Re: DSK to NIB Instruction

[Andy McFadden <fadden@fadden.com>]

Ed Eastman <noone@nowhere.net> wrote:
>  > Is there more to it than checking overlap bytes?
> 
> Yes...  None of the disk image formats retain sync bytes or track to 
> track alignment information.  But if the nib works in an emulator, then 
> it should be convertible back to a real disk and work also.
> 
> The NIB image is as follows (more or less):
> Each 1A00 byte chunk is a tracks worth of bytes with some overlap.  Take 
> the Nibble image back to a real Apple II and use the EDD analyze and 
> write routine to put the bytes back on the disk one track at a time. 
> (Sounds easy, huh?)  If only I could find my EDD source code.

A track usually holds a smaller amount of data, e.g. $1850 bytes.  If
you know the actual track length, you still have to expand or contract
the data so that it occupies the exact amount of space.  You can't
remove actual data, so you need to add or remove sync bytes, preferrably
from the "seam", i.e. the large area of sync bytes that the track
formatter writes first.

If nibble counting is employed, you can change 9-bit sync bytes to 10-bit
sync bytes to make the track longer, or vice-versa.

All of which is easier if you know where the sync bytes are.

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