the perfect expression of Windows," said Microsoft product team member Panos Panay. "It's exactly what Windows was designed to run on."

To show its durability, Panay dropped the device on stage, saying, "You can drop it 72 different ways." He also displayed some units modified as skateboards, with wheels attached, used by one team member.

Michael Gartenberg of the research firm Gartner said Surface "is a new category of device and one that will make sense for many consumers."

Surface, which seeks to challenge Apple's market-ruling iPads and rivals built on Google's Android software, will be among Windows-powered devices sold at Microsoft "pop up" stores to open Friday in the United States and Canada.

The news comes two days after Apple introduced its iPad mini in a bid to crowd out lower-priced offerings by rivals Amazon, Google and Samsung.

Surface -- a late entry in the market -- has a 10.6-inch (26.9 centimeter) screen and starts at $499, challenging the larger-format iPads.

But Surface appears to be a cross between a tablet and a PC, equipped with a flip-out rear "kickstand" to prop it up like a picture frame and a cover that, when opened, acts as a keypad to switch into "desktop" mode for work tasks.

It launches in a crowded market for tablets from Apple, Google, Amazon and others, amid forecasts that global tablet sales will surpass those of PCs within a few years.

Some analysts say the Windows RT system used on Surface and other devices offers Microsoft a chance for a fresh start in controlling both hardware and software in a single device.

The new mobile system "represents the best shot Microsoft has against Apple and Google," said Roger Kay at Endpoint Technologies Associates. "WinRT is where things are going."

Windows, the first version of which was launched in the 1990s, remains the dominant PC platform with some 90 percent of the world market. But in the mobile world, it is struggling against Apple's iOS and Google's Android system.

Microsoft reported that pre-sales of Windows 8 have outstripped those of its predecessor by 40 percent.

The Redmond, Washington-based company next week will provide details on its new Windows Phone 8 operating system designed for its push into the smartphone market.