Devices with less than 8″ of screen will have their desktop restricted to a “Apps” that are downloadable from the Store:
…Taking to Twitter to clarify media queries, Belfiore explained that any device with an integrated display of 8″ or larger diagonal size will be treated as a ‘desktop’ device with access to the Desktop user interface and full support for all legacy Win32 applications. Anything smaller than 8″, however, will be locked away from the desktop user interface – bringing the restrictions of Windows RT to Windows 10, despite the hardware supporting legacy applications just fine.
Thankfully for those who have invested in Windows 8 devices featuring smaller screens and who have already filled them with legacy applications for use in Desktop mode, there’s an exception to Microsoft’s new rule: existing devices, such as the popular Linx 7 tablet, will retain Desktop capabilities if upgraded to Windows 10. ‘We’ll upgrade and keep the experience consistent with what [you] have,‘ Belfiore explained…
This will make Windows 10 function much like the now defunct Windows RT (Windows 8 for “ARM” processors) tablets.