One of the more important changes to the Windows 8.1 update for Windows 8 and RT is its pervasive support for portrait mode. This feature, primarily aimed at 7- and 8-inch mini-tablets, portrait mode works across the OS and the built-in app and is aimed primarily at reading scenarios.
Note: I haven’t been able to test the portrait mode functionality in Windows 8.1 with a true mini-tablet yet, but will as soon as possible. I did, however, test it with a Surface tablet.
According to Microsoft’s Jensen Harris, making portrait mode work properly was a key design goal of Windows 8.1. It enables what he calls a nice page experience, where each screen’s worth of info can be thought of a page, whether you’re in a reading app—Nook, Kindle, whatever—or elsewhere in the OS, or in other apps.
Proper portrait mode support also requires that the built-in apps work properly. In the Preview build, many but not all of the apps are already working, primarily the ones you might think of as reading apps. For example, the News app works great in this mode.
Maps works well too.
Xbox Music, not so much.
I’ll have more to say about portrait mode once I get more relevant hardware.