The Windows Insider program, adopted to provide a public beta for the PC version of Windows 10,[REF] is used to provide a public beta version of Windows 10 Mobile for selected devices [REF].
Microsoft originally stated that all Lumia smartphones running Windows Phone 8 and 8.1 would receive updates to 10, but Microsoft later reiterated that only devices with the "Lumia Denim" firmware revision and at least 8 GB of internal storage would receive the upgrade [REF].