Lumia 520 running on Windows 10
Lumia 520 with 512MB of RAM will also get Windows 10

Joe Belfiore, vice president responsible for Windows of Microsoft, today has revealed on Twitter that his team are working with Windows 10 for the phone with 512MB of RAM, including the Lumia 520. “Our ambition is to make Win10 available on such devices, “Belfiore said, “and the feature may be different. “So we can guess that Windows 10 will be available on all Windows Phone 8.1 devices today, but in the low or mid-range model will not have enough end features such as a high-end models.
The vice president also added that the release date for Windows Phone Developer Preview 10 will also vary depending on the device. Initially there will be a group of devices to be tested first, then turn to the left. Belfiore promised us that the Preview above will be available this month, but first the company need to complete the internal testing before releasing it to the world wide.