Hello, C0x, you wrote: C0x> Hello, VTT, you wrote: VTT>> Hello, C0x, you wrote: C0x>>> By means of function ChangeDisplaySettingsEx I can install CDS_FULLSCREEN through devmode structure. C0x>>> and how me to receive for the given monitor value of flag CDS_FULLSCREEN? C0x>>> the Primary goal to define, whether game on the computer in Fullscreen mode is launched now or not. VTT>> it seems To me that CDS_FULLSCREEN has no relation to that, something is opened on weigh the screen or not. C0x> Then what for application causes ChangeDisplaySettingsEx before entering in fullscreen mode? C0x> From here I logically assumed that for me it will be familiar that something now entered into a full screen mode. VTT>> to define, whether openly any window on weigh the screen probably it is necessary to walk on all windows of top level, to learn their overall dimensions and to compare to screen resolution on which they are opened. CDS_FULLSCREEN The mode is temporary in nature. If you change to and from another desktop, this mode will not be reset. I.e. this flag is underlined not for passage in a full screen mode, and for indication of that parameters change temporarily and will be then returned reversely that happens just at any full screen applications more often. More shortly with a title of a flag they . About it Raymond Chen explicitly wrote. Besides, I do not think that call ChangeDisplaySettingsEx is still used at passage in a full screen mode (anyway, it is explicit). With the advent of DXGI one call IDXGIFactory:: CreateSwapChain or IDXGISwapChain:: SetFullscreenState became enough. C0x> I so understand that passage in a full screen mode of game it not simply creation of a window on weigh the monitor screen. C0x> on mine there is a difference for example in start of game and development Google Chrome in all screen. Though I can be mistaken. In my case these two situations it is necessary to distinguish. Probably simply full screen mode, and "an exclusive" full screen mode which here is meant existed in XP and older systems. Like as earlier all windows it was drawn in one the general screen and full screen application could acquire exclusive access to it for maximum productivity. But now at each window the and at passage in a full screen mode it is used directly.