Microsoft is planning to roll out a new browser when it debuts Windows 10, according to sources. But IE isn't going completely away. It turns out that what's actually happening is Microsoft is building a new browser, codenamed Spartan, which is not IE 12 -- at least according to a couple of sources of mine.

Spartan is still going to use Microsoft's Chakra JavaScript engine and Microsoft's Trident rendering engine (not WebKit), sources say. As Neowin's Brad Sams reported back in September, the coming browser will look and feel more like Chrome and Firefox and will support extensions. Sams also reported on December 29 that Microsoft has two different versions of Trident in the works, which also seemingly supports the claim that the company has two different Trident-based browsers.

However, if my sources are right, Spartan is not IE 12. Instead, Spartan is a new, light-weight browser Microsoft is building.

Windows 10 (at least the desktop version) will ship with both Spartan and IE 11, my sources say. IE 11 will be there for backward-compatibility's sake. Spartan will be available for both desktop and mobile (phone/tablet) versions of Windows 10, sources say.