The Apple IIGS is designed to be used with the vast majority of Apple IIe
hardware and software. However, there are some design differences that will
cause some products to be incompatible with the Apple IIGS.
Some programs, especially games, depend on particular timing loops to operate
correctly. If you find that a program does not work on an Apple IIGS, use the
control panel to change to normal mode. Fast mode on the Apple IIGS will
change timing loops to the point that some software will not operate
correctly.