[khedoros1]

Sorry, my comment was badly-worded. I was thinking about older systems having 16-bit memory spaces, into which all IO is mapped (including the cartridge). So all but the absolute simplest games would need bank-switching hardware.

Looking at the Genesis and SNES, each exposes a 24-bit address bus. I was speculating that the increased area would be enough that bank switching wouldn't be necessary (the largest SNES game seems to be around 48Mbit, right? A little over a third of the CPU's memory, although I haven't looked up where the cartridge data's window is usually mapped).

Of course, there's the added fun of external coprocessors and such.