Microsoft revealed details on how Windows 8 will scale on high-DPI tablets, full details at The Tech Report.
Windows 8 will support three scaling modes: 100% for regular displays, 140% for "HD tablets," and 180% for "quad-XGA tablets." The size chart below sheds some light on what those labels mean and what effect they'll have on UI scaling:
"HD tablets" will have 1920x1080 panels, while "quad-XGA" offerings will cram 2560x1440 pixels into similar-sized displays. As Microsoft points out, keeping UI elements the same size on such devices is crucial, since smaller buttons and widgets are harder to touch. The company will help developers optimize their apps for high pixel densities with Visual Studio 11, which includes a Windows Simulator with various resolution and screen size combos.