different size what? Is it like the difference between 120 and 220? The difference is in the number of shots?
Different size Polaroid.
The prints they produce (and with it everything that goes into the back to make that possible) are different in size.
I know there are backs that can accommodate both sizes, but they are few, and i don't know what the Mamiya backs requires. It probably takes 100-series only.
The films themselves were different too, the 80-series catering for amateur use, the 100-series intended for professional use.
Now that Polaroid has stopped making instant film, we'll have to look at Fuji to still find some to feed our Polaroid backs.
I don't think they offer something equal in size to the Polaroid 80-series.