With mappers, you can see a part of the main memory as a "window", it only show a portion of the program there. Writting to $8000 and up just activate the mappers features. If you were coding in the good old DOS age and used EMS memory, it's must the same like mappers, except that EMS was using RAM memory...

.ORG $8000
LDA #$7F
PHA
LDA #$FF
PHA
RTS