This is something I've been wondering about for a while, since I haven't played any games like this. Some RPGs, such as ones on the 360 (or calculators ) are split into multiple parts (for consoles, one disc is one part) due to size reasons. How are the games split in these parts gameplay-wise? Do the different parts contain similar maps, or are there different continents or such for different parts? Is it common to be able to go back to earlier parts of the game? And also, is the change of part usually paired with something like a plot twist?

Most calculator games that are setup like that are old ASM games that were for both the 83 and 83+ as well as BASIC games. Those games are limited to the RAM size so they had to be split in multiple parts.

Examples are Mystique, Illusiat 7, 9, 10, 11 and 12. 7 and 9 were updated later so chapter switching is done automatically, though. (In the others, you still need to save, exit, archive/unarchive stuff then reload your game).

Other examples of games that are like that are Final Fantasy: Tales of Magic 1 and 2 and The Verdante Forest. Shadow of Narkemen was like that too, but only the first part was ever finished. Illusiat 2002 was like that too, but it was lost in a mem clear. It was even larger than Illusiat 12 but shorter.

Most of the time, when you arrive to a new part, there's no comeback, but in FFTOM, sometimes it's possible to come back.

In Illusiat 10, in the final chapter, you return to the same area as in the first one, but everything is destroyed. In Mystique, if I remember the same thing happens, but in some cases, the areas you visit again are accessed in different spots. In Illusiat 12, Chapter 7 and 8 share the same areas for the most part, but each chapter contains different events.