Windows 10 devices with screens smaller than 8 inches won't have the desktop mode, Microsoft's Joe Belfiore confirmed on Twitter. These devices will be limited to Metro-style apps and have ARM processors. Traditional Windows applications will only work on the devices with screens larger than 7 inch.
In a follow-up tweet, Belfiore added that existing 7 inch devices powered by Windows 8.1 will also be provided with a desktop when upgraded to Windows 10.
Start screen is dead in the large screen devices. In Windows 10 build 9926, Microsoft has completely removed the option for launching the Start screen when Windows boots. So the desktop users with the large screens will be accessing live tiles from the new Start menu only.