Apple Cinema Display (30-inch DVI) has 1280 x 800 as the maximum available resolution

When you connect an Apple Cinema Display (30-inch DVI) to one of the products noted below, you may find that the highest available resolution is 1280 x 800, even though the optimum resolution for the display is 2560 x 1600. The maximum resolution available when this display is connected to a single-link DVI port is 1280 x 800; you must connect the display to a dual-link DVI port to access the higher resolutions available to the display.