"Using a PowerPC iMac screen for an Intel iMac"に関する回答I am using an external monitor with my iMac Intel 5,1 (EMC2118) after the internal monitor quit. The Mac boots up in extended mode, (2 screens wide) I took it in to the Genius Bar to see if they could switch it over to mirroring the internal monitor. The genius did it with a couple of keystrokes. BUT, the same command (or any others I can find) will not work with MY (original) keyboard or a couple of spares. Apple tech support had no clue what I was talking about. The workaround aln't pretty - I had to blindly find & drag the HD icon from the dead screen to the functioning one, then drill down to the control panel to change the display to mirrored.