[Coco] OS-9 and RS-DOS disk structures

[William Astle]

On 14-12-30 03:39 PM, Allen Huffman wrote:
> But I forget the format of double sided sectors for an OS-9 disk. Does it put the first 40 tracks (front side) then the next 40 tracks (back side), or does it interleave them top/bottom/top/bottom or something like that? I guess I never thought about the physical sectors/sides since OS-9 treated everything as Logical Sector 0 to MAX.

It alternates between sides:

Side 0, track 0
Side 1, track 0
Side 0, track 1
...

Most things that handle multiple sides do the same. This is where the 
notion of a "cylinder" comes from, referring to all instances of a 
particular track across all addressable sides. (You stack the tracks up 
and you get a cylinder.)

It does run through all 18 sectors on side 0 before going on to the 18 
sectors on side 1 though.