PAL uses only 50Hz refreshrate compared to 60Hz on NTSC Systems. If you are now using an NTSC game in an PAL system only 50 FRAMES of those 60 are displayed in 1 second. So the game will actually run slower. That also works the other way round. Using a PAL game on an NTSC system lets the game run faster than intended. Some Systems are able to adapt the framerate according to the system used (sms, genesis come to mind) but not all. If you want to use a PAL romset you should check if the used emulator supports switching between PAL/NTSC or maybe even has an autodetect feature. Additionally not all Monitors/TVs support PAL/NTSC.
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