The "write through" mechanism, whereby writes to an area which is currently mapped as ROM actually write to the underlying RAM, still functions, wherever the ROM is mapped. However the write through mechanism cannot be used to access the register page. Write through also does not operate to the RAM from the register page.
At reset, page 0 is visible in the range &0000-&3fff. DFxx is reset to 0 at this time(logical page is set to 0). This means on GX4000 page 1 will be visible at &c000-&ffff. On the Plus, it depends on /EXP. If /EXP is low, page 1 will be visible at &c000-&ffff, otherwise page 3 will be visible and CPM will be auto booted. On an unmodified GX4000, selecting logical page 7 using DFxx doesn't select physical page 3, instead it selects physical page 1. The appropiate hardware is not activated as it is on 464 and 6128.
===Analogue paddle ports===