[Updated below] Microsoft’s Windows 8 will offer new start screen optimized for tablet/slate computers that uses a tile interface reminiscent of the company’s Windows Phone interface.

Windows Chief Steven Sinofsky is on stage right now giving a sneak peak of the interface, talking with Walt Mossberg at the D9 conference down in California. The operating system isn’t expected out until next year, but the preview is being watched closely to see if Microsoft and its hardware partners can field credible rivals to the iPad and Android-based tablets.

[Follow-up: Windows 8: A radical change for Windows, and a huge gamble for Microsoft]

AllThingsD.com’s Ina Fried has an early look at the interface along with comments from Microsoft executives about the company’s approach. The tiles include a large “Store” tile, apparently confirming that Microsoft plans to offer Windows apps through a marketplace.

Update: To clarify, this isn’t just an optional Windows interface for tablets. As shown in the Microsoft video below, users will be able to switch to a more traditional Windows desktop, but the new start screen is for all versions of the operating system. “This is the new version of Windows. It’s going to run on laptops, it’s going to run on desktops, it’s going to run on PCs with mouse and keyboard, it’s going to run on everything,” says Microsoft’s Jensen Harris toward the end of the video.

Also see this Microsoft post providing a summary of the announcements. Among the features highlighted by the company in the post:

Fast launching of apps from a tile-based Start screen, which replaces the Windows Start menu with a customizable, scalable full-screen view of apps.

Live tiles with notifications, showing always up-to-date information from your apps.

Fluid, natural switching between running apps.

Convenient ability to snap and resize an app to the side of the screen, so you can really multitask using the capabilities of Windows.

Web-connected and Web-powered apps built using HTML5 and JavaScript that have access to the full power of the PC.

Fully touch-optimized browsing, with all the power of hardware-accelerated Internet Explorer 10.

Microsoft says a Windows 8 device is “really a new kind of device, one that scales from touch-only small screens through to large screens, with or without a keyboard and mouse.”

Live blogs: Thisismynext, AllthingsD.com, CNet News.com and Engadget.

Mossberg asked at the outset about Microsoft’s exclusion from Google chairman Eric Schmidt’s reference last night to the “Gang of Four” consumer platforms running the modern Internet. Sinofsky replied that nothing that starts with a gang of four ends well.

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