Basically, it can page a couple of megabytes (maybe 4 I can't remember off hand) into and out of the 16 bit address space as 2, 4, 8Kb pages.
The really nice thing is how well the 6809 can do relocatable code. Made paging things in to and out of RAM flexible.
I do recall, I used 2 pages, 16Kb RAM for my projects.
Page one, run main code and page in subroutines as needed. I could put graphics data under the main code too. The draw routines got called in page 2, meaning page 1 could go away for a while.
It worked well. Maybe it was the Atari featuring different page sizes.
How are people putting 2 Megabytes into the machine? I never did one of those upgrades, though I did add a 6309.