The upcoming Windows 10 Anniversary Update will add some new display sizes for both PC and Mobile compared to the current version of the OS.
Microsoft's MSDN support page ( via NPU) for hardware requirements show that for Windows 10 Mobile hardware devices, the display size can now be as large as 9 inches for the Anniversary Update, up from the current 7.99 inches. Windows 10 PC products can also have displays as small as 7 inches, which is a change from the previous 8 inch requirement.
Windows 10 Mobile products must also have an auto-flash for the Anniversary Update and Windows 10 PCs products need at least 2GB of RAM, up from the current 1GB. Also, they need 16GB of internal storage for the 32-bit version of the OS and 20GB if they use the 64-bit version. The Anniversary Update will be released for free for all Windows 10 PC and Mobile products, along with the Xbox One game console, later this summer.