When Microsoft unveiled the very first test build of the mobile version of its upcoming Windows 10 OS early in February, it was built to run only on selected Lumia handsets, specifically the Lumia 630, 635, 638, 730, and 830 smartphones. According to the company, this is due to a limited number of partitions that can be done on the test build. 

Good news, though, for those who have Windows phones apart from those listed. Microsoft will be releasing a second test build of the Windows 10 mobile operating system that would accommodate and support the majority of existing Windows smartphones. The build is expected to be released in the opening weeks of next month.

According to a blog post on the official Microsoft blogsite, the company's team had initiated what they call "partition stitching," mainly a feature code that would allow the team to re-size the partitions and make it larger. This in turn will allow the new build of Windows 10 for phones to be upgraded in most of the existing smartphones running on Windows. 

Gabe Aul, head of Microsoft's Insider program, said that the partition stitching was released by the company's main code branch in the latter half of last week, after testing the code on different devices. 

Aside from broadening the range of phones on which the second build of Windows 10 for phones could be updated, the new upgrade also allows support for devices that don't have China Mobile Operator support. It was not included in the first build. 

No specific date has been named for when the second build will roll out.

Aul said, "I cannot guarantee a date for a new build. What I can tell you is that we feel great here about the partition stitching code and current builds, but we likely still have at least one more week of engineering to do to ensure we get a great build for the expanded list of devices."