Well, I have the same exact problem and I asked around and everyone kept telling me it cant be the dual chip, and kept offering suggestions like using the mame optimized for AMD 64 etc but none of them worked!! The only thing that worked was setting the processor affinty to 1, but no one would listen.. Good news, it took me a while but I finally found something that works for me and mame. I finally found a program called Processor Affinity Utility you can find it here You tell it to change mame.exe or mame32.exe (or what every the exe of the mame version you are using) and everytime that process runs it will change the affinty for you. If you look in the help file there are command line options to run it automatically and minimize so you can put a shortcut in the startup folder of windows and have the program autostart and minimize to system tray. its something like, "C:\Program Files\ProcessorAffinity\ProcessAffinity.exe" /M /Q Hopes this help you as much as it helped me. It took me a lot of hunting to find a suitable solution. Good Luck