As more and more Windows 10 PCs and tablets are released, and plans for Windows 10 Mobile smartphones start to emerge, we will likely see a variety of form factors from third-party OEMS using the new OS. Microsoft has posted some recommendations for form factors and hardware devices that those companies can use to make their products.
The smartphone form factor guidelines all use Windows 10 Mobile, of course, but each of the three examples shown have very different designs and hardware. Microsoft considers a Value Phone to be between 3.5-5-inches, with just 1GB of RAM and between 4-8GB of storage. Such a phone will have Cortana support but not for Continuum for Phone. The Premium Phone recommendations show a 4.5-5.5 inch screen, 2GB of RAM and between 32 to 64GB of storage, along with support for Cortana, Continuum for Phones and the facial unlock Windows Hello security system.
The Value Phablet, according to Microsoft, could be between 5.5-7 inches, but with 2GB of RAM and with just 16GB of storage, with support for Windows Hello and Cortana. A 7-inch tablet could also run on Windows 10 Mobile, with support for Continuum for Phones, according to the Tablets form factor recommendation page. Larger tablets could use the regular Windows 10 desktop OS.
It's important to point out that these designs and hardware specs are just recommendations by Microsoft to OEMs. There's no stopping those hardware makers from putting in a regular Windows 10 OS inside an 7-inch tablet, and they could decide to put in more powerful hardware parts inside a phablet size of a device. However, the support pages do show the kinds of products Microsoft would likely like to see OEMS make and sell to the public.