Subject: I have a 27" Apple Cinema Display, why can't I get 2560x1440 resolution but do get 1280x720?
Explanation: There are three different scenarios why this could happen
Your graphics card doesn’t support dual-link resolutions up to 2560x1400. Make sure that your graphics card supports dual-link DVI and can output dual-link resolutions as Apple’s Cinema Display only supports three specific resolutions (2560x1440, 1280x720, 800x600) if your graphics card is limited to a single link (maximum supported resolution 1920x1200), then second supported resolution with above-mentioned resolutions becomes 1280x720.
Your graphics card supports dual-link resolutions up to 2560x1440 but it only outputs 1280x720. This only applies to ATI/AMD graphics cards and this issue only shows up in Windows OS where the drivers are not compatible with Apple’s 27” Cinema Display. When using the same graphics card on a Mac OS based machine, you can get up to 2560x1440 resolution.
Your graphics card is capable of outputting dual-link resolutions up to 2560x1440 but you’re only limited to 1280x720. If you have another display connected to the same graphics card where AT-DP400 is connected to (this can also apply to built-in displays for laptops), when mirroring your displays, your graphics card will output based on lowest common denominator supported resolution; for example, if your laptops built-in display supports up to 1366x768 and Apple Cinema Display supports (2560x1440,1280x720,800x600), your graphics card will choose 1280x720 as it becomes a lowest common denominator supported resolution for both monitors.
In order to have individual resolutions for each monitor, under display preferences, you can switch to the extended display mode and set the resolutions for each monitor separately
Article ID: KB01417