Since Microsoft first announced that some Windows Phone 8.1 devices would be upgraded to Windows 10 Mobile, questions have loomed about precisely what the required specifications would be. In particular, devices with 512MB of RAM have been rumored to be left off of the upgrade path. Today, Microsoft finally opened the floodgates, announcing the official rollout of Windows 10 Mobile and providing an initial list of supported devices.
However, there's bad news on the 512MB RAM front. In response to the direct question of whether those devices would be supported, Microsoft answered as such on Twitter:
@coreyd_0512 We do not have plans to put W10M on devices with 512 MB ^TJ
— Windows Insider (@windowsinsider) March 17, 2016
If you peruse Microsoft's official list, you'll see that only 1GB devices are supported, with the Lumia 635, 636, and 638 specifically listing 1GB versions. And so while Microsoft has confirmed their decision, it wasn't terribly difficult to deduce.
While some people would likely argue that their 512MB devices ran Windows 10 Mobile just fine in the Windows Insider program, Microsoft did have to draw the line somewhere. It's entirely possible that their internal testing indicated potential issues with less than 1GB of RAM, or that certain features were problematic.
In any case, a firm answer is better than speculation. We'll continue to keep you updated on the nuances of Windows 10 Mobile's release, and hopefully more of it will be of a more positive nature.