Tomorrow, January 21, is Microsoft's second "big reveal" event for its coming Windows 10 operating system. (The first was in late September, when the company offered an overview of its Windows 10 strategy and technical preview plans.)

But tomorrow will not be the day Microsoft releases the first preview of the mobile version of its Windows 10 operating system, according sources close to Microsoft. Instead, the first public release of the Windows 10 mobile SKU -- which sources have said will work on both Windows Phones and smaller Intel- and ARM-based tablets -- won't happen until some time in February 2015.

Microsoft officials declined to comment on the availability date. But I'm confident the February timing is solid, based on my knowledge of the track record of my sources. I don't know whether Microsoft also will time the release of the next technical preview build of Windows 10 for desktops so that it coincides with the mobile version in February.
Read more: First Windows 10 mobile preview, due in February, key to Microsoft's OneCore vision | ZDNet