Microsoft showcased Windows 10 on smartphones last month, and announced that most of the devices running Windows 8 would be eligible for a free upgrade to Windows 10 operating system, even the ones with relatively weaker hardware specifications.
Gabriel Aul, who is leading the Windows 10 Insider programme, tweeted that he is testing Windows 10 on a Nokia Lumia 635 and using it as his daily driver. Apparently, Windows 10 is running "very smooth" on the Lumia 635 in spite of it being equipped with just 512MB of RAM.
— Gabriel Aul (@GabeAul) February 10, 2015
Microsoft had announced that some of the features of Windows 10 might not be available for all existing devices due to complications with the hardware. The final builds of Windows 10 are expected to hit the existing devices starting summer.