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For all the time I used OS9/6809, I never ran accros a sector
size other than 256 bytes.
The big issue was different disk formats.
96 TPI vs 48 TPI. 16 sectors / track vs 18 (coco) sectors/track
Dbld sided vs single sided. Dbl vs single density.
And most severe problem What format was Sector 0, Track0
Std: always single density, 16 sectors/track.
Coco: DSDD 18 sectors/track.

Os9/6809 had many assumptions about 256 byte structures
built in to it, including almost all of the memory management
routines.