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.
Any card that is used in the Apple IIe auxiliary slot cannot be used on an
Apple IIGS, since there is no auxiliary slot in the IIGS, and no other IIGS
slot has the signals present in the Apple IIe's auxiliary slot.