[Coco] DECB directory question

[Darren A]

On 12/20/10, Mike Rowen wrote:

> I need help trying to understand the disk directory structure on track
> 17 and well the FAT structure. Just a SS 35 track disk.
>
>   For a file entry, byte 13 contains the number of the first granule
> of the file. Is this number an index pointing to a specific byte in
> the FAT? I know that the FAT contains one byte per granule. So, for
> example let's say byte 13 for a given file entry is 06. Does this
> point to byte 06 in the FAT?
>

If the file's first granule is 6 then byte 6 in the FAT will indicate
whether or not there is a 2nd granule allocated to the file.  This
continues in a kind of linked list fashion.

>From Disk Basic Unravelled:

A granule data byte, which has been allocated, will contain a value,
which is the number of the next granule in the granule chain for that
file. If the two most significant bits (6,7) of a granule data byte
are set, then that granule is the last granule in a file’s granule
chain. The low order four bits will contain the number of sectors in
the last granule, which the file uses.


Darren