Windows 8.1 Tips: More Windowing Options for New Style Apps
On Windows 8, users could split their screen to run up to 8 apps on two 2560 x 1600 monitors. Depending on your screen size, some may only be able to split and run 2 apps. On Windows 8.1, you can do all that and more – you can add another app and resize it so that it runs horizontally (see screenshot). However, that works only if the developer has allowed it for the app.