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A game from an IBM PC seems to run, but the screen is all messed up. Why?

April 26, 2017IBM messed pc run screen

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A game from an IBM PC seems to run, but the screen is all messed up. Why?

1 Answer

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Welcome to the wonderful world of not being exactly compatible with the IBM PC. The graphics subsystem of the PCjr is compatible with the CGA standard at a high level (BIOS), but software that directly accesses registers or memory is not guaranteed to work. Software might do this for performance reasons, which is good, except that it limits portability. Sometimes the bad program can be patched to interact correctly with the video hardware. I will be digging this patch out and making it available soon. (Email me if “soon” hasn’t arrived yet for you.) If these patches don’t work, you’re out of luck.