When it first announced the Windows 10 Mobile update, Microsoft assured users that it would provide the upgrade to all existing Windows Phone 8 Lumia devices. While the statement is largely true, we now have more information for those wondering about what happens to devices from other manufacturers, especially low-end devices, which are often left out of software upgrade in the mobile world.
It seems that while most phones - regardless of whether they were made by Microsoft/Nokia or another manufacturer - will receive the new OS but, unfortunately, those with only 4 GB of internal storage are unlikely to receive to make the cut. As Microsoft's Windows 10 Mobile page in German confirms, devices need at least 8 GB of internal storage to be eligible.
Such devices were already unable to enroll in the Insider Preview, which led many to believe that they would be ineligible for the finished product as well, and it seems that their fears have now come to pass.
The list of devices affected is rather short and likely only represent a very small portion of the Windows Phone pie: Alcatel One Touch Pixi 3 Series, Nokia Lumia 530, HTC 8S, Blu Win JR and JR LTE, Yezz Billy 4, Karbonn Titanium Wind W4, Kazam Thunder 340W, Thunder 450 and 450WL.
The reason for this is, of course, rather simple: devices with such low amounts of storage simply don't have enough space. With Microsoft pursuing a shared base across all its devices, the size of its Mobile OS has increased significantly compared to Windows Phone 8 and, as such, such devices can no longer function satisfactorily.
Notably, almost all of these are non-Lumia devices and, given that Lumia phones account for almost all the Windows Phones in the wild, this requirement is likely to affect only a few. Contrary to Microsoft's promise, however, it would seem that at least one Lumia device, the 530, will also be unable to receive the upgrade - unless Microsoft changes these requirements in the future or figures out a way to bypass them for the Lumia 530.