MMU

Directly under the CPU registers, and the fastest way to answer "what is actually mapped where right now".

Next MMU Mappings lists all eight 8K slots with the physical page number in use and the slot type — ROM in orange, or Bn naming the 16K bank the page belongs to. The page shown is the one really in effect, whether it came from NextREG 0x50–0x57 or from legacy 128K paging.

128K Bank Mappings shows the port 0x7FFD state: the selected RAM Bank, the ROM select bit, and whether paging is Locked (red when it is — a locked 0x7FFD is a classic cause of "my bank switch does nothing").