I guess it 'renders' the whole frame in some buffer, and then copy-pasting it to Notepad takes less than 1ms, leaving you with at least 940ms of each second wai

I guess it 'renders' the whole frame in some buffer, and then copy-pasting it to Notepad takes less than 1ms, leaving you with at least 940ms of each second waiting for key input (assuming 60fps). And might have overestimated the copying time by few orders of magnitude, maybe copying takes just a microsecond ? Another thought: do you even need to bring notepad to focus in order to copy contents to it? Maybe it's not in focus at all, and just happens to be the only thing on the screen?